Downwind faster than the wind, part 2

Discuss

476 Responses to “Downwind faster than the wind, part 2”

  1. LeavingHalfway says:

    @#53 joelphillips:

    The forces acting on the cart are:
    1) Gravity
    2) A reaction to gravity perpendicular to the treadmill
    3) … friction at the bearings …
    4) A reaction to the momentum that’s being given the the air that’s being pumped backwards by the propellor.[eh? acceleration?]

    Re 3), I think you’re forgetting Rolling Resistance.

  2. ThinAirDesigns says:

    C’mon Foetusnail — take your medicine like a man. You made an empty assertion regarding the direction the cart would go in the wind/fan. You made a prediction that the prop would windmill and the cart would go backwards and then ask that we prove you wrong:

    >You know what, these guys have taken
    >their cart outside. You know what happened?
    >The propeller, much to their surprise,
    >acted like a windmill and the cart went
    >backwards. Prove I’m wrong. Take it off
    >of the treadmill and without giving it a
    >push hit it with a hairdryer and post the
    >video.

    We did prove you wrong. The cart goes forward just as we said it would. Cowboy up and get over it.

    Unless you gain some physics understandings, your other predictions regarding this device will continue to be just as off base as this one.

    >AND AT [WHAT] TIME DID YOU EXCEED THE WIND SPEED?

    The above is just a misdirection ploy to distract from your total failure to predict the behavior of the cart. But so what, you’re not fooling anyone so I’m happy to answer the question:

    In the fan shot, the cart certainly did not exceed the wind speed and we didn’t intend it to. A house fan would be a silly and non-productive way to test a DDWFTTW cart. It does however work just as well as your suggested hairdryer to demonstrate self-start.

    In the first street shot, the cart certainly did not exceed the wind speed and we didn’t intend it to. We’re on a busy city street with a no-steer cart and only wanted to get self start video

    In the second street shot, I can’t tell you if we did or not, but I can tell you we didn’t intend to. We’re on a busy city street with a no-steer cart and only wanted to get self start video.

    As far as leaves and stuff blowing by — of course … the laws of physics dictate that it takes time to accelerate any object. It doesn’t happen instantly and thus there will be times early on when the wind is in the obvious winning position.

    JB

  3. davidglover says:

    Charles Pratt over at Make Magazine saying it doesn’t work after his popsicle stick cart test is like me proclaiming birds can’t fly after I throw a penguin off a cliff.

  4. dustbuster7000 says:

    I think I’ll confine my comments to the devices I’ve seen in the video, which might not include all of the other options, but so far what I see is:

    1. Cart with propeller connected to wheels via transmission.

    2. Tailwind caused propeller to spin, which drives wheel forward via transmission.

    3. Cart accelerates.

    So far, no controversy. At some point:

    4. Cart reaches speed of tailwind.

    At this stage, ignoring loses (friction of various kinds) and storage (inertia of various kinds), the propeller stops providing any acceleration, since the apparent wind speed over its blades is zero.
    Any slow down by the cart will cause the relative windspeed to rise above zero, the propeller will be driven once more and the cart will speed up again.

    However, since the mechanical system is designed to turn the cart wheels forward in a tailwind, any acceleration from the cart would cause an apparent headwind, which would tend to slow the propeller down and decelerate the cart. So unless there is some fancy stuff happening to either the blade pitch or the transmission, this device cannot cause the cart to go faster than the wind. And this is for the ideal friction-less, inertia-less case.

    Spork et al, ball, your court.

  5. Anonymous says:

    “A mechanical car where some parts of the car arrive at the destination before other parts do will at some point “run out of lever or screw” and stop.”

    Now exchange the screw with a propeller (also called airscrew), and the nut with the air. This way you have an infinitely long screw that wont run out, as long as the wind blows. And see, you get the cart in question.

  6. Mark Frauenfelder says:

    Please remember not to resort to name calling or insults while discussing this. Let’s all be civil.

  7. GregLondon says:

    thinair@321: As has been shown on this thread repeatedly, you’re missing a key point — *I never made the offer to you*.

    Oh, gawd, my whole argument collapsed because of that one technicality!!! The horror!

    You guys have been acting like a bunch of meat puppets(*) since you showed up, so you started to blur together a bit for me.

    (*) since you all seem to be unfamiliar with the internet, replace “meat puppet” with “shill”. If you don’t know what “shill” is, I don’t know what to tell you.

  8. FoetusNail says:

    I won’t believe it until I see it running over the ground. This video is probably not rigged, but this does not mean this vehicle will move over ground faster than the wind. On the treadmill the vehicle is not moving faster than the wind, it is stationary in moving air. If the treadmill belt’s linear displacement exactly matched the cart’s wheels angular displacement, then the force of the wind (blowing at 90 degrees to the propeller’s direction of rotation) is being balanced by the electric motor. Because the cart’s speed relative to the wind has not changed and is balanced by the motor the cart can run in place over a powered belt. Cool, but not the same as running downwind over the ground at any speed.

    Taken off of the treadmill and placed on the ground, as the vehicle accelerates the difference between the airspeed and the vehicle’s ground speed would decrease. If the vehicle could conceivably reach the same speed as a following wind it would eventually be like riding in a hot air balloon, where the balloonist experiences a dead calm once the balloon’s velocity matches that of the air. Once that happens the cart would not have any force acting on the propeller.

    So I would say, while the cart may move by the wind it will never travel faster than the wind, in fact its top speed will be at some point where the difference between the air’s velocity and the cart velocity still has enough power to balance out the forces of rolling friction and the frictional loses of the drive train. Since the cart is traveling with the wind the only drag would be the spokes of the wheels, everything else would be acting like a ship sailing in a storm without sails, using only the pressure of the wind on the rigging. Conceivably, a very well made cart’s speed may get close to the wind speed, but will never exceed wind speed.

  9. JohnInDC says:

    Isn’t “downwind faster than the wind” just another way of saying the vehicle, once started, is capable of propelling itself indefinitely into a headwind?

  10. Anonymous says:

    > (Tom replies): could I also visualize this
    > concept of yours as a “reverse Ferris Wheel” with
    > the ‘chutes “opening as they move over the top
    > back toward the yo-yo” ?

    Absolutely. One of the standard configurations for explaining this is a Ferris wheel with vanes halfway between the hub and rim. They present themselves to the wind while on the bottom, and feather themselves the rest of the time.

    For practical applications, the propeller design is both easier to implement and more efficient.

  11. davidglover says:

    Let me help everyone out, every time you deny that it works in any way you are going to get your butt handed to you by the 2 guys who built it and know that it works, keep posting, but be warned skeptics are just ignorant blabbers who haven’t seen the light….yet.

  12. ThinAirDesigns says:

    Me:
    >1:48 seconds of not touching it before
    >it fell off the back.

    Travis08:
    >The problem I see with the original video
    >is you suggest that that it can’t be
    >kinetic energy because you show that it
    >runs out in 7 seconds.

    In that test, we have the treadmill set at max speed (10mph). We also have the treadmill at max slope (or near max slope, can’t remember).

    >You do this by holding the car stationary
    >for almost a 2 count, then lift the car
    >off the track showing it runs out in a
    >seven count.

    Yes, once the wheels of the cart are turning to match the treadmill belt, I lift it off the belt and time how long it takes to coast down — that measurement demonstrates how long the vehicle will run in ‘no load, free spinning’ mode.

    >Next you hold the car stationary on the
    >track again, and let in run for about twice
    >as long, suggesting that it must be more
    >than kinetic energy powering it. HOWEVER
    >the second time you charge the car up (by
    >holding it stationary on the moving
    >treadmill) you charge it up for about a
    >4 count.

    “Charging” (your term) consists only of allowing the wheel speed to match the belt speed. This only takes a second or so to reach maximum “charge”. A 2 second charge is the same as a 2 minute charge — once the wheels match the belt speed there is no more charging going on. Any difference in the amount of time I hold it to the belt is just a function of me trying to get it balanced and steered straight on the belt before releasing it.

    As you can see from the above, “charge” it all you want and it’s still only going to freely turn to “seven Mississippi”.

    >This would provide twice the runtime and
    >allow you to count past seven. About the
    >time the car should run out of stored energy
    >you cut the camera.

    A: As described above, twice the charge time will not result in twice the run time.

    B: The video you refer to where the cut was made after a few seconds is not the raw footage, but rather a collage cut from other footage in our archive. That ‘MythBusters Challenge’ video isn’t the video we would necessarily choose to prove or disprove any particular point, but rather was edited to fit the voice over.

    Here is the raw footage to which you refer:
    http://www.youtube.com/watch?v=1pSYALWQ-nI

    You will notice that in this, the full video, the device runs uncut for 1:38 *after* I release it rather then the few seconds you see on the OP video.

    During this 1:38, I only gently steer the device to keep if from wandering off the edges and top of the treadmill.

    Hope this helps:

    JB

  13. ThinAirDesigns says:

    Nelson:
    >Like it or not the onus is on you to
    >provide a proof to anyone who asks it,

    ROFLAO!!! You can’t just put “onuses” on me — you haven’t been given “onus authority”. Your position would only be true if I cared whether I convinced you personally (or not).

    I don’t. I’m interested in a bigger group than just this one. As evidence of this interest, notice that I didn’t start this thread nor ask that it be started. I appreciate that this sort of attention might help us in our quest, but I certainly don’t have any obligation to jump when you say “onus”.

    I’ve been at this long enough to know that some people see it, and the others just accuse us of ignorance, naivete and/or fraud. We want to see it on Mythbusters because people understandably tend to place just a bit more credence on their results.

    In the end, our quest for Mythbusters is just a round’a’bout way of accomplishing what you wish — the presentation of credible evidence. Perhaps it’s not the way you would do it, but then it’s not your idea. Have one of your own and you can do it your way.

    JB

  14. cmpalmer says:

    I’m pretty sure no one will read this comment unless they start from the bottom, but…

    I’m not sure if I believe the entire theory behind what is happening in the video or not, but here is my proposal for an outdoor test setup:

    Make a precision vehicle like the one in the treadmill video, but add two things:

    1. A small radio-controlled servo for steering

    2. A very small, low drag as possible, anemometer on the front as isolated as possible from the prop-wash. Either collect data on the vehicle or have it transmit the wind-speed telemetry. The anemometer should be able to read wind speed from the front or rear.

    The electronics can be very lightweight and would be also considered on the control vehicle.

    Then take the vehicle out to a very, very flat surface on a windy day.

    With the vehicle on the ground perpendicular to the wind, the anemometer on the vehicle should read the same wind speed as a stationary anemometer on the ground. Wind is not extremely laminar in most places, so you couldn’t compare micro-conditions from the stationary anemometer to the vehicle down the “track”, but you could correlate the readings to identify gusts.

    Release the vehicle and use the radio-control to steer it as straight as possible with minimal controlling (to eliminate accusations of tacking).

    As long as the vehicle is traveling slower than the tail wind, the on vehicle anemometer should read wind blowing from behind. If the vehicle maintains a steady speed while reading exactly zero, then it’s traveling at the same speed as the wind. If the anemometer reads a head-wind, then the vehicle is traveling faster than the wind.

    Instead of a spinning anemometer, I would suggest a small vane attached to spring loaded self-centering potentiometer or attached to a flexible shaft with force-detecting resistors. That should be easier to zero out and could be made quite sensitive and light without greatly affecting the drag on the vehicle.

    As a control vehicle, replace the propeller with a suitably sized sail but keep the chassis and electronics the same.

    Do numerous trials with both vehicles, graph and average the results correlated with the stationary anemometer, and see if the average speed (once it gets up to speed) can be shown to be significantly greater than the wind speed.

    Even if the DWFTTW vehicle never averages greater than wind-speed, it would still be a significant result if it could consistently outperform the same vehicle chassis equipped a sail, particularly if you could quantify and take into account the drag of the vehicle.

    FWIW, I believe everything about the claims of the vehicle up to a certain point. I think the wind is pushing on the cart and propeller and I think the energy from the wind is turning the geared propeller to push it faster than it would go with the wind alone, even to the point that if the machine is made to suitable precision it may average exactly wind speed. However I can’t see any way whatsoever that it could maintain a speed greater than windspeed except through gusts and the flywheel effect. If if the prop moves it faster than the wind and the resulting headwind had no effect on the prop, it still would no longer be taking any external energy and would *have* to drop down below wind speed before it would begin to extract any wind energy.

    I think all the treadmill proves is the efficiency of the cart design and that the drag of the cart is drawing enough energy from the treadmill to drive the propeller. Keep slowing down the treadmill enough and see if the cart still travels faster than the treadmill. Keep reducing it to zero MPH. That is the same condition as the cart coasting along at exactly wind speed.

  15. ThinAirDesigns says:

    MrFricative,
    I’ve got a thought experiment for you if you please:

    You wake up suddenly at my house — a place you’ve never visited and with no idea how you got there. You look out the window and see me standing in the middle of the street with this silly little DDWFTTW cart in my hand.

    You walk out the door, issue the appropriate “WTF?” and notice a 10mph wind blowing down the street from the south to the north. You comment on it, and I say “the air is actually quite still … it’s the ground that’s moving” I continue with the explanation: “this entire town is on a giant treadmill — houses, trees, streets, everything is moving south at 10mph”

    Now, let’s pause the above for a moment and get to the heart of the treadmill equivilancy matter here –

    Can you devise a test, or do you believe one can be devised that can be executed in the middle of the street to determine whether I am telling the truth and indeed we are on a treadmill or not? You are allowed to enlist the services of anyone and any organization you wish, from Steven Hawking on down. I have also provide you absolutely endless funding in your quest.

    Is there a test, and if so would you describe it.

    Thanks

    JB

    Would you mind detailing the test for us that could determine

  16. ThinAirDesigns says:

    Codesuidae:
    >but the question to be answered was whether
    >the air was still and the town was moving
    >south at 10mph or if there was a 10MPH wind
    >from the south and the town was still.

    I’m sorry Code, but that was NOT the question to be answered. Following is the question taken verbatim from that post #351

    >Can you devise a test, or do you believe
    >one can be devised that can be executed
    >in the middle of the street to determine
    >whether I am telling the truth and indeed
    >whether we are on a treadmill or not?

    Notice the critical “treadmill” portion of the question.

    Anyway, I’m betting that you and I understand the “equivalency” issue and agree on it.

    The back and forth is fun games though — reminds me of the old legendary Civil Engineering Professor question: “I hold in my hand an altimeter, how can it be used to determine the height of a skyscraper?”.

    Let me know if you aren’t familiar with that one.

    JB

    PS: I also just noticed that I referred repeatedly in my last few posts to #350 when I in fact meant #351. My apologies.

  17. ThinAirDesigns says:

    Sorry for the lousy editing on my last post … everything below my initials was to have been deleted.

    Carry on.

    JB

  18. FoetusNail says:

    Obviously, it runs in place on a treadmill, but if it works outside on the ground, why don’t they include video of the blessed event?

  19. FoetusNail says:

    If they had in fact proved their cart works as they claim to have done, would there be 260 comments? With the extent of their argument being anyone who doesn’t believe them and asks for further proof of their claim is a fool. No this thread would be just long enough for a few of us to say, wow, that’s cool.

    I wouldn’t waste my time or money building this dust collector. I can have a lot more fun with a remote control car from wal-mart that will run all over my yard, instead of running in place on a treadmill I don’t own. I’ve seen the video, it ain’t that exciting. The truth is if this works someone else will eventually prove it beyond a shadow of a doubt. You can bet on that!

    Hell, there would probably already be one for sale in the toy department near the remote control cars.

  20. SubductionZone says:

    When spork first brought this up on Mythbusters I was one of the nonbelievers and called it a hoax just like many people are on this site. Now I started to doubt my surety when I was educated a bit by spork et al. about sailing. For example it seems that many of the doubters on this site disbelieve the well documented fact that ice yachts can easily reach a speed where the direst down wind portion of their speed is faster than the wind. You can easily check this out yourself by doing a little Google searching on ice yachting. I am not providing links since they may be viewed as biased, get your own on this subject you will see that spork did not lie to you.

    Once you start to realize that you can run faster than the wind downwind this device seems a lot more probable. One thing you have to realize also is that even if you are going faster than the wind directly downwind is that you are still within the wind. You do not jump into some mysterious vacuum. So the possibility of using the difference between ground speed (zero) and windspeed (in this case we will say 10mph) is still there.

    What disappoints me is the inability of certain people to not see how the treadmill is a perfect example of a frame of reference equivalence to a steady tailwind at the treadmills running speed. When I saw sporks first crude cart that actually worked I was one of the first to congratulate him and JB and offer my apologies, he accepted it much more graciously than his postings seemed to indicate he would.

  21. airshowfan says:

    Dustbuster,

    I still insist that the spinny thing is a prop, not a turbine. See comment 198.

  22. ThinAirDesigns says:

    GregLondon:
    >Uh, the first doesn’t show it get up to
    >steady state, someone just blew a fan on
    >it. I could blow a fan on a kleenex box
    >and make it move.

    That’s correct, and if we were told that a kleenex box would move backwards when we say it moves forward we would have blown on a kleenex box to prove we were right.

    Don’t play dumb Greg — you read the thread and know darn well why the video was posted. FOET predicted it would go backwards challenged us to demonstrate otherwise. We did.

    Game, set and match on that issue.

    JB

  23. GregLondon says:

    And once you’re over wind speed, though

    Once the vehicle is moving at wind speed, there is zero air movement over the vehicle. It is moving 10 mph in a 10 mph tailwind. Standing on the vehicle you’d feel no airstream.

    But you’d still have friction in the axles, which would slow you down. But they get energy to overcome the friction by bleeding off speed from the vehicle which they use to turn the prop, which then pushes air back, which then speeds the vehicle up faster than it was before. And this goes on indefinitely, like a wiley coyote contraption.

    I did something similar one time when I was a kid playing with my lego toys. I made a little car with two axles and put a rubber band between the front and back axles, but with different diameter pulleys so the back axle spun faster than the front. Then I’d push the car, and the front axle would turn but also make the back axle turn even faster, which would then keep it moving forward indefinitely. I’ll bet you money if you don’t believe me.

  24. spork says:

    >> You are allowed to enlist the services of anyone and any organization you wish, from Steven Hawking on down

    What – he can’t ask for MY help? : )

  25. ztoop says:

    There seems to be some confusion on this board about the distinction between forces and changes in energy. You don’t need a source of energy to apply a force to something (i.e. the force of my butt on my couch.) but you do need energy to apply that force over some distance (i.e. the energy need to lift my butt off of the couch.)

    To find a steady state to this situation (i.e. given a constant wind speed the craft will reach a constant speed which may be zero) then all we need to do is balance the forces. However, if the forces are unbalanced, it will cause the craft to accelerate.

    Now, if we think of the craft as going the exact same speed as the wind, then the wind causes no drag (or acceleration of the craft). If the craft had no propellor, then the drag from the wheels would oppose the motion of the craft, causing it to slow down (acceleration opposite to the direction of the motion). This craft will slow until the net force of the wind is equal to the drag. The wind provides the power to overcome the drag in this situation.

    However, with the propellor (which is attached to the front wheels) also applies a force. Pressure gradients across the blades cause a net force to be applied to the blades in the direction of travel. There is some friction on the blades which introduce more drag in the situation ( but think of airplanes: the engines face forward because that friction is less the amount of lift you can obtain). The net result is that the craft feels a net force forward if the propellors provide more force than all the drag combined. This net force results in an acceleration forward, causing it to go faster than the wind, until the force of the blades is offset by the drag on the blades, wheels, and headwind. This objects isn’t going to oscillate significantly like some propose because friction is only a dissapative force.

  26. FoetusNail says:

    Dustbuster, I already made that assumption. No, their claim is that their cart is powered by the thrust of the propeller. If it was turbine or windmill powered, like boat in hudman’s link, it would probably go faster than this silliness they continue to say they have proved.

  27. HUDMAN says:

    Greg, I hate to break it to you, but your “tumbleweed” cannot reach the windspeed, much less outrun it.

    Think about this… Your device produces no thrust. If it produces no thrust, what happens when you place it on a treadmill? (I hope you don’t need a treadmill to find out) Just think about it… It flies off the back of the treadmill at blazing speed.

    Why is this? Because there is no part of your cart that is traveling slower than the wind, in order for it to use the wind to propel it forward to outrun the wind. Confusing huh? Well, simply put, your cart will outrun its power source.

    Why doesn’t spork’s cart outrun its power source? Let’s answer that question with another question… What part of spork’s cart is traveling slower than the cart itself, and not outrunning the tailwind that’s powering it? The thrust. That’s it! The thrust is not outrunning the tailwind, therefore the thrust does not outrun its power source, and since the thrust is generated by the cart, the cart propels itself beyond the speed of the wind.

    And here’sa bit of food for thought…

    #1 – If someone cannot explain it to you, it might be THEIR fault, but most of the time, it’s YOUR fault, because you simply cannot understand it. The way I look at it, it needs no explanation, as it’s self-explanatory. I’ve been on the Mythbusters thread with spork & JB almost from day one, and I understood it immediately, without a “formal” explanation. Now, why is that? It shouldn’t be anybody’s “job” to explain it to you, but as long as they are trying, pay attention, open your mind, and try to learn.

    #2 – If you disagree with something, and you express your disagreement in a negative way, that’s fine. But, once you feel like you have “seen the light,” you shouldn’t start pretending to be the “expert,” and fool yourself by further thinking that you can explain it better than those that have attempted to explain it to you. Expecially when you are just plain wrong.

  28. Anonymous says:

    I’d like to offer another explanation on how it works. First lets simplify the model by considering zero wind and imagining ideal machine with zero energy losses.

    Consider a cart rolling along at 10 MPH. We connect a generator to the wheel, and use the spinning wheel to generate 10 watts of electricity. We are pulling power out from the wheels, and this puts a drag on the wheels causing the cart to slow down. We then send this electricity up to run a propeller generating thrust. We are imagining a perfect zero loss machine – energy coming from the wheels equal the energy going into the prop – the drag on the wheels will exactly equal the thrust at the prop. Energy is conserved, the cart does not change speed. This ideal cart can coast at any speed. This ideal car can pulling draw any amount of energy out of the wheels and perfectly balance it by pouring all of that energy into thrust at the prop.

    In the real world all machines have losses to friction and other causes. In the real world this machine can still draw any amount of power out from the wheels, but energy losses mean you are putting slightly less power into the prop and getting slightly less thrust at the prop. It can be going any speed and it can draw any amount of power from the wheels, but it will always gradually slow down as energy is lost to friction etc. However that was assuming zero wind. If there *is* a wind, then that wind will in effect *add* to the force that will exist at the propeller. You can draw 10 watts from the wheels to spend 9 watts driving the propeller, and the wind adds to the prop force. Even if the cart is moving faster than the wind, the wind still adds to the force at the prop. A ideal cart could maintain speed with zero wind, so a less-than-ideal cart can maintain speed with some wind (and it can accelerate up with greater wind). The slower-than-cart wind still helps, the slower-than-cart wind still effectively adds to the thrust.

    Drawing power from the wheels (slowing the cart) to drive the propeller for thrust is very counter intuitive, but when there is a wind it really does supply the required energy to power the machine. It’s a weird arrangement, but everything involved is basic ordinary physics. The forces and energy budget are pretty easy to verify with introductory-level college physics. The messiest part is the formula for calculating how much thrust a propeller will generate. There’s a PDF out there where an MIT professor verified all the calculations proving it works, although I don’t have the link handy.

  29. dustbuster7000 says:

    JB, can you confirm my description of your claims in post #392

  30. arkizzle says:

    Greg@257, sounds like you’re thinking along the right lines with the parallel boards, seems more intuitive, and some people upthread mentioned similar setups. I had a look for some online sims but got nothing, unfortunately.

    I wish I had more to add to all this, but I’m really enjoying the finding-stuff-out bit. (Not so much the escalating hostility behind some of the comments, though, as frustrating as all this might be.)

  31. ThinAirDesigns says:

    Foetusnail:
    >The truth is if this works someone
    >else will eventually prove it beyond
    >a shadow of a doubt.

    Yes, “someone” will.

    JB

  32. ThinAirDesigns says:

    Me:
    >That’s correct, but tape yourself to the
    >prop and tell me you don’t feel any wind
    >on your face.

    Greg:
    >Look, just say you don’t know how it
    >works and at least you’ll be honest
    >about it.

    >What you’re yapping about here though
    >is pure pseudoscience.

    See Greg — pure transmit mode on your part. There’s nothing “pseudo” about the wind on the prop — it’s very real and additionaly, for me to say that I don’t know how it works would be a lie and thus I’m not going down that path.

    Best wishes on your transmissions — I’m sure you’ll find plenty receivers tuned to your frequency.

    JB

  33. FoetusNail says:

    Your position would only be true if I cared whether I convinced you personally (or not).

    If you don’t care why did you respond? Why are you still here? We are only asking you to do what you claim to have done, but now refuse to do until someone sees your bet.

  34. dustbuster7000 says:

    Airshowfan, if its a prop, where is it getting is power from?

  35. FoetusNail says:

    That cart reached its final velocity in the second clip and neither running man, who did catch the cart, or the cart ever showed any signs of going as fast as that debris fly past. He caught the cart, but he never stood a chance of catching any of that debris.

  36. arkizzle says:

    gpomputius:

    It invalidates this bit: “From this assumption, it follows that this DDFTTW craft will constantly move at 1 mph in a windless room, in spite of friction. That, my friends, is perpetual motion. Which is impossible. Thus one of our assumptions is false. QED.

    Nowhere in this statement have you supplied an energy input, therefore assuming Perpetual Motion. You left out the wind by saying “windless room”, or the treadmill. It’s your choice, but the energy has to come from one of them, so no PM.

  37. tyler the perfect child says:

    this guy sounds like data from star trek. if data says its so, it must be so. if the captain says make it so, then well, you gotta?

  38. Alex_M says:

    Well.. I’ve got a physics degree and don’t really see what the fuss is about.

    Wind-powered vehicles haven’t worked strictly by being pushed by the wind since the days of square-rigged ships. Once you accept that (‘counterintuitive’) idea, the idea of moving faster than the wind becomes a lot more difficult to dismiss out-of-hand.

    Also, as a recreational sailor, I know for a fact that sailboats _can_ move faster than the wind.

  39. tkaraszewski says:

    My previous comment seems to have been entirely ignored, but that’s ok, a lot of people in this thread seem more interested in the idea that they may be able to win an argument on the internet than the idea that this device can go faster than the wind.

    As I said in my previous comment, I do think the small model on the treadmill works as advertised, and is in fact exceeding the windspeed.

    However, I have some questions for its designers:
    How fast is the treadmill going? It seems to be indicated in a previous post that the treadmill was set at 10mph.

    How fast is the car going, relative to the treadmill? It seems to barely be moving forward, at a fraction of a mile per hour.

    If the car can go 10% faster than the wind in 10mph of wind, that certainly proves the theory that going downwind faster than the wind is possible, but it’s not necessarily useful.

    That car was designed to have the minimum possible amount of mass and drag. If that tiny car takes a 10mph wind to get it up to a speed such that the power of the propeller can overcome the friction generated from the wheels, and then again reaches its new limit of friction with an additional 10% increase in speed, you have to ask yourself, “If an actual vehicle, big enough and sturdy enough to carry a person was built, with orders of magnitude more mass and friction, how fast would the wind have to blow in order for it to generate enough power for the propeller to overcome the friction generated by the wheels across the ground?”

    It seems unlikely that this wind speed would be commonly seen outside of large, dangerous storms like hurricanes.

    If that’s actually the case, it’s still an interesting toy,but not practical as an actual “vehicle” let alone on a boat, where people would most want it, seeing as the amount of friction is *far* greater than in a car.

    Also, how slow can you run the treadmill and still have the car make forward motion? Does the car accelerate noticeably faster with the treadmill on its highest speed setting?

    I’m actually interested in being educated here, and I’m not out to prove that I’m right to everyone commenting on this post, so if anyone has any real insight, preferably from the builders of the model, I’d love to hear your thoughts.

  40. ThinAirDesigns says:

    DJQueue:
    >So, the propeller is working in reverse,
    >using energy from the wind to generate
    >mechanical force to move the wheels,
    >correct?

    DJ, check out my post #173 for an explanation of how we know that the prop is never working “in reverse”.

    JB

  41. ThinAirDesigns says:

    Dustbuster7000:
    >The ‘spinny thing’ is causing people
    >confusion, since they are used to thinking
    >of a propeller as a source of thrust.
    >And Airshowfan is right, is cannot be
    >both turbine (collector of energy from
    >the air) and propeller (outputer of
    >energy to the air. In this design,
    >the ‘spinny thing’ can only be a turbine.

    Dustbuster, you are half right:

    A: The spinny thing cannot be both a turbine and a prop.

    B: On our design, it never acts as a turbine, and always acts as a prop.

    See post #173

    JB

  42. SubductionZone says:

    Dustbuster, I see one clear mistake in your previous post. The apparent wind speed over the propeller is definitely non zero. Even you admitted that it is rotating. The speed of rotation of the propeller is real and definitely a factor.

  43. ztoop says:

    FYI, I have not seen this contraption actually work except for in these videos, and was a bit hesitant to believe it myself. However, after about 3 hours of thinking about this instead of editing my paper, I think I got the mechanics down.

  44. ThinAirDesigns says:

    Foetusnail:
    >If you don’t care why did you
    >respond? Why are you still here?

    Because it helps us towards our goal.

    >We are only asking you to do what you
    >claim to have done, but now refuse to
    >do until someone sees your bet.

    You really should keep your posters straight — I have *never* offered anyone a bet regarding this craft.

    JB

    • Antinous says:

      ThinAirDesigns,

      I, on the other hand, do have ‘onus’ authority. If you have nothing substantive to add, perhaps you should withdraw from the discussion.

  45. travis08 says:

    Thanks JB, that cleared it up for me.

  46. HUDMAN says:

    “”any acceleration from the cart would cause an apparent headwind, which would tend to slow the propeller down and decelerate the cart.””

    Actually, the tailwind is trying to decelerate the propeller much more than an apparent headwind. The propeller actually likes the apparent headwind, as the apparent headwind is actually trying to turn the propeller in the direction it is already going.

    I’m not spork, but, ball back in your court.

  47. FoetusNail says:

    As I sit here thinking about this cart, trying to rock my kid to sleep, I suddenly realized that a well made cart without a propeller will go faster than this cart with a propeller. Imagine a cart with a sail traveling downwind at the same speed as the wind (ignore friction), now what would happen if you connect a drive train to the carts wheels to turn a propeller? Not only do you need to overcome mechanical friction, but also the drag of the prop. Since the only force in the system is that supplied by the wind, then everything must equal that force. And since the prop traveling at the same speed as the wind is only being turned by the wheels the the prop produces only drag and contributes nothing to forward motion. So, if I were to bet on this, my bet would be, a cart with a sail will travel faster than the cart in this video. In fact if they want to prove anything they should build another identical cart without the propeller and add a sail with about 180 sq inches of sail area and have a race.

  48. FoetusNail says:

    Spork, what is this “exploits the energy available at the ground/air interface” hokum. When one googles this search string “ground/air interface” -radar -signal +aerodynamics, only two search results come up, both linked to the physics forum which is also discussing this hoax. If one includes omitted results there is a grand total of 11 results all of which link to the same forum, again discussing the same hoax.

    You may notice I removed the results for radar and signal, as the technology that uses this phrase are commonly discussing ground penetrating radar.

  49. GregLondon says:

    Actually Greg most of this thread consists of them trying to explain to people who do not want to understand due to their own misconceptions.

    “the wind” is not an explanation. It might be a good place to start but it doesn’t explain anything. making up phrases like “ground/air interface” doesn’t help. responding to questions with “bet me, come on, bet me you mother fckrs!” is also a questionable scientific approach. So to is not having any sort of written plans, drawings, specifications, explanation of what you did so that people can attempt to reproduce what you did. “Convince me that you want to learn, and I’ll send you my propcycle” is just weird.

    If you do not get the fact that the treadmill is an excellent way to test a steady tailwind at the speed of the treadmill

    The treadmill is like the least of my concerns.

    then you are not going to understand anything as complex as the aerodynamics involved

    I don’t understand it. I’ve said as much. In trying to understand how it works, it became abundantly clear that these guys don’t understand it either.

    I think I said pretty early on that this thing might very well do something cool, weird.

    but they can’t explain it because they don’t understand it.

    I’m an electrical engineer, former rocket scientist, worked in avionics, done life critical flight software, and I’ve flown fixed wing and helicopters. I don’t understand how this thing works, but it sure as hell ain’t because these guys explained it and I didn’t want to listen.

  50. neurolux says:

    OK, I think I know how it works. The “props” are actually sails. They don’t blow wind backwards. The wheels rotate the sails. Now…

    We know that a sailboat can travel faster than the wind, but only at an angle to the wind. If you wanted to travel faster than the wind in the direction of the wind, the best you can do is tack back and forth.

    With this vehicle, the vehicle doesn’t need to tack back and forth, because the rotating sails do the equivalent of tacking. This allows the vehicle itself to travel in a straight line.

    Does that make any sense, or am I full of crap?

  51. ThinAirDesigns says:

    As spork points out, in the second outdoor video, the initial half turn is CW from the rear (normal direction).

    As the brunt of the gust hit the cart, the wheels can’t grip the pavement enough to resist the desire of the prop to spin backward and so for a bit it does.

    Once the device gets nearer the speed of the wind, there is less relative airflow to spin the prop backwards and the friction of the wheels wins the battle — spinning the prop in the normal direction.

    From ~15 seconds on you are seeing the ‘wagon wheel’ effect with the prop maintaining it’s CW direction.

    In the first outdoor video, a sharp eye might be able to see the rubber bands that we have stretched around the hard plastic wheels. This is the primary reason that the wheels don’t slip and the prop never reverses in that first video.

    The rubber bands wouldn’t stay put very long out on the pavement so we left them off for the later video. We now have a set of similar wheels with a soft rubber rim which doesn’t require the use of the rubber bands.

    JB

  52. ThinAirDesigns says:

    Again, for all the folks out there who are claiming that the treadmill in a still air room is not a valid testing environment for a DDWFTTW vehicle, please address the following:

    ——————————–
    You wake up suddenly at my house — a place you’ve never visited and with no idea how you got there. You look out the window and see me standing in the middle of the street with this silly little DDWFTTW cart in my hand.

    You walk out the door, issue the appropriate “WTF?” and notice a 10mph wind blowing down the street from the south to the north. You comment on it, and I respond by saying “the air is actually quite still … it’s the ground that’s moving” I continue with the explanation: “this entire town is on a giant treadmill — houses, trees, streets, everything as far as the eye can see and beyond is moving south at 10mph”

    Now, let’s pause the above for a moment and get to the heart of the treadmill equivilancy matter here –

    Can you devise a test, or do you believe one can be devised that can be executed in the middle of the street to determine whether I am telling the truth and indeed whether we are on a treadmill or not?

    You are allowed to enlist the services of anyone and any organization you wish, from Steven Hawking on down. I will also provide you with absolutely endless funding in your quest.

    A: Do you believe such a test exists or can be devised?

    B: Can you please describe it for me.

    Thanks

    JB

  53. GregLondon says:

    Well, if I’ve learned anything, it’s that you can’t get someone who doesn’t understand something to explain it in a way that can be understood by others.

    If I get some cycles I’ll tinker around with some 2×4′s and whatnot and see what I can see.

  54. airshowfan says:

    #181: No. That’d be UP-wind.

    I propose a new question: Can one of these things be made to walk downwind faster than the wind? ;)

  55. ThinAirDesigns says:

    Hi CM. Well thought out test you propose. You have most stuff covered, but there are still a few details that would cause consternation amongst the ranks — the biggest one would be how you make sure that you have the cart going directly downwind. There are ways of course to handle that as well.

    Good thinking.

    CMPalmer:
    >Keep slowing down the treadmill enough and
    >see if the cart still travels faster than
    >the treadmill. Keep reducing it to zero MPH.
    >That is the same condition as the cart
    >coasting along at exactly wind speed.

    Zero MPH is not the same condition as coasting with the wind speed, but rather the condition where there is no wind whatsoever.

    The same condition as moving at the wind speed is where the treadmill *is* moving and the cart is rolling on the belt in such a way that it isn’t moving relative to the still air in the room.

    Our best cart will beat the wind down to 2.7mph and which point the friction overcomes the power of the wind. It is certainly possible to build an even lower friction and more efficient version that would operate at a lower speed, but to us there is no real point to that effort.

    JB

  56. spork says:

    “How fast is the treadmill going?”

    We’ve made a pile of videos (search spork33 on YouTube). We can run it as slow as 2.7 mph (below that the cart won’t keep up with the belt), and up to its max of 10 mph. At 10 mph it will advance up the tread even at its highest incline.

    “How fast is the car going, relative to the treadmill? It seems to barely be moving forward, at a fraction of a mile per hour.”

    Again, it depends on the settings. At 10 mph on a level treadmill I would guess it advances at maybe 3 mph – but that’s a guess. It doesn’t have much room to get up to speed.

    “If the car can go 10% faster than the wind in 10mph of wind, that certainly proves the theory that going downwind faster than the wind is possible, but it’s not necessarily useful.”

    Not unless you’re looking to have a pissing match on the internet. In that regard this thing is more successful than any invention I’m aware of.

    “If an actual vehicle, big enough and sturdy enough to carry a person was built, with orders of magnitude more mass and friction, how fast would the wind have to blow in order for it to generate enough power for the propeller to overcome the friction generated by the wheels across the ground?”

    We have undertaken a massive campaign to get this on the Mythbusters. I envision Adam and Jamie riding full scale carts at Alameda Naval Air Station. I have little doubt that they can succeed in 10 to 15 mph winds. During the early summer these winds are very common at that location.

    “If that’s actually the case, it’s still an interesting toy,but not practical as an actual “vehicle”…”

    This as value as a brainteaser. It will never have value as a vehicle.

    “Also, how slow can you run the treadmill and still have the car make forward motion?”

    2.7 mph

    “Does the car accelerate noticeably faster with the treadmill on its highest speed setting?”

    Absolutely.

  57. Anonymous says:

    Really guys, using simple physics this is easily figured out: (Look at the “real” experiment outdoors, cart blowing along the wind at at speed greater than the wind)

    1. Assume the cart is able to (like anything using sails) move at speed slightly slower than the wind.
    This gives us on specific speed of the cart= vector1

    2. At this point, the wheels driven by the the wind relative to the ground (the wheels and propellor are connected) will result in a certain rotation speed of the propellor. This will give an additional thrust (normal plane proppelled propulsion) relative to the air around it. If the air around the cart is almost still relative to the cart (as it will be if the cart is driven by the wind, see above), the cart will get the second speed component = vector2.

    Total speed = vector1 + vector2

  58. FoetusNail says:

    Tkaraszewski, the cart in the video is not moving faster than the wind. It is stationary in the wind. The belt may have a linear displacement greater then the speed of the wind, but this proves nothing. Take it outside with an identical cart with a sail as I described earlier, video tape the event, then post the results. Until they do this they have proved nothing. The increased load of the propeller’s drag and the mechanical friction of the drive train will make this cart the loser.

  59. GregLondon says:

    The wheels are what make the prop spin, not the wind.

    The vehicle is a closed system. it is like a sealed flask with water/vapor/etc in it. The wind is like a bunsen burner and it is the only thing that has any energy to add.

    The vehicle cannot bleed off energy, put it into the prop, and then make the vehicle go faster. That would be a perpetual motion machine.

  60. ThinAirDesigns says:

    Dust, your summary of our claims in #392 are 100% correct though not complete. There is one tiny clarification I would like to add:

    Dust:
    >So we are clear then, you claim that
    >the ‘spinny thing’ is always acting
    >as a propeller

    This is totally true in any mode related to our claim. It is possible that during ‘self-start’ (something not part of our claim) the prop *may*, at speeds well below TWS, reverse direction momentarily for reasons discussed in posts just above this.

    I have another post in the works addressing some inaccuracies in your post #383.

    Later.

    JB

  61. Cowicide says:

    I smell longhorse manure. Does anyone else smell longhorse manure around here?

  62. R says:

    I had a rediculously long response to this, but then it occurred to me that that the best explanation of the simplest qualitative one, which has already been said, and which could be proven though some pretty simple physics if someone wanted to derive the equations.

    The treadmill powers the forward motion of the of the cart. What might not be entirely obvious to some when they’re trying to picture, conceptually, how this is possible, is that the propeller is angled DOWN. When the cart is held against the mat and the wheels are accelerated, the propeller not only pushes the cart forward, but down so that there is adequate friction between the wheels and the mat for the mat to keep spinning the wheels and powering the cart’s propeller even when you take your hand off it.

    In the other video, it’s obvious that the propeller cart doesn’t ever move faster than the speed of the wind plus the speed given to the cart by the initial push.

  63. tomtheblacksmith says:

    Wow, have I learned a valuable lesson: it is inadvisable to use the word “impossible” in a web posting, or anywhere for that matter. Henceforth I shall perhaps substitute the word “dubious” or “seems unlikely”.

    A friend sent me the link to this site for fun. When I went to look at this clip(s), I discovered that my browser would not view any of the videos, so, just for fun I decided to “solve” the question by pure brainpower alone. My first response was obviously based on an incomplete understanding of the problem. With some clues from a very pleasant co-poster I believe I have figured out the “missing link” (literally) that makes it not only possible, but explainable. Thanks again Chris, I learned two important sump’ns.

    Tom the Blacksmith

  64. FoetusNail says:

    Spork make the video I suggested. Take the cart outside and have a race with a cart without a prop. Hell, for that matter put a cart without a prop and drive train on the treadmill and see if it doesn’t shoot of the end, no matter how fast you turn up the belt speed. Until you post video of a race between two carts, you are the one in a pissing match.

  65. Nelson.C says:

    So, the treadmill is turning the wheels, which turns the prop which produces thrust which pushes the cart up a slope (which is that of the treadmill)? Forgive me, but that doesn’t look like it has anything to do with the original issue. As someone pointed out above, the energy is coming from the treadmill, and doesn’t prove anything about DWFTTW, the wind having nothing to do with it.

    If you wanted to prove the case of the original video, then the readings from an anenometer on the chase vehicle would be a good first step, as well as a wind direction indicator – not a rag hanging behind the propellor, but a professional meteorologist’s device, on the chase vehicle. Finding a level place to stage the experiment and demonstrating that it is level should not be difficult either, and neither is showing that there is no tow rope.

    Really, there’s no need for the treadmill experiment that I can see, just a little more rigour in the initial experiment.

  66. codesuidae says:

    I agree that the spiny thing is a prop. The question:

    Where does the energy come from to allow me to indefinitely overcome a 1 mph headwind and whatever friction is in my axles?

    Is a pretty good one. Here’s how I’m currently thinking about it (I could be totally full of crap though):

    At the start the air is still, the vehicle is still and the belt is moving backwards at some speed.

    The belt pushes the lower rim of the wheel backward and the vehicle center of mass begins to accelerate backward, but does not instantly match the speed of the belt. The inertia of the vehicle provides a counter-force at the wheel hub causing the wheel to rotate around it’s hub.

    As the wheel begins to rotate the prop spins, accelerating the stationary mass of air around the vehicle in the same direction the belt is moving. This action of accelerating the air backwards has a reaction force acting forward on the vehicle center of mass, reducing the reward acceleration of the vehicle.

    The hub of the wheel now has additional resistance to the force applied by the belt which causes further increase in the rotation of the wheel and also the prop, increasing the forward thrust.

    At some point an equilibrium is reached. Depending on the various parameters (friction losses, gearing, prop parameters, etc) the vehicle may be going backward, sitting stationary, or moving forward.

    I would suppose that a vehicle with a sufficiently efficient variable gearbox could dynamically adjust it’s gearing to allow it to self-start and quickly accelerate to near the theoretical maximum forward velocity. It seems unlikely to me that the configuration that allows maximum forward speed is also the configuration that would self-start when stationary relative to either medium.

    If the vehicle is still on the moving belt, energy is required to overcome the various friction losses.

    The vehicle is a machine that is mechanically coupled to two mediums, the belt via the wheels and the air via the prop. The body of the vehicle is also coupled to the air, but very weakly when compared to the prop.

    Because the two mediums are moving relative to each other, a potential mechanical energy is present in much the same way as a hot surface and a cold surface represent a potential thermal energy.

    The device sits in the interface as a conduit between the potentials. As the energy flows through it, some is diverted to another use, just as is done when we use the flow of heat from one place to another to generate electrical energy.

    In one of the related videos on youtube you can see a similar device that does the same thing while coupling to two belts (a couple of parallel boards with relative motion).

    In both cases the diverted energy is used to move the vehicle, with some proportion of the diverted energy lost to friction.

    If the machine is efficient enough the harvested energy can be used to move relative to one medium at a rate greater than the difference between the two mediums.

    If this is an accurate analysis (not say it is or isn’t) such a machine running on a treadmill wouldn’t necessarily be self starting on still ground in the wind because the coupling is different.

    On the treadmill the machine is starting up with inertial mass working against the wheel-belt coupling (machine moving relative to ground). In the wind on still pavement the machine is working with the coupling between a prop and the wind (machine moving relative to the air).

    Since the coefficients of coupling of the two interfaces is different a machine that self-starts when the initial state is moving-relative-to-ground might have a different configuration than a machine that self-starts from the moving-relative-to-air state. I’d suppose the difference would be in the prop configuration.

    Dude, this would be a fantastic MythBusters episode! Someone should make a video and… oh, wait..

  67. arkizzle says:

    Greg:

    Now we demand video of your cart.

    Then we demand explanations in much broader (and narrower) terms.

    Then a different video of the cart.

    Then we will accuse you of a hoax, (in fairness, I don’t believe you called hoax, outright).

    Then we will blame you for our lack of understanding.
    __

    I bet, pretty quickly, you will dislike the tone of the conversations and accusations, and will walk away – or be entirely less helpful.

    Personally, I’m really impressed that you stuck at this thing so long, and built your own model to try test and understand this intriguing puzzle, but now you are in a similar position to the other-cart guys at the top of this thread. Hopefully your experience as giver-of-information in this regard will be less fraught with negativity and aggressive demands for proof.

    It’s only for a laugh, after all.

  68. GregLondon says:

    Greg, what understood law of physics is being violated? The problem is, in this case, you don’t understand the physics involved.

    The basic principle being violated is that these guys don’t know why this thing does what it does but they claim it isn’t flywheeling, it isn’t simple inertia, and so on. If they don’t know how it works, exactly, then they can’t rule out that they are misunderstanding what is happening.

    Case in point:

    Where do we get the energy from? From the fact that the air is not at rest relative to the ground. The air is “going by” the cart at a slow speed (which – if this helps you think about it – helps the propeller get “a better grip” on it), while the ground is going by at a faster speed. The cart’s wheel-prop setup is like a gear that “connects” the air to the ground, and takes energy from the difference in velocity between the air and the ground. So after the vehicle goes by, the air at that spot is moving at a speed that is closer to that of the ground, and the vehicle moves forward to grab the next bit of air and push that towards the back (as the ground passes, towards the back, even faster) as it pushes itself forwards.

    This isn’t an aeronautical engineer talking. I don’t know what this guy does for a living, but if he designs aircraft I’d sure as hell not want to be flying in one at altitude.

    Here’s an article about autogyros

    http://en.wikipedia.org/wiki/Autogyro

    THey work because they have an engine and propeller that pushes the airframe forward. And as the airframe goes forward through the wind, the rotor on top windmills and keeps rotating and so keeps generating lift.

    The energy comes from the engine pushing it forward. This overcomes the drag on the rotor and keeps it spinning.

    In a helicopter the engine is tied directly to the rotor (well, gearbox, clutch, belt, are in between, but whatever), and the engine adds teh energy needed to overcome the drag on the rotor, to keep it spinning. If you lose your engine on a helo, the clutch kicks out automatically, disconnecting the engine shaft from the rotor, the rotor spins freely, and you’ve got about a second or two to drop collective and haul back on the cyclic. If you don’t, drag on the rotor will slow it down to the point that you drop straight down, and the blades fold up vertically around you.

    When you autorotate, you trade off altitude to keep the wind going up through the rotor blades and keep them spinning. YOu can then use cyclic, collective, and pedals like normal, and steer to a landing spot. WHen you get down to about 50 feet, you have one chance to do a flare, which allows you to bleed off your forward speed in exchange for more rotor speed, which then gives you some momentum that you can trade off by hauling up on the collective to stop your descent, hopefully just above the ground.

    At every step, I can tell you where teh energy comes from to keep it in the air.

    Now compare that to this: Where do we get the energy from? From the fact that the air is not at rest relative to the ground.

    What does that even mean? I’ve got a vehicle with wheels tied by a gearbox to a propeller. ANd I’ve got friction in the axles and in the prop. Where do I get the energy to overcome that friction, I ask?

    the air is not at rest releative to the ground?

    What does that even mean? I’m flying a helicopter, I’ve got potential energy (altitude), kinetic energy (forward speed), and angular momentum (in the rotating blades) that I keep trading off as I’m heading down.

    Who cares if the air and ground are moving by my vehicle at different speeds? Where is the energy coming from? I’ve got forward speed of my little propeller cycle. I’ve got angular momentum in the prop/gearbox/axle. I’ve got no potential energy because I”m always on a flat surface. And I’ve got some wind moving relative to the ground.

    But if I’m moving at 10 mph in a 10 mph tailwind, I don’t even have wind.

    But I still have friction. So where do I get the energy to overcome friction?

    These guys haven’t explained this. THey haven’t explained how this operates in enough detail so that it is clear they really understand what’s going on rather than they’re misinterpreting the data. If they’re aeronautical engineers, I want to know who they work for so I never fly or ride in any of their aircraft.

  69. GregLondon says:

    thinair: Your position would only be true if I cared whether I convinced you personally (or not).

    wait, what?

    I appreciate that this sort of attention might help us in our quest,

    You’re on a quest?

    but I certainly don’t have any obligation to jump when you say “onus”.

    I think I just discovered a new logical fallacy: Argument by Apathy. It’s sort of like shifting the burden of proof, except that would take work.

    In the end, our quest for Mythbusters is

    ah, so it’s a quest for fame. And not explaining things and instead stirring up a lot of ruckus is actually a means to an end. Get a lot of people writing into Mythbusters, maybe you’ll end up on the show. That at least explains some things.

    just a round’a’bout way of accomplishing what you wish — the presentation of credible evidence.

    Er, what???

    Do you have any scientific training whatsoever? Credible evidence would be a better video. You haven’t made one. Credible evidence would be design specs for your vehicle so people can reproduce your work. You haven’t made them either. Credible evidenence would be just about anything that you guys are not doing, which is to do one rather sloppy youtube video, and then flock into any blog that googling ‘ddfttw’ happens to find and stirring up a ruckus.

    Perhaps it’s not the way you would do it, but then it’s not your idea. Have one of your own and you can do it your way.

    I’m actually willing to wager money that this device wasn’t originally your idea either. But whatever.

    This at least explains the rather strange not-scientific attitude, “bet me” instead of actual evidence, and so on. I wouldn’t be surprised if spork’s bet is nothing more than yet another way to try and stir up more publicity. Maybe Jamie and Adam will invite you guys onto the show and get your fifteen minutes of fame or whatever.

    sheesh.

  70. Nelson.C says:

    ThinAirDesigns, I don’t want you to eat humble pie. I don’t even want to be right. I want the science to be right. I want the plans so that I can make a stab at determining on paper whether the torque on the wheels could be sufficient to generate enough thrust from the propeller via the gears to propel the cart. I’m willing to be convinced if the evidence supports your contention, but there is no evidence.

    A parts list is not a plan. I could make a pretty mobile from the parts list, or any of several designs for the cart. If I build a cart that doesn’t work as advertised, will it be because I built the cart wrong, or because your intepretation of the physics is wrong? If you publish the plans we can save ourselves a lot of to-and-fro.

  71. FoetusNail says:

    Subductionzone, have you ever sailed a boat faster than the wind, I have, in fact at one point I taught sailing. Do you understand the concept of apparent wind and do you realize there is a point of sail directly downwind where iceboats and sailboats never exceed the speed of the wind?

  72. Anonymous says:

    Tom,

    just in case you haven’t found them yet, here are the plans for the cart:

    http://www.rtfa.net/2008/12/04/downwind-faster-than-the-wind-dwfttw-plans

    To visualize the concept in general, using just wheels/gears:

    http://forums.randi.org/showpost.php?p=4252145&postcount=1645

    Hope that helps you a bit.

    Greetings,

    Chris

  73. GregLondon says:

    The links to the “data” have been provided on this thread as well as parts lists and build advice.

    You posted a link to a .pdf with specs for the vehicle? Or you posted a link to another blog full of your rantings? One is “data”, one isn’t. Most people can figure out which is which.

    If you wish to build one and test one, I’ll give you my personal contact information and help you in any way you wish.

    I wish for you to provide a link to a pdf or similar document the explains how to build the vehicle. Then I can at least try to visualize this thing running in a tailwind. You screaming “But it works, I will be vindicated” and spork going “bet me, come on, bet me”, isn’t explaining it in enough detail to even think this through as to what its doing.

    Yeah, yeah, I know, “the wind”, “the wind”.

    spork: I’d love to help out off-camera if they wanted it

    Jamie: So, spork, if that’s your real name, can you tell me how this thing works so Adam and I can try to build one for the show?

    spork: Come on, bet me. Bet me a million dollars it won’t work. Bet me. BET ME!!!!

    Adam: Uh, could you tell me the gear ratio?

    spork: BET ME YOU COWARDS!!! BET ME!!! A BAJILLION DOLLARS I TELL YOU!!! MONEY MONEY MONEY ALL MINE!!!!

    Jamie: Oooookaaayyy. Maybe someone could just explain to use how it works and we’ll just take it from there.

    ThinAir: It’s the wind.

    Adam: OK, we got a fan set up in a windtunnel, so we’ve got wind. But how do we design it to take advantage of teh wind to make it go faster than the wind?

    ThinAir: It’s the WIND, The WIND, THE WIND!!! HOw many times do I have to tell you its THE WIND!!!

    Jamie: Actually, zero times would have been sufficient. We figured out that much when we saw the propeller on the video. So, does the wheels drive the propeller or does the propeller drive the wheels?

    ThinAir: 100% of the time is it the side of the belt moving down from prop shaft to wheel shaft that remains under tension.

    Adam: OK, well that’s at least one thing specific. So the wheels push the prop and the prop pushes the cart?

    Airshowfan: I insist this because, on the video, that’s clearly how it works. In the video, the cart accelerates from being at rest relative to the air.

    Jamie: Wait. On video? Have you ever built one of these things?

    Airshowfan: I’m not saying.

    Adam: Maybe we should break for lunch and talk about it over some food.

    ThinAir: I’m not eating humble pie.

    Jamie: OK, I have an idea, lets build a catapult, put all of you guys in it, and see how far we can throw you.

    Adam: That works for me.

  74. Mr Bungle says:

    Quite simple really:

    1. The cart can be thought of as initially wind driven (sails for instance). This will result in a finite speed close to the speed of the wind.
    This results in the air being almost still relative to the cart.

    2. The speed given in point 1. will result in a certain rotational speed of the propellor, as this is connected to the wheels by gears. This in turn will result in additional thrust relative the “still air” by means of normal propelled propulsion.

    Add upp the two, and voila, a total speed greater than the speed of the wind.

  75. codesuidae says:

    Oh yeah, regarding coupling; when starting on a treadmill the wheels start to turn because the inertial mass of the cart keeps it in place. When starting the other way around, sitting still in moving air, a still prop with a narrow blade width (cord?) might not generate enough force to get the thing moving. A more fan-like prop might work better, but would have consequences for high-speed operation.

  76. GregLondon says:

    arkizzle: along the right lines with the parallel boards,

    Yeah, except so far, everything I come up with jams up adn doesn’t actually get the sled to move faster than 10 mph.

    I imagine a wheel, with a skinny axle. The top board is on the axle. and the outer rim of the wheel drives another small gear, and that small gear is on the bottom board. Push the top board and the wheel just kind of creeps along.

    I found a sim online, but it didn’t let you change the configuations to anything like we’d need for this gizmo.

  77. Nelson.C says:

    ThinAirDesigns: I apologise if I gave the impression that I thought you were the “scurrilous rogue” in that sentence. I meant to say that scientists are the rogues who won’t take a gentleman at his word, insisting that everything should be tested; in this formulation, you are meant to take the place of the gentleman.

    Alas, though it pains me to admit it, I am as mechanically adept as three lame hedgehogs in a paper bag. I do not wish to build your fabulous machine; when it failed to work, I wouldn’t know whether it was down to my lack of mechanical skill or conceptual problems with the design. Neither do I wish to commit myself to the costs of mailing a ready-built contraption across the Atlantic.

    As I said before, I want to understand it theoretically, or see a video of a rigourous experiment. I do not feel that this is an unreasonable request.

  78. spork says:

    “Take it outside with an identical cart with a sail as I described earlier, video tape the event, then post the results. Until they do this they have proved nothing. The increased load of the propeller’s drag and the mechanical friction of the drive train will make this cart the loser.”

    That’s why my wager has been available for 3 years now.

  79. arkizzle says:

    In fairness, the Mythbusters bit was ‘out’ from the get go, I think it’s even mentioned in the OP video.

    Now I’m gonna shut up.

  80. ThinAirDesigns says:

    Bill Barth:
    >I’m in agreement with everything but
    >your last paragraph

    Wow, that’s a lot of agreement. LOL. Let’s get to the disagreement part.

    >Here’s a thought experiment for you.
    >Consider the following two cases: 1)
    >Still laboratory air, a treadmill
    >surface moving at 10mph, and 2) wind
    >blowing at 10mph, stationary ground.
    >So far, two apparently equivalent
    >situations. Insert the vehicle in both
    >cases, stationary w.r.t. the lab in
    >case 1 and moving forward at 10mph in
    >case 2 (giving them the same relative
    >speed to their ground). Release the
    >vehicles.

    Done

    >In the case 1, the treadmill initially
    >slows a fraction due to the increased
    >load (you agree we’re extracting energy
    >from the motor), but the speed control
    >in the treadmill compensates by supplying
    >a little more current to the motor, thereby
    >adjusting the speed back to 10mph.

    Maybe the treadmill has a feedback loop for the speed controller and does as you suggest. Most likely ours does not as it’s a rather cheap home version. It more likely is just providing fixed logic for the speed control with no feedback from actual belt speed. Either way, for reasons you’ll see next, I’m willing to move forward with your experiment.

    >Based on this, and the thrust from the
    >prop, the vehicle maintains its position.

    (Since you haven’t defined any performance chacteristics of the cart in this experiment, I will assume we are using our cart in the experiment)

    The above will not be true for our cart. Our cart will not maintain it’s position, but rather it will launch itself to the front of the treadmill where something or someone will have to stop it or it will drive right off the top of the belt.

    >But, what does this imply about case 2
    >(outdoors)? The small speed drop of the
    >treadmill is equivalent to a small drop
    >in the wind velocity everywhere outside.
    >Given that this isn’t feasible based on
    >how fluid flows work, the local flow must
    >be different around the vehicle outdoors
    >than it is in the treadmill case.

    I am completely befuddled by that last paragraph. In both cases — indoor and out, we remove the same velocity from the air relative to the rolling surface.

    Perhaps you are saying that since we are in a closed room the ultimate “butterfly causes a hurricane” openess of the outdoors can’t occur and to that I would agree. If I were to place the treadmill outside in the driveway and show the results would this answer your concerns regarding the treadmill test?

    I’ll address your other comments in a seperate post for clarity.

    JB

  81. FoetusNail says:

    Arkizzle, the prop cannot give any extra push.

    Build a very efficient cart with a sail. Make the sail area large enough and the frame thin enough that almost all of the forward motion is generated by the sail. Place the cart on the ground with a ten MPH tail wind. Let’s assume our highly efficient cart is going downwind at 9.8 MPH. Now couple a propeller to the wheels. The efficiency of our machine is reduced because we have now added mechanical friction and the drag of the propeller to the existing mechanical and rolling friction. The only energy being applied to our machine is the wind energy on the sail. This energy is going to be completely consumed by the rolling friction, mechanical friction, and the drag of the propeller with any remaining energy used to move our machine forward. This new machine with a propeller will obviously be going slower than the machine with only a sail. Where is the extra push?

    Now imagine this scenario. We have an airplane traveling at 100 MPH. attach a propeller to the front of the plane that is turned by the planes forward motion, like a child running with a pinwheel. Connect that prop to another prop on the back of the plane. Is there any extra push, or have we just increased the total drag of our airplane?

  82. ThinAirDesigns says:

    Bill Barth: (post #165)
    >You could see this if you were to do
    >long-term average energy consumption
    >tests on the treadmill in a carefully
    >controlled environment with good power
    >conditioners. The energy used by the
    >treadmill will be slightly higher with
    >the prop-and-cart device on it compared
    >to a run with only the cart and a weight
    >to compensate for the missing prop (hold
    >the latter in position with a rigid bar
    >or set of strings).

    The above is absolutely right on, and a point missed by many, including the ‘perpetual motion’ crowd. Nice catch.

    >This energy is the missing energy that
    >prevents a outdoors version of the vehicle
    >from running downwind at greater than the
    >true wind speed.

    This of course is where we part and I’d like to engage you on this point if you will: Let’s imagine for a moment the cart holding it’s own, not moving foward nor backward on a treadmill set at 10mph. I state that this is the cart running downwind the exact same speed as the wind. You likely disagree and that of course is why we’re here chatting.

    First, we must get down to basics — “For every action, there must be an equal and opposite reaction” Agreed?

    Hopefully there is two things you and I can stipulate:

    A: we agree on the “equal” rule above.
    B: the treadmill, through it’s electric motor, is providing energy to the device.

    Considering those two stipulations, in the steady state, 10mph treadmill scenario that I described above, what is keeping the device from dropping off the *back* of the treadmill? The device has only two interfaces — the ground interface (wheels) and the air interface (prop).

    If the device is holding stationary on the moving treadmill, we know that the air interface must be exerting *exactly the same force* forward on the device as the treadmill is exerting rearward. Agreed?

    I mean, it’s like pushing two boats apart floating on a lake — I simply can’t exert more force on one boat than the other. The law won’t allow it. I can turn around, switch my feet to where my hands were and visa-versa — same result.

    Saying that the device will hold steady on the treadmill and yet won’t go the exact speed of the wind is like saying that one boat can ‘push’ more than the other. If the prop, working only through the air can hold the cart still against the force of the treadmill, then by rule of law, the air interface is as powerful and effective as the ground interface.

    JB

  83. FoetusNail says:

    Screw your wager! Smoke screen! Prove your claim or go home, this ain’t youtube.

  84. SubductionZone says:

    Greg, they have tried to explain it to you countless times. You just don’t like the answers. Like people who don’t want to believe the laws of thermodynamics no matter how often they are explained there will be some people who continue to believe in “free energy”. Some people have this so well ingrained in them (that free energy does not exist) that anything that smacks of it will be discounted automatically. Even when it is demonstrated for them and explained to be perfectly natural. Even something as simple as tacking against the wind can seem to be counterintuitive when you first encounter it, I mean come on the wind is blowing against you and yet you are sailing into it, so does this little cart. But if you see something enough in real life you realize there must be a logical explanation for it and you realize that the sails are working with the keel to extract energy from the wind. Well in the same way the propeller acts as a sail and the wheels as a keel, allowing this vehicle to extract energy from the difference between the speed of the wind and the speed of the ground.

  85. dustbuster7000 says:

    @JB

    Right, I read post #173, which is basically a restatement of post #389.

    So we are clear then, you claim that the ‘spinny thing’ is always acting as a propeller. Spork claims that this is a wind powered vehicle. I assume the two of you are on the same page with regard to how this thing works?

    So to summarise your position on how this cart works; the propeller pushes air towards the rear of the cart, causing the cart to move forward AND that the cart is wind powered, i.e. the wind is the source of power for the vehicle. Yes?

  86. EyeSpy Guy says:

    Spork, AirshowFan, ThinAirDesigns, I commend your patience. Really, I do. gently trying to correct people who can not be bothered to read previous posts nor do any thinking or research for themselves. Spoon feeding the obstinately ignorant. It is a credit to you all how you manage this without losing your cool, nor being condescending. I admire this.

  87. LaserRage says:

    #181: The 1st cart didn’t constantly accelerate. You can see the telltale flip back and forth and the prop change speeds. Best I can tell, this isn’t a perpetual motion machine, it’s an afterburner (after-winder?). Now that I think I understand how they work, I’d believe that one of these things could possibly be faster than the wind in a direct tailwind for a period of time.

    And that’s what the goal is, right? To build a machine powered solely by the wind that moves at a rate faster than the wind for some period of time. Not forever.

    I don’t think that they were ever put forward as perpetual motion machines.

  88. SubductionZone says:

    Okay spork can get a bit excited, especially if you accuse him of perpetrating a hoax when he is actually posing a very interesting brain teaser. And Greg if you do have all of those credentials you do have to agree about the equivalency of the treadmill at 10 mph and a 10 mph tailwind. Now the flight credentials don’t impress me all that much seeing how many pilots got POAT wrong. The important thing to remember is that this device gets its energy from the difference between wind speed and ground speed. That is why it is not over unity or anything like that, no wind equals no energy. And I know you may think that you are “outrunning” the wind if you go faster than it, but you are still within it. Look up some sites that show you the available power in the wind, the wheels on the cart act like a keel and allow you to extract the difference between the speed of the wind and the ground.

  89. GregLondon says:

    In fairness, the Mythbusters bit was ‘out’ from the get go, I think it’s even mentioned in the OP

    True, but while I might say something like “this would be a good thing for mythbusters to look into”, I wouldn’t attempt to create a myth, stir up publicity about it, offer outlandish wagers, and create a general ruckus, just so there’s a slim chance that they’ll ask me to come on their show.

    If I bothered to build the damn propeller cycle thingy, you’d be damn sure I’d have a spec published on the web that everyone could see, I’d use off the shelf parts so anyone could go to Home Depot to build the thing, I’d do a whole bunch of control experiments, I’d have a write up with all the data and hopefully some sort of bell curve emerged from that data, and if I shot a video, you’d be damn sure I’d be showing you all sorts of different simultaneous angles. And I’d probably obsess about it till I figured out a way to build an enclosed track wind tunnel so as to avoid using a fricken treadmill.

    Which is the main reason I haven’t built one of these things because I’d be gone for six months and I don’t think I’d have a lot to show for it in the end. I don’t have a lot of reason to believe this is anything other than really low friction, flywheels, and some weirdness that comes from not being able to see wind.

  90. shMerker says:

    I just realized what’s going on here. People are assuming that the vehicle outpaces the wind and creates a vacuum behind itself and then has to fall back onto the wind to continue gaining power. But the propeller doesn’t create a vacuum. Quite the opposite. It’s filling in that space and creating a vacuum ahead of itself.

    It’s like if I was standing on top of a rising platform and I jumped, I would be moving a bit faster than my elevator, but only briefly as there would no longer be any elevator beneath me. So what I’d need would be a ladder. If I was hanging from a ladder being lifted by a helicopter I could rise significantly faster than the helicopter until I ran out of ladder. Since I can climb a ladder then it muse be able to make a machine that can climb a a ladder that is driven by rotating axle so we can power it with an electric motor, combustion engine, whatever. In fact, scrap the motor, lets go green. Let’s just say our ladder-climbing automaton is driven by a wheel and that our ladder is being dragged against a smooth vertical surface as the helicopter rises. As long as there is more ladder ahead of our contraption and as long as it is held against the wall to keep generating power, the only limit on climbing speed is the efficiency of our engineering (of course climbing speed will remain proportional to the speed at which the helicopter is rising. It is the power source after all). If we replace the ladder with air molecules (which makes our air climbing mechanism a propeller) and turn this whole thing sideways we basically have the scenario in the video.

    That was fun.

    None of this speaks to how the vehicle gets moving at wind speed to begin with.

  91. FoetusNail says:

    Spork, No you don’t understand because you don’t believe us. It is exploiting the energy available at the ground-air interface you rube. Our video on a powered treadmill, proves it will work outdoors. It is exploiting the energy available at the ground-air interface you rube.

  92. FoetusNail says:

    I’m sure everyone has played with one of those little propellers on a stick, that you power by rubbing your hands together. Think about how much power you impart to that stick to get an essentially weightless toy airborne and then remember how short a flight it is once the toy leaves your hands and gravity and drag take over.

  93. ThinAirDesigns says:

    More Bill Barth:
    >Imagine riding a propeller-less cart which
    >is traveling at the same speed as the wind
    >(be it outdoors or on the treadmill). Don’t
    >worry for a moment about what’s keeping it
    >at speed. There is no breeze to feel while
    >you are there. Spinning a prop while riding
    >in this cart requires energy. You can crank
    >it with your hand, you can run an electric
    >motor, but you can’t get the energy from
    >the wind because there isn’t any.

    I disagree with your last statement above, but before I can demonstrate the fallacy of it, I must first determine your position on the following:

    Do you agree or disagree that land yachts, ice-boats and other craft with traditional sailing rigs can achieve downwind VMG’s (velocity made good) greater than 1.0 while on an angled broad reach? That is to say that the downwind component of their angled path can be greater than the true wind speed.

    Ice-boats and land yachts regularly achieve downwind VMGs of greater than 3.0. Earlier in the thread I posted links to support this well established fact. If you disagree, we can discuss it. If you agree, I will continue my response to your thought experiment.

    JB

  94. spork says:

    We have explained it many times, in many ways, on many forums. We have posted the parts list and the critical points for the build. This is 5.7 oz of almost nothing – not exactly rocket science.

    I have even offered to build these things and ship them for my direct cost, putting my own time into each one. I have about 12 of them on order.

    We’re not quite so keen to repeat the entire thing every other post for people that simply want to insult and berate us. Thanks anyway.

  95. FoetusNail says:

    Eyespy Guy, their video proves nothing. At no time during the video does this cart ever go forward relative to the supplied wind, except at a small fraction of the wind speed. The linear displacement of the belt and angular displacement of the wheels means nothing as long as the cart stays stationary relative to the wind. Take off the prop and put on a sail and that cart will run with the wind off the end of the treadmill.

  96. ThinAirDesigns says:

    LaserRage:
    >And that’s what the goal is, right? To
    >build a machine powered solely by the
    >wind that moves at a rate faster than
    >the wind for some period of time. Not
    >forever.

    To meet the “steady state” requirement of my claim, the device needs to be able to do it as long as the wind blows. Also, it can’t do it by using stored energy of any kind during any given run.

    JB

  97. toilet says:

    #300 – see #221 and #224. For latecomers who are still wondering where this “extra” energy could potentially be coming from, Alpinwolf’s #115 and #239 are great posts.

  98. spork says:

    “Spork, AirshowFan, ThinAirDesigns, I commend your patience. Really, I do. gently trying to correct people who can not be bothered to read previous posts nor do any thinking or research for themselves. Spoon feeding the obstinately ignorant. It is a credit to you all how you manage this without losing your cool, nor being condescending. I admire this.”

    I’ll assume this is intended for AirshowFan and ThinAirDesigns. I think we all know I have a bit of a hair trigger when it comes to being insulted. I have all the time and patience in the world for skeptics, and people that just generally want to know how it works. But I quickly tire of being told it’s a scam and that I don’t know the first thing about physics or aero. Why do I care? I honestly have no clue.

  99. ThinAirDesigns says:

    Arkizzle:
    >In fairness, the Mythbusters bit was ‘out’
    >from the get go, I think it’s even mentioned
    >in the OP video.

    Yes, not only in the video, but Mark references such in his OP statement. It’s not some hidden agenda.

    >True, but while I might say something like
    >”this would be a good thing for mythbusters
    >to look into”, I wouldn’t attempt to create
    >a myth, stir up publicity about it, offer
    >outlandish wagers, and create a general
    >ruckus, just so there’s a slim chance that
    >they’ll ask me to come on their show.

    Other than when very special experts are needed for such thing as specialty firearms and explosives, I don’t believe I’ve even rarely seen outside individuals on the show.

    Adam and Jamie understandably like to build their own stuff and do their own tests. Any talk that we are hoping for some 15 minutes of fame by being on Mythbusters is misplaced as we don’t expect to be on Mythbusters.

    Our desire to see the project on Mythbusters is limited to the desire to see someone who won’t be accused of cheating perform the tests — a status we are smart enough to know we will never achieve.

    It’s a cool device that surprises folks — perfect for that venue we believe.

    JB

  100. ThinAirDesigns says:

    Foetusnail:
    >Do you understand the concept of apparent
    >wind and do you realize there is a point
    >of sail directly downwind where iceboats
    >and sailboats never exceed the speed of
    >the wind?

    Foet, with the above you’re traveling down the wrong side of a well worn path: See posts #279 and #280.

    JB

  101. kingharlo says:

    I think that Neurolux nailed it up at #95.

    That isn’t a propeller at all, the angle of each propellor blade with respect to the wind is the equivalent of 2 sails on a close reach rotating around an axis.. which is why the propellor can spin faster than the wind, which is why the wheels can spin faster than the wind.

  102. codesuidae says:

    @257 GregLondon

    Here’s what I’ve been trying to visualize lately. Imagine two 2×4′s set soem distance apart. In between them, you put some machien that has wheels between the two boards. one board is stationary. The other board starts moving. Would it be possible to have the machine between the two boards extract the energy of the motion of the two boards and move faster than the boards are moving?

    I mentioned that in my previous posts. You can watch the video of the machine:

    http://www.youtube.com/watch?v=ZVSjA7Rhccs&feature=related

    It moves a little oddly, probably because it uses a rubber band to link the two sets of wheels (guessing, can’t see the linkage in the video), but the principle is obvious. You can get the same behavior by simply stacking the wheels.

    The machine is coupled to the two moving planks and uses the potential energy embodied in the relative motion to move itself. This is the same as using the moving wind rather than a second plank, except that it is harder to couple the device to the wind.

    In the plank-plank device the wheels coupling to the two mediums are of equal size. They are able to couple with equal efficiency. Imagine if the top set of wheels were made of teflon, or if the to board were very crumbly, such that the top wheel would easily lose traction. In this case it would be advantageous to adjust the 1:1 gearing between the wheels up to something that couples more effectively to the top board.

    Replace the top board with the wind, and the top wheels with a prop that couples effectively to wind and the device still works.

  103. Anonymous says:

    Nelson, Fetus, and Greg:

    What’s wrong with the yo-yo experiment as an easy-to-build and analyze proof of principle? Here’s a video, posted earlier:

    http://www.youtube.com/watch?v=E7vcQcIaWSQ

    (I’m the same commenter as #211 above.)

  104. tomtheblacksmith says:

    Greetings Anonymous Chris,

    Just for the record, I have not seen any of the videos. Alas my computer is so old that it has a little kerosene “pilot light” in the back, so I am arguing based on pure logic and my understanding of physics.

    You describe two kinds of vehicles, one with a windmill on it, and one that is driven faster than its mechanical input by a screw, these are two different arguments.

    A cart with a windmill driving its wheels will (with sufficient wind) be able to travel any direction you wish including directly into the wind, just not directly downwind. If the blades of the windmill arrive at the destination (point B) at the same time as the rest of the cart, then they are in fact moving at the same speed as the cart, and will be becalmed as soon as the cart reaches the speed of the wind, and will therefore stop receiving force from the wind.

    An “ordinary” windmill when stationary is nothing more than a bunch of little “sailcars” on sticks rotating around a central point at a direct right angle to the wind. Indeed the tips of the blades can travel “faster than the wind” in a circle so once the blades reach a certain velocity, the tips begin to generate “negative” force, that is they try to “blow air forward” in the direction that the wind is already blowing which requires work, which slows the entire blade down to a “terminal velocity”.

    If you put this windmill onto a cart and allow it to drive itself directly downwind, as soon as it gets to the speed of the wind, the wind “stops blowing” (as far as the windmill is concerned) and the windmill isn’t going. If the tips of the windmill part spin too fast, they essentially “put on the brakes” by becoming a fan which is trying to blow air the wrong direction (forward) which isn’t going to help it go faster than the wind.

    A vehicle driven by a screw and nut or some other type of mechanical advantage is really just a very complicated form of lever, and it will stop going as loon as you reach the end of the lever, or screw or whatever. You could put a sail onto lever or a nut which drives a screw mechanism (and cart) “faster than the wind” but only until you run out of screw, then you are all done.

    The screw and cart and lever and whatever become part of what is known in mechanics as a “four part linkage” and the “hidden link” is the ground that the vehicle is traveling upon. You won’t run out of ground to drive over, but as soon as the nut reaches the end of the screw, or the lever reaches the end of the stroke, the cart stops.

    In summary, any “sailcar” that is traveling DDW is becalmed as soon as it (and all of its component parts) reach the exact speed of the wind. You could indeed drive a vehicle powered solely by the wind from point A to point B “faster than the wind” but for some portion of the trip you have to drive it at some angle to the wind, however slight it may appear, to do so.

    A mechanical car where some parts of the car arrive at the destination before other parts do will at some point “run out of lever or screw” and stop.

    Tom the Blacksmith

  105. FoetusNail says:

    Arkizzle, now take away the sail.

  106. codesuidae says:

    Pay close attention to that part where Vw drops to -3 and the cart experiences a 3 mph apparent headwind.

    That air-vehicle relative wind definitely causes drag on the vehicle which requires power to overcome. The power that the vehicle can extract from the air-ground relative wind goes to doing that. At some point the power extracted and the various drags reach equilibrium and the vehicle does not go any faster.

    And remember the only thing pushing this cart is the tailwind. The only thing turning that wheel, which turns that prop is that negative tailwind.

    Sort of. Thinking of it as the wind pushing the vehicle, as if it were a simple flat sail, is not accurate. The prop is a method of linking into, or coupling to, the air, just as the wheel is a method of linking to the moving ground.

    A flat sail is to the air like a skid is to the ground. The skid the skid can ‘grab on’ and link the vehicle to the ground, but that’s it. A wheel can do that, but it can also transfer mechanical potential.

    The prop is like a wheel for the air, it can perform like a flat sail, simply grabbing hold of the air by blocking it’s passage, but it can also transfer mechanical potential elsewhere.

    The vehicle extracts power through letting the wind work against the ground through the linked prop and wheels, both of which operate on the air or ground, but without being attached to them, as a sail or skid is.

  107. GregLondon says:

    Someone who conceives a device from first principles, designs, builds, predicts and then demonstrates those predictions through testing “doesn’t know how it works”.

    You didn’t concieve of this device. You didn’t design it. You copied something you saw someone else do, and you reproduced some result but you don’t know why.

    And topics that receive repetively high posts counts are ‘boring, meh who cares?’ topics

    Now you’re just being a pain. I said it would be “meh, who cares” for a lot of the mythbuster audience. Their demographic involves a lot of “lets watch something get blown up, set on fire, dropped from a big height, or shot with a gun” type folks. When the women start wearing baggy clothes like Jamie and Adam, I expect them to lose another demographic too.

    This doesn’t blow up, catch fire, involve firearms, ballistics, catapults, dynamite, or even souped up engines. It is an overblown sailboat, not exactly the sort of thing that “can you remove cement from a cement truck using dynamite?” crowd would be terribly interested in.

    Would the do a bit on this? Maybe. But they’d be sure to put it in an episode where the other myth involves howitzers.

  108. kingharlo says:

    I think that Neurolux nailed it up at #95.

    That isn’t a propeller at all, the angle of each propellor blade with respect to the wind is the equivalent of 2 sails on a close reach rotating around an axis.. which is why the propellor can spin faster than the wind, which is why the wheels can spin faster than the wind.

  109. spork says:

    “If I bothered….”

    Exactly.

  110. codesuidae says:

    #328 FoetusNail

    We all agree the only energy propelling this thing over the ground is wind energy, once we remove the cart from its motor.

    This is true, but calling it simply ‘wind energy’ doesn’t necessarily provide an accurate picture for many people’s intuitive understanding of how the power to move the vehicle is derived.

    It would be more accurate to say that the energy propelling this thing over the ground comes from from the difference between the air speed and ground speed.

    some of believe we are going to magically create enough energy at the ground/air interface to turn a prop, which would then create enough added thrust to propel this cart ahead of the wind energy used to propel the cart

    Much of the objection centers around the belief that once the cart has reached the speed of the wind that there is no more ‘wind energy’ to be had.

    This is true for vehicles that get their motive power by a simple sail, such as a balloon. Conceptually they are just attaching to the moving air and going along for the ride.

    This is not true for vehicles that get their motive power by utilizing not just the motion of the wind, but the motion of the wind relative to the ground.

    The objection that once the vehicle reaches the speed of the wind that there is no longer any wind does not apply to to this sort of vehicle because it is not using the absolute wind speed, as a balloon does, it’s using the difference between the wind speed and the ground speed.

  111. SubductionZone says:

    Foetusnail, I haven’t. And I do understand there is a point where a boat will not exceed the speed of the wind. But then as a sailing instructor you should understand that there is a point where the downwind portion of your speed is greater than the speed of the wind. In other words if you release a balloon of neutral buoyancy so that it floated directly downwind you should be able to beat it in a race by tacking back and forth with the wind, where the direction of the race was straight down wind.

  112. Eseck says:

    It kinda reminds me of how the size of an ant lets its legs support its weight, but if you make it proportionally larger its legs won’t support itself.

    Which might me why it works so well when it’s smaller.

  113. jackofsometrades says:

    I thought of an analogy to help explain this phenomenon. Instead of wind, imagine a string moving at a constant velocity along a flat track. Is it possible to design a vehicle that can use the string to move faster than the string? The answer is yes, and can be easily demonstrated by “walking the dog” with a yo-yo. This is not perpetual motion; it does not violate any laws of physics; still, it is pretty cool. I’m wondering if it might have any real-world applications…

    JC

  114. ThinAirDesigns says:

    Foetusnail:
    >Let’s assume our highly efficient cart is
    >going downwind at 9.8 MPH. Now couple a
    >propeller to the wheels. The efficiency
    >of our machine is reduced because we have
    >now added mechanical friction and the drag
    >of the propeller to the existing mechanical
    >and rolling friction. The only energy being
    >applied to our machine is the wind energy
    >on the sail.

    The last sentence above is where you are in error. The wind energy on the sail is not the “only energy being applied”. Why you leave out the thrust from the prop you just added, I have no idea.

    >This new machine with a propeller will
    >obviously be going slower than the machine
    >with only a sail.

    There’s nothing “obvious” about it in light of the fact that multiple devices have been created in the real world that go faster. I know you don’t believe it, but perhaps one day you will.

    >Now imagine this scenario. We have an
    >airplane traveling at 100 MPH. attach
    >a propeller to the front of the plane
    >that is turned by the planes forward
    >motion, like a child running with a
    >pinwheel. Connect that prop to another
    >prop on the back of the plane. Is there
    >any extra push, or have we just increased
    >the total drag of our airplane?

    The above scenario is identical in form to running a belt from your car’s front wheels to the back wheels and expecting to have a net gain: In both the airplane and the car, we have no relative motion to exploit for our energy gain — in the case of the plane, the air is not moving relative to the air and in the case of the car, the ground is obviously not moving relative to the ground.

    To extract energy, there must be relative motion between two mediums and the energy extraction device must have an interface with *both* mediums.

    JB

  115. FoetusNail says:

    Explain the statement “it exploits the energy available at the ground-air interface”, please. And please explain why once results for radar and signal are omitted and aerodynamics are added, the only search results for that phrase are found on forums discussing this hoax.

  116. FoetusNail says:

    But I quickly tire of being told it’s a scam and that I don’t know the first thing about physics or aero.

    I have not written one word other then to say, your video proves nothing, and your wager is a smoke screen. The only request I have made is the same request any peer reviewed publication would make, come back when you have proof. You know as I do your cart essentially remains stationary relative to the wind machine.

    If this worked his video would prove it in the manner I suggested. Because a well run test with an identical sail powered cart, with credible witnesses would settle this once and for all, but he doesn’t want to settle this, he is enjoying this little hoax. It is not a scam until he rips someone off.

  117. codesuidae says:

    Now imagine this scenario. We have an airplane traveling at 100 MPH. attach a propeller to the front of the plane that is turned by the planes forward motion, like a child running with a pinwheel. Connect that prop to another prop on the back of the plane. Is there any extra push, or have we just increased the total drag of our airplane?

    This is a fundamentally different situation because the props are coupled to mediums with no relative potential energy (probably negative potential in the case of axially configured props).

  118. FoetusNail says:

    Subductionzone, no sailboat, NO SAIL POWERED boat, cart, vehicle of any kind sails directly into the wind.

  119. Pyros says:

    I don’t have the answer, but I think there is every reason to believe that this could shape up to be another airplane-on-a-treadmill style debate only to be resolutely solved by tv’s Myth Busters.

  120. Clemoh says:

    the whole thing was addressed back in post 97.

  121. FLG says:

    Here’s my thoughts on it.

    So the wind creates the initial movement. Not by turning the propeller, but by merely pushing against it, causing the wheels to turn, thus causing the prop to turn.

    The prop is pulling (or pushing, I don’t know) air backwards, while the wind is pushing forwards. Thus craft is able to move faster than the wind. But only because there is a force constantly acting on it.

    At least I think that’s how it works. I don’t really know much about this sort of thing.

  122. misterfricative says:

    Re Spork #296 and Thinairdesign #297, OK, I’m back, and yes, I’m convinced. I thought I had several demonstrations to show that the inertial reference frames were critically non-equivalent, but none of my demonstrations panned out — because of course the inertial frames *are* equivalent. So if the minicart works on the treadmill, then it must also be possible for JG’s free running cart to work on the road. I offer my sincere apologies to Jack Goodman for calling his video a fake. (Although in mitigation, I have to say that Youtube videos are pretty notorious for fakery, and man, it sure looks like a fake! If I was going to fake this out, then that’s *exactly* how I’d do it, from the framing right down to the deliberate mistake ['Oh, I left the brakes on'].) Anyway, my bad. Sorry.

    So I’m now a ‘believer’. And I also think I finally have a reasonable understanding of how these DDWFTTW carts actually work. In an effort to dispel some of the confusion about this, I’ll [cross]post this on the other, more recent thread…

  123. banjology says:

    Clearly these plastic spork wielding scientists have got me convinced! Did you all see how many mississippi’s that thing kept going for?!

  124. FoetusNail says:

    Spork just do this, call the local cops down, take the cart outside and shoot the cart with a laser and show the anemometer’s and the gun’s displays on tape together.

  125. GregLondon says:

    So, apparently, my little propeller cycle will reach steady state at around 11 mph ground speed with a 10 mph tailwind. Meaning I’ll feel a 1 mph headwind if I’m in the cockpit, driving this little widget.

    And my question still remains unanswered. Where does the energy come from to allow me to indefinitely overcome a 1 mph headwind and whatever friction is in my axles?

    My wheels are turning the propeller, but that doesn’t tell me where the energy is coming from to overcome friction indefinitely. If I bleed off forward speed, I can spin up the prop. but to bleed off speed I’ve already slowed down, so it’s too late.

    I’ve got a 1 mph headwind, so I can’t really use that to make me go forward faster. Because they swear up and down that the prop doesn’t drive the wheels. IF the prop doesn’t drive the wheels, if the wheels drive the prop, then the headwind isn’t something I could somehow leverage to go into the wind faster.

    The thing is I’m not saying this gizmo doesn’t somehow find a steady state faster than the wind. I’m saying these guys haven’t explained it sufficiently enough that I’m convinced they haven’t misinterpreted their data and it’s simply a big flywheel with near zero friction so things spin for a long time.

    If spork can’t get anyone to take him up on his bet, but he’d still like to make some money off of this, he could sell little cycle-propeller kits. or maybe plans. Or something. Ihaven’t seen anything concrete.

  126. Oceanconcepts says:

    re. #198 from AIRSHOWFAN

    And in any case, I really really don’t think that the downwind component of a sailboat’s velocity exceeds the wind speed, but I am not as qualified to state this for sure as other people who participate in this discussion and who have actual knowledge of sailing.

    Sailboats (and even more so land sailors, iceboats and other lower friction sailing devices) can indeed have a downwind component to their velocity that exceeds, often considerably, the wind speed. You will almost never see fast racing sailboats heading directly downwind, even if the mark they are heading for is located directly downwind, because they will get there faster by tacking at some angle to the wind. Most electronic instruments for sailing have a “VMG” (velocity made good) function to help find the optimum angle for getting to a mark fastest. It’s almost never to head directly downwind.
    Like you, I’m puzzled at the unwarranted skepticism. While maybe a bit counterintuitive (like sailing an iceboat at a 60 mph in 20 mph of wind with a VMG downwind of 1.5X wind speed), it is not impossible.

  127. sleestax says:

    My Laser racing wife isn’t home right now to confirm this, but my experience sailing Cats is that they CAN go faster than the wind on a reach downwind. By sailing 70-80 degrees off the wind (called a close reach I think) you can go much faster than the wind in a Cat and some monohulls. I believe iceboats are more than capable of it also.

  128. Anonymous says:

    Also there ıs an other source of energy created by treadmill and not transferred to the vehicle usıng the wheels: the wind caused by the surface of the treadmill moving relative to the air in the room. It is small but will move air against the device powerfully enough to cause some additional forward pressure on the device.

    The treadmill experiment is totally unsound and not a correct model of the actual problem.

  129. Bill Barth says:

    @274 ThinAirDesigns: It is pretty clearly established that on a broad reach land and ice boats can achieve downwind components greater than the true wind speed. I don’t dispute it.

  130. FoetusNail says:

    And that difference would be what, 10 mph? Lets see the wind is moving at 10 mph and the ground is stationary, hmmm, 10 minus zero equals what, wait, wait don’t tell me, hmmm, oh I know 13.

  131. Matt Jarpe says:

    That looked like a dangerous fork/spoon hybrid to me. These guys clearly don’t hesitate to mess with things mankind was not meant to.

  132. ThinAirDesigns says:

    Sodesuidae:

    Nice analysis over the last few posts. I’d have to dig pretty hard to come up with anything I disagree with and it wouldn’t be substantial nor critical.

    Thanks

    JB

  133. codesuidae says:

    Explain the statement “it exploits the energy available at the ground-air interface”, please.

    I don’t suppose you saw my post at 218 where I said:

    The vehicle is a machine that is mechanically coupled to two mediums, the belt via the wheels and the air via the prop. The body of the vehicle is also coupled to the air, but very weakly when compared to the prop.

    Because the two mediums are moving relative to each other, a potential mechanical energy is present in much the same way as a hot surface and a cold surface represent a potential thermal energy.

    The device sits in the interface as a conduit between the potentials. As the energy flows through it, some is diverted to another use, just as is done when we use the flow of heat from one place to another to generate electrical energy.

    The ‘ground-air interface’ is just referring to that place where the machine has access to both mediums. A floating balloon doesn’t have access to the ground, and a wet badger in a hole doesn’t have access to the air/wind. The device, sitting on the ground and in the wind, has access to both and so can, if properly configured, exploit the potential energy there.

  134. smellison says:

    ummm… this isn’t science. whatever you decide about the actual physics of this idea, (and I side with the “This Is Bologna” group) you must at least recognize that this was a wholly unscientific process by which they reached their conclusions. Where, in any of this, was the anemometer?

  135. ThinAirDesigns says:

    Nelson:
    >If you publish the plans we can save
    >ourselves a lot of to-and-fro.

    Yep, but then I’d have to draw the plans up and so we’re stuck with a parts list, pictures, published build advice and in the end if that isn’t enough — “to-and-fro”.

    I have made the following offer numerous times to numerous critics: Engage me in a way that convinces me your actually interested in learning about this device and I’ll box one of mine up and sent it to you(I’ll pay the one way shipping). All I’ve ask is that the individual video document a good faith effort to make it work, post the results and return the craft to me.

    I’ve yet had anyone take me up on the offer, which leads me to believe that most critics complaints about me not posting the plans in the format they want is just a bunch of sniping rather than an actual desire to test one.

    The opportunity is there to convince my I’m wrong.

    JB

  136. badger500 says:

    I got to about comment 250 or so before I could go no longer, but GregLondon, very enjoyable posts!

    Energy free lunch buffets are so fun.

  137. 850 says:

    Aaaannnddd…. it’s self steering?

  138. PharSyght says:

    There are two cases here. One on a treadmill, powered by the treadmill, the other is outside powered by the wind. I have now read a ton of other forums and magazine articles about this debate that has been going on for years, and there is still one piece of info I can’t find.

    The relationship between wind pushing on the cart, and the treadmill making the wheels turn. Maybe this is my own shortcoming, but I don’t see how the power from the electric motor, without a fan pushing on the back of the cart to simulate the wind, is at all equal to wind alone. If there is a fan and a treadmill to offset the forward motion, the situation is very similar, but driving the wheels with a treadmill to turn a prop is not the same thing. In one the power is from wind, the other from the wheels.

    I understand the concept of lift pretty well; thanks for posting the NASA article thing to help make sure I had that right. I understand that the moving prop is like taking a sailboat, and that a sailboat can move faster than the wind. This all makes perfect sense to me.

    I am not convinced it can really work, but I understand how it might. What I don’t get is how a stationary street and wind, is anything like a moving treadmill without the wind. On the treadmill the propeller pushes near stationary air and does provide thrust as you would expect, derived from the power of the treadmill.

    If someone can explain this correlation, I think it will all make sense to me

  139. toilet says:

    You could also try to put floaties on it, swap the front wheel for a boat prop, stick it the the water and see if it’ll travel faster than a sailboat. DWWFFTASB?

  140. ratwerks says:

    #267: I do not recognize your authority, ‘onus’ or otherwise. If you’d read the thread (I have because I find willful smug ignorance a fascinating human spectacle) you’d be aware that ThinAirDesigns has arguably said more of substance than any other participant.

    How can any thinking person countenance
    the continual accusations of fraud and failure to explain in the face of torrents of evidence and explanation? Worse still, to fashion charges of yet more bad behavior aimed at people who’s only ‘crime’ is to have found and demonstrated something pretty cool?

  141. spork says:

    “It is pretty clearly established that on a broad reach land and ice boats can achieve downwind components greater than the true wind speed. I don’t dispute it.”

    Yes, and they do so by exploiting the energy available at the interface of surface and air.

    Moreover, our cart goes DDWFTTW using exactly the same principles. All you have to do is imagine that ice boat on a continuous broad reach spiraling downwind on a cylindrical earth (over which the wind is blowing parallel to the earth’s axis). The sail of this ice boat would be tracing the identical path, and experiencing identical kinematics and aerodynamics as one of our prop tips. Put such an ice boat on both sides of this cylindrical earth and you’ve got both blades of our prop.

    Now we can shring the whole thing down to two sails mounted to a shuttle sailing downwind faster than the wind on a giant coarsely threaded rod. The rod simply enforces the same constraint that the blades on the ice did – namely that the sails have to follow a 45 degree downwind heading.

    Finally, we get rid of the big threaded rod, and replace it with a cart that enforces the same kinematic constraints using its wheels and transmission. But in the end we still have these two blades that might as well be ice boat sails, because they maintain a continuous 45 degree downwind course faster than the wind. And they do it because they have exactly the same interaction with the wind and with their kinematic constraints.

  142. DSCN3879 says:

    I’m going to make a giant version of this in space so that photons can push me faster than the speed of light!

  143. Icaruswing says:

    Okay,
    I may be missing something – but when a propeller driven by the wind, and moving with the wind, reaches wind speed wouldn’t the pressure needed to drive the prop fall off? and as the vehicle surpassed wind speed, wouldn’t the prop actually start to turn in the other direction – as the wind would actually start to blow in the opposite direction at that point?
    How does the vehicle work around this?

  144. codesuidae says:

    @307 JackOfSomeTrades:

    That’s a great analogy, I like it. It’s even better than the two boards example in the video, and trivially easy to demonstrate with a clear wheel, axle and string.

    It could be done with a couple of those clear disks that come on the top and bottom of packages of DVDRs.

  145. ThinAirDesigns says:

    Code:
    >Regarding the barometer; I love that story!

    My fave: take it down to the facilities department and say ‘I’ve got a nice altimeter here that you can have if you tell me how tall the building is’.

    >to me the most pleasing proof would be
    >a vehicle that demonstrates the principle
    >while carrying a person.

    I agree, technically sound proof: treadmill. Let’s have a blast and kick the wind’s A88 proof: Let me get in the sucker.

    With our energy problems on the forefront, perhaps the NHRA can have at Downwind Dragster division. First ‘dragster’ to 11mph wins.

    BTW, I’ve got a manned version on the drawing board (I don’t mean that literally FOETUSNAIL, I don’t work the way you think I should work and it’s really just in my head) I actually think I may drive the prop with fishing line to prove our point about what drives what.

    JB

  146. af2008 says:

    I am not sure if anyone noticed, but I showed that the ground speed is can be faster than the wind speed in #162 (for a or x negative). I didn’t have much time to finalize things as I had to rush off. I think there was a small mistake in that a=tan(theta), where theta is the difference from being perpendicular to the wind.

    Greglondon #186, consider the frame moving with a car at 10 mph in a 10 mph tailwind, so there is no wind in this frame and the car is stationary. Since the wheels are turning, so is the propeller. You will agree that there is no wind in this frame, and a propeller in a static fluid generates a force forward. Thus the car is pushed past 10 mph by the propeller.

  147. FoetusNail says:

    Because the prop is only being driven by the energy already applied to the sail. Whatever *thrust it generates* would only be subtracted from the wind energy acting on the sail.

    Which multiple devices? Sailboats on plane going across the wind and generating an apparent wind, or sport kites doing the same, have nothing in common with sailboats or sail carts going directly downwind. I spent many years racing, don’t try to BS me on this one.

    Call the cops shoot the speed and show both the anemometer and laser displays simultaneously with credible witnesses. This simple test wouldn’t cost a dime. By the way why don’t we see an anemometer in your video?

  148. ThinAirDesigns says:

    Bill Barth:
    >It is pretty clearly established that on a
    >broad reach land and ice boats can achieve
    >downwind components greater than the true
    >wind speed.

    Excellent — things are getting easier.

    Back to your statement regarding riding our propeller-less cart at the same speed as the wind:

    >but you can’t get the energy
    >from the wind because there
    >isn’t any.

    To demonstrate the mistake in the above, let me propose my own thought experiment:

    Imagine this for moment: Let’s take two ice-boats and send them on mirror tacks (broad reaches in sailing terms) downwind. They zig out at 45 degrees, and zag back towards each other. When they meet up on the direct downwind line, we send them back out to do it again. Now we have two boats whose downwind component of their path is greater than the wind itself.

    Now, imagine a telescoping pole between the two ice-boats with a seat and a set of controls in the middle. The pilot gets in the seat (pointed straight downwind) and turns the ice-boats loose. Now we have a vehicle whose chassis, pilot, controls, and most importantly it’s CG is travelling DDWFTTW, powered only by the wind, steady state — and as a bonus, it’s not violating a single law of physics.

    The most interesting thing is what the pilot feels when the VMG of the craft reaches 1.0 (same speed as the wind) — absolutely no wind whatsoever.

    As you stated above, one could easily think “you can’t get energy from the wind now because there isn’t any”, but yet in spite of that conclusion, soon enough the pilot feels wind on his face and the ‘impossible’ has been done. The key of course is “apparent” wind on the sails rather than any wind related to the cart chassis.

    As you can see, just because sitting on the chassis of a DDWFTTW vehicle we don’t feel any wind, does NOT mean:

    >you can’t get the energy
    >from the wind because there
    >isn’t any.

    The energy is there even though you don’t feel wind on your face — one only must come up with a practical way to keep the sails on a broad reach — and in the case of our cart, it’s done with a simple prop who’s kinematic constraint to the wheels replicates the constraint of the ice-boat skate perfectly.

    Follow?

    JB

  149. bodgetastic says:

    If you remove the inefficiencies of the gear train from the equation, the spinning of the propeller should spin the wheels at the speed required to match the wind speed and stay stationary, if not move backward a little due to drag on the propeller and airframe.

    The spinning of the propeller should also create a low pressure area above it’s face, creating thrust. If you add in some of the crazy effects the wing (prop) tip vortices probably play, I imagine you could account for the forward motion.

    Has anyone tried to measure the acceleration of the little carts from a stand still? From there you’d be able to back out the apparent force and see if it can be matched to any of the mechanisms at work.

  150. travis08 says:

    For those that suggest this may work on a treadmill but not in a wind tunnel, isn’t the notion that it is moving forward relative to the treadmill just as amazing?

    If the original premise INSTEAD was that they built a machine that could move forward against a moving treadmill wouldn’t you be arguing just as passionately that that isn’t possible?

    p.s. I have no idea who is correct here, just that a contraption that could do this outside in the wind, or inside against a treadmill seem equal. Inside the treadmill is powering it, outside the wind is powering it.

  151. ThinAirDesigns says:

    Well Bill, I see that Spork posted a related and similar thought experiment just before I did. Now you have two to chew on.

    JB

  152. toilet says:

    There was no anemometer because there was nothing blowing it — there’s a gear drive on the front wheel. It’s propelled by wind, going faster than the wind.

  153. dustbuster7000 says:

    Subductionzone, let me suggest an alternative ‘equivalent situation’ test for the model in the video. Wait for a clear, still day. Take the treadmill outside and put model on it and get it up to speed(or use something else to achieve the same spinning of wheels and propeller). Now the wheels and propeller are in an equivalent position and speed to that in the ‘same speed as wind speed case’, no relative wind, wheels and prop spinning. Remove model from treadmill and place on level ground on a still day. If device works as claimed, it should accelerate until it reaches equilibrium between thrust (from prop) and retarding forces (drag and friction) and stay at that speed indefintely.

  154. Anonymous says:

    Hello Tom,

    that is where the confusion comes from. The prop works as a prop, not as a windmill/turbine. When the cart moves forward, the prop pushes air backwards. The movement of the cart will make the prop spin, through the coupling between wheels and prop.

    Think of the prop as an airscrew, and you pretty much have the situation with a screw & nut. The screw is the prop, the nut is the moving air.

    Another way to look at the principle: Take a YoYo, put it on the table so that it can roll, with the string coming out below the center of the YoYo. Now pull the string. The YoYo will move in the same direction as you pull, but faster than the speed of the pulling.

    Now replace your hand with a parachute, and you have something that will travel downwind faster than the wind, completely driven by the wind.

    As i like to explain, when viewed from behind, the prop’s surface facing the wind is moving forward slower through the wind than the cart. So if the cart is at windspeed, the wind can still push on the surface of the rotating prop.

    Greetings,

    Chris

  155. manicbassman says:

    #148: It doesn’t, the whole thing is a scam…

  156. SubductionZone says:

    Foetusnail, my last post seems to have disappeared in the the ether. But yes, I realize there is a point with a sail where if you go directly down wind you will not exceed the speed of the wind.

    Do you realize that there is a point where your downwind speed is faster than the wind? In other words you could beat a balloon in a race floating directly downwind by tacking back and forth with the wind.

  157. Anonymous says:

    Tom,

    forgot to mention. You said:

    “…but for some portion of the trip you have to drive it at some angle to the wind, however slight it may appear, to do so.”

    And that’s exactly what the prop’s blade do. They move at an angle to the wind.

    Greetings,

    Chris

  158. Pyros says:

    I don’t think there is anything wrong with sailing faster than the wind if you want to.

  159. GregLondon says:

    Actually I got my M.S. in aero

    Uh, the issue around you beign known only as “spork33″ is that any anonymous knucklehead could claim to have a masters degree in aeronatical engineering, or doctorates in Theology and Canon Law *, for example.

    Have you put your real name next to your claims?

  160. dagfooyo says:

    I watched the treadmill for quite a while, thinking “yeah, so? you’re keeping it going with the spork!” Then I realized they were intending to make us think the treadmill was moving from right to left. It seems pretty clear to me that the treadmill was running left to right. The spork wasn’t preventing the vehicle’s unchecked acceleration off the mill, it was providing something to push against to keep the wheels and propeller spinning.

  161. af2008 says:

    PS – The key thing to remember in this entire exercise is the blades of the propeller are not in fact moving directly downwind. The propeller is moving perpendicular to the wind, and so can move at an arbitrary speed, like a sailboat sailing perpendicular to the wind.

  162. spork says:

    “I wouldn’t be surprised if spork’s bet is nothing more than yet another way to try and stir up more publicity.”

    Nope, it’s just an indication of how little patience I have for people that tell me this is definitely fake. For people that are skeptical, or wonder how it works, I offer the best explanations I can. For the people that call me a fool and a charlatan I offer the bet. And it’s quite real.

    “Maybe Jamie and Adam will invite you guys onto the show and get your fifteen minutes of fame or whatever”

    Maybe, but I kind of doubt it. We’re both old and ugly. We just want to see the goofy thing demonstrated, and the myth put to rest. How cool would it be to see those two racing against a neutrally buoyant balloon at the Alameda Naval Air station!?

    So no, I don’t expect, or particularly want to see my face on TV, but I’d love to help out off-camera if they wanted it.

    As far as my 15 minutes – I’ve already got close to 20 minutes of fame. For what it’s worth, you’ve most likely already seen my ugly mug on the tube once or twice. Also been featured in a couple of kiteboarding magazine articles, have a page in the book “A Day in the life of the NHL”, and currently am seen flying at the coast for one of the months on the paragliding calendar. If you really want to know my identity, that should probably be enough.

    But Adam and Jamie are my heroes, and I’d love to meet them.

  163. ThinAirDesigns says:

    Foetusnail:
    >no sailboat, NO SAIL POWERED boat,
    >cart, vehicle of any kind sails
    >directly into the wind.

    Well, except for the one in post #280 and the prop cart and others.

    JB

  164. FoetusNail says:

    1. Why is it that the propeller doesn’t start turning until the wheels contact the belt?

    2. As soon as the cart is picked up off of the belt the propeller starts to stop.

    3. I admit I made a mistake, these guys don’t even have a wind source. I was assuming they had a fan blowing the prop.

    4. They start by showing a cart outside with a wind, but then move inside with only the belt.

    5. Notice that at no time did Spork think it important to correct my error and state, hey Foetus there ain’t no fan.

    In their video the cart is powered solely by the belt and the prop provides enough thrust to reach equilibrium with the belt. This is complete and utter BS.

    These guys are just trying to get on mythbusters, to garb a few seconds of fame beyond youtube.

    I’ve been awake for almost a day and a half, I should get more sleep, but the kids have been sick. The youngest just went to sleep and we need to leave the house in 4 hours.

  165. FoetusNail says:

    You know what, these guys have taken their cart outside. You know what happened? The propeller, much to their surprise, acted like a windmill and the cart went backwards. Prove I’m wrong. Take it off of the treadmill and without giving it a push hit it with a hairdryer and post the video.

    For the last time, the treadmill video proves nothing, while the cart is using thrust to keep pace with the belt, the cart is not powered by the wind. The cart is powereed by the belt motor. This is why he has to hold it in place while the propeller gets up to speed. The thrust is angled downward just enough to avoid slipping, though they do admit they have had problems with slippage.

    Until they put this thing down in some wind, on a stationary surface, they have proved nothing.

  166. FoetusNail says:

    P.S. Thanks Pharsyght.

    Everything I said above concerning the behavior of this cart outside still holds true, a sail powered cart will spank that thang.

  167. GregLondon says:

    codesuidae, sorry, wasn’t trying to say it was my idea, just that it’s the thing I’ve been trying to visualize.

    That video is interesting.

    If the top board is analogous to the wind, then the that video is showing the vehicle moving into a headwind, which one could assume it would feel if it were moving at 11 mph in a 10 mph tailwind. So I’m trying to visualize the ground moving and the machine moving forward and the “air” moving as a tailwind and seeing it all work out, and I lose track of it. It’s not exactly the same as moving 11 mph with a 10 mph tailwind, so I don’t know if it all works out, but I can see the point your video makes.

    I’ll ponder it some more.

  168. FoetusNail says:

    Sailboats can sail faster than the wind, but not directly downwind. In America Cup racing the downwind leg is no longer sailed directly downwind. To sail faster than the wind, boats must be able to get on plane, as they gain speed they create a relative wind that is a combination of actual wind speed and the boats speed. As you go faster and faster you trim the sails closer and closer.

  169. FoetusNail says:

    Like I’ve said many times before, prove it. If they could prove it they would, but they can’t so they make up a bunch of mumbo-jumbo and excuses for not taking the thing outside and racing it side by side with a sail powered cart. Racing two identical carts, the one in the video and another with an identical chassis, but equiped with a sail, will obviate the need for all the sensors, etc. Have a race with credible witnesses and tape the results.

  170. FoetusNail says:

    Don’t just keep repeating yourself, prove it JB.

  171. Anonymous says:

    Hi Foetusnail:

    what is this “exploits the energy available at the ground/air interface” hokum.

    It’s usually called the wind. It’s real enough, and can provide quite a bit of power. I wrote my best take at explaining this effect in #211 above, but here’s another take: If the two media meeting at the interface were fixed in place, but one was hot, and the other cold, no one would be surprised that you could build a device that moved. It’s a vehicle, moving relative to both media, with the drag overcome by power from running a heat engine. Wind is similar, but the power available is mechanical, not thermal. The engine running a Bauer cart is therefore mechanical, coupled to both media via the wheels and propeller. The confusing part is handling the moving frame of reference. Recall that a neutral balloon, moving at exactly the downwind speed, requires no power source… but a power source is available, and could be applied to move against drag in an arbitrary direction with respect to either media. You can therefore do better than a neutral balloon, by using the power available, and the carts that have been constructed appear to do so. Certainly no principle bars them from working as advertised.

    From the words you select, I sense some remaining skepticism. Nevertheless, you’re still here, so you appear to be interested. May I ask about your technical background, so that we could have a shared basis for further discussion? I’ve provided my own background in the previous comment.

  172. Anonymous says:

    Actually, an iceboat, or a wheeled racing cart with sails (on a dry lakebed), can attain a speed quite a bit larger than the wind speed, perhaps better than could be done with a boat. Less drag. Note that the total speed is NOT in the direction of the wind; the component of velocity directly downwind is never greater than the wind speed.

  173. Pyros says:

    Any Smart People who might like to weigh in, per chance? Someone who may have gone to college?

  174. GregLondon says:

    isn’t the notion that it is moving forward relative to the treadmill just as amazing?

    Not if you hold the vehicle on the treadmill until the propeller can get up to speed (inject energy into the system), and then let it flywheel for a while until it finally bleeds off. Meanwhile that flywheel is spinning a propeller that is giving it a little push forward.

  175. ThinAirDesigns says:

    LOL — spork, your “20 minutes of fame” comments reminds me that I’ve also already had my Discovery channel fame — only I got the better part of a full hour.

    I was featured in an hour show for Discovery Channel where I led the US team to a Gold Medal at the 2001 World Hang Gliding Championships in Greece.

    If you want a good laugh, here is an exerpt from that show: Yes that’s me bashing my brains out.

    http://www.youtube.com/watch?v=tGn38NrRURI

    Incidently, the producer for that show was Judy Plavnik — long time Executive Producer for MythBusters.

    Again, I can’t imagine why I would end up on any Mythbusters episode even on the off chance that they happen to like our idea. And seeing how I’ve already had my 15 minutes, I’m over and out in that department.

    JB

  176. tomtheblacksmith says:

    Greetings, Anonymous Discuss,

    (Anonymous Discuss wrote):and run the string in a loop around both pulleys so that when the parachute reaches the yo-yo pulley, it just goes around the axle and moves forward to the front pulley, so that it can start again

    (Tom replies): could I also visualize this concept of yours as a “reverse Ferris Wheel” with the ‘chutes “opening as they move over the top back toward the yo-yo” ?

    Before I can adequately get my mind around this concept I must be able to visualize it in a “proper machine form” and ropes and parachutes really would not work for me in a practical sense.

    Tom the Blacksmith

  177. FoetusNail says:

    Now take away the sail.

  178. ThinAirDesigns says:

    Foetusnail:
    >Explain the statement “it exploits the
    >energy available at the ground-air
    >interface”, please.

    To mediums moving relative to each other:

    A: ground
    B: air

    At their interface (where they meet) there is usable energy to be extracted and exploited. Well known examples of this include sailing and wind turbines.

    JB

  179. SubductionZone says:

    Foestusnail, I never said that any boat does sail directly into the wind. Though this cart may be altered to run directly into the wind. We were speaking of the speed of a boat or a cart’s downwind portion of its velocity. Are you saying that the downwind component of an ice yacht cannot be faster than the wind?

  180. Nelson.C says:

    Well, science is like that, full of scurrilous rogues who won’t take a gentleman on his word, the scoundrels!

    Personally, when I’m disbelieved, I do the best I can to prove what I believe to be the truth, and if that doesn’t work out, I retreat from the arena. I don’t hang around harrumphing about how insulted I am by these skeptical blackguards.

    How is it easier to build a dozen or more machines and post them off to the four corners of the world, than to sit down at a drafting table and draw the plans? How is it easier to glower at all the insulting remarks, than to consolidate the links to the data and post them? Why are ThinAirDesigns and Spork working so hard to make me disbelieve them?

  181. ThinAirDesigns says:

    Foetusnail:
    >Like I’ve said many times
    >before, prove it.

    We did prove it — and if you would attempt to address post #350, it would help you understand that fact.

    JB

  182. johnd says:

    A sailing friend of mine told me there was once a time when the wind pushed a sailboat through the water. Think Christopher Columbus, the Nina the Pinta and etc. Of course those boats couldn’t go faster than the wind. But he pointed out and SLEESTAX wife will confirm, modern sailboats aren’t pushed by the wind except when it’s directly behind them. Most of the time modern sailboats are pulled along by differences in air pressure. And they can go faster than the wind.

  183. spork says:

    “spork, your “20 minutes of fame” comments reminds me that I’ve also already had my Discovery channel fame — only I got the better part of a full hour.”

    Oh – is it gonna be that way? I may have to pull out the screen grap picture of me and the hooker while I’m high-fiving Colbert at the taping of his show.

    Plus, in high school I won trophies for building the best toothpick bridge AND the best cardboard boat.

    Plus – my guy won the election (and I won $500 as a result).

    Indeed my life has been full and meaningful.

  184. codesuidae says:

    And that difference would be what, 10 mph?

    That’s correct!

    Let Vw be the wind velocity.
    Let Vg be the ground velocity.
    Let Vc be the cart velocity.
    Let Vd be Vw – Vg.

    As measured from the ground Vg is 0MPH and Vw is 10MPH. Vd is 10MPH.

    As measured from the wind Vg is -10MPH and Vw is 0MPH. Vd is 10MPH.

    Notice that Vd is independent of Vc, it doesn’t matter at what speed Vc is moving, the relative speed between the wind and ground remains 10MPH.

    If Vc relative to the ground is 5MPH then as measured from the cart Vg is -5MPH and Vw is 5MPH. Again, Vd is (5-(-5)) 10MPH.

    If Vc relative to the ground is 13MPH then as measured from the cart Vg is -13MPH and Vw is -3MPH. Vd is (-3-(-13)) 10MPH.

    In all cases the mechanism on the cart, provided it can be mechanically coupled to both the wind and the ground while it is moving relative to both of them, can extract power from the 10MPH difference. This power can be used to accelerate the cart relative to either medium.

    A balloon, a simple sail, since it is coupled to the wind but not the ground, can’t use the difference between the two to generate power.

  185. eclectro says:

    Because nothing engenders trust like the username “spork33″.

  186. Anonymous says:

    The version powered by the treadmill is just that: powered by the treadmill. It is not powered by the wind, but driven through a gear reduction by wheels powered by the treadmill. Nice demonstration of motive power, but clearly NOT wind power.
    For a wind-powered machine to move faster than the wind, the wind driving the propeller would first of all need to be blowing faster than the vehicle was traveling. When the vehicle reached the speed of the wind, the relative motion of the wind would cease and the pressure on the propeller become zero.
    If you don’t believe it, take a ride in a hot air balloon and hold up an old-fashoined pinwheel… the kind we used to buy at fairs for a quarter. Like being in a roon inside a house, the pinwheel will not turn unless you blow on it. The balloon moves at the same speed as the wind, and there is no relative motion to turn the pinwheel; much less a propeller. None.

  187. Alpinwolf says:

    Oi. Suitable brain-teaser, truly.

    I know this post is long, but I hope it helps someone.

    It’s like riding a bike! No, really.

    I get it, I know it’ll work without building it, but it took me a few hours to chew through. I’m not an engineer (yet) but I am an aircraft mechanic, and theory of flight, autorotation, prop pitch control, turbine vs. fan, etc. are all necessary to achieving the certification.

    This strikes me as both as-complex-as- and as-simple-as Euler’s Identity.

    So here’s my stab at the explanation for the skeptical. (Don’t get me wrong, the world needs more skeptics)

    Firstly I concur that Outside-with-Wind and Treadmill-no-Wind are equivalent reference frames, since the critical thing is the difference in the speeds of the rolling surface and the ambient air. Move one or the other, or both. As long as there’s a notable difference, an observer in one can measure Kinetic Energy in the other.

    Regarding the real-world outdoors model:
    Initial state has the cart at rest, with a tailwind. The big flat areas of the blades are not turning, but are collecting wind. So at this point they act only as sails to push the cart forwards. The blades have a high Moment of Inertia, and would take a bit of juice to start rotating (from the wheels) but the wind does not rotate them. (The wind would have a tendency to counter-rotate them, but the leverage is poor due to gearing and pitch.) In a frictionless environment (except for perfect traction, like gear-wheels on a rack), it might take a while but it would all slowly start spinning as the wind pressure pushes the cart down the path, again, sail-like. In this real world, the human push start is necessary to overcome static friction, which peaks higher than dynamic, plus other things. Like that it probably needs to get up to a critical speed before it can accelerate.

    If the blade pitch was flat (co-planar with the plane of rotation) then the blades would continue to act as sails, up to a max of the wind speed (optimally) but prolly somewhat less in reality, due to rolling resistance (friction). The Moment of Inertia of the system would be moot once equilibrium was met between the wind-push and the rolling resistance.

    So there’s, oh, 2 to 4 of these inefficient sails twirling uselessly on an axle, driven round and round by the driveline coming from the wheels. Except that these sails are actually shaped and angled to be a fair propeller if spun the right direction. Which they are. Spinning.

    Here’s where the energy question might be breaking down for some. The wind pushes the cart along, but does not push the blades around. The blades are doing dual duty depending on where in the mission profile the thing is operating.

    Energy goes here:
    Wind –> impacts “sails” –> pushes cart forward –> rolling wheels drive high-inertia blades around –> …and back to the narrative:

    So the force of the wind has (perhaps with help) overcome stiction and inertia, and the wind is getting slower relative to the cart. But the air stream is just getting warmed up relative to an ant riding on a blade tip. Even within this one system there are multiple reference frames that need to be addressed. As the blades rotate faster, the relative air stream they care about is being made by the spinning. At first the plain wind was pushing on the “underside” of the blades (facing rearwards). But as the spin increases, the wing-walking ant notices the breeze coming more and more from the leading edge direction.

    At the magical time that the cart is rolling along at wind speed, the relative wind of the cart is zero, and the blades would contribute nothing if their pitch was flat. But they’re not flat. At this point, the driver feeling no wind, any positive pitch would produce thrust to the rear.

    As I see it here, in an overly-simplified way, it’s kinda like a Pelton wheel. (wiki) The wind pushes forward, and the thrust is pushing some air back at it. Flying low with a tailwind.

    But the blade pitch is always positive, and the generated thrust does not come on like a switch, but is a continuum. Well, sorta. The relative air-stream to the blades has to get above the stall angle, but then it’s a continuum. Lift (thrust) increases with the square of the speed of the air-stream over the airfoil, so while rolling and air resistances are increasing, thrust is increasing more.

    So the wind speed pushing on the cart is getting cleverly multiplied into rotational speed of these lifting surfaces, which generates additional thrust to augment the wind-push.

    Energy map again:
    Wind -> sails -> accelerating forward motion -> rotates the sails -> generates increasing thrust.

    Just as humans have a specific capacity to output power, but we can move faster with clever manipulation of leverage (bicycle), so too can this critter harness the wind to move faster than one might expect. Also, as with the bicycle, there is a limit, an equilibrium point.

    Above the ambient wind speed, that wind can only help to offset the Form Drag, but provides no further inherent thrust. As ground speed increases, blade spin speed increases and so does lift, but also Induced Drag on the prop, making for a resistance torque in the driveline. Also the blade-local relative air stream, or Angle of Attack, approaches zero (asymptotically I think), which means no lift, but they’re still churning through the air. There’s a point of diminishing return.

    So forces at equilibrium:
    (Ambient Wind) + (motion-generated Thrust) = (Rolling Resistance) + (air Drag on the Cart) + (Drag of the Prop)

    I think the air resistance on the cart at these speeds will be quite negligible.

    And if you get the thing going at the improbable rate of 1.5x to 2x wind speed, and kill the wind, inertia will keep it going for a little bit, but the the AOA will be ruined, no more vector bonus from the wind, and the whole thing glides to a halt.

    And the ant gets off and pukes.

  188. SubductionZone says:

    Foetusnail, they have submitted quite a few youtube videos that support their claim. No hoaky editing jumps or anything, just a straight forward video of the cart running on a tread mill. Now if you don’t understand the concept of inertial frame of reference equivalence that is not their fault. That is just a matter of high school physics. If you do not even understand high school level physics there is not much point in arguing with you.

  189. GregLondon says:

    Hudman, just for you I changed the document and added two new drawings. If you look at the .pdf, page 5 shows a time lapse and page 7 shows a rope and pulley equivalence which proves (1) it works (2) what the tradeoffs are (speed versus force) and (3) that the point where the wind engages the wheel, that part of the wheel doesn’t outrun the wind.

    Your device produces no thrust. If it produces no thrust, what happens when you place it on a treadmill?

    The tumbleweed probably won’t work on a treadmill because it needs wind to act as a lever against. Page 5 and 7 explain it.

    There is no prop, but it doesn’t need a prop to run faster than the wind. It just needs to be designed right.

    It should however be able to go nearly twice as fast as whatever your tailwind is. If you’ve got a 5 mph tailwind, this thing should run at 10 mph minus friction. Not sure what speed you prop-cycle is seeing, but if you put the tumbleweed in a 20 mph wind, the theoretical top speed would be 40 minus drag.

    If you put it on a treadmill indoors, it will probably coast to a stop. If you put it indoors and put a box fan behind it, it should zip across the floor.

    I’ve been on the Mythbusters thread with spork & JB almost from day one, and I understood it immediately, without a “formal” explanation.

    Yeah? Can you tell me prior to experimentation what the top speed of your prop cycle is? Or do you have to try and to find out?

    I can tell you the tumbleweed will have a theoretical top speed of twice the tailwind speed. And I never had to run any test trials to figure that out.

    Intuition is useless if you can’t predict any hard numbers. If you have to experiment to know what it will do, then you can’t predict. And if you can’t predict, you don’t really understand. You’ve memorized the answers.

  190. ThinAirDesigns says:

    GregLondon:
    >Have you put your real name next
    >to your claims?

    To people such as Mark Frauenfelder, Charles Platt and many others who have initiated personal contact our real names are known.

    JB

  191. travis08 says:

    Not if you hold the vehicle on the treadmill until the propeller can get up to speed (inject energy into the system), and then let it flywheel for a while until it finally bleeds off. Meanwhile that flywheel is spinning a propeller that is giving it a little push forward.

    They are claiming that it can go indefinitely on the treadmill.

  192. ratwerks says:

    Foetusnail, you are so very close to seeing this. Since the propeller is turning as the cart moves forward the tips of the propeller trace a spiral in the air. That spiral, as the cart moves directly downwind, shows the propeller blades traveling at an angle to the direction of travel.

    Here is a fresh thought experiment. Take a chart of open water and form it into a cylinder with diameter == propeller length. Move the wheels on your cart so that they will bear on the inside of the cylinder. Fix pencil stubs to the ends of the prop and to the centerline of the cart so that they will mark the chart. Push your cart through the tube from one end to the other. Unroll the chart and note the relationship between the prop pencil lines and the cart pencil line. You will see that the propeller ends travel at a constant downwind angle that is not directly downwind.

  193. GregLondon says:

    You will agree that there is no wind in this frame

    Yes.
    and a propeller in a static fluid generates a force forward.

    sure why not.

    Thus the car is pushed past 10 mph by the propeller

    in exchange for what?

    At most, you have a flywheel effect that will get you beyond 10 mph for a time. But you start with two basic facts and then assert the conclusion you want. As it is, you just got something (additional forward speed beyond 10 mph) for nothing.

    This is what I mean by this not being explained. Everytime you do something in an autorotation, you have to transfer energy from one form to another, from altitude to rotor speed, from forward speed to rotor speed, and from rotor speed to hover.

    What does my little propeller cycle give up to get past the 10 mph spot? Where does the energy come from? You can’t create it or destroy it, you can only move it around, so where did you get it from? If it’s a flywheel, you could spin it up, get to 10 mph ground speed in a 10 mph tailwind, and then the flywheel will keep the prop spinning for a while as you continue to accelerate. You trade off flywheel inertia for forward speed, not much different than an autorotation, really.

    But if the flywheel loses inertia, then that means your propeller will slowdown, and that means you lose your additive force, so your groundspeed tapers off, until you come to a halt.

    Yes, instantaneously, 10 mph ground speed in a 10 mph tailwind, you’ve got some force from the prop that could accelerate you. But you have to trade off that additional kinetic energy from somewhere. And no one can explain where it came from. Since no one can explain it, I have no reason to believe it is anything other than flywheeling the energy into velocity.

  194. HUDMAN says:

    JB – Ouch! That hurt just watching it.

  195. HarveyBoing says:

    From the original creator’s PDF:

    By ten mph the lift of the propeller is 552 grams and the force to turn the wheels at that speed is 402 grams

    In other words, it’s a perpetual motion machine. It creates more energy than is put into it. That is, you can apply 402 grams tangentially to the wheels, and get back 552 grams out the propeller.

    Last I checked, all perpetual motion machines are bunk.

    As for the video, it’s cute that he’s got a tell-tale to try to indicate wind direction. But putting it directly behind the propeller makes it useless. A more useful design would put the tell-tale on an outrigger, well outside any effect of the prop.

  196. dustbuster7000 says:

    @ Hudman

    “Actually, the tailwind is trying to decelerate the propeller much more than an apparent headwind. The propeller actually likes the apparent headwind, as the apparent headwind is actually trying to turn the propeller in the direction it is already going.”

    Both of you above sentences say pretty much the same thing, that an apparent headwind will accelerate the propeller and cause the cart to likewise accelerate. This is not the case. If a tailwind causes the cart to accelerate in the initial stages (i.e. from rest up to wind speed), then a headwind can only cause the propeller to slow down, unless there is something else happening in the transmission or the propeller has an adjustable pitch mechanism for the blades, neither of which are mentioned or seem to be present from the videos I’ve seen.

  197. GregLondon says:

    I don’t know. When I first started flying helicopters, it completely weirded me out that you could land without engine power using autorotation. The air flowing over the blades would keep the blades spinning and generate lift. Of course, you put energy into the blades by losing altitude, but you could actually “fly” your helo down to a survivable landing. You had to be at least a few hundred feet up though, or if you weren’t that high, you had to have an airspeed above a certain value. below that altitidue and below that speed was the dead zone where an engine failure meant you were in serious trouble.

    I don’t know what’s going on with these little gadgets. I don’t like them putting them onto treadmills because the moving belt adds energy to the car. all of a sudden you’re spinning the wheels/propeller really fast in stationary air. And the propellor, shaft, and front wheels of that little gizmo looks to be almost 90% of the total weight of the machine. Which means you could store a lot of rotational energy in the spinning wheel that would take a long time to bleed off in the speed of the gizmo on the treadmill.

    If the non-rotating mass of the gizmo was greater than the rotating mass, I think you’d see the bleed off happen a heck of a lot faster and you’d realize that it isn’t really steady state. They seem to be doing it for a few seconds and then it veers off the side so they have to stop and reset, but a few seconds isn’t steady state.

    I will say that I’m a firm believer in teh conservation of energy so I don’t think they’re getting something for nothing here. It’s just that it’s either some hidden transfer of energy (suddenly spinning the wheels adds a lot of energy that takes a while to bleed off) or they’re cheating somehow (going downwind, getting a burst of energy from gusts and then bleeding it off over time)

  198. HUDMAN says:

    You guys have me smoked. I think I’m on a couple of Super 8′s somewhere in my father’s closet winning a few motorcycle races.

    I was asked to be on an “Experiment Island” episode. Once I found out there was no money, I turned it down. – Still looking for my 15 mins.

  199. codesuidae says:

    Can you devise a test, or do you believe one can be devised that can be executed in the middle of the street to determine whether I am telling the truth and indeed whether we are on a treadmill or not?

    Can I use a sextant, or does ‘in the middle of the street’ mean I can only use local references?

    Does the local gravitational potential count? A sensitive gravimeter could be used to determine if the city was moving relative to the density variations within the Earth.

    :D

  200. delphi says:

    wow Cool video

  201. GregLondon says:

    So, after finally reverse engineering this thing down to the bones, I wrote up a spec that describes how this bloody thing actually works, and how to build a device that will go directly downwind faster than the wind without any moving parts.

    Now that I’ve written it up, I don’t know why there is any controversy around this other than no one understood it well enough to explain it in plain english.

    Spec is here:
    http://www.greglondon.com/tumbleweed/

    FoetusNail and/or Codesuidae, I’d appreciate it if you could check my work. Either it works, you don’t even need a prop, and the whole thing is about as interesting as a block and tackle, or I’ve been up way too long… And I trust you guys to be rigorous.

  202. stcorbett says:

    the classic DWFTTW argument is about a vehicle traveling directly down wind. It is not traveling 80 degrees to the wind with the downwind component of it’s velocity being larger than the velocity of the wind.

    That said, the above scenario is entirely possible (as sleestax mentioned)

    My $0.02: in both DWFTTW videos, we are not seeing true DWFTTW, we are actually seeing a cart oscillate in direction back and forth around the direction of the prevailing wind. On average, the cart travels faster than the prevailing wind.

  203. af2008 says:

    Lets do some math.

    The propeller rotational frequency is w, the propeller fins make angle a from perpendicular at some propeller radius rp, the wind velocity in the car’s frame is u, wheel radius rw.

    The force by the propellor is:
    Fwind=c*(u-a*w*rp)
    where c is some constant. (This makes sense as w is how fast the propeller would have to spin so that the wind moving past the propeller is moving with u). u=vw-vg (wind speed and ground speed); taking into account gear ratio x, Then vg=rw*x. So w=vg/(rw*x) and:

    Fwind=c*(vw-vg-a*rp*vg/(rw*x))

    This will only be zero if:

    vw=vg(1+a*rp/(rw*x))

    so:

    vg=vw/(1+a*rp/(rw*x))

    so vg=vw only if a=0 (the case of a sail). This happens because we lock the rotation of the propeller to the rotation of the wheels.

  204. FoetusNail says:

    WOW, that really proves everything, a video of a compund belt wheel disquised as a cotton spool. This just keeps getting better and better.

    Answer the second question, why is it that this phrase is only found on a thread discussing this baseless claim that your machine will work once removed from its motor?

  205. FoetusNail says:

    You mean like riding on a train, put the two carts down side by side on the moving train and race them.

    JB why do you have to hold your cart down to get it up to speed before letting go? Did you just have to do that when you set the cart down on the train, a surface with the same linear velocity as the cart in your hand. No, you just set it down and let the wind energy push against the frame which turns the wheel, which turns a prop that produces thrust AND drag. When you place your cart on the treadmill it is no different than turning on a motor, or engaging a clutch.

  206. arkizzle says:

    Greg, I can’t help but feel you are either being willfully obtuse or you just don’t get it.

    Frankly, I hate it when someone pulls “you just don’t get it”, but you seem to be asking some questions that even I can see have been answered already, and can surmise the answer to, without a pilot’s license.

    I genuinely don’t know how much faster than windspeed this machine will go, or if it’ll just bob around the mark by utilising small gusts etc. But I absolutely get the principle of what is being presented, and I don’t think it’s because I don’t have as intricate an understanding of fluid dynamics or aerodynamics as you and am somehow falling for the hocus.

    Anyway, I hope you don’t take this comment negatively, I just think you are getting wound up when you could just make one and see what it does.. It’s an interesting project, no matter the result; either it doesn’t work and you are right, or it does and you’ve built a magical new thing to stump your flying buddies with :D

  207. arkizzle says:

    VIDEO or it didn’t happen.

  208. Clemoh says:

    Would this discovery not lend a little more weight to wind power as a way to generate electricity?

  209. spork says:

    >> JB – Ouch! That hurt just watching it.

    I’ll take your word for it. I had to look away when I saw his legs.

    Then he pawned off that beat up wing on me!

    “I think I’m on a couple of Super 8′s somewhere in my father’s closet winning a few motorcycle races.”

    HOLY COW! How big is your father’s closet!? I don’t think I could even fit my motorcycle in my closet.

    “I was asked to be on an “Experiment Island” episode….”

    Hmmm… is that like “marijuana experiments” or “you and your best friend at camp” kind of experiments? : )

  210. ThinAirDesigns says:

    Travis08:
    >They are claiming that it can go
    >indefinitely on the treadmill.

    The problem is only keeping the device on the threadmill with out a tether — with no steering, it wants to wander off.

    Here’s one where we place a couple thin boards under the edge of the belt to form a fence of sorts and then balanced the speed of the treadmill against the slope to sort of make it hover.

    http://www.youtube.com/watch?v=dgHBDESd38M

    1:48 seconds of not touching it before it fell off the back.

    JB

  211. ThinAirDesigns says:

    Ratwerks:
    >#267: I do not recognize your authority,
    >’onus’ or otherwise. If you’d read the
    >thread (I have because I find willful
    >smug ignorance a fascinating human
    >spectacle) you’d be aware that ThinAirDesigns
    >has arguably said more of substance than any
    >other participant.

    Thanks Rat — I was in response to that admonition going to put together a post listing all the Post #s of the numerous contributions I have presented as compared to the rantings of certain critics.

    I decided that it’s generally just better not to talk back to the moderators no matter how convincing the evidence.

    Peace Antinous.

    JB

  212. ThinAirDesigns says:

    Foetusnail, no matter how hard you want to you, you can’t just rationally say that this whole treadmill test is just a couple crazy guys trying to pull the wool over the naive.

    There are many sharp people on this thread stating the same thing that we are — the treadmill @10mph in a still air room IS the indentical testing environment as a street with a 10mph tailwind.

    Now you can disagree if you wish, but remember — it’s not just a couple of nuts with an axe to grind telling you this. You would do well to come to an understanding as to *why* these other independent folks are sidin with us on this. Put your intuition aside and ask a couple of them to go over post #350 with you.

    It will pay off for you in the long run.

    JB

  213. spork says:

    We’re extremely happy to have you join us in the light. It’s ironic that so many question the method of using the treadmill for two reasons…

    First – we use the treadmill specifically because there have been such a huge number of complaints about the uncontrolled conditions of Goodman’s experiment/video. The wind is not constant, he may be going downhill, he isn’t going *directly* downwind, there’s probably a vehicle towing him…

    These are all things we felt we could easily demonstrate properly for people using a treadmill. We naively thought this video would end the controversey rather than fan the flames. We came to learn that there is simply nothing that can be done on video that would truly satisfy the sceptics. Thus we offered to loan JB’s cart out, published the parts list and some minimal build notes (I was lazy), and did a number of specific tests and videos in direct response to the critics concerns. As you can see, that approach hardly satisfied most.

    The second reason I was surprised that people weren’t happy with the treadmill is that it seems so much LESS believable to some that the vehicle would not only hold it’s ground but *advance* on a treadmill that’s trying to toss it off the back. In fact JB’s first reaction when we considered the treadmill was “shoot – we must be wrong – there’s no way a vehicle could advance on a treadmill”. It’s just so counterintuitive. Of course he quickly came to realize that it would indeed advance on a treadmill, and thought nothing could be a more powerful demonstration (which I tended to agree with).

    In any event, they truly are the same from the point of view of the cart.

    And we’re very happy to have another person that understand that this thing works – and how it works.

  214. GregLondon says:

    Now we demand video of your cart.

    If you actually read that document, all 15 pages of it (it’s mostly drawings, so quick reading), then you probably wouldn’t be demanding video because you’d know it would work.

    Then we demand explanations in much broader (and narrower) terms.

    If you read it, I very much doubt you would be needing much more.

    Then a different video of the cart.

    Again, it is explained in plain english such that no “intuition” is needed and you don’t need to experiment to get answers.

    Video is pointless at that point.

    Then we will accuse you of a hoax,

    The whole thing is explained in one high school physics level rope and pulley diagram on page 7.

    You cannot look at that and tell me the numbers don’t add up. pull rope at 5 fps, pulley moves at 10 fps. The math is simple enough that you’re calling “2*3=6″ a hoax.

    “(in fairness, I don’t believe you called hoax, outright).”

    I started out asking for explanations. How do you overcome this. How does it deal with this. The answers were either the ramblings of people who don’t actually understand how it works, or of people who understood how it worked on an intuitive level, but couldn’t explain it.

    “The wind” type answers were pretty much saying “you just have to intuit it”.

    Well, no, you don’t “have” to intuit is. It’s fairly basic in operation and can be explained in plain english.

    Then we will blame you for our lack of understanding.

    I blame your lack of understanding on the simple fact that you haven’t read my document.

    Hopefully your experience as giver-of-information in this regard will be less fraught with negativity and aggressive demands for proof.

    I don’t know what you expect people to do when presented with something shrouded in gobbedly gook explanations. I certainly am not going to believe every claim that some random internet guy makes just because they might think I’m being negative if I doubt him.

    I asked for explanations. No one could explain it in any formal way. Everyone believes they understand it, but they all appear to be “intuiting” how it works, which means they have to do a lot of handwavium to explain it, hoping the otehr person will “intuit” it on their own.

    So I stopped asking for explanations and tried to figure it out on my own. After a few days, I did. I wrote it up in a plain language explanation that requires no intuition. And I was able to use the concepts to create a new design. If every propeller cart that everyone uses all look the same except for scale, then I highly doubt that people understand it on a design level.

    If they did, they would have quickly gotten rid of the propeller. It isn’t needed.

    Now, I’m presenting the plain english explanation of how it works. It comes down to a simple rope and pulley diagrams from high school science class. It requires no intuition. It requires no handwavium. And it allows you to design any sort of machine you want.

    If “giver of information” is the goal, which is better “You have to intuit it” (waving hands) or “5+5=10, see?”

    Whatever. I think if some people have been working on this thing for years trying to get it to work, trying to prove other people how it works, then my guess is that they might be somewhat attached to their intuition of how it works. And I wouldn’t be too terribly surprised if someone who has been trying to get this to work for years suddenly becomes resistant to the idea that a few pages of basic diagrams can explain how it all works.

    Not saying that’s going on, but it would be in the realm of a human reaction.

  215. spork says:

    “I admit that I don’t understand the physics involved, so I don’t really know whether DDFTTW is possible, but I am siding with Charles on this because I’ve never known him to be wrong when it comes to math, physics, or electricity.”

    Well Mark, you’re about to be disappointed. Platt is most definitely wrong this time. I suspect you’ve seen that I’ve offered him a $100K bet with odds 10 to 1 in his favor (his $10K against my $100K). I’ve also proposed writing the followup article for your mag to set the record straight, which is only fair to your readers and the maligned Jack Goodman.

    Why not let your readers build exactly the cart I did for $40 worth of off the shelf parts, and see for themselves how easily this can be done?

  216. GregLondon says:

    I’d have to draw the plans up and so we’re stuck with a parts list, pictures, published build advice and in the end if that isn’t enough — “to-and-fro”.

    This only reinforces the point that you guys don’t actually know how this works, because you can’t actually create a design that is repeatable.

    When you engineer something, you have to design it for tolerances, so that it works the same way no matter what specific part you put in. As long as it is within some tolerance, it’ll work.

    Engage me in a way that convinces me your actually interested in learning about this device and I’ll box one of mine up and sent it to you … I’ve yet had anyone take me up on the offer, which leads me to believe that most critics complaints about me not posting the plans in the format they want is just a bunch of sniping

    First of all, you guys all refuse to even disclose your names publicly. And you want me to give you my address? No thanks. From my point of view, I see a pseudonym on a screen and I’ve got nothing else to go on. Not to mention, what I see of spork is that his priority isn’t about explaining this, it’s about getting someone to bet him a hundred thousand dollars.

    Dear Sir, Confidential Business Proposal. Having consulted with my colleagues and based on the information gathered from the Nigerian Chambers Of Commerce And Industry, I have the privilege to request your assistance to transfer the sum of $47,500,000.00 (forty seven million, five hundred thousand United States dollars) into your accounts. The above sum resulted from an over-invoiced contract, executed, commissioned and paid for about five years (5) ago by a foreign contractor. This action was however intentional and since then the fund has been in a suspense account at The Central Bank Of Nigeria Apex Bank.

    Seriously, did you guys just discover the internet or something? How do you think you guys come across to folks who don’t know you, as a bunch fo people running around underpseudonyms with large sums of money being mentioned at the same time as lawyers and escrow accounts?

    You’re behaviour is indistinguishable from a con artist, regardless of what your intentions might be.

    Second of all, if you send me a URL to a spec, I can look at it now and possibly figure out how it works now, without having to resort to experimentation.

    Einstein was big on thought experiments. They’re fairly inexpensive.

  217. GregLondon says:

    VIDEO or it didn’t happen.

    You know, if you’re attempting some form of payback against me, technically, you ought to stick to whatever demands I made of you and the other guys who initially came on the thread.

    I don’t think I ever said I needed video to understand it, or that video was proof that it worked.

    I mean, you can try to throw that in my face, but it just doesn’t have the “poetic justice” factor that you think it does if I never actually cared too much about the videos or made similar demands of spork and the rest of the scooby gang.

  218. ThinAirDesigns says:

    Mark Frauenfelder
    >I admit that I don’t understand the
    >physics involved, so I don’t really
    >know whether DDFTTW is possible, but
    >I am siding with Charles on this because
    >I’ve never known him to be wrong when
    >it comes to math, physics, or electricity.

    There’s a first time for everything Mark, and when it comes to the physics of this device, Charles has left you high and dry this round.

    The device beaks no laws of physics and will kick the winds A88 three ways to Sunday.

    Build one and try it for yourself — takes only an hour or so and perhaps $70 in parts.

    JB

  219. jonjonz says:

    I think several people have nailed the particulars but have not stated them as a whole.

    1. Sailboats CAN travel faster than the wind when their sail is flying at at angle of 45 to 90% to the wind.

    2. The propeller on the vehicle shown is traveling in a similar angle to the wind, hence it can easily generate enough power to move the vehicle faster than the wind, how much and how long is a function of how efficient it is.

    At least thats my take. It will be interesting to see this proven one way or another. thanks for sharing it here.

  220. ThinAirDesigns says:

    Foetusnail:
    >You know what, these guys have taken
    >their cart outside. You know what happened?
    >The propeller, much to their surprise,
    >acted like a windmill and the cart went
    >backwards. Prove I’m wrong.

    Ok, here you go (times 2)

    http://www.youtube.com/watch?v=QTAd891IpRs

    http://www.youtube.com/watch?v=kWSan2CMgos

    No surprise, no windmill and no backwards.

    JB

  221. Clemoh says:

    It’s the same theory that tells a swimmer that keeping your fingers apart when you are swimming makes you go faster. The low pressure in front of the propeller draws the propeller forward, increasing speed. It could only go so fast, though, until the drag coefficient of the vehicle overcomes the low pressure draw. The propeller, as it spins, has far more surface area any other part of the vehicle, and so the drag coefficient would be unlikely to adversely affect the speed of the vehicle.

  222. Plethora_Jenkins says:

    I’ve just spent the best part of the last five hours reading comments on this thread. I also read some of the thread at the James Randi Foundation website. Before reading the threads I appreciated that a yacht could exceed the windspeed by using tacking, but I was unclear on whether using tacking would allow the yacht/iceboat/land yacht to travel so fast that the downwind component of the vehicle’s speed exceeded the windspeed.

    I checked out a couple of websites for world record holding landyachts, and found one of them had a really good graphic showing the envelope describing the yacht’s maximum speed at any angle relative to the wind direction. The current world record holder can manage something like 95 mph at 20 degrees angle to a 30 mph wind. This makes the downwind component of the yacht’s speed about 89 mph, which is considerably faster than the 30 mph wind.

    Armed with evidence that the downwind component of a land yacht’s speed could be several times the windspeed, I had the clanging realisation that device spork demonstrates in the youtube videos is possible.

    After the patient (and sometimes – understandably – worked up) explanations from spork, airshowfan and thinairdesigns, I think I understand this as much as I’m going to without properly appreciating the vector mathematics that lets wind powered craft go faster than the wind in the first place.

    I have to confess that when I first saw the video on boingboing some months ago, I was reactionary and filled with disbelief, till I read some sites written by people who sail. Having seen the treadmill video, I grokked that stationary air, moving ground was equivalent to moving air and stationary ground.

    So, I’d like to build one for myself. I’ve seen the link to spork’s list of parts, but also read that you might be offering kits of just enough components to build one device. I’d really like to get a kit of parts. How do I go about arranging this?

    I have a modest machine shop out the back, but I think it’d be sensible to follow your advice and build exactly the device you’ve demonstrated in the videos before I mess about with cutting bevel gears, changing bearings, and mucking about with wheel sizes and gear ratios.

    I *think* this is possible, up to some maximum speed that is a multiple of the wind speed. I *think* I understand, largely, how such a thing is possible, and I’m pretty sure I understand that there’s a maximum speed for any given windspeed, limited by friction, drag, and all the different parts of the device, but I’m now at the stage that I have to build one for myself to be sure.

    In closing, I wish I had the patience exhibited by some of the people in this thread, and I’m glad I have more patience and forebearance than other people in this thread.

    oh, and I registered with boingboing just to comment on this thread. I hope it does turn out to be a Monty Hall-esque problem, because it’s certainly been entertaining watching so many people get so angry about something that’s reasonably easy to test, but apparently much easier to get worked up about.

  223. RedShirt77 says:

    >>Would this discovery not lend a little more weight to wind power as a way to generate electricity?

    It would lend itself to new windmill design, perhaps oscillating ones.

    but folks here seem generally right. This can’t be tested effectively outside of a wind tunnel with the cart on a 90* track so it can’t tac to build speed.

  224. ThinAirDesigns says:

    For those who don’t believe that the treadmill is a ‘real world’ experiment:

    In a 10mph wind, ride your bike straight downwind at 10mph. Do you feel any wind on your face? Of course not — everything is perfectly calm and yet your speedometer clearly says “10mph”.

    Now, go indoors and put your bike on a treadmill set at 10mph and pedal until stationary. Do you feel any wind on your face? Of course not — everything is perfectly calm and yet your speedometer clearly says “10mph”.

    There is *no* scientific test, no matter how sensitive the instrument which can determine if it is the air that is moving and the road bed still, or if the road is moving and the air is still. Invent such a test (even if it uses a stupid DDWFTTW cart) and the Nobel is yours. Seriously.

    JB

  225. Takuan says:

    plane takes off.

  226. ThinAirDesigns says:

    Foetusnail:
    >Because the prop is only being driven by
    >the energy already applied to the sail.
    >Whatever *thrust it generates* would only
    >be subtracted from the wind energy acting
    >on the sail.

    Nope, the prop geared to the wheels is a system totally independent of your flat sail — as demonstrated by the fact that our cart works *without* a flat sail.

    Clearly if the prop spins *without* a flat sail installed, it’s not “only being driven by the energy already applied to the sail”.

    >Which multiple devices?

    At least 5 different teams have independently built and tested DDWFTTW prop carts with the same results each time. I accept that you don’t believe it, but your lack of belief doesn’t make it not true.

    >Sailboats on plane going across the wind
    >and generating an apparent wind, or sport
    >kites doing the same, have nothing in common
    >with sailboats or sail carts going directly
    >downwind.

    Sail carts going directly downwind have *everything* to do with “sailboats on plane across the wind and generating an apparent wind” if the sail carts sails are “on a plane across the wind and generating an apparent wind” — as ours are.

    >I spent many years racing, don’t
    >try to BS me on this one.

    When it comes to physics brainteasers, perhaps your “many years of racing” haven’t prepared you as well as you think. Just a thought.

    JB

  227. FoetusNail says:

    The cart in the video is no different than a motorized cart traveling on a motorized belt. You turn on the motor wait for it to get up to speed, then match the wheel speed with the belt speed and set it down.

  228. FoetusNail says:

    Sailboats move forward across the wind by flow turning. The flow of wind across the sails is turned, by trimming the sails as to maintain a laminar flow over the leeward side of the sail as well as the wind that is turned by the windward side. This the equal and opposite force created by turning the flow of the wind then reacts against the centerboard or keel which prevents the boat moving with the wind, so the boat moves forward. Though there is always a sideways component to the boats direction of travel. In other words the bow points in one direction, but at the end of a tact you will be leeward of that mark. Somewhat like an airplane side slipping on approach.

    P.S. Don’t believe any of this Bernoulli Principle reasons for the way in which planes develop lift or sails develop thrust. That stuff has finally been debunked by NASA. Flow turning is what produces lift. This is why symmetrical airfoils which have equal distances top to bottom, like a fabric sail or the wing of a Extra 300 S, and supercritical airfoils which can actually have greater lengths on the lower surface develop lift. Laminar flow and turning that flow produces an opposite but equal force that pushes the plane up or working against the resistance of the centerboard or keel moves a boat forward. Planes and large sailboats literally turn the flow of tons of air.

  229. codesuidae says:

    To Spork and Co., first, thanks for being so incredibly patient with this investigation, I would have resorted to wet badgers by now.

    Second, I would like to see your treadmill experiment done with the cart tied to a string running over a pulley and down to a beam balance (or other sort of scale that can handle a dynamic load, most cheap digital scales wouldn’t work) such that the cart was held stationary and the net force generated by the prop would be measured on the scale.

    This would give an interesting snap-shot of the behavior of the system at the moment when the cart speed is equal to the wind speed.

    For visual effect on the video you might add little dangly bits of string on the vehicle like they do in some wind tunnel tests (maybe you’ve done this already, I haven’t looked at your youtube videos yet). This might help people to visualize the airflow a bit better and avoid the confusion some have had about whether there is a fan or not.

    Fun and fascinating stuff for sure, you should write a book about it :)

  230. Michael says:

    Gee, Spork and Thinairdesigns, why complain that BoingBoing is not “letting” us build the machine for $40 or $70 of parts, and link to plans yourself?

    Just sayin’. Cause we have HTML here. And I for one would be rather interested.

  231. codesuidae says:

    if you send me a URL to a spec, I can look at it now and possibly figure out how it works now, without having to resort to experimentation.

    I’m curious what aspect of the machine you do not understand?

  232. Anonymous says:

    It would be nice if someone made a serious effort to document an attempt & also explained the underlying theory. Wired had an article about this, but did an uncharacteristically bad job, almost to the point of making me think they were taking part in a hoax.
    As a hang glider pilot, I know it’s possible to tell which way the wind is blowing by circling, and I know why – the wind is not a group of air particles all moving together coherently. This is why moving ten miles per hour in the direction of a ten mile an hour wind is not the same as standing still in zero wind.
    The forward motion of a downwind cart, assuming it CAN do “DWFTTW”, MUST be taking energy from the wind somehow. If proponents claim this isn’t the case, they should apply for the JREF million dollar prize, as this will greatly help their research. I’m going over the physics, and if it’s possible I’m confident I’ll figure out why – I’ve got a really good track record with this kind of stuff. If anyone else with a better understanding of aerodynamics wants to help with a tidbit or two of information, please do, as all the articles I’ve read so far have been pretty empty.

  233. flytch says:

    a sail boat can sail faster then the wind on a reach… a reach is sailing 90 degrees to the wind… this is in fact what is happing here… the propeller sailing in a reach… it is 90 degrees to the wind! so it can then go faster then the wind and thus propel the vehicle faster then the wind…
    no one is saying this can not be done without wind to power it…

  234. ThinAirDesigns says:

    Nice work Misterfricative.

    As it did you for a bit, the treadmill equivilence drops a lot of people. They can’t wrap their head around the electric motor being involved. In the end though it turns out to be the perfectly equivalent way to prove the theory in a far more repeatable and controllable environment.

    Interestingly enough, most of those same people have no issue sayng “put it in a wind tunnel” — well, the electric motor on the wind tunnel is even bigger.

    The power to move the mediums relative to each other has to come from somewhere — outside it’s solar, inside it’s electricity, but the cart never cares and in fact can’t tell the difference.

    Thanks for responding to #297. I essentially repeated that post at #351 and have asked many times over for the critics to address it and you are the only one so far to return with an answer — and to your absolute credit, the correct one.

    Congrats on untwisting the brain.

    JB

  235. ThinAirDesigns says:

    GregLondon:
    >First of all, you guys all refuse to even
    >disclose your names publicly. And you want
    >me to give you my address?

    No I do not.

    As has been shown on this thread repeatedly, you’re missing a key point — *I never made the offer to you*.

    JB

  236. ThinAirDesigns says:

    Foetusnail:
    >For the last time, the treadmill video
    >proves nothing,

    Unless you sort out Post #351 and come to the same conclusion that Galileo, Newton, Einstein and all other accepted physicists for centuries have come to, it’s not going to be the last time.

    It’s one of the most basic tenets of physics that motion is relative and there is no test which can determine which object is ‘actually’ still and which is ‘actually’ moving.

    Road still, air moving — same as ‘air still, road moving’. Argue with the greats, not me.

    JB

  237. ThinAirDesigns says:

    FOETUSNAIL:
    [quote]Don’t believe any of this Bernoulli Principle reasons for the way in which planes develop lift or sails develop thrust. That stuff has finally been debunked by NASA. [/quote]

    And I suppose you can provide us with a NASA link to this debunking? ? ?

    That’s what I thought.

    JB

    • Anonymous says:

      This has been well-known for a VERY long time. Read Stick & Rudder sometime, the “lift” argument is nonsense.

  238. arkizzle says:

    Greg, I really don’t mean that absolutely. I certainly don’t have the answers, and I suppose you just know more about the subject than me to be unsatisfied with the answers so far.

    I still think building one would answer a lot of your questions.

  239. babyface says:

    I believe some people have difficulty to imagine the powers of wind (as in “air molecules moving relative to the ground”), and that makes the DDWFTTW concept so un-intuïtive.

    But, if you would replace the air by another, more dense medium, like water, or just imagine a really dense liquid metal (like mercury).
    Just think about it: the cart would simply “shoot” forward along its propellors pitch inthere, because that would be BY FAR the movement of least resistance. The dense medium would simply “avoid” that the propellors go any other direction through it, as that would mean much more effort, so the propellor will be pushed nicely “sideways” through the media along its propellor-pitch. If the pitch is “positive”, it will run faster than the medium, if it is “negative”, it will run slower (or even against). If pitch is zero (propellor acts as a classic “square sail”), the speed will be equal to the medium (who would believe that…)

    Eventually, the “true-world” speed would be marginally different though, to compensate for frictions (cart versus medium, rolling resistances, and drag of the propellor).

    I guess the above analogy makes the whole DDWFTTW easier to understand intuïtively, at least for me. But not easier to demonstrate though, and surely, some people would argue it doesn’t prove it can be done in air…

    If one thinks about the threadmill analogy in such case, it is intuïtively also much more obvious that it would take really some power from the threadmill against the wheels of the cart to keep up the speed. So it is more intuïtive that this is the external source of our power to speed up the cart, and also maintain speed against all mentioned losses.

  240. spork says:

    Again, we’re very happy to have a “convert”. I’m actually quite confident that Mr. Platt will be converted when sufficient evidence comes in. I understand his frustration that we don’t just do the simple test of doing this outdoors in the “real” wind, but I don’t think he appreciates how difficult it actually is to find truly suitable conditions outdoors. We chose a treadmill specifically because we thought it answered all doubts (boy – were we wrong).

    “So, I’d like to build one for myself. I’ve seen the link to spork’s list of parts, but also read that you might be offering kits of just enough components to build one device. I’d really like to get a kit of parts. How do I go about arranging this?”

    PM me on the hang gliding forum if you would (the link above where I mention my new build notes).

    But please catch me right away. I’m planning on ordering parts later today.

    By the way – this is not a money making deal for me. I am passing the parts along at my cost, and expect to put a couple of hours of my time into each one.

  241. Nelson.C says:

    Is there a video clearly showing the windspeed and that the cart is going faster than the wind? The only one I’ve seen is the one referenced in the first line of the post above, which only shows the wind direction with the aid of a rag at the beginning of the video. (As it’s tied behind the propellor of the cart, it doesn’t show anything useful after the thing has started.)

  242. arkizzle says:

    I dunno, seems an awful lot like the uber anticipated Plane on a Conveyor Belt MythBuster’s episode.

    At this point, you sound like a grouch.

  243. ThinAirDesigns says:

    Foetusnail:
    >By the way why don’t we see an
    >anemometer in your video?

    Because it’s pretty much accepted when a room has all it’s windows and doors closed there’s not going to be much of a use for one.

    Remember — it’s a physics brainteaser making no extraordinary claims … we’re not going for a Nobel here.

    JB

  244. Anonymous says:

    Hello Tom,

    well, it is no problem to say that something is impossible. But then, one has to make 100% sure that it really is, or has to use the “i think it is impossible” phrasing instead.

    But what is more important: If someone is not 100% clear about whether something is possible or not, that person should dig into the topic and analyze it, instead of barely denying the possibility. Alas, we are just mere humans, and we do make errors. Nothing wrong with that, as long as we are able to admit the error later.

    No one of us has 100% right knowledge of 100% of the things out there. Heck, even a lot of PhD’s, scientists and so on get fooled by this cart and simply claim “impossible”, without further thinking. I’ll call that “denial bias”, as opposed to “confirmation bias”.

    You did the right thing. You couldn’t really understand it first, it looked impossible to you, and you said that. Then you took your time to analyze it further, and came to a different conclusion afterwards and admitted that you were wrong in your assumptions.

    If you look around the net and read the various threads about this cart, you will find that quite some people are not able to do that. They reject the possibility that they might be wrong. Some kind of elitist “i know everything” stanza.

    My guess is that this is partly caused by the sheer amount of crackpottery on the net. After seeing hundreds of over-unity crapola’s, and seeing their proponent argue for it, it can surely become some kind of reflex to deny things immediately if they are not directly understood and look suspicious. There just has been too much crap out there.

    Otoh, i think that this behaviour is not good. We might miss something truly innovative or new in that noise. So, unless it can be shown with certainty that something is bunk, it should be analyzed and evaluated, even if it looks ridiculous at the start. That might sound a bit crackpottish, since a similar argument is used by these crackpots, but i think it’s true.

    In any case, it has been nice chatting with you about this stuff.

    Greetings,

    Chris

  245. ThinAirDesigns says:

    Michael:
    [quote]Gee, Spork and Thinairdesigns, why complain that BoingBoing is not “letting” us build the machine for $40 or $70 of parts, and link to plans yourself?[/quote]

    Michael .. are you on crack? Where have I “complained that BoingBoing is not letting us build the machine”?

    Please to find and post that quote for me.

    Thanks

    JB

  246. arkizzle says:

    1. Why is it that the propeller doesn’t start turning until the wheels contact the belt?

    Because there is no wind, and the belt is providing the power to turn the prop.

  247. spork says:

    >>
    Note that the total speed is NOT in the direction of the wind; the component of velocity directly downwind is never greater than the wind speed.
    < <

    Is too.

    >>
    Any Smart People who might like to weigh in, per chance? Someone who may have gone to college?
    < <

    Actually I got my M.S. in aero, and JB and I built the cart and made the video you see above. I assure you it's quite real.

    >> Because nothing engenders trust like the username “spork33″.

    Sorry, spork1 through spork32 were taken.

    >>Last I checked, all perpetual motion machines are bunk.

    I’m with you 100% there. But this is a wind powered vehicle.

    >>
    As for the video, it’s cute that he’s got a tell-tale to try to indicate wind direction. But putting it directly behind the propeller makes it useless.
    < <

    Look again at the location of his tell-tale.

    >>
    it completely weirded me out that you could land without engine power using autorotation
    < <

    Yup, it seems wierd, but the two blades are simply two glider wings chasing each other in a circle when you're in an auto. You still have cyclic and collective, so it flies just swell.

    >>
    I think you’d see the bleed off happen a heck of a lot faster and you’d realize that it isn’t really steady state. They seem to be doing it for a few seconds and then it veers off the side so they have to stop and reset, but a few seconds isn’t steady state.
    < <

    We can hold it back with the homemade spork for as long as we pay the power bill. We made one video that shows it holding its own unassisted for 1 min, 38 secs. To do this we had to slow the belt down and incline the treadmill to the point where it wouldn't advance on the belt.

    >>I will say that I’m a firm believer in the conservation of energy

    Me too.

    >>… so I don’t think they’re getting something for nothing here.

    We’re not.

    >> It’s just that it’s either some hidden transfer of energy… or they’re cheating somehow

    Nothing hidden, no cheating. I’ve posted the parts list and build plans all over the internet. I’ve even offered the parts kits at my cost (and significant time investment on each one) so anyone can try this for themselves.

    >>
    Would this discovery not lend a little more weight to wind power as a way to generate electricity?
    <<

    It ends up we were far from the first to discover it. And unfortunately it has no such useful purpose.

  248. FoetusNail says:

    AND AT ONE TIME DID YOU EXCEED THE WIND SPEED?

    I notice some debris go flying by at about four times the speed of your cart, which it never seems to catch up too. That stuff must be going two or three times the speed of the wind.

  249. spork says:

    “Yeah, I’m grouchy. And they still don’t understand how this works.”

    Even though I’ve described it accurately hundreds of times in hundreds of ways. Now Greg is kind enough to explain to us how it “really works”.

    I haven’t gone to the trouble to look at his page, but I’m willing to bet he’s got it wrong. Let me know if I need to go point out where.

  250. gpomputius says:

    I believe that you can’t go faster than wind when going directly downwind because:

    Imagine the air as particles hitting your craft, pushing it downwind. Once you match speed with the particles of air, they no longer hit your craft and thus can’t push it to move faster. Because you are going straight downwind, you can’t take advantage of the “relative wind” elegantly described in the sailing links above, by which you gain speed by changing direction of the wind. I believe that’s why the sailing links say “you can’t travel directly downwind faster than the wind speed.”

    I can think of two counterarguments to the above, but they both strain the definition of a vehicle.

    First off, you could use two special sails or sailboats that are traveling at 45 degree angles relative to downwind (and which reverse directions by reversing the directions of their sails). For example you could drag a boat downwind using two faster vessels going downwind at opposite angles. The fast boats would zig zag, crossing each others paths while towing another boat downwind. If you called the whole apparatus a single craft, you could achieve the claimed DDFTTW, but why not just use the zig zag method with a single craft and go downwind even faster?

    The second method would take advantage of lighter than air materials to briefly achieve faster than downwind speed. If you attach a cork to a string, and attach the string to the bottom of a glass filled with water, the cork will float like a balloon in the glass of water. If you move this glass, the cork will accelerate faster than the water (because the wave of water hitting the cork will make the lightweight cork move more than the heavier fluid surrounding it). Note that the cork only moves faster than the water while the water accelerates. When/if the water slows down this process will work in reverse as the cork is slowed by colliding with slow water particles in front of it and will decelerate faster than the water thanks to its lower mass. However, during a short chunk of time the cork will move faster than the water (from the acceleration until the deceleration). This should analogize perfectly to wind (which works like the water) and a lighter than air craft (which works like a suspended cork). You can outrun the wind in this method (in a hot air balloon perhaps?) but only while the wind is picking up speed.

  251. arkizzle says:

    If you actually read that document, all 15 pages of it (it’s mostly drawings, so quick reading), then you probably wouldn’t be demanding video because you’d know it would work.

    See, that’s pretty much what the OP guys said. And I did read your document, but like it or not, I will need video or first-hand-experience of your system working before I believe it does what you propose.

    And “payback”? C’mon, I have no dogs in this fight, I thought the conduct of a few ‘locals’ in this thread was utterly below their standards and left them sounding like a bunch of children.. I tried to calm the mood several times, and called bullshit when I thought people were being dicks.

    It’s Devil’s Advocate (as annoying as that can be), if anything. There was some pretty aggressive demands made of these people, who owe you nothing, but hung around because (presumably) they enjoy the topic.

    If you think your internet-words are any more convincing than anyone else’s, you are mistaken. I read your pdf when you posted it and frankly I wasn’t convinced. I’m not an engineer or a physicist though, but I genuinely can’t picture how it works without something to lever between the ground and wind, as far as I can tell, it just spins along.

    Video or it didn’t happen. (An entirely reasonable request, whether, or not, you factor in all the other things being demanded up-thread)

  252. Antinous says:

    Manners, please.

  253. travis08 says:

    1:48 seconds of not touching it before it fell off the back.

    The problem I see with the original video is you suggest that that it can’t be kinetic energy because you show that it runs out in 7 seconds.

    You do this by holding the car stationary for almost a 2 count, then lift the car off the track showing it runs out in a seven count. Next you hold the car stationary on the track again, and let in run for about twice as long, suggesting that it must be more than kinetic energy powering it. HOWEVER the second time you charge the car up (by holding it stationary on the moving treadmill) you charge it up for about a 4 count.

    This would provide twice the runtime and allow you to count past seven. About the time the car should run out of stored energy you cut the camera.

    The video you linked to showing that the car can go indefinitely never shows how long you held it on the track charging it, nor does it go indefinitely, it falls off the back.

  254. toilet says:

    #208 posted by datura

    It’s not encountering a headwind as it moves up the treadmill?

    To re-use an existing analogy, imagine you’re biking at 10mph with a 10mph tailwind. How much wind do you feel on your face? Put the bike on a treadmill set to 10mph and pedal at 10mph. Again from the same point of reference (the bike seat) how’s the air feel? Start pedaling at 11mph, what’s the air speed feel like now in both cases?

  255. FoetusNail says:

    Your cart does not work without a flat sail except on your powered belt. As I’ve said before, your video proves nothing. In the video the cart is powered solely by the belt and the prop provides enough thrust to reach equilibrium with the belt’s linear velocity.

    Throw away the belt, mount the motor on the axle, because that is the essence of your contraption. The only thing your video proves is that if you put a motor on your axle and drive a prop your cart will move forward, this is nothing more than a wheeled airboat. All you’ve done is use a belt to transfer power from the motor to the wheels and a shaft to transfer power from the wheels to the propeller. Why not mount the motor on the cart and run a belt around the wheel and the motor shaft? The only difference is that instead of running in place it will actually be a real toy that goes places.

  256. FoetusNail says:

    It is this kind of silliness that proves none of you are degreed engineers. No engineer would ever say something as silly or snake oily as the statement you made up. An engineer would simply say the machine uses wind energy to propel itself over the ground or they might say the machine converts wind energy into mechanical energy. Also, a degreed engineer would have plans immediately available. I never met an engineer of any kind that did not start every project with sketches and mathematics, with the end result always being a detailed CAD dwg. You offer none of these things for review, yet expect everyone to just believe this hocus-pocus.

  257. FoetusNail says:

    And at WHAT time did you exceed the wind speed?

  258. Tarantio says:

    Well, let’s consider what’s happening to the cart.

    When traveling at a speed less than that of the wind, a significant portion of the wind will be accelerating the cart forward directly, and a significant portion of the wind will be accelerating the propeller rotationally. As long as the propeller is moving, it will also be accelerating the cart forward, proportionally to its speed (or maybe the square of its speed, or something?). Nothing should be slowing it down but friction.

    As the cart approaches the speed of the wind, the effect of the wind on the cart will drop down to zero, leaving only friction and the force provided by the propeller, spinning with its significant momentum. Tentatively, I’d say that it sounds possible for this situation to result in some amount of forward acceleration, and a speed higher than the wind.

    As soon as it does this, though, the air through which the cart passes will exert a force on it, pushing against both the cart’s and the propeller’s momentum. It would be difficult for me to imagine this force, plus friction, not being able to reduce the speed of the cart at least to the speed of the wind. How long it would take, I don’t know.

    Based on this amateur analysis, I’d guess that the speed of the cart oscillates a bit, and probably cannot obtain a continuous speed greater than the wind. The only thing that gives me pause is my absolute lack of knowledge of the field of fluid dynamics. Turbulence and eddy currents can do some crazy things.

  259. FoetusNail says:

    The treadmill just doesn’t mean a damn thing about how this cart will behave outdoors in wind. All this video proves is that someone has designed and built a very nice little cart that can run in place on a treadmill. This is a nice accomplishment, but beyond this it still proves nothing.

    Post video proving your device works outdoors and exceeds the speed of the wind pushing it and we will believe you. But you will never do either of the two tests I suggested, because if you did you would debunk your own myth, and you would never get on mythbusters. Actually, I would be very surprised if mythbusters ever decides to waste their time on your cart. If anything they would probably ask you the same thing, tape a race or call the cops.

    BTW, how did you like the links provided earlier?

  260. Takuan says:

    first Ecclesiastes: “Has happen? Gunna be agin. Nuthing new undur teh sunz.10 Kitteh can not sez “OMFGZ sumthing new!” is jus REPOST!.11 New kittahz 4gitz old kittahz, new kittahz 4gitd bai even newer kittahz.”

  261. gpomputius says:

    A proof of impossibility, based on one reasonable assumption (besides the assumption of DDFTTW movement):

    If the craft moves downwind at 11 mph, and the wind moves downwind at 10 mph, is this equivalent to the craft moving at 1mph, and the wind moving at 0 mph? I believe it is, thanks to all that “inertial reference frame” mumbo jumbo. This is my assumption. From this assumption, it follows that this DDFTTW craft will constantly move at 1 mph in a windless room, in spite of friction. That, my friends, is perpetual motion. Which is impossible. Thus one of our assumptions is false. QED.

    What’s funny is that this problem can be solved entirely theoretically, but because this is the internet people argue about it for hours and reach no conclusion. This is one debate with a clear right answer. Scientists understand this kind of large scale motion very well. In fact this is the one field where experiments are barely useful because our scientific understanding is so accurate, unlike medicine, chemistry, neurology, etc. The physical experiment is so much more likely to have errors than mathematical models that for theoretical questions like “possible top speed” the experiment causes more problems than solutions. Unless well defined laws of Newtonian motion are wrong, laws of physics properly applid will provide the answer. Thus I think the strongest argument is that the science guy referred to in the original post thinks it’s bunk. That guy must know at least one aeronautical engineer or researcher, which is all it would take to get the right answer.

  262. FoetusNail says:

    Now take away the motor.

  263. spork says:

    “Based on this amateur analysis, I’d guess that the speed of the cart oscillates a bit, and probably cannot obtain a continuous speed greater than the wind”

    I just can’t keep up. I’ll just say that the offer I have for Platt is open to anyone that likes – my $100K against your $10K. I will prove that this vehicle powered solely by the wind can and will go directly downwind, faster than the wind, steady state.

    • Antinous says:

      spork & thinairdesigns,

      This comment thread is intended to be a discussion, not a press conference. If you have any information to add to the discussion, feel free. But please stop saying the same things over and over.

  264. GregLondon says:

    I genuinely don’t know how much faster than windspeed this machine will go, or if it’ll just bob around the mark by utilising small gusts etc,

    That pretty much sums up the opposite sides of the discussion.

  265. arkizzle says:

    *cough cough*

    * You can’t polish poop.

    * It is better to hit a golf ball straight through a tree than around it because it is 90% air anyway.

    * It is impossible to separate two interlocked phone books due to the massive amount of friction between the 800 pages of each book.

    * Goats can be startled into fainting.

    * You can charge an MP3 music player like an iPod by plugging a USB cable into an onion that has been soaked in electrolyte fluid for half an hour.

    * A driver will use more fuel when angry than when relaxed.

    * A flag cannot flap in a vacuum.

    * A truck carrying birds will be lighter if the birds fly around than if the birds sit/stand.

    * A regulation NFL football will fly farther when filled with helium as opposed to compressed air at regulation pressure (13 psi).

    http://www.mythbustersresults.com

  266. Nelson.C says:

    Thiairdesigns @231: I’m beginning to suspect that you are not arguing in good faith.

    You quite plainly are making an extraordinary claim, going purely by the amount of fuss this thing has kicked up.

    Never mind the treadmill experiment, where are the facts and figures for the open air test? What speed and direction was the wind? Was it constant during the test? Was the road level? If you’re so sure that the energy is coming from the wind, please give a cogent explanation of how it works, with the relevant physical equations and hard numbers. If you can’t supply all of this, then your demonstration is simply a bust. Hoax or self-deception, it has as much credibility as cold fusion, for similar reasons.

  267. spork says:

    >>For the last time, the treadmill video proves nothing…

    Seriously? Do you promise?

  268. spork says:

    >> Dude, this would be a fantastic MythBusters episode!

    My thoughts exactly

  269. Alpinwolf says:

    I wanted to suggest Free Body Diagrams to the self-taught, but without numbers for the forces, that gets tough. (However I do recall there were some force measurements, in grams, from some of the treadmill tests.)

    But it could still be useful. While a helicopter accelerates enough air downward to account for it’s lift (while taking off), a hovercraft shakes loose the bonds of earth with a lot less power. I’m sure we can all imagine how, if one were to kidnap a djinn, (or an ifrit, whatever) and make the ground *pooff* out of existence below the hovering craft, that it would promptly plummet. The ground provides a Normal Force in response to the air pressure under the skirt, pushing back on the air cushion, which pushes up on the underside of the craft. Presto.

    If you draw a hovercraft FBD without the Normal force from the ground, you’ll be wondering how the fuck it stays afloat.

    (How the Normal Force arises is an entirely different discussion, but it’s there, else tables and tall buildings would FAIL.)

    If you have a Cessna idling on the ground in still air, but the prop was moving the air it was churning at 10 mph to the rear, the plane would want to roll forwards. Thus: brakes. If it was pointed into a 10 mph headwind, there would be very little load on the prop and engine, and no thrust. You wouldn’t need breaks. (Well, maybe to keep from rolling backwards.) You need to have that stationary ambient air to *ahem* thrust against, or there will be no acceleration. The stationary air provides the reaction force.

    When the free-range prop-skate gets to ambient speed, the wind might seem to be still, but you need that for the prop thrust to work against. If you made that djinn get off the couch and switch off the wind, the prop thrust would be rendered impotent. So the wind continues to provide a push to the prop wash and the cart, even when the cart is going (a little) faster.

    Indoors and out, the motive force for acceleration is the fan.

    Indoors, the energy source, as (mostly) agreed herein, is the treadmill, which will show a slight power draw increase, or a velocity decrease at constant power. (The tread, not the cart.)

    And outdoors… Yeah, it’s the wind. There is nothing else. I’m not trying to be frustrating, but this makes me think of a one-man, one-chair Musical Chairs game, but the guy has a blindfold on, and can’t find his seat. (“No-no, a little to your right… Now turn around.. Ooooh you’re so close!…) Wind is the energy source for a square rigged vessel running downwind, and that same wind is the energy source for this more-efficient machine. More efficient. Not perpetual.

    I’m afraid the injection of energy from the external source (still the wind) is not a machine motion thing, nor chemical, nor electrical, etc. It’s bleeding off the KE of the air, to push the backwash, to push the prop, to push the frame, giving the cart additional KE down the road. And this would not work to push the cart faster than ambient if it were not for the backwash thrust from the fan.

    I’m not too sure how broad-reach sailing works, (though I’m sure I can find it), but there does seem a consensus here. So with that in mind, the “cylindrical Earth with axial wind” model, reduced to a propshaft, makes a kind of sense to me that fits the rest like another jigsaw piece.

    The mention of a VMG of over 3.0 being achieved (if I’m understanding this right) should indicate that this little machine could be able to approach that value as well. This kinda throws a wrench in my “energy reflector” analogy, but doesn’t really refute my general argument. It just means the design is even better at collecting wind power than I gave it credit for.

    Still. Not. Perpetual.

    When KE is extracted from the wind, since the mass is the same, the velocity is lessened. I think AirShowFan said this as well. Instead of blowing at 10 mph, it will have been stalled down to, oh, 7 mph, close behind the craft. And it’s not the thrust I’m talking about. This is a real loss of energy, but with the wind trying to keep going, that small amount of loss is dispersed throughout, well, the whole atmosphere. So you can’t watch it as easily as billiards.

    And as for the matched-speed wind pushing on the thrust air, and not the vehicle, remember that since air is a fluid, it makes pressure and flow fields that affect neighboring air. It’s not like BB’s.

    Flow visualization wind tunnels are a great tool. There’s lotsa vids around showing smoke flowing over airfoils, cars, geometry quizes, etc. They do a good job of conveying a conceptual sense of things like flow fields, the “equal transit time” fallacy, Newtonian lift, etc.

    Here’s a good one from U. of Cambridge. There are NASA ones too, but they’re older, fuzzier. Notice how the air in front of the “wing” is already deflecting before arriving at the solid obstacle.
    http://www.metacafe.com/watch/yt-6UlsArvbTeo/how_wings_work_smoke_streamlines_around_an_airfoil/

    I totally get the frustration of the builders, but I’m not one of them, and have not winded myself (sorry) on explaining this everywhere else. Okay, maybe I’m not sorry about the pun, sue me. I’m sure not gonna make a mission of re-explaining this on their behalf, but I’ve been told I bring a unique perspective on things, and given the usual thoughtful crowd here, I felt like sharing. Or trying to.

    But I must admit that the vitriol that has tainted some comments is rather wearying.

    I apologize if any of this seemed condescending or anything, that’s not my intent. If I had a tablet or a scanner, I’d prolly draw it out myself for y’all and link to it here, but I do not haz. So I’m doing my best to convey to an audience that I generally admire the tricky business of fluid dynamics and mechanical advantage.

    Everyone have a scooby snak and some tea, and chillax.

  270. ThinAirDesigns says:

    Tarantio:
    >The only thing that gives me pause is my
    >absolute lack of knowledge of the field of
    >fluid dynamics. Turbulence and eddy currents
    >can do some crazy things.

    You can take yourself off of pause. Neither turbulence nor eddy currents are utilized with this device.

    It is powered by longstanding sailing principles utilized in a clever and non-intuitive way.

    JB

  271. Anonymous says:

    The small cart with the orange propeller, while elegant, is not wind powered, it is being powered by the treadmill (and the wind). The treadmill turns the wheels, which turns the gears, which turns the propeller. The wind provides a little extra umph. There is a short clip of it in an outdoor setting where wind is providing the power, but there is no indication that the cart moves faster than the wind.
    The premise of the tread-mill is that a stationary object in moving air is equivalent to a moving object in stationary air. To make proper use of that principle, they would need to put the cart in a wind tunnel and show that it can move forward over stationary ground upwind. That is what it would take to be equivalent to moving down wind faster than the wind-to-ground speed.

  272. Bill Barth says:

    Yes, Alex @141, but sailboats can’t have a velocity in the true wind direction that’s higher than the true wind velocity nor can they have a velocity higher than the apparent wind.

    This device is designed to run straight downwind. The wheels turn the prop so that it eventually produces thrust. At a standstill on a stationary surface with a tailwind, the resistance to the air passing over the device is enough of a force to start it rolling. This, due to the drivetrain connecting the wheels and prop, starts the prop to turning, too. Based on the angle of the prop blades and the wind speed, there is a forward velocity (less than the true wind speed but greater than some minimum threshold bigger than zero, say, maybe 1mph) at which the prop is no longer an aerodynamic drag producer in the direction of travel of the vehicle (though the body of the vehicle still is). I.e., conditions at which the mass flow through the prop is essentially zero.

    So, the argument must be as follows:

    Since the local flow (over the rest of the vehicle) is still a tailwind at this point, the body drag will continue to accelerate the vehicle, but since any further acceleration will cause the propeller to begin producing thrust, the vehicle will continue to accelerate more and more until vehicle speed surpasses the true wind speed.

    This is, in fact, why the treadmill test works. Friction is small enough that the thrust produced in the 3-10mph range is enough to overcome the rolling resistance and allow the device to accelerate on a flat treadmill or stay stationary on an inclined one, but there’s a problem when it comes to taking the treadmill out of the picture.

    You could see this if you were to do long-term average energy consumption tests on the treadmill in a carefully controlled environment with good power conditioners. The energy used by the treadmill will be slightly higher with the prop-and-cart device on it compared to a run with only the cart and a weight to compensate for the missing prop (hold the latter in position with a rigid bar or set of strings). This energy is the missing energy that prevents a outdoors version of the vehicle from running downwind at greater than the true wind speed. The wind cannot provide any extra energy once the device is traveling at the same speed as the true wind. In fact, if the device is traveling faster than the true wind, the apparent wind will begin to cause drag which will rob the device of speed. This is drag that must, but cannot be, overcome by the prop because there is no source of energy to keep driving it.

    There is also the fact that the rotating propeller makes an aerodynamic drag perpendicular to the direction of travel of the composite vehicle. This drag creates a torque that counteracts the push from the wheels through the drivetrain. Without the treadmill adding energy, there’s nothing to counteract this tendency to slow the prop.

  273. Anonymous says:

    I’ll weigh in here real quick (I haven’t read all the comments) and point out why this video doesn’t support the hypothesis. I hope someone got here before I did, but in case not…

    The reason their experiment does not prove that it’s possible to make a craft move faster than wind solely powered by wind, is because the experiment does not mimic what it intends to mimic. When the craft is moving at the same speed as the air, the speed of the air relative to the craft is zero. Right? Right. In this video, the speed of the air relative to the craft NEVER reaches zero; it always pushes on the back of the craft.

    All this experiment showed was that the force of the wind closely matched the force that the treadmill had against the wheels. That doesn’t help anyone.

    And for the same reason, the video certainly did not disprove the momentum explanation. Whoever said that the momentum of the propeller was causing momentary faster/than/wind speeds (when the wind died down) was correct. The craft itself had some momentum too. There is no way to sustain craft velocity that exceeds the velocity of the wind.

    Mark, good call on trusting the guy from Make.

  274. arkizzle says:

    Foetus, you possibly need to back slowly away from this thread.. There is only so much bangin’ on about a thing you can do before you start to repeat yourself and begin to sound loopy.

    Perhaps it would serve you better to invest the $40 and see if it works to your own satisfaction, as the people onboard don’t seem to be able (or willing, beyond making a wager) to provide the info you need.
    _

    OTOH: Where are you guys off to so early in the morning? Sounds like you need some sleep! :)

  275. airshowfan says:

    #145/146 and 148: How can it not be apparent to you that the propeller is a propeller, NOT a turbine? It is not being spun by the wind or driving the wheels; It is being powered by the wheels, pushing against the air! The very fact that the vehicle in the video starts at wind speed (at rest relative to the air) should make it very clear that a DWFTTW cart has a propeller on top, not a turbine.

    The thing on top is a propeller, not a turbine.

    The thing on top is a propeller, not a turbine.

    (I guess it might act as a turbine while the cart is accelerated from “at rest relative to the ground” to “at rest relative to the air” but the threadmill experiment skips this step, and like I keep saying, a sail would do just fine at this step).

    Another way of looking at it is that the propeller makes more thrust than it would if the wind were not there. Propellers get less efficient when there is air blowing past them. So if there were no wind (still air at rest relative to the ground), a cart with a propeller driven by the wheels would indeed come to a stop in a little while (conservation of energy); if it didn’t, it would be a perpetual motion machine. But since the air is moving along with the cart, the propeller gets a bit of a boost in how much thrust it makes, so it makes more thrust than it would if the air were not moving relative to the ground.

    #158: I second that.

  276. FoetusNail says:

    BTW, note the heavily reefed mainsail. Those guys are fukin crazy!

  277. airshowfan says:

    I’m not 100% sure of this, but it seems to me that the sailboat thing (i.e. saying that a DWFTTW cart is possible “because the prop moves at an angle to the wind, like a sail”) assumes that the prop is a turbine. I don’t see how the sailboat angle thing applies if the prop is a propeller generating thrust (rather than a turbine that is spun by the wind and that powers the wheels).

    I still insist that the spinny thing is a propeller and not a turbine.

    I insist this because, on the video, that’s clearly how it works. In the video, the cart accelerates from being at rest relative to the air. So the spinning thing is clearly not a turbine, since the cart barely moves relative to the air.

    Now, that is not to say that it is IMPOSSIBLE to have a DWFTTW cart where the spinny thing is a turbine powering the wheels. Maybe it’s possible. It’s just not what the video shows. So if we’re talking about a cart like the cart on the video (or like the cart that the video CLAIMS to show, if you want to be really skeptical), let’s assume that the spinny thing is a propeller. In that case, the sailboat wind angle thing is irrelevant, right? And in any case, I really really don’t think that the downwind component of a sailboat’s velocity exceeds the wind speed, but I am not as qualified to state this for sure as other people who participate in this discussion and who have actual knowledge of sailing.

  278. FoetusNail says:

    And that is the only truthful thing you guys have said. And that is why you will never provide any further evidence of your cart’s ability to travel faster than the wind outside without a motor or sail.

  279. SubductionZone says:

    Taking it outside will not please the overly skeptical either since they will always say something on the order of “you did not correctly measure the wind speed” or some other such nonsense. Unless you can come up with an explanation why the conveyor belt test is not equivalent to a tailwind I suggest that you quit complaining.

    I just watched the outdoor video again and you could see a piece of paper go by the cart when it started out but it looked like the cart accelerated to about the same rate at least.

  280. arkizzle says:

    I know, I was being inclusive :)

  281. GregLondon says:

    Foetusnail: why do you have to hold your cart down to get it up to speed before letting go?

    He doesn’t know.

    The one thing that explains 99% of this thread is that these guys don’t understand how it works and can’t explain it.

    Trying to get them to explain it, or trying to get them to understand the issues you see around why it might violate laws of physics, is going to do nothing but drive you batty.

    They don’t seem to care if they drive people batty, but I’d hate to see you do that to yourself.

  282. Alpinwolf says:

    I fear it sounds like a couple posters have trod down the path of darkness. Beware these twin beasts: Fear of getting your passionate argument disproved; and Confirmation Bias.

    I’d like to add to the energy question, but I’d like to ask that folks read my treatise at #115 first.

    I am not affiliated with ThinAir or Spork in any way, I’ve just mulled the details a lot.

    I could see the whole shebang running in my internal version of Solidworks, but I was having trouble identifying the continued energy transmission mechanism, until just before reading #221, which confirmed and crystallized the process for me.

    Remember this: In this contraption, whether indoors or out, the airfoils in question are always a propeller, sometimes a sail, and never a turbine. The difference between a propeller (or impeller), and a turbine is not semantic, but technical, and diametrically opposite. Propellers put their driven kinetic energy into redirecting and pushing the medium (air, water, whatever), whereas turbines gather the energy of a flowing medium and convert that kinetic energy to rotational motion.

    This cart has a pusher prop. It doesn’t make for a good sail, but on such a tiny craft, it can do double-duty, as being a surface for the wind to push on, which then transfers to the support frame. As soon as the blades begin to turn, they help improve their efficiency as sails, since the rotation moves the relative wind impact vector from a slip angle, towards a more Normal position. As the blades spin faster and the relative air speed decreases, the apparent air stream for the prop transitions from [behind the cart] to [perpendicular to the concave side of the blade] to [parallel to the plane of rotation] to [closer to parallel to the blade pitch].

    Sails, like a square rig, are almost similar to a turbine in that they collect the energy of a flowing medium, but they transmit the force directly to a framework (mast and boom, etc.)

    Now just as an optimized hovercraft on a glassy floor defies gravity by thrusting a mass of air as a cushion against the ground and doesn’t even touch, so too does the cart’s propeller thrust a mass of air backwards, which runs into a wall of air advancing at (around here, it seems) 10 mph, that we call wind.

    There are similarities to wing-in-ground-effect flight/ lift/ hover.

    The energy to continue to push this machine past ambient wind speed does indeed still come from the wind (in the outdoors model) at the interface of the thrust air with the wind air. They make for an action-reaction pair. While the thrust air is keeping the cart ahead of the wall of wind, that wall also keeps pushing the thrust cushion ahead. The wind is not gonna give up, it keeps advancing, and provides a squishy but implacable wall for the thrust air to push off of.

    The wind pushing the cart via the thrust-cushion puts energy into the mechanicals by forcing the cart past fixed ground, which forces the wheels to turn. Again: lack of wind-to-ground differential = no energy for the system. Just because the wind is no longer felt by the driver’s face doesn’t mean it’s no longer felt by the vehicle. That prop would have a lot easier time pushing that air backwards if it weren’t for the wind wall pushing back at it (forwards), and then effective thrust would be diminished, and the whole schmear winds down.

    So a new energy path (not inconsistent with my earlier ones, just refined.):
    Wind –> thrust air mass –> propeller blades –> propeller mast (cart) –> rolling the wheels –> driveline –> Turning the prop through relatively still air –> Induced Drag (technical term) and Thrust.

    I know that last stage sounds circular, and I fear that some may then dismiss my whole reasoning. But keep reading:

    Where on a direct downwind run a square sail acts as an energy catcher’s mitt, this leverage multiplying system, while violating no rules, acts as an energy reflector. If you shine a laser at a black carpet, there is a continual energy impulse impacting the carpet, pushing at it, with the meager force that photons can convey. If you shine that laser squarely at a mirror, the photons are not just absorbed, but returned the way they came, making for double the momentum transfer.

    I’m pretty sure the upper limit for equilibrium for this device in optimized conditions is 2x ambient wind speed.

    Please, I ask y’all: I’ve not heard much response to my #115 post, and don’t want adoring fans, but I thought I did kinda good there, and if you think that post plus this is either unclear or specifically wrong, I’d love to attempt this whole communication thing some more.

    But I steadfastly maintain that the wingwalker ant still pukes.

  283. ThinAirDesigns says:

    Codesuidae:

    You’re welcome to use either of those:

    Let’s say that you use your sextant and determine that everything points to “no treadmill”. You use your gravimeter and get your ‘confirmation’. You then turn around and give your answer “no treadmill”

    I simply smile, open up the trap door in the street and show you that we are indeed in a treadmill moving at 10mph. DAMMIT! you scream … how could my sensitive instruments have been wrong?

    I just smile and open up one more trap door and show you that the first treadmill is sitting on top of a second treadmill going north.

    Newton still rules.

    :D

    JB

  284. FoetusNail says:

    The cart is not being pushed by the wind on the treadmill.

    Now that you have proved you will take it outside, race it against another cart with a sail or just run beside it dropping confetti.

  285. Plethora_Jenkins says:

    >>PM me on the hang gliding forum if you would (the link above where I mention my new build notes).

    I’m having trouble finding it in this huge thread. I’m searching through all your posts, but if you could tell me the post # it’d be very handy.

    >>But please catch me right away. I’m planning on ordering parts later today.

    Will do. As soon as I find the link. :-)

    >>By the way – this is not a money making deal for me. I am passing the parts along at my cost, and expect to put a couple of hours of my time into each one.

    I gathered that from some of your other posts. I think that’s very cool of you.

  286. Anonymous says:

    From Greg’s document:

    “Trying to get the builders to
    explain how said machines actually work resulted in an amazing amount of unobtainium, handwavium,
    and complicated invented phrases that don’t mean anything.”

    Of course, he doesn’t show up any math, but rather _also_ tries to explain it with phrases.

    Also there is a notable lack of “I got it wrong first” or “I apologize”.

    “Why in the world do all the designs out there right now use propellers?
    I don’t know the answer to that one.
    I believe it might be because the people who built the propeller driven machines didn’t understand what
    was going on exactly and so just tinkered with something until they got it to work.”

    Of course, it is still the other people’s fault. Note that he _also_ doesn’t know why a propeller, but implies that the other don’t know. It’s a bit, uhm, strange to tell others that they have no clue, while having no clue of his own.

    The document is worth a read, pretty nicely shows that some people are 1) not able to say sorry, 2) complain about given explanations and their style while coming up with the same style themselves, and 3) fail to see that.

  287. spork says:

    >>
    This comment thread is intended to be a discussion, not a press conference. If you have any information to add to the discussion, feel free. But please stop saying the same things over and over.
    <<

    I’ve done nothing but respond to the comments made. And I don’t think I’ve repeated myself.

  288. GregLondon says:

    There’s nothing “pseudo” about the wind on the prop — it’s very real and additionaly, for me to say that I don’t know how it works would be a lie and thus I’m not going down that path.

    Which is a long-winded way of saying you can’t explain it. It may be real, but you can’t explain where the energy is coming from other than “the wind”. If I say “the wind” makes a helicopter fly and someone asked how I can turn in midair, and I still say “the wind”, the request for more detail, and the complete lack of any detail in the response would be a red flag that I don’t know the answer and am trying to cover.

    You don’t know how this thing works, which means you don’t know if you’re understanding it correctly or if there is something else goign on that is making it do what it does. If you dont understand what it does, you cannot say with any certainty what is causing it to do what it does.

    I can say “it’s all flywheel effect” and you really have nothing to disprove that other than saying “the wind” over and over.

    All you’ve got to go on are whatever observations you made, and whatever guesstimates you divined out of those observations. All of which apparently boil down to “the wind” being some magical source of power that needs no further explanation.

    You either don’t know what your talking about, or you do know but are completely unable to articulate it in any fashion. Given “the wind” is your pat answer to every question, I’m guessing it’s the first.

  289. joelphillips says:

    @43.

    The premise of the tread-mill is that a stationary object in moving air is equivalent to a moving object in stationary air

    No, the premise is that that the stationary object in stationary air on moving ground is equivalent to a moving object in moving (same direction) air on stationary ground. Which seems pretty reasonable.

    The video seems pretty credible to me. However, for completeness, I’d like to see an experiment that demonstrated that the treadmill wasn’t creating any eddy currents in the air that were blowing in the opposite direction to the treadmill at the height of the propellor.

  290. davidglover says:

    #151 “Have you put your real name next to your claims?’

    I don’t care if they call themselves BullTwinkleTiddlyPanda33 What they have does what they say.

    Wind pushes the cart (if outside), wheels turn the prop (treadmill), prop pushes air. Most everyone knows ice boats are way faster than the wind to a down wind point. The prop is a rotating angled sail. Same deal. Just hard initially to get your head around a wheeled/geared/prop toy can climb an inclined treadmill Safe difficulty I had at first with the Flying Spaghetti Monster.

  291. zerocarbonista says:

    “Charles Platt made a miniature model of the vehicle and came to the conclusion that there is no such thing as a wind-powered vehicle that can travel faster than the speed of the wind.”

    No propellers involved, but the Greenbird craft travels downwind faster than the speed of the wind.

    It is currently on Canyon Ferry in Montana about to attempt the Ice Speed Record. There is also a land version of the craft that was in Australia this year.

    Check out the site/blog. Greenbird is also on Twitter.

  292. toilet says:

    And the beret goes to… Alpinwolf!

  293. GregLondon says:

    At this point, you sound like a grouch.

    Yeah, I’m grouchy. And they still don’t understand how this works.

  294. GregLondon says:

    anon@437: Of course, he doesn’t show up any math,

    Dude, like spork has formulas for any of this. I tried getting a spec and people said they could ship me their machine. There is no math to show up. There are no drawings to show up. It’s all a bunch of mumbo jumbo.

  295. gtbernstein says:

    Why this hasn’t been tried in an ACTUAL controlled environment, not this completely unscientific controlled environment? Why don’t they do this test in a real wind tunnel. One with a flat level surface that does not move and a consistent wind source that can be controlled.

    Whether people want to admit it or not, a moving surface does add other variables that aren’t being accounted for. When someone proves this experiment in an actual controlled environment. And as is standard, is proved again in another actual controlled environment, I will believe it. Until then, it is just a theory.

  296. spork says:

    We have one video that shows JB moving a tell-tale to show the gradient for a critic. I think that will show you what you want to see.

  297. Bill Barth says:

    @221 ThinAirDesigns:

    I’m in agreement with everything but your last paragraph. You’ll note that in my original post, I said that I believed that the treadmill experiment was legit (i.e. not a hoax), but that it fails to represent a wind-driven test.

    Here’s a thought experiment for you. Consider the following two cases: 1) Still laboratory air, a treadmill surface moving at 10mph, and 2) wind blowing at 10mph, stationary ground. So far, two apparently equivalent situations. Insert the vehicle in both cases, stationary w.r.t. the lab in case 1 and moving forward at 10mph in case 2 (giving them the same relative speed to their ground). Release the vehicles.

    In the case 1, the treadmill initially slows a fraction due to the increased load (you agree we’re extracting energy from the motor), but the speed control in the treadmill compensates by supplying a little more current to the motor, thereby adjusting the speed back to 10mph. Based on this, and the thrust from the prop, the vehicle maintains its position.

    But, what does this imply about case 2 (outdoors)? The small speed drop of the treadmill is equivalent to a small drop in the wind velocity everywhere outside. Given that this isn’t feasible based on how fluid flows work, the local flow must be different around the vehicle outdoors than it is in the treadmill case.

    Consider also the following:

    Imagine riding a propeller-less cart which is traveling at the same speed as the wind (be it outdoors or on the treadmill). Don’t worry for a moment about what’s keeping it at speed. There is no breeze to feel while you are there. Spinning a prop while riding in this cart requires energy. You can crank it with your hand, you can run an electric motor, but you can’t get the energy from the wind because there isn’t any. If I try to extract it from the road that’s rushing, by that’s fine, but then I have to look carefully at what’s propelling my cart to see if I slow down or not.

    Now, assume for a sec that I take a stick and drag it along the ground pretty hard so that my cart appears to slow (assume that the propulsion mechanism doesn’t instantly compensate). I’ll start to feel a little bit of a tailwind (either b/c I’m backing up w.r.t. to the lab, or b/c I’m losing speed w.r.t. to the fixed earth). That tailwind will provide some thrust as it blows over the cart, but that thrust is not enough to prevent me from slowing. Aerodynamics being what they are, the wind can’t perfectly compensate for the friction of dragging my stick.

    Now let’s put these two together: If I attach the prop to the wheels, I’ll certainly be able to come up with a situation that produces net thrust, but not forever. I may even accelerate for awhile. If the prop is fixed pitch (like in the present experiments), it has a maximum efficiency, and will eventually be unable to balance the drag due to the now impinging headwind. If the driving force was a car on a long pole pushing me along, or a treadmill motor keeping the road at constant speed, if I cut this power, drag on the rotating prop, and drag due to the headwind will start to steal my speed. They will steal so much speed, that I will eventually drop through even and settle out at some forward velocity less than the true wind speed.

    Finally, another thought example for you. Since you agree that the treadmill motor is supplying some energy, what happens if we measure the energy draw to the treadmill with a properly weighted cart with no prop which is held stationary on the treadmill, and then limit the power the treadmill can draw to this level when we put the prop-and-cart back on the treadmill? Clearly the vehicle will fall off the back from lack of input power! Since we don’t have a way to add energy to the moving wind outside, clearly, we can’t put back the power lost to running the cart outdoors in a breeze and therefore it must slow down.

  298. FoetusNail says:

    Pay close attention to that part where Vw drops to -3 and the cart experiences a 3 mph apparent headwind. And remember the only thing pushing this cart is the tailwind. The only thing turning that wheel, which turns that prop is that negative tailwind.

    Lets build a new cart, with a 50 sq in sail and a clutch. Under sail power alone this cart will approach 10 mph. Now engage the clutch and drop the sail. What is the thrust to drag ratio of the propeller? Have you ever been on a boat when the sails are suddenly dropped?

    Does anyone remember how much harder it was to pedal their bike after setting that little generator against the tire to power just one feeble little headlight? Did you ever play with one of those little propellers on a stick? Do you remember how hard you had to rub your hands together to get that essentially weightless toy airborne and how quickly that propeller stopped once gravity and drag took over?

    Ask yourself how much energy, how hard would you have to push that cart with your hand to turn that prop fast enough to produce the required thrust, while overcoming the drag of the propeller? Now how far will that cart coast when you stop pushing? Now you are going to get that energy where, the wind blowing on the frame? Get serious. The wind whose speed relative to the cart is zero mph when both are traveling at the same speed. See the speed of the wind relative to the ground is unimportant, because the only power coming into this system is the wind pressure on the cart’s frame. The only power to turn that prop is from the tailwind. And when both the wind and the cart are traveling at the same speed the difference is zero.

    Now drop your sail, meaning reduce the power coming into the system by 90 something percent, and engage that clutch, or in other words stop pushing that cart and let it coast.

  299. Tarantio says:

    Oh, don’t worry Spork. I don’t need a demonstration, this is interesting enough to me in the abstract.

    If you do happen to have an explanation for what outside energy source counteracts the force of friction while the cart is moving faster than the air around it, or why this wouldn’t be necessary, I’d love to hear it, though.

  300. ratwerks says:

    This discussion reminds me of the Monty Hall Problem ( http://en.wikipedia.org/wiki/Monty_Hall_problem ) in that there is a correct answer, the correct answer is in some way counter intuitive and some people with the wrong answer get increasingly abusive and creative in their attempts to ‘prove’ that their wrong answer is correct.

    JB and spork33 have claimed nothing impossible here. The truth of their claim in no way depends on their ability to explain it or demonstrate it to anybody’s satisfaction. People working from the belief that their claim is extraordinary or impossible should examine that belief so they can find the source of their error and correct it.

    As for the MHP, it took me loosing a bet to get me to examine my mistaken belief and accepting the truth on that one.

  301. FoetusNail says:

    at least? that’s not the bet.

  302. ThinAirDesigns says:

    GregLondon, I have a limited amount of time to answer questions so I focus on those who seem to be interested in listening rather than just transmitting.

    Just because you don’t agree with answers given, doesn’t mean that answers weren’t given — this seems to be a concept lost on you.

    I’ll give you an example:

    You have repeatedly asked(paraphrase) “where does this extra energy come from?”. Greg, *asked and answered* — it has been stated clearly that this is a wind powered device. If you can’t figure out that our answer is “the extra energy comes from the wind”, I can’t help you.

    I know you don’t accept that the wind is still blowing across the ground when the cart is moving the same speed as the wind, but just because you won’t accept that fact, it doesn’t mean we haven’t answered you.

    Again, you don’t have to agree with our answers, but saying we haven’t provided any is just not a comment that the record supports.

    Best wishes.

    JB

  303. GregLondon says:

    This news flash just in: several small children were swept away today while running around the schoolyard with pinwheels in their hands. They started running, the pinwheels started spinning, and before you know it, “the wind” picked them up and carried them off to places unknown.

  304. Alpinwolf says:

    Egad. Another novel. I guess I find it’s too complex for the Cliff Notes version.

    After trying to answer “But where’s the energy come from?”, I’m not even gonna touch “But why’s the rum gone?”

    Best o’ luck!
    -AH

  305. GregLondon says:

    >>You know what, these guys have taken
    >>their cart outside. You know what happened?
    >>The propeller, much to their surprise,
    >>acted like a windmill and the cart went
    >>backwards. Prove I’m wrong.
    >
    >Ok, here you go (times 2)
    >http://www.youtube.com/watch?v=QTAd891IpRs
    >http://www.youtube.com/watch?v=kWSan2CMgos
    >No surprise, no windmill and no backwards.

    Uh, the first doesn’t show it get up to steady state, someone just blew a fan on it. I could blow a fan on a kleenex box and make it move.

    The second one, you should watch it again at about 16 seconds in. Just as it starts moving, it looks like the prop starts spinning one way, then reverses and goes the other way for a couple seconds, then reverses again before it runs off down the street.

    I don’t know what kind of gear box you got that lets it do that.

  306. arkizzle says:

    Let’s all continue this in the other thread..

  307. Anonymous says:

    Hello Tom,

    “Does that make my position any clearer?”

    Yes, it does indeed. And in fact, yours is the more correct explanation for it. Mine was only a try to visualize what is going on by a purely mechanical point of view.

    But you are right that in reality it is the thrust generated by the prop that pushes against the air. So, for the best case, you have Vcart = Vwind + Vthrust. Of course that is without accounting for losses and friction.

    Greetings,

    Chris

  308. Bill Barth says:

    Lay out your terms for the bet. I might be interested in taking it.

  309. arkizzle says:

    ..is this equivalent to the craft moving at 1mph, and the wind moving at 0 mph?

    And the ground moving backwards at 10mph. (treadmill)

    QED Fail.

  310. FoetusNail says:

    BTW, you know what happens when you couple a balloon to the ground? It stops.

  311. GregLondon says:

    I insist this because, on the video, that’s clearly how it works. In the video, the cart accelerates from being at rest relative to the air.

    Er, wait a second. I thought you observed these things directly yourself??? Did you work on these machines with spork and whoever else or your own machine or no?

  312. Anonymous says:

    Here’s the intuitive explanation, yes, it is possible:

    Picture a conveyor belt between two wheels of diameter D. Then put it on another two wheels of the same diameter D. The lower set of wheels are the running wheels that touch the road. If the lower set of wheels turn clockwise with angular velocity W, then the conveyor belt wheels move anticlockwise at W. Therefore, as this machine moves down the road, all the points of the conveyor belt surface are stationary with respect to the road.
    Now, if you enclose the lower part of the conveyor belt in a casing, and planed a row of masts and sails on the surface, then the sails will always be stationary compared to the surface of the road, regardless of the road speed of the vehicle.
    The wind will always exert one and the same force on the sails, regardless of speed, because they will always be stationary with respect to the road. This is what’s going on, but the propeller arrangement confuses the issue.
    To understand how it works with a propeller, you need to picture an Archimedes screw instead of a conveyor belt, that “unscrews” itself in the direction of travel as fast as the vehicle is moving downwind.

  313. Anonymous says:

    Hello Tom,

    sorry, but that Anonymous wasn’t me. I tried to create an account on here, but BoingBoing’s mail-server is configured wrongly (the HELO string doesnt match the server’s name when looked up in the DNS system), so the anti-spam measures on my mail-server reject the confirmation mails. So i have to write as Anon, but i alway sign my posts with

    Greetings,

    Chris

  314. HUDMAN says:

    Place an electric engine on the cart that spins the propeller with 5 mph of thrust and place it in a 10 mph tailwind. Does it outrun the wind?

    Does a plane with 100 mph of air speed flying in a 10 mph tailwind have a 110 mph ground speed?

    Place a fan, turned off, on the ground. It does not turn over if a 10 mph gust of wind hits it from the front, but turn the fan on… Does it turn over if a 10 mph gust of wind hits it from the front?

    The answer of course is yes to all the above. (Actually more info might be needed on the 3rd one) But, what does all this mean???

    THE THRUST FROM THE PROP IS THE SAIL!

    Just because the cart uses mechanical advantage to to exceed its power source (the wind) doesn’t make it impossible.

    Can a 100 lb weight lift a 150 lb man? Sure it can, all you need is 2 pulleys and a rope. How about a 50 lb weight lifting a 150 lb man? Sure, rope + 4 pulleys. 25 lb weight lifting a 150 lb man? Sure, rope + 7 pulleys.

  315. ThinAirDesigns says:

    Nelson C
    >I’m beginning to suspect that you are
    >not arguing in good faith.

    You are welcome to your own conclusions.

    >You quite plainly are making an extraordinary
    >claim, going purely by the amount of fuss
    >this thing has kicked up.

    I guess I wasn’t aware that the term “extraordinary claim” was governed by how many people agree or disagree with something.

    By your above definition, a claim of the supernatural is not an extraordinary claim as most people on earth believe in it and thus it creates little fuss.

    No, I think you’ll find it generally accepted in the scientific community that “extraordinary claims” are those that can’t be explained by the simple and known laws of the universe and that conversly, “ordinary claims” can be explained through the application of the known.

    We solidly fall into the latter.

    >Never mind the treadmill experiment

    Sorry — you just demonstrated your inability to grasp the significance of that test. You can just “never mind” evidence that you don’t understand, but that attitude won’t allow for much learning.

    >If you’re so sure that the energy is coming
    >from the wind, please give a cogent explanation
    >of how it works, with the relevant physical
    >equations and hard numbers.

    Been there and done that — about a hundred times before this thread started. It’s not my job to convince you of anything … you can do the homework and look it up, or not. You can ask questions (or not) and I’ll give answers as I have time.

    >If you can’t supply all of this, then
    >your demonstration is simply a bust.

    One more flaw in your thinking — reality is never a bust.

    >Hoax or self-deception, it has as much
    >credibility as cold fusion, for similar
    >reasons.

    I certainly understand your position and as a skeptic myself, I don’t disrespect it — but there is one big difference between this and cold fusion — our results are repeatedly obtainable to anyone who wishes to build the device.

    JB

  316. GregLondon says:

    Even though I’ve described it accurately hundreds of times in hundreds of ways.

    a hundred different versions of mumbo jumbo and gobbedly gook is still mumbo jumbo. The fact that you’ve been trying to explain this on the Randi thread, for hundreds of posts, the Mythbuster threads for hundreds of posts, and we had three fricken threads here on BB with hundreds of posts, and people are still confused, should tell you that maybe its your explanation, not them.

    I wrote up a ten page thing that is mostly drawings. the actual device is explained in a couple pages. several pages are used for a description of the thing I built and pictures.

    Now Greg is kind enough to explain to us how it “really works”.

    In plain english, yes.

    also, if some people read it and are still confused, I’ll actually assume that it’s my explanation that’s at fault and try and fix my document. I won’t be telling them to bet me a bajillion dollars if they don’t understand my explanation, I’ll be trying to figure out a better explanation. A couple of drawings and a couple of paragraphs of text explain the basic principle.

    I haven’t gone to the trouble to look at his page, but I’m willing to bet he’s got it wrong. Let me know if I need to go point out where.

    Dude, I’m absolutely certain at this point that you don’t even understand how your device works. You got it to work by evolution, by trial and error. You started with someone else’s design, a propeller on a cart, and you didnt understand it well enough to simplify it or change it in any fundamental way. You copycatted a cart with a propeller, and you ended up with a cart with a propeller.

    And you’ve been working on this for how long??? I’ve been looking at this for some number of days (since whenever that ddfttw part 2 thread was started) and that’s how long it took for me to figure out that you don’t need a prop or a pulley or any movign parts to go directly downwind faster than the wind.

    I’m willing to bet he’s got it wrong.

    OK, $50 to charity.

    Make the check out to “Amnesty International”.

  317. GregLondon says:

    It’s Devil’s Advocate (as annoying as that can be),

    The label is sort of irrelevant, I think.

    Video or it didn’t happen. (An entirely reasonable request, whether, or not, you factor in all the other things being demanded up-thread)

    I added two drawings this morning. page 5 and 7. If you still don’t get it conceptually, then that’s the best I can do.

  318. bonafidebob says:

    The simple/light vehicle on a treadmill is very interesting, but I think we’re asking ourselves the wrong question here. Instead of “how does this work?”, we should perhaps ignore the commentary (it is the internet after all) and instead be asking “what’s the easiest way to make that video?”

    IMHO a small fan positioned out of shot to the rear of the treadmill blowing forward would produce exactly the effect seen in the video.

    The first part of the video (with the contraption outdoors) would be most easily produced by towing the contraption with a bit of fishing line.

  319. SubductionZone says:

    Greg, have you ever watched an old western. Those stage coaches were amazing, they could move forwards while their wheels moved backwards, they must have had some pretty amazing gear boxes too.

  320. Anonymous says:

    You CAN sail faster than the wind on a windsurfer.
    See wikipedia entry on apparent wind,

    http://en.wikipedia.org/wiki/Apparent_wind

    basically, apparent wind is the wind you feel blowing in your face when you start moving forward.
    this website has a good explanation of how it is used on a windsurfer:

    http://web.singnet.com.sg/~dgswee/

    In sailing, the sails are always trimmed to suit the wind direction for maximum drive. As the boat picks up speed, the strength and direction of the wind on the sails change because of the effect of the apparent wind. The wind becomes stronger and the sails have to be sheeted closer in to maintain correct trim. The effect becomes more pronounced as the speed of the boat increases in relation to the true wind wind. Because windsurfers very often sail at speeds considerably faster that the true wind, the trim of a windsurfer’s sail bears no relation to the direction of the true wind. When a windsurfer is sailing on a broad reach at speed, his sail is sheeted so close in that he appears to be sailing upwind. This is because the apparent wind has moved well forward and is now coming from the front quarter.

  321. ThinAirDesigns says:

    Jackofsometrades: (#307)
    >This is not perpetual motion; it does
    >not violate any laws of physics; still,
    >it is pretty cool. I’m wondering if it
    >might have any real-world applications…

    It really is a case of the opposite — this device takes something that is done regularly in the “real-world” and places it it in a new environment:

    When a sailboat tacks into a head wind and progresses through the water, it it doing exactly what we are doing physics wise. The boat uses the wind/water interface to beat the water current, and we use the wind/ground interface to beat the air current.

    JB

  322. ThinAirDesigns says:

    Foetusnail:
    >JB why do you have to hold your cart
    >down to get it up to speed before
    >letting go?

    Foet, I will happily answer your above question, but since we’re off to a good start at an actual exchange, how ’bout we agree to quid pro quo — I’ll answer a question you have, and then you answer a question I have.

    It that fair enough?

    Agree and I’ll promptly answer the excellent question you asked above.

    JB

  323. arkizzle says:

    Greg, for interests sake, what do you think of AlpinWolf’s ideas?

  324. SubductionZone says:

    With one difference Foetusnail, there is no freaking motor on the cart. Now you are just grasping for straws.

  325. Tordelback says:

    Extraordinary claims require extraordinary proof. An apparent perpetual motion machine begs for it. I wouldn’t be getting irate when asked for such proof, just be flattered that everyone thinks your claim is remarkable, and be prepared to defend it.

  326. spork says:

    “Just as it starts moving, it looks like the prop starts spinning one way, then reverses and goes the other way for a couple seconds, then reverses again before it runs off down the street.

    I don’t know what kind of gear box you got that lets it do that.”

    It’s a 1-to-1 90 degree gearbox from the tail rotor of a radio controlled helicopter. The part numbers are in our parts list. The prop spun backward at first because the gust was abrupt and the wheels lost traction.

  327. joelphillips says:

    #85 – There’s no theoretical limit to how small rolling resistance can be made, so we can add that in to (3).

    #84 – You’re confusing force with energy. The force the cart exerts on the air is backwards, so the reaction pushes the cart forwards.

  328. arkizzle says:

    The small speed drop of the treadmill is equivalent to a small drop in the wind velocity everywhere outside.

    I don’t think this is correct. I think it only decreases the wind velocity at the specific contact ponts around the carts-frame and the propellor surface, there is always more wind everywhere else, ready to swoop in to maintain the general forward velocity of the fluid as a mass.

  329. Michael C says:

    Greg, you’re on the right track when you think of “leverage”: if we can push at part of the machine that is moving forward slower than the rest of the machine, we can make the rest of the machine move forward faster.

    You’re wrong when you say that “the people who built the propeller driven machines didn’t understand what was going on exactly and so just tinkered with something until they got it to work”. They knew exactly what they were doing. They used a propeller instead of a paddle wheel sort of thing because a propellor is more efficient.

    Your “tumbleweed” engine should move in the direction of the wind. The question is: will it go faster than the wind? The thrust produced by the wind on the parts of the machine that are moving forward slower than its centre will need to overcome the drag of the air on other parts that are moving forward at the speed of the centre, or even faster. Can you ensure that this is the case?

  330. Alpinwolf says:

    @ #240 Toilet- ‘Fraid I’m a bit like “Bones” (the anthropologist): I don’t know what that means.

    If I helped with comprehension, schweet. If it means I’m too long-winded.. er, sorry?

    Anyways, Bill, Greg and Foetus, please let me know if my thoughts make any sense to you.

    -AH

  331. FoetusNail says:

    Not everything you see is a product of the video frame rate. The initial reversals are all happening to slowly to be a result of the camera. You can actually see the prop stop and reverse at 15 or 16 sec.

  332. bardfinn says:

    I concur with #43 posted by Anonymous.

    Treadmill =/= Tailwind.

    The treadmill demonstration merely showed that the treadmill was able to transfer enough energy to the propellorkart to move it gently uphill (while continuing to move at the same rate), overcoming a small amount of frictional resistance and gravitational inertia. This is what the treadmill was designed to do, except with a 170 pound human. It doesn’t demonstrate that there is an ability of the kart to translate windspeed into a greater groundspeed.

  333. ThinAirDesigns says:

    To those asking “how much faster than the wind will the device go?”, the answer from us is “we don’t really care”.

    Faster than the wind it a bit like the sound barrier — once you break that barrier, adding 50mph on top of it isn’t all that interesting.

    Among people who accept that faster than the wind is possible, no one is saying “Yeah, 1.1x wind speed is possible, but 1.4X is not”.

    The key to any DDWFTTW demonstration is to clearly be faster than the wind for long enough to demonstrate “steady state” Since most people don’t agree that a device can even *equal* the speed of the wind rather than beat it, even a steady demonstration of DDWTSSATW (directly downwind the same speed of the wind) means laws of physics are being broken. Depending on the test, a treadmill can be more impressive (DDWTSSATW) or the outdoors may be (DDWFTTW).

    This devide doesn’t gently dance around at the speed of the wind, desperately waiting for a little gust here or there to propel it ahead of the wind (which wouldn’t qualify for our claim anyway). No, it goes out and blasts through the true wind speed with absolute authority and leaves the wind cryin’ for it’s Momma. We’ve demonstrated this repeatedly but we recognize that many will never believe it.

    We’ll just pick off the unbelievers one at a time. :-)

    JB

  334. ThinAirDesigns says:

    So GTBernstein, how much more “controlled” do you want than a still air room? We close the windows, we close the curtains, we turn off the AC — how much more “still” do you think the air can be made?

    I mean, if you think we faked the video, so be it — but think about what you’re saying … you can’t get any more still or controlled than a closed room.

    JB

  335. zafner says:

    Consider a magical equivalent machine with no friction from the bearings or the ground and no drag on the prop. If the machine is moving at windspeed, the wheels are rotating at windspeed and driving the prop, which is producing some amount of force, pushing the machine forward. So if we add back in the friction and the drag from the prop and it’s still less than the thrust produced by the prop, which isn’t really that amazing, the machine would respond by moving forward faster. Have I missed any forces?

    Hey Spork: maybe you remember me from some forum we were on right after the initial boingboing post. To refresh your memory, we’ve been kiteboarding about the same amount of time. I just want to say that this discussion — and all its various iterations — is the most fun I’ve had online since I got my first internet connection in about 1996. Thanks very much, and keep fighting the good fight! This is fantastic. I love watching people learn stuff.

    I hope somebody takes your bet, for real. That would be hilarious.

  336. ThinAirDesigns says:

    Tordelback:

    It is others claiming “extraordinary”, not us. It is others claiming “perpetual motion”, not us (how on earth you call something pm when you remove it’s power source and it stops is beyond us.)

    Every single time a boat tacks it’s way upwind it is using the very same principles this device uses — very, very ordinary in fact. We’re astonished at the reactions frankly.

    JB

  337. bardfinn says:

    Also: The vehicle that is on the treadmill would – if not modified to reverse the gears – move /backwards/ relative to the wind when supplied with a tailwind that moves the prop.

    Gonna sleep on it.

  338. spork says:

    “If you’re willing to let me define the test plan and the goal, and you’re willing incur any costs of independent testing, I’d probably be interested having my attorney draw up a contract setting everything out (at your expense, of course–don’t worry, she’s relatively cheap as lawyers go!).”

    Contact me via PM on the JREF forum if you’d like to set this up: http://forums.randi.org/showthread.php?t=128483&page=38

    I won’t be paying your attorney.

  339. mrgoldenbrown says:

    I think that most people here agree that one can sail a boat faster than the wind by sailing at an angle to the wind, even if the downwind component of the boat’s velocity vector never exceeds wind speed. Aren’t the propellers in all these gadgets moving at an angle to the wind? And if so, doesn’t that let them ‘cheat’ the normal limits on how fast we think they can go?

  340. FoetusNail says:

    Zafner, why would anything move faster when you increase friction and drag, without increasing power? Now that’s hilarious.

  341. SubductionZone says:

    Actually Greg most of this thread consists of them trying to explain to people who do not want to understand due to their own misconceptions. If you do not get the fact that the treadmill is an excellent way to test a steady tailwind at the speed of the treadmill then you are not going to understand anything as complex as the aerodynamics involved.

  342. tomtheblacksmith says:

    (Chris wrote): The important thing is just to keep in mind that there is a surface on the cart that moves slower (or “backward”) relative to the cart moving (or at standstill). This is, i guess, what many people overlook initially, and instead assume the cart to be one static object pushed by the wind.

    (Tom replies): To be sure you undestand my argument, IMHO all parts of the propeller are moving at the same velocity as the cart, so the propeller is actually becalmed upon the cart, but the air that it “grabs” from the still mass of air (in which it is traveling) and “pushes” back becomes the physical coupling between the propeller and the wind following behind.

    The rearward moving mass of air is the “missing link”, and it is actually the sail.

    In my hypothesis, the wind coming from behind never touches the cart or the propeller itself (once it’s going). It logically can’t, since the cart is already traveling at least as fast as the wind, so the wind is pushing against the expanding mass of air moved back by the propeller, and that air pushes the propeller, and the propeller pushes the cart “ahead of the wind”.

    Does that make my position any clearer? I realize that we agree, I am just haggling over details that I consider crucial to dispelling the myth that this is not possible.

    Tom the Blacksmith

  343. GregLondon says:

    Actually, if the device can move faster than the wind, then the device should be able to move in zero wind if you give it a push. i.e. you should be able to go into a large, sealed building, with a smooth floor, give this thing a push, and it should accelerate to some non-zero speed, yes?

    I mean, if the argument is that the treadmill is a legitimate experiment, then an enclosed building should be equally legitimate. Yes?

    I think the treadmill is creating a flywheel effect that invalidates the treadmill as a legitimate experiment. It injects energy into the propeller, gives it angular momentum, and turns it into a flywheel that could store plenty of energy to keep the thing moving for a time. until something like a gust of wind or a nudge from the treadmill spins the flywheel up again.

    I’d say mythbusters ought to put down a hundred feet of straight model railroad track (so you don’t have to worry about steering and fishtailing) in a hangar, enclose it in a plexiglass tunnel so we can see inside, then blow a fan down one end to create a fixed velocity wind. and see what happens.

    One of the weird things about helicopters is that when you’re moving slow or hovering, you can get into your own downdraft and start to sink like a rock. Adding power only makes it worse. You have to move forward to get out of the column of air. I’m not sure if the treadmill is doing that (creating a horizontal column of air that spins the propeller), but it is one of those weird things about aerodynamics that is not intuitive.

    Just another reason I’m leary of considering the treadmill a valid scenario.

    Again, if it moves faster than the surrounding airspeed, couldn’t you start in a sealed building, give it a push, adn it should continue to accelerate to some non-zero velocity?

    If that isn’t valid, then I don’t think the treadmill is valid. And if the treadmill isn’t valid, then it’s a hundred feet of railroad track on a polished concrete floor, and a windtunnel of some sort that is the only valid method.

  344. Grimnir says:

    Thank you Alpinwolf. I was about to explain it the same way but far less clearly.

    Spork mentioned that the wind didn’t drive the propellor but instead pushed the car, and it all fell right into place for me fully-formed, though I should have been able to figure that aspect out from the treadmill.

    And you know, all the posturing and chest-thumping going on with regard to skepticism is really quite detrimental to science. “My understanding of the universe is perfect and complete and thus anything that isn’t totally obvious to me must therefore be assumed to be a hoax until rigorously proven otherwise” seems to be the attitude. As if this were so preposterous a claim as to require peer review.

    I mean, come on, this is a good high school physics-style thought experiment, a fun brain teaser, you don’t need to get all HOAX! up in our faces just because you haven’t figured it out. I mean, I’m sure it is some truly glorious mana for those who originally figured it out that you with your posturing can’t wrap your head around it and need to excuse your inadequacy with accusations, but really, you’re just hurting the spirit of science and discovery. So cut it out– your lazy-minded cynicism is as bad as naivety– at least the naive get to live in a world of mystery and hope, and they’re just as likely to be right on any particular issue. Rejecting ideas out of ignorance is not more desirable than accepting them– if you’re serious about science you use your brain and properly work out the problem.

    Because science is not a dogma: it is a process.

    Peace.

  345. LaserRage says:

    In the treadmill example, the propeller is a propeller, not a turbine. The treadmill is acting as a motor, powering the propeller through the wheels, and the propeller… um… propels the cart forward. The gearing between the treadmill and the wheels is high enough to have the propeller move the cart forward.

    On the road, in the wind, it is a turbine — the wind is providing power to the wheels. While the treadmill is providing power constantly, the wind will only provide power so long as the relative wind speed is greater than zero.

    Note: with modern sailboats sailing at an angle to the wind, the relative wind speed can be greater than the actual wind, hence you can sail faster than the wind, just not directly downwind, which is what this problem is about.

    Once you hit zero relative wind, the “thing on top” would stall out. I think I agree with GregLondon at #136, here.

    In the original video, I’d guess that energy from wind gusts pushed the cart over the average windspeed.

  346. tomtheblacksmith says:

    (Why DWFTTW is not possible, short version)

    In a “stationary” mass of air such as a closed room, all of the air “particles” are racing about rather quickly, but colliding with each other other and any other object randomly and evenly, thus any object placed in the room will experience equal “pressure” on all sides and thus will remain stationary itself.

    If we attempt to move that object in any direction relative to the “stationary” mass of air, the air directly “in front” of the object must be moved out of the way, which requires work. The faster we try to move the object, the greater the amount of air that must be displaced, so an increasing amount of work is necessary to keep the object in motion as the relative speed difference increases.

    “Wind” is really nothing more than a large “stationary mass” of air that is moving relative to the ground. If you (or the aforementioned object) were floating up in the moving mass of air and moving exactly with it 1:1 you would experience equal pressure on all sides, just exactly as in the closed room.

    Now imagine an object sitting on the ground, with the “wind” moving past it. The amount of “pressure” that it would “feel” from the wind is exactly equal to the amount of force that it would take to move the object at that same speed in the “stationary air”. The two situations are exactly the same as far as the air and object are concerned, it doesn’t matter which one is moving relative to the other, the only thing that matters is that the motion of the object relative to the air is going to generate a force which increases with the rate of relative movement.

    If there is no relative movement (either object moving through air, or air moving past object) there is no force generated, and no work is being performed, nothing happens.

    Now we imagine our theoretical “wind vehicle” sitting on the ground with wind moving past it, thus generating a force in the direction of the wind. As the speed of the vehicle begins to increase relative to the ground, its speed relative to the wind decreases, so the force decreases, so the acceleration decreases. At first the vehicle accelerates very quickly, but as the vehicle gets closer and closer to the same speed as the “wind” the acceleration becomes nil, and the vehicle becomes “stationary” in the moving mass of air, and moves across the ground “exactly with the wind”.

    In the real world, an actual vehicle sitting on actual ground would experience some resistance to movement, which is called “rolling resistance” because the wheels are touching the ground and the vehicle has weight. In order for this resistance to be overcome and to make the vehicle move relative to the ground some force is needed. If “wind” coming from behind the vehicle is to supply this force, the “wind” must be moving past (faster than) the vehicle with enough speed to generate this force. Therefore, the wind coming from behind the vehicle has to move faster than the vehicle to generate enough force upon the vehicle itself to overcome rolling resistance and thus keep the vehicle in motion over the ground. Therefore it is not possible for a vehicle to travel faster than the wind that is pushing it, if the wind is coming directly from behind.

    A wind vehicle (like a sailcar) can easily move across the ground “faster than the wind” that is pushing it, but only at an angle to the wind. If the vehicle is driven at an angle to the wind, then it never achieves the same velocity as the wind (in the direction of the wind), so the pressure exerted on the “sail” does not drop to zero as the vehicle ground speed increases to match the speed of the wind. Since there is still pressure on the “sail” there is force available to accelerate the vehicle across the ground, but at an angle to the wind. As you drive closer to a right angle with the wind, the movement of the “sail” relative to the movement of the wind becomes less (closer to the maximum possible), so the force on the sail increases until the vehicle is either scooting sideways “faster than the wind” or it tips over or skids sideways.

    Tom the Blacksmith

  347. FutureNerd says:

    This could work, although I haven’t studied the particular design. It’s not perpetual motion or cheating because wind traveling relative to the ground really is a source of power.

    Attach a parachute to the middle of a tall pole. Hinge the bottom end of the pole to the ground. The top of the pole will move twice as fast as the parachute (for a short time).

    Tie a long, superstrong thread between a parachute and the axle of a little red wagon. As the parachute pulls the wagon along, the turning of the axle will slowly reel in the thread, pulling the wagon closer to the parachute, i.e., moving the wagon faster than the parachute (until the whole thread is around the axle).

    There’s a way to gear a fan to the wheels that’s equivalent but doesn’t run out of thread.

    So it’s not theoretically impossible but it does depend on the efficiency of the setup.

  348. arkizzle says:

    ThinAir:

    I think people are requesting something like a wind-tunnel with controlled wind-speed and no hands, etc. Or even just running it outside against actual wind.

    Don’t mistake this clarification for disagreement with the notion. I’m prepared to believe this is possible, but there is a clear obtuseness to saying “don’t worry, it’s all equivalent” when you could just do the experiments outside as requested rather than on the treadmill, or organise a wind tunnel (which I understand costs money, but people seem interested enough to chip in).

  349. joelphillips says:

    Here’s some thoughts about the force balance:

    The forces acting on the cart are:
    1) Gravity
    2) A reaction to gravity perpendicular to the treadmill
    3) The contact points of the wheels are stationary with respect to the treadmill, so the the friction acts on the cart at the bearing, i.e. where the axle meets the wheel. The direction will point somewhere between “down the treadmill” and “behind the cart (parallel to the ground)”.
    4) A reaction to the momentum that’s being given the the air that’s being pumped backwards by the propellor.

    The counter-intuitive thing is that (3) can be made pretty small – I don’t think that there’s a theoretical minimum to how small friction in a bearing can be made. So it’s entirely reasonable, that, given a well-designed propeller and bearing that (4) – (3) results in a net “forwards” force. Now, since the resultant of (2) and (1) can be made arbitrarily small by choosing a small angle for the treadmill, the cart can move forwards.

  350. GregLondon says:

    The thing on top is a propeller, not a turbine.

    Great. Now, how do the wheels put energy into the propeller to speed up the vehicle?

    When you autorotate a helicopter, you trade off potential energy of altitude for kinetic energy to keep the blades spinning. Where are you getting the energy from?

    Without the propeller, you say friction will eventuall bring it to a halt. With the propeller, you say it can run indefinitely. Where does the energy come from that overcomes constant friction?

    I don’t care if they call themselves BullTwinkleTiddlyPanda33 What they have does what they say.

    yeah, sure. If spork is willing to bet a hundred thousand dollars, but he doesn’t want to reveal his name, something ain’t right somewhere. He also made appeals to authority, citing his masters degree in aeronatical engineering.

    Google “essjay wikipedia” and then tell me I should take his credentials at his word.

  351. ThinAirDesigns says:

    Airshowfan:
    >I still insist that the spinny
    >thing is a propeller and not a
    >turbine.

    Your observations regarding prop vs turbine are all spot on. The spinny pinwheel thingy on the back of the cart always acts as a prop and not a turbine.

    JB

  352. airshowfan says:

    It’s been said before, not just by me: The claim is that this is self-sustaining, not that it is self-starting (which this particular cart may or may not be). The question of whether the cart can travel faster than (or at least at the same speed as) the wind is different from the question of whether the cart can get UP to that speed. This cart might not be capable of accelerating from “at rest with respect to the ground” to “at rest with respect to the air” unassisted. That doesn’t matter, since it’s a less interesting question (a sail could do it), and distinct from the question of whether a DWFTTW mechanism is self-sustaining.

    Comment #346 assumes that “the mechanical system is designed to turn the cart wheels forward in a tailwind”. This is not true (the spinny thing is a propeller, not a turbine). But the comment is right in that, in order to do BOTH (be a turbine during acceleration and then a propeller during DWFTTW travel), the system would need either a Reverse gear or a propeller that could reverse the angle of incidence on the blades. Starting the experiment AT wind speed (i.e. setting the cart down and getting all the parts to spin up) skips the acceleration-from-rest part, and gets to the interesting part.

    So, why do they need to hold it down? Either because the cart isn’t self-starting, or because their treadmill is not long enough to give the cart the room it needs to self-start (i.e. accelerate up to wind speed) which could be dozens of feet.

  353. IamInnocent says:

    Why do people put so much time and energy into something this stupid (or simply debating it) is beyond me. How can so many people hallucinate themselves that this has the least bearing on life, that is makes one iota of sense I can’t explain but it never stops: is this perpetual motion?

    Jean

  354. ThinAirDesigns says:

    >I mean, come on, this is a good high
    >school physics-style thought experiment,
    >a fun brain teaser, you don’t need to
    >get all HOAX! up in our faces just
    >because you haven’t figured it out.

    Well said Grimnir. It’s a very simple device that is maddeningly unintuitive.

    JB

  355. airshowfan says:

    I have never built (or even personally seen) a DWFTTW cart, and I am not affiliated with the builders. I don’t know why some posters here assumed/deduced otherwise. I do, however, think that DWFTTW is possible, and am trying to explain the reasoning behind my intuition, and I think the video is a very good illustration.

    And by the way, I apologize for oversimplifying the effect of air speed on a fixed-pitch propeller’s thurst (#180), which led GregLondon to conclude that I am not an engineer (#186). I guess I wanted to say it in as few words as possible, and try to not write yet another big block of text. In any case, AlpinWolf has explained it well in #289.

    (I am an engineer, by the way. But I still do not think that this experiment requires an engineering paper or CAD drawings to get its point across to a general audience. For some people (like me and others on this thread), the video and a basic understanding of where the energy is coming from (from the difference in velocity between the ground and the air) are enough to make us trust that it works and say “Okay, that’s neat”).

    One more thing: If it is indeed completely undeniable that sail-boats and ice-boats reach VMGs (had to look that up… thanks everyone for providing and explaining the sailing lingo) of greater than one (let alone three), then who could doubt that DWFTTW is possible? As has been stated, just arrange some of those sails around some axis so that they go around circularly (or back and forth) rather than just to one side, and the whole assembly will go forwards DWFTTW. (Or maybe the better question is: Why aren’t people saying “No, impossible, that would be a perpetual motion machine!” about boats that can do VMG>1?)

  356. Anonymous says:

    Vehicles used in sailing are known as sail wagons, sand yachts, or land yachts. They are typically three-wheeled vehicles that function much like a sailboat, except that they are operated from a sitting or lying position and steered by pedals or hand levers. Land sailing works best in windy, flat areas, and races often take place on beaches, air fields, and dry lakebeds (playas) in desert regions. Modern land sailors, generally known as “pilots,” can go three to four times faster than the wind speed, because of Bernoulli’s principle.

    On Wilkopedia. There was also an episode on Scrapheap Challenge to build a sand tacht. The expert claimed that they could achieve speeds of upto three time wind speed.

  357. airshowfan says:

    I think it would be useful to keep in mind that the machine is not “wind powered” or “treadmill powered”. It is powered by the difference in velocity between the treadmill and the air.

    So from the point of view of the air (or from a balloon), it looks treadmill powered, while from the point of view of the treadmill (or from the “road”), it looks wind-powered. In the end it’s the same thing.

    (So yes, after the machine goes by, the difference in velocity between the air and the ground is reduced. That’s where the energy comes from – it’s not perpetual motion).

    I was skeptical of DWFTTW but I came around… back when this issue was first mentioned on BoingBoing. What made me come around was trying to imagine two long flat solid things (say, two thin boards of wood, parallel) moving relative to each other (say, one board lying on the ground and another being dragged steadily in one direction) and then trying to come up with some system of gears and wheels that would engage the two boards and move itself in the opposite way as the board that was moving, or move the same way as the moving board but FASTER. This is possible if you think about it a little bit. Maybe tomorrow I will draw up a little animated GIF of one idea for how to do this.

    I could give you my academic and professional credentials in aeronautics-related engineering but they will mean nothing until I come up with an analysis for these DWFTTW prop-driven carts. Again, if tomorrow is a slow day at the office (I just started a new job so the day will probably consist of getting the phone hooked up and things like that) I might get started on such an analysis. And, to be 100% honest, until the math in an analysis confirms my hunch that DWFTTW is possible, it’s just a hunch.

    But I have to say, some of the comments on this thread are by people who like to throw around physics-sounding words but who don’t understand the physical relationships involved, or don’t understand what the experiment is about. E.g. #9 (the wheels power the prop, not vice versa – it’s a propeller, not a turbine), #21 (some machines increase force while decreasing distance or speed, like a lever or a car’s transmission), #27 (I don’t think “drag coefficient” means what you think it means… in any case, drag only starts to slow down the cart once it’s going faster than the wind (i.e. up the treadmill through the air) at a pretty good steady speed), #28 and #43 (the treadmill test is as valid as a wind-tunnel test, since both are inertial frames), #30 (everything you said is right, but in the case of DWFTTW carts, the propeller is providing thrust and not drag or lift), #36 (you CAN push it to go faster, since you have a spinning prop, and are not relying only on drag to keep moving relative to the road), #38 (when set at the treadmill the craft is already at wind speed, and the prop does manage to accelerate it past that – we are not debating how to get UP to wind speed, just whether the cart accelerates from there, which in the video it does, and remember that the prop is a prop and not a turbine), and #47 (I don’t think “eddy current” means what you think it means).

    Bottom line: Do the experiment. Or at least a thorough mathematical model (which is what I plan on doing). Until then, what good is it to just keep saying “The evidence MUST have been faked”? At least you have to admit that’s not science.

  358. Bill Barth says:

    Spork @61: I was thinking mostly of you describing your test plan and exactly what your claim is.

    If you’re willing to let me define the test plan and the goal, and you’re willing incur any costs of independent testing, I’d probably be interested having my attorney draw up a contract setting everything out (at your expense, of course–don’t worry, she’s relatively cheap as lawyers go!).

  359. GregLondon says:

    I know you don’t accept that the wind is still blowing across the ground when the cart is moving the same speed as the wind, but just because you won’t accept that fact, it doesn’t mean we haven’t answered you.

    Good lord man.

    My propeller cycle is movign across the ground at 10 mph. There is a 10 mph wind going in the same direction as me. I am sitting in an open cockpit and I feel absolutely no wind on my face.

    Now, the tow vehicle disconnects the cable. My propeller is spinning and generating some thrust, so I accelerate. But I have to get that energy from somewhere. Saying “it comes from teh wind” doesn’t answer anything. It’s a handwave that means you don’t know what you’re talking about. See ponds-fle

    WHether this thing works or not, you guys have certainly not proven. But you all have made abundantly clear that even if it does actually work, you have no idea how it works.

  360. arkizzle says:

    Thanks AlpinWolf, I found your explanations useful and illuminating, if only for the anthropomorphic nature of your examples.

    Frankly I think we could put a few hundred million dollars into an Extreme Rotational Acceleration Training Initiative, the likes NASA has never seen, and could guarantee the ant doesn’t puke (we’d need the best and brightest ants, of course, but we have many to choose from).

  361. SubductionZone says:

    Foetusnail, if you watch the videos in both of them when there is a gentler breeze whether from a fan or from a tailwind the propeller rotates clockwise when observed from behind. When they restart it and there is a sudden gust it does move counterclockwise at first, but when the wheels regain traction it moves clockwise.

  362. dewexdewex says:

    Dear chaps,

    I adapted your design and made it into a special hat with a propeller on it.

    Whilst I don’t seem to be getting to work any quicker, I always get a seat on the train.

    Dave.

  363. spork says:

    “yeah, sure. If spork is willing to bet a hundred thousand dollars, but he doesn’t want to reveal his name, something ain’t right somewhere. He also made appeals to authority, citing his masters degree in aeronatical engineering.”

    If you want in on this bet contact me via PM on the JREF forum if you’d like to set this up: http://forums.randi.org/showthread.php?t=128483&page=38

    You’ll get my real name, my real autograph on the contract, my real money in escrow, and plenty of evidence of my credentials if you really care.

    And in the end, I’ll walk away with your real money.

  364. arkizzle says:

    Bill, are effin’ insane?

    Try the science on before you put down $10k (eg, build your own for $40, first).

  365. spork says:

    “If you do happen to have an explanation for what outside energy source counteracts the force of friction while the cart is moving faster than the air around it, or why this wouldn’t be necessary, I’d love to hear it, though.”

    The short story is that the vehicle exploits the energy available at the ground/air interface. But you should come over to the Randi forum if you want to discuss it in any detail. I can’t keep up with this thread.

    http://forums.randi.org/showthread.php?t=128483&page=33

    “Lay out your terms for the bet. I might be interested in taking it.”

    We both put the funds in a common escrow account, select a mutually acceptable panel of judges, I demonstrate the cart can do as claimed, escrow funds are wired to my account.

    “IMHO a small fan positioned out of shot to the rear of the treadmill blowing forward would produce exactly the effect seen in the video.”

    Probably would. You should check the video where we pan left and right to show there is no fan.

    “Actually, if the device can move faster than the wind, then the device should be able to move in zero wind if you give it a push”

    Very briefly – until it coasts to a stop.

  366. spork says:

    I’m amazed at the folks here that admit they don’t understand how this thing works, but somehow they’re sure we don’t either.

    Several people have offered very good accounts from various valid perspectives. I’d say “you know who you are”, but I suppose everyone else thinks they are too.

  367. FoetusNail says:

    If you insist on using this made up phrase at least state it properly, “we use the air and ground interfaces”. An air-ground interface is only one interface, where the air and ground meet, which is why one of the most common uses for that phrase is in a discussion of ground penetrating radar, when describing the behavior of radar waves moving from one medium into another. The most common interface most people would have experienced of this type is the way in which different frequencies of light bend as they pass through the air into the glass of a prism, and then exit the prism into the air. The light rays only bend at the two interfaces or in the case of a rainbow millions upon millions of interfaces as sunlight is bent by moisture droplets in the air. If anything you are describing two distinct interfaces, plural.

  368. jackofsometrades says:

    I am also an engineer, and want to try to shed some light on the apparent gap between intuition and reality.

    First, let me clear up a misunderstanding that a few people seem to have. The wind is trying to turn the propeller in one direction, and the forward motion of the cart turns it in the opposite direction; the wheels win this competition. In other words, the wheels drive the propeller, not the other way around. This places some constraints on the gear ratios and propeller pitch, but can easily be achieved.

    Now, for the bigger flaw in our intuition: Consider the cart at zero relative wind speed (either stationary on the treadmill or moving downwind at the same speed as the wind). In order for the cart to go faster than the wind, it must have a positive (forward) acceleration in this state. That is, the forward force on the propeller must exceed the horizontal, backward force acting on the wheels.

    As the pulley examples demonstrate, there is no such thing as a Conservation of Force Law, only a Conservation of Energy Law. (See Post #341: “to lift a load with pulleys you must pull in more rope than the actual lift, trading distance for force.”)

    Energy is force times distance, and its derivative, Power, is force times velocity (assuming constant force). So, what the propeller is doing is trading velocity for force. The propeller can have a greater force than the force on the wheels exactly because it has a lower velocity. The air coming off the propeller is not actually moving backwards (relative to the ground, that is), in fact it is still moving in the same direction as the cart, only slower.

    The cart will go faster than the wind as long as the propeller generates more thrust than the load on the wheels. This can be guaranteed with the right combination of gear ratios and propeller pitch. Of course, you also have to overcome friction losses, but if you follow this argument, you should agree at least in principle that DWFTTW is theoretically possible. But then, seeing is believing.

  369. joelphillips says:

    It’s not perpetual motion. There’s energy being put into the system – the treadmill in the case of the video in this post; the wind in the case of the original model.

    To get a perpetual motion machine, you’d need to do something like turn off the power to the treadmill and have the cart keep it turning. Spork and co. don’t make any such claims about it and, in fact, if you look at the forces I described above, the force that the cart exerts on the treadmill is to slow it down (it’s the reaction to the friction in the bearings). Which is just as it should be.

  370. Anonymous says:

    Tom,

    while i agree with your post, as far as it is about a single object relative to the air.

    But try to see the cart not as a single entity, but for what it is: an object made of several parts. While all parts are “connected” to the same cart, some of them are moving. These are the wheels and the prop. Even more, as you can see, the prop is connected to the wheels. Now remember that the prop, or better: it’s blades, does indeed have an angle to the wind.

    Now assume the cart is standing still, and a wind is blowing from behind on it. The prop’s blades are by far the biggest surface. So, the wind applies a force to the prop. Part of that force goes “into” the cart’s body, making it move forward on it’s wheels, the other part wants to rotate the prop, as if it were a turbine.

    Since the wheels and the prop are connected, as soon as the cart moves the prop starts to spin and works as a prop, it rotates against the “bias” that the wind applies. All that is needed for that to start is that the prop’s blades are big enough to catch enough force from the wind to overcome the friction to move the cart forward, plus the force needed to make the prop spin.

    At this point we have a surface that moves at an angle through the wind. Imagine the cart from the side, the prop to the left, cart moving from left to right. Draw a horizontal line through the center-point of the prop. Draw another horizontal line, but this time crossing the middle of a wheel. Now imagine the prop rotating, at the moment where the blade passes through that line, from where it just started to pass that line, to where it is about to leave that line. Since the prop acts as a prop, the profile of that blade passing by looks like a backslash, “\”.

    The cart moves forward, so the distance from the start position at the left to the center of the wheel increases, as you can measure at the line. At the same time, the length of the line through the prop’s center, from the start at the left is shorter. That means, that the surface of the prop’s blades actually move slower through the air than the cart itself.

    This is a grossly simplified “how it works”. Think of the prop not as a prop, but more as a literal air-screw. Once you think of it as that, take a look here: http://www.grogware.com/ddwfftw/
    Especially the second video, where he uses a thread and a “nut”.

    Hope that helps you a bit to understand.

    Greetings,

    Chris

  371. danddmurray says:

    Total and Utter CROCK -

    In real life, as this thing speeds up, the speed of the wind relative to it decreases – so, when it is going as fast as the wind, the wind speed becomes zero, and it looses all power to the propeller.

    But it will slow down long before that, when the force required to move it matches the force generated by the propeller – always, and forever, slower than the wind.

    On that treadmill, the force of the wind will always be there. It is like sitting in a sail boat. blowing on the sail…

    Crockeroni C. Crockington!!!

  372. zafner says:

    Foetusnail.

    The magical, frictionless machine would have to accelerate forward, reaching an equilibrium speed faster than the wind, because there’s a force on the prop pushing it forward. At issue is whether the friction and prop drag, when added back in, are less than this force.

    Yes?

  373. ThinAirDesigns says:

    Arkizzle:(#125)

    The experiment *has* been done outside and most everyone claims it’s a fake (see the first Boing Boing round). We bring it inside where we can control the conditions and everyone says “take it outside”. It’s hilarious really. Most folks aren’t going to believe no matter what.

    As far as the wind tunnel test goes — people need to think that one through … really. Wind tunnels are designed to test devices that run *into* the wind. People don’t stop to think that this device has to be turned around and run downwind — in other words, it’s going to smash into the back wall of the tunnel in just a few moments.

    Find a wind tunnel in the world that has the half mile or so needed to get the device self started, then up to speed, then proplerly tested, then stopped.

    I think the notion is just hilarious really — the wind tunnel guys would just say “hey morons … you’re apparently unclear on the concept of a wind tunnel — the device is supposed to sit still in the tunnel”

    And thus the treadmill, where it can sit still and be instrumented.

    JB

  374. FoetusNail says:

    Listen, these guys keep saying they’ve proved this, but the only thing they show as proof is a cart motorized using a treadmill. This treadmill powered stationary cart is not proof that this cart can exceed wind speed outside without a motor or sail. They then start to tell us we cannot understand their proof, which they have not provided, because we are not believers. This is the same circular argument without proof people use to try and convince me in the existence of gods. Since you don’t believe us you cannot understand us. Then when we ask them if they would do a simple test that would prove their actual premise that this cart will run faster than the wind without using a motor or sail, they quickly balk, using this silly place your bets argument or claiming it would be too expensive. Sorry, but I understand them very well. They are perpetrating a hoax using this video of one thing to offer proof of another thing, in hopes of getting a spot on mythbusters, who would quickly and completely bust this silliness apart in a heartbeat.

  375. airshowfan says:

    Sorry, ThinAirDesigns, I answered the question before your post was up…

  376. ThinAirDesigns says:

    GregLondon:
    >I am sitting in an open cockpit
    >and I feel absolutely no wind on
    >my face.

    That’s correct, but tape yourself to the prop and tell me you don’t feel any wind on your face.

    You’re confusing the chassis of the cart with the sails. This confusion is not a “me” problem, but a “you” problem.

    JB

  377. tomtheblacksmith says:

    Hi Chris,

    Thanks for the clarification/explanation. We are discussing a “propellermobile” instead of a “windmillmobile”. Got it.

    (Chris wrote): “that’s exactly what the prop’s blade(s) do. They move at an angle to the wind.
    (Tom replies): If the cart is moving directly downwind with the wind, there is no wind as far as the propeller is concerned, so the propeller receives no force to help the cart go forward.

    (Chris wrote): “So if the cart is at windspeed, the wind can still push on the surface of the rotating prop.”
    (Tom replies): If the cart is moving directly downwind with the wind (at windspeed), there is no wind as far as the propeller is concerned, so the propeller receives no force to help the cart go forward.

    (Chris wrote): As i like to explain, when viewed from behind, the prop’s surface facing the wind is moving forward slower through the wind than the cart.
    (Tom replies): If the cart is moving directly downwind with the wind, there is no wind as far as the propeller is concerned, so the propeller receives no force to help the cart go forward. Also, If you choose any point on the propeller and measure its forward velocity, I think that you will find that it is moving exactly the same speed as the cart, otherwise it would be left behind somewhere…

    May I offer some speculation at this point? Since I am working “blind” other than your description, let me offer two possible “mind experiment” scenarios from my “mind’s eye”:

    First, I make a “windmillmobile’ and set it on the road facing downwind. The wind blows, the cart moves forward and eventually achieves a steady forward velocity, but alas slightly slower than the wind. Disappointing, but not an entirely unexpected result.

    Not being the type to give up easily, I then build a “propellermobile” and set it on the road. The wind blows, and the cart moves forward and evenually is going the same speed as the wind and… then I am surprised to observe that the cart is actually still accelerating and is now “going faster than the wind that is pushing it. For real. This would be a possibility, and perhaps somewhat unexpected. At this exciting moment, perhaps I have about run out of road, so I hit the brakes and call the papers, publish a website, etc… If I didn’t know better.

    What has actually happened is: once the propeller and cart (which actually have the same forward velocity as long as they are attached to each other, I promise) have reached exactly the speed of the wind, The propeller is no longer receiving energy from the wind so the momentum of the propeller (which is now acting as a flywheel) begins to expend its stored energy and actually starts to “screw the cart forward” into and through the moving mass of air, and at that moment the cart would then truly be “going directly downwind faster than the wind” for real… but only until the excess energy were used up. Depending on the mass of the propeller this “flywheel – forward screw effect” could last for quite a while, maybe even long enough to confuse me into thinking I had discovered something really interesting.

    Then (alas) the cart would slow down a bit until it was going quite a bit slower than the wind so the wind would now be exerting force upon the propeller again so the car would accelerate again and the process would repeat as long at there were enough wind, road, etc.

    If this were done say, in the middle of Nevada or someplace where I could get a good long run, over a long enough distance I would find that the average speed of the cart is actually slighty less than the average wind speed due to rolling resistance and mechanical losses… but it could in fact travel in cycles, with the bursts of speed “directly downwind faster than the wind” followed by “catch up” periods where it is travelling a good deal slower than the wind, but storing up enough energy int the momentum of the propeller to temporarily “leap ahead” of the wind in cycles.

    I think if I/you/we were to release a helium balloon (ballasted to stay at a reasonable height) ahead of the cart it would be exciting to see the cart “try to catch up” for a while, only to fall back again after a while, then zoom forward again… but after a while the ballon would steadily pull ahead and “win the race” even though it is moving essentially 1:1 with the wind, but with no “rolling resistance”.

    So, in summary: as a result of my “mind experiment” I conclude that it is in fact possible for a wind powered “propellermobile” cart to move DDWFTTW, but only for a relatively short period of time, and this is due to a temporary/cyclical “flywheel – forward screw effect” of the propeller. Over a long trip, the cart would actually spend slightly more of its time travelling a bit less than the speed of the wind, and so the average speed for the trip would in fact be less than that of the wind.

    (Chris wrote): Take a YoYo, put it on the table so that it can roll, with the string coming out below the center of the YoYo. Now pull the string. The YoYo will move in the same direction as you pull, but faster than the speed of the pulling. Now replace your hand with a parachute, and you have something that will travel downwind faster than the wind, completely driven by the wind.

    (Tom replies): For simplicity, I will refer to this clever device as the “Parachute/YOYOMobile or PYYM for short. For the PYYM to work, the parachute must
    A: always be moving slower than the wind, in order that the wind will exert force upon it. If the parachute were to achieve the same speed as the wind, it would collapse.
    B: Be physically ahead of the YO-YO.

    So, the wind is rushing past the parachute, thus pulling upon the string. Meanwhile, the YO-YO is busily reeling up the string and catching up with the parachute from behind, since the YO-YO part is “moving faster than the wind”.

    In Summary: In order for the “YO-YO part” of the PYYM “system” to move forward “faster than the wind”, The “Parachute part” must be moving quite a bit slower than the wind. If you calculate the difference between the velocities of the two components of the “system” you will find the actual velocity of the “system” to be less than the speed of the wind. Also, you will quickly run out of string, so the experiment will end when the “YO-YO part” catches up with the “Parachute part” and rolls the parachute into a ball.

    The PYYM is another example of a mechanical advantage device, like the screw car or the lever car. A pully (YO-YO) and rope (string) is basically a “circular lever” and the same limitations of the “four part linkage” apply. In this case you run out of string instead of screw or lever, but the same basic problem is that such devices (while very clever) cannot travel very far, so they make impractical vehicles.

    Tom the Blacksmith

  378. ThinAirDesigns says:

    LaserRage:
    >In the treadmill example, the propeller
    >is a propeller, not a turbine.
    — snip —
    >On the road, in the wind, it is a turbine …

    Sorry LaserRage, but the above is not true. There is no difference in the behavior of the device on the treadmill or on the road — the two situations are *identical* to the cart.

    The prop is *always* acting as a simple prop and turned by the wheels. This is evident from our experience with our larger cart where we have a long loose cogged belt drive. 100% of the time is it the side of the belt moving down from prop shaft to wheel shaft that remains under tension.

    We have seriously considered removing the belt drive entirely and replacing it with two spools where fishing line is drawn from the prop spool to the wheel spool — this would clearly demonstrate the the prop never acts as a turbine.

    JB

  379. Anonymous says:

    Check out http://scienceblogs.com/goodmath/2008/12/windpowered_perpetual_motion.php

    Look at the very top of that Blog entry. Seems that MarkCC finally agrees to this machine.

  380. Ahoj says:

    As a physicist (though not beyond undergrad as of yet) the treadmill thing is totally pointless. the creator of the video should be slapped around with a wet badger for thinking it proves anything.

    And if we are talking about force created just from the wind flowing, it would never ever cause the craft from moving faster than the wind. The force from behind, for a craft at wind speed for example, would never equal the force of the air pushing against it.

    however, if you could create a pressure differential from front to back of the propeller it could provide the needed force to go beyond windspeed F=-gradP. so if this pressure difference is attainable at wind speed it can counteract the push back from going over wind speed.

    to create this pressure difference one would simple replace just slanted fins of an old fan designed propeller with air foils. once they get moving fast enough they can create the pressure difference.

  381. ThinAirDesigns says:

    God I hope sure Bill follows through. Expensive high school physics lesson though.

    JB

  382. jonasgerson says:

    This is actually simple problem – and no, you don’t even have to think about eddy currents or any aerodynamics at all. As a matter of fact you don’t even have to worry about balancing the forces on the cart.

    The wind, pushing on a sail/object, is able to provide a certain amount of work in order to move that object. Proportional to the sail size you’ll get more of it from the wind.

    The problem of what’s being proposed in these carts is that they may break the 2nd Law of Thermodynamics, hence all the fuss.

    What that does mean is that by having the wind push / turn the propeller, where the energy obtained by the wind will be proportional to the square of the radius (it’s circular).

    So the question to answer is: Can the propeller capture enough energy from the wind to move the mass of the cart faster than the wind? i.e. can it provide enough power (work/time) to turn the wheels in the gearbox so that the car moves faster than the wind?

    What IS NOT HAPPENING is the propeller capturing energy from the wind to then propel the cart faster than the wind. That DOES break the second law. The gearbox question is different, however.

    I would say not, but you could calculate this, given the mass of the car. There’s a wind-power factor fo 20%, so you can only capture a maximum of 20% of energy available to the blades (wind turbines follow this rule).

  383. spork says:

    >>…using this silly place your bets argument…

    That’s not an argument. Tht’s m tryng t sprt ccky fl frm hs mny.

    >>They are perpetrating a hoax…

    Place your bet.

  384. FoetusNail says:

    The thrust from the prop in your example comes from an engine with what a 100 HP.

    In this example the thrust comes only from that tailwind pushing on that frame and turning that wheel, which in turn turns the propeller.

    You really have no idea what mechanical advantage is do you.

    In your last examples, don’t forget to lift a load with pulleys you must pull in more rope than the actual lift, trading distance for force. To lift a 150lb man with 75lb of force 4ft you pull in 8 ft of rope. To lift a 150lb man 4ft with 25lb of force you must pull in 24ft of rope. To lift a 150lb man 1ft with a 6:1 lever you must apply the force of 25 lbs for a distance of 6ft, again trading distance for force.

  385. cmpalmer says:

    @ThinAirDesigns (#268):

    Regarding my notes on the RC/anemometer equipped cart. As long as the wind is blowing faster that the cart, you could use a wind vane on the vehicle to automate the steering. When the wind speed drops below the effective range of the wind vane, you just keep going straight. Or you can use a stationary wind vane as a steering control input (dicey) and log the direction along with the speed (as long as the wind direction is fairly steady and laminar – eddies and cross-winds would screw up the data.

    Whether or not the Mythbusters take it on, I think the Make/hacker/tinkerer community ought to design an acceptable test vehicle for outdoor test. I posted the first notes on such a design above.

    Who knows, even if DWFTTW is impossible, it would be fun exercise in telemetry and controls and it might prove to be useful in illustrating principles.

  386. datura says:

    A funny hoax, to be sure, but I’m afraid it cannot be true. Lots of comments above seem to get it.

    This device may be able to turn its wheels faster than the wind, but get it off that treadmill and it will never go faster than the wind.

    Why is that? Because once it does, it’s encountering a headwind, not a tailwind! The propeller is turning because the cart is standing still and the air is moving. Let the cart move and eventually that difference in air velocity to cart velocity will go to 0.

    Nice try! I hope none of you lost any money on this one ;)

  387. joelphillips says:

    #60 – okay, “air currents created by eddies”.

  388. Bill Barth says:

    JB: I believe that the treadmill test indoors with no wind works as shown in the video, so I presume that this is not what Spork wants to wager about. My understanding of the physics leads me to believe that the treadmill adds energy in a way that a system with no motor would not. Thus my potential interest in a proper test and the wager.

  389. GregLondon says:

    subduction: Greg, have you ever watched an old western. Those stage coaches were amazing, they could move forwards while their wheels moved backwards, they must have had some pretty amazing gear boxes too.

    Yeah, I’m familiar with frame rate conversion issues. Did I mention a year I spent designing real-time video processing asics? It’s called aliasing. I watched the clip a few times to make sure it wasn’t aliasing.

    spork: The prop spun backward at first because the gust was abrupt and the wheels lost traction.

    Hey, spork, could you call off your attack dog, shill, whatever he is? I point out a valid observation, and he starts making up bedtime stories about video sampling rates.

  390. ThinAirDesigns says:

    The voices of reason are multiplying and getting louder.

    Soon it will only be FOET screaming “for the last time, your test means nothing”. and Greg throwing out the canned “even if it works you don’t know how it works”.

    Hopefully there will be a few unbelievers left when the MythBusters episode rolls around.

    JB

  391. GregLondon says:

    Greg throwing out the canned “even if it works you don’t know how it works”.

    Well, you don’t, so I’m not sure what your point is.

    Hopefully there will be a few unbelievers left when the MythBusters episode rolls around.

    If they put this on Mythbusters, they are seriously hurting for stuff to do. This is so esoteric that most people will hear the “myth” and go “meh, who cares”. It’ll be on an episode that also tries to bust whether a watched pot boils or not. And then throw it all in a cement truck and blow it up with dynamite because it’s too boring otherwise.

  392. Cloudform says:

    I find it beneficial to imagine this experiment taking place submerged inside a giant stream of molasses instead of air.

  393. Nelson.C says:

    ThinAirDesigns, I’m not putting any onus on you, that’s just how science is done: you publish your results, you publish your methodology, you publish your apparatus design, so that others can try to duplicate your experiment as faithfully as possible.

    If you don’t take this thing seriously enough to do the science properly, then why should anyone else take it seriously?

    Honestly, just link to the data, link to the plans. What is so difficult about that?

  394. airshowfan says:

    #63 – the claim that the vehicle can accelerate from rest (relative to the ground) to wind speed (at rest relative to the air) on wind power alone is not the main claim here. The main claim here is whether, once at wind speed (i.e. not moving relative to the air), the vehicle can stay there, maybe even accelerate.

    I’m happy to ignore the question of whether it’s self-starting and focus on the question of whether it’s self-sustaining. Especially since that’s the harder question. Anything with a big-enough sail can be blown by the wind into a speed that is JUST lower than wind speed, and stay there.

  395. toilet says:

    “An engineer would simply say the machine uses wind energy”

    They tried, unfortunately it wasn’t detailed enough for some…

  396. Anonymous says:

    I wish that rather than offers to lay money on the line, which is a notoriously pseudoscientific practice (as if a bet could be mistaken for evidence!) the proponents of this DWFTTW could just give us the shorthand physics explanation for why this works, which actually would convince any skeptics.

    Am I right in understanding that a pressure difference is where the extra force comes from that pulls the thing faster than the wind pushing it? Is that correct? The sailboat generates a wavefront or something?

    And it’s not perpetual motion because of what now? Where does the air pressure difference come from, and why won’t this just cause it to accelerate indefinitely? Is it some sort of self-balancing system where you’re cruising at 2 knots in a 1 knot wind?

  397. arkizzle says:

    Again, (and with the running-length of the wind tunnel taken on board) I think there is an obtuseness to your attitude. I totally understand that you have been arguing the same shit with different people for some time, but there are things you could do to help yourself out.

    The problem people have with the first video is the camera doesn’t show what, if anything, is leading the cart. There was probably no need to bring it inside to stifle sceptics, the guy could have made another video with the camera panning etc.

    Of course there would be more questions after that, but there is no point getting pissy with “We bring it inside where we can control the conditions and everyone says “take it outside”.” If this wasn’t an interesting and perplexing thing, you wouldn’t be doing it. You wouldn’t still be here and elsewhere answering questions if all the questions had been answered.

    To be clear: I’m on your side (as it were), but there is room for you to make your own video of your cart running outside, and panning around, as requested by lots of folk.

  398. airshowfan says:

    #64, Why do you think that what is happening in the video is anything other than what you describe in the second half of your post?

    People keep forgetting that the vehicle is not kept at wind-speed by drag (since, yes, the drag when you’re going at wind speed is zero). It’s kept at wind-speed by the thrust from the prop. (It might GET to wind speed by drag, but that’s another question).

  399. HUDMAN says:

    [quote] HOLY COW! How big is your father’s closet!? I don’t think I could even fit my motorcycle in my closet. [/quote]
    Sounds like a personal problem why you would even want to. And.. when you take the bike out of the closet, my question is are you, “Coming out of the closet…” with your bike?

    [quote] Hmmm… is that like “marijuana experiments” or “you and your best friend at camp” kind of experiments? [/quote]
    Um… No – Info below (Spoiler: It was a real flop, but not literal, like in JB’s 15 mins. of fame)

    [link] http://www.imdb.com/title/tt0471996 [/link]

  400. tomtheblacksmith says:

    Creetings Chris,

    (Chris wrote): just in case you haven’t found them yet, here are the plans for the cart:

    (Tom replies): Thank you for the links, but I am going to wait until I have solved this to look and see if I am right (or not). All I started with was the statement DDWFTTW and a picture in my mind of a cart with a windmill on it. A friend sent me the link to this page, but I have not read any of the thousands of posts (I don’t care to) or seen the videos ( I currently can’t) so as I said I am taking this challenge on purely logical arguments. I rather thought it would be fun to figure it out for myself. Also, I wouldn’t be caught dead on one of these message things, because people are often mean and usually wrong (most often in direct proportion), So I have signed in with a pseudonym. I can escape if need be. Since your replies are courteous and intelligent, I figured it would be fun, at least until somebody got ugly.

    (Chris wrote): While my model is simplified, the more correct one would be to look at the thrust the prop generates. So, the speed of the cart would be the velocity of the wind plus the velocity that the prop generates. Also, it not only generates thrust, on the other side of the prop it tries to produce a vacuum, trying to “suck” the cart into forward direction.

    (Tom replies): In “Newton’s World” (where we currently live) There is no such thing as “suction”, only “pressure” or lack thereof. “Suction cups” like you use to hang stuff on windows would not work in space, for example: It would be impossible to hand little suction cup Xmas trees on the outside of the Shuttle windows in orbit due to lack of atmospheric pressure… but I digress, sorry.

    Your argument that a propeller “generates thrust” is inadequate to explain the DDWFTTW phenomenon, because to “generate thrust” requires energy, and that energy has to come “from behind” in the form of wind, and we have already established that there is no “wind” onboard the cart, because it is already at windspeed (or as you assert above windspeed).

    Here is my current thinking:
    I was originally thinking of the “windmillmobile” which I think we both agree would not travel DDWFTTW because there is no “wind” on board the cart, except maybe “negative wind” which would be encountered if the cart were actually to go DDWFTTW. This kind of “stuck” in my head for a while, which is counterproductive. I’m better now, thanks.

    Once you got me going on the propellermobile concept and then the “reverse ferris wheel” concept this idea began to take shape, sort of. If for example we gear the ferris wheel so that the top of the wheel is going backwards, then when we push the top car (‘chute) from behind, the cart moves forward “faster than the wind”. This would work if you push on it with your hand or something, I’m OK with this.

    The main problem with this idea is that the ‘chutes, while admittedly “traveling backward into the wind” don’t really have enough “sail area” to collect enough energy to account for the 1:1 forward motion of the car plus the energy required to accelerate the car FTTW. Yes, the concept is OK, but the mechanism would probably not yeild sufficient “thrust” to be useable. We need a different approach. Here it is:

    My current best explanation of:

    A. Why DDWFTTW is in fact very possible: A wind powered vehicle (sailcar) moving on the ground requires a only certain amount of energy to move forward at any given speed, but in fact the affixed sail can be much bigger than the car actually requires just for constant forward motion. In essence, a car with a fixed sail ten times bigger than it needs has the capability to collect much more energy than it needs to go forward, but it still can’t go DDWFTTW because the fixed sail presents exactly as much “frontal area” as “collection area”, so for it to accelerate forward into the mass of air in which it is traveling would require an input of energy which is not available. In other other words, with a fixed sail, the best you can hope for would be 100% of the wind velocity minus the energy used by “rolling resistance”. In even more words, in order to go DDWFTTW, we need a “sail” that is bigger than the car actually needs for forward motion, but has no “frontal area”.

    B. How I think it probably works:
    At first glance, seems that the propeller of the “propellermobile” is not a very big sail, and even if it were big enough, it would still suffer from the “defects of the fixed sail”, but it in fact does not.

    When the propeller spins (in still air), there are at least three different phenomena occuring which contribute to the production of “thrust” but rather than enter into an entire diatribe called “Toms’ Propeller Theory”, lets just say that as the propeller spins firstly it “bats” some air molecules from its path, and “herds” the molecules behind itself. As each blade passes a given point it is creating a “deficiency” of molecules directly in front of itself, and a “surplus” of molecules behind it.

    In front, atmospheric pressure rushes in to the partially vacated space, and behind the the air “piles up”. This translates into “lower air pressure in front” and “greater air pressure behind”. This means that if we apply energy to a spinning propeller, it has a tendency to be “pushed forward” by the difference in pressure.

    Critical point: Since air is compressible, when you push on it it pushes back equally hard (if it doesn’t have enough time or a way to flow around the sides of the “pusher”).

    Even though we normally don’t see it, air has area, volume and mass, which means it has inertia. If the propeller spins quickly enough it creates a physical “disk” (or at least a kind of a “donut slice”) of air behind it that is at higher than atmospheric pressure, so this “invisible disk” essentially “presses forward” on the spinning propeller and simultaneously “presses backward” upon the air behind it.

    I submit that this “invisible disk” of air which is created immediately behind the propeller actually becomes the “sail” and since it has many, many times the “area” of the propeller itself, it is capable of “collecting” much more energy from the wind behind it, and could collect enough energy to account for the rolling resistance of the car plus the additional acceleration needed to go FTTW. Since it is constantly being re-supplied with air from in front of the propeller, it is an “ever expanding spring” which allows the propeller to “push itself ahead of the wind”, just exactly as it would do in still air. Also, the spinning propeller has essentialy “no frontal area” providing resistance to additional forward acceleration, so it meets the requirement for forward acceleration.

    The “invisible disk” of air is the “missing component” that I failed to recognize right away, but an expanding mass of dense air is as much a “physical object” as a propeller or a wheel, and is in fact necessary for this to work at all.

    So, in summary:
    A. DDWFTTW is possible because a wind powered vehicle can have a “sail” that is big enough to be capable of collecting much more energy than it needs for forward motion including enough energy for additional forward acceleration FTTW, provided that the “sail” has “no frontal area” or resistance to forward acceleration.

    B. A spinning propeller can act as an effective “sail” by creating an “ever-expanding” flat circular disk of air behind itself as it spins, and essentially has “no frontal area” since there is reduced pressure in front of the propeller. As the flat circular disk of air expands, it pushes against the wind coming from behind and the propeller equally, providing the physical “coupling” needed or the propeller to be able to move continually “ahead of the wind”.

    The “ever-expanding disk of dense springy air that becomes a sail” is the “invisible component” that makes the system make sense. It is not perpetual motion because the area of the “disk” can easily be made into a large enough “sail” to collect enough force from the wind to power the car upon which it rides, plus the “missing energy” required for the car to accelerate ahead of the wind, and since it is an “ever-expanding spring” (I must think of a better way to say this) it doesn’t require the “inertia effect” that I mentioned in my earlier description, it will work continually.

    Caveat:
    A. It may not be “self starting”, or it may take a very long time to get going, or you may have to push it to start. Once it gets going to “critical speed” it should go DDWFFTW continuosly. I’m not sure if this counts as “cheating” or not. If the stationary propeller was a big enough “sail” to get the cart started even a little, I think it would “pick up and go” after a bit, so maybe cheating isn’t necessary.

    Test:
    The other way to think of “wind” is to think of the Earth (Our Home!) as a very large “spherical treadmill” rotating inside of a “stationary sphere” of air. Therefore, if your “propellermobile” can go forward (in perfectly still air) on a treadmill faster than the treadmill is going back, then it is definitely going DDWFTTW. In other words, at some critical speed, it should start to pull ahead and keep pulling steadily. If it jerks and releases, it is the “flywheel effect” mentioned earlier. If it pulls and keeps pulling, it actually is going DDWFTTW for sure.

    Ok, did I get it right? That took several hours to figure out.

    Tom the Blacksmith

  401. ThinAirDesigns says:

    Airshowfan:
    >Sorry, ThinAirDesigns, I answered
    >the question before your post was up…

    No worries Air — I appreciate your thoughtful and well reasoned posts.

    In the end, as you know, you didn’t answer the question completely — you only gave the two possible reasons. I can still answer the question for Foet to absolute precision with explanation if he decides he wishes to exchange with me.

    JB

  402. nwhitehe says:

    Airshowfan, #60: Thanks for your comment, that cleared up the issue in my mind. In my mind I’m thinking of two planks laid side by side, both of which have nails in them. One plank is fixed, the other is dragged along. Can you build a contraption that hooks to the nails and travels faster than the plank being dragged?

    The answer is clearly yes. If you just connect to the moving plank, you can only ever go as fast as it is dragged. But if you connect to both the fixed and moving planks, you can use some mechanical tricks to multiply the difference in speeds and make it work.

    I haven’t thought too deeply about the actual propeller powered contraptions, but they seem to fit the same model. They are connected to both the moving plank (air) and the fixed plank (ground) with a mechanical link that can multiply speeds (gears and wheels).

  403. ThinAirDesigns says:

    Bill, the details of course you need to work out with spork, but if you two can’t come to terms, it won’t be because you wish to see an outdoor test — he’ll have no problem with that.

    JB

  404. Daneel says:

    @251, the prop force would also have to overcome the energy being removed from the propshaft to spin the prop in the first place.

    In the treadmill case, the propshaft is powered by the treadmill’s motor, so the prop extracts this energy and uses it to provide thrust to move the cart up the treadmill.

    In the wind case, the energy source is the force of the wind pushing the cart along – but we’re going at the same speed as the wind, so this input is 0. Surely, for the craft to accelerate beyond this equilibrium, the energy taken out of the shaft would have to be less than the energy the prop puts back – doesn’t that imply greater than 100% efficiency of the prop?

    Since said propshaft is unpowered (in the wind case, but not in the treadmill case), for the system to accelerate the prop would have to generate more energy than it’s extracting from the shaft – doesn’t that imply a prop with an efficiency of greater than 100%?

  405. davidglover says:

    I think I know these 2 guys, spork and thinair. Be careful I think they work in the computer graphics field. Think, monofil line, magnets, fake levels, and giant sucking machines. Someone should bet them. Mythbusters should take these charlatans on and expose their crazy lies!!!!! :) Just kidding they are real.

  406. spork says:

    “As a physicist (though not beyond undergrad as of yet) the treadmill thing is totally pointless.”

    I guess you didn’t cover the basic high school principle of equivalence of inertial frames yet. Please see if you can get your money back. I see sign shaking in your future.

  407. Anonymous says:

    You’ve almost got it, Tom. Instead of the yo-yo just winding up the string, put another pulley out ahead of us on a stick, and run the string in a loop around both pulleys so that when the parachute reaches the yo-yo pulley, it just goes around the axle and moves forward to the front pulley, so that it can start again. Attach two or three of these parachutes to the string, equally spaced. When they’re moving forward to the front pulley, they’re moving faster than the rest of the machine, so they contribute to the average forward motion (and since this runs continuously, it’s clear that the speed of the yo-yo equals the speed of the whole apparatus). And importantly, when the parachutes are on their way forward, run them through a tube so that they don’t provide any significant drag that would impede the forward progress.

    Discuss.

  408. Tarantio says:

    Somehow I missed that the propeller was mechanically connected to the wheels in the first cart in the video. This changes things, of course, so I’ll have to reconsider the situation.

    Still not sure of anything, but definitely just as interested.

    Thanks for the link, Spork.

  409. ThinAirDesigns says:

    Ark, you’re totally underestimating what people complain about. Towing is only *one* of the complaints people had: Gusts, not straignt downwind, downhill, batteries, weaving, etc.

    It’s always something.

    Don’t get me wrong — we *have* run this device out in the wind … we simply have not yet had the time to set up a test that would convince the folks who aren’t convinced now. It seem rather silly to spend the effort, just to be told we’re cheating. That’s why we hope the MythBusters will do it — people don’t always agree with their results, but they rarely accuse them of cheating.

    (Or perhaps Bill and Spork will work out the details and we’ll get it on for money).

    JB

  410. GregLondon says:

    You’ll get my real name, my real autograph on the contract, my real money in escrow,

    The more you talk, the more I smell a con.

    My name is posted beside all my posts. I can think of no legitimate reason for secrecy. It isn’t like your some kind of chinese dissident hiding from the government or something. The only reason that I can think of for you wanting to maintain your anonymity is because this is all a con.

    Whether you’re conning yourself into thinking this is true or not, I don’t know. But anonymous experts with masters degrees professing to know how to break some intuitive rule of nature and willing to bet large amounts of money on it isn’t exactly forwarding science. When asked to explain things, the response is generally vague or even poorly done. Energy keeps entering the system magically. When pushed on it, your response over and over again is to shove your bet in someone’s face, as if that proves you’re right.

    Ever watch “The Sting”? The big twist at the end was that the FBI were actually in on the sting, that Hooker hadn’t betrayed Gondorff to the feds, but that the whole thing was a whole bunch of handwavium to convice the mob boss that hooker was dead and gondorff would end up in prison, and that he hadn’t been had.

    The thing about science and conmen is that scientists don’t usually know where the con is takign place, they don’t know where the handwave is occuring, so they don’t know they’ve just been had.

    And here you are, some anonymous guy on the internet, with a great new gadget that defies the understood laws of physics, with no schematics, and no design spec, and no details. With a huge wager you throw in anyone’s face, and with no name so maybe you can slip away with Hooker and Gondorff after you’ve taken the mob boss’s money.

    I said I’d wager you $50 to the charity of your choice, but you haven’t taken me up on it. Maybe because you can’t take that kind of money in a suitcase?

    At this point, I don’t think I’d even wager you the $50 to charity unless you disclosed your information publicly.

  411. ThinAirDesigns says:

    Nelson:
    >Honestly, just link to the data, link
    >to the plans. What is so difficult
    >about that?

    The links to the “data” have been provided on this thread as well as parts lists and build advice.

    If you wish to build one and test one, I’ll give you my personal contact information and help you in any way you wish.

    I know how this story ends and it isn’t with me eating humble pie. The device works as we say it works and as more and more people build and test these devices it will become evident. I’m perfectly comfortable with that process.

    We didn’t set out to change the world through publishing data that will satisfy you regarding this craft and any additional testing isn’t being down to convince us … only others, so we will be spending time and money for additional testing at our own pace.

    As I said, let me know if you wish to be a tester who gathers data of the sort you consider credible. I encourage folks to put our claim to the test.

    JB

  412. ThinAirDesigns says:

    Greg:

    If they put this on Mythbusters, they are seriously hurting for stuff to do. This is so esoteric that most people will hear the “myth” and go “meh, who cares”. It’ll be on an episode that also tries to bust whether a watched pot boils or not. And then throw it all in a cement truck and blow it up with dynamite because it’s too boring otherwise.

    LOL — yeah, as evidenced by the unusually high post counts associated with this topic. LOL

    The “reality” you live in is a very odd and amusing place(from a distance that is). Someone who conceives a device from first principles, designs, builds, predicts and then demonstrates those predictions through testing “doesn’t know how it works”. And topics that receive repetively high posts counts are ‘boring, meh who cares?’ topics.

    Your canned assertions clearly don’t fit the data, but I do admit, you certainly have added a healthy slice of entertainment to the thread – props on that one.

    All the best to you.

    JB

  413. GregLondon says:

    spork: The important thing is to get absolutely minimal friction and the correct advance ratio. This means you should definitely start with exactly the prop, gears, and wheels specified. There is a big gear and a little gear. The little gear goes on the axle and the big gear goes on the prop shaft.

    Hey, look at that. What did I say? I said I would guess that if you put a 10 mph wind across the prop, the wheels will want to run at 100 mph or something. The whole thing works because you’ve got a massive ratio between air speed over prop and wheel speed over ground.

    start with a 10 mph fixed tailwind.

    ground speed -> airspeed over prop -> desired wheel speed -> result

    0 -> 10 -> 100 -> accelerate
    1 -> 9 -> 90 -> accelerate
    2 -> 8 -> 80 -> accelerate

    8 -> 2 -> 20 -> accelerate
    9 -> 1 -> 10 -> accelerate
    9.1 -> 0.9 -> 9 -> decelerate.

    look at that. if you’ve got a big enough gear ratio, you find a steady state at ~9.05 mph.

    Now, throw in a one mile an hour gust

    9.1 -> 1.9 -> 19 -> accelerate

    it should steady out around 10.

    10 -> 1 -> 10 -> steady state.

    So, you’ve got the vehicle up to 10 mph from a gust. let the vehicle be light enough and as little friction as possible and it can coast. And because you’ve got the prop spinning, it acts as a flywheel to help keep it spinning, which keeps the wheels turning at 10 mph.

    The gust dies down, and suddenly you’re moving at 10 mph in a 10 mph wind.

    get a 2 mph gust, and you steady state at 11. The gust goes away, and suddenly you’re going faster than the wind until you bleed off the flywheel and the inertia of the vehicle.

    Here’s a couple questions for you.

    (1) if you lift the vehicle off the ground and put a 10 mph wind over the prop, how fast (in mph) do the wheels want to turn?

    (2) if you lift the vehicle off the ground and put a 12 mph wind over the top, then change the wind to 10 mph, how long does it take the wheels to get back to 10 mph?

    (3) if you take the prop off, leave everything else the same, and get the machine moving at 12 mph over smooth ground, then release it, how long does it take to get down to 10 mph?

    The thing is, I haven’t heard you explain how you go faster than the wind. I’ve only heard you say it works. But if you can’t explain how it works, then you can’t be certain that you’re not misinterpreting the data.

    In the video, someone compares this to a bee flying. that all the doubters are saying that theoretically a bee can’t fly, and are doubting this because they’re attached to their theory. But all you’re doing is argument from ignorance.

    http://www.infidels.org/library/modern/mathew/logic.html#ignorantiam

    “Of course the Bible is true. Nobody can prove otherwise.”

    The other thing you’re doing is shifting the burden of proof.

    http://www.infidels.org/library/modern/mathew/logic.html#shifting

    “OK, so if you don’t think the grey aliens have gained control of the US government, can you prove it?”

    Uh, no. That isn’t how it works. You have to do the Mythbusters thing and prove it or disprove it. You can’t simply say “I’ve tried everything I can think of, so it must be true”.

    You can’t explain it, so you don’t really know if you’re misinterpreting your data. You don’t know if you’ve got a flywheel effect going on. You don’t know if you’re adding energy to the system with the treadmill.

    And then when the doubters come at you, you throw the bet in their face. Well, your bet doesn’t prove anything either, nor does it explain anything.

    If you really want to show a respect for science, you’d either say “this is exactly how it works” or you’d say “I don’t know why this is happening and there may be something that I’m missing here”. But you’ve gotten so sure of your interpretation that you’re willing to bet 100,000 dollars.

    Certainty is a feeling. It’s an emotional response. If you’re this certain but don’t actually have the explanation to go with it, then you’re getting carried away with your emotions.

    Stop playing with the treadmill. It adds energy to the system. figure out a way to have wind moving over the vehicle. I asked you a couple of basic questions that you ought to be able to answer rather easily. Get some hard data.

  414. ThinAirDesigns says:

    Airshowfan, if you don’t mind I’d like to have an exchange with you regarding something you voiced in your post #198:

    >So if we’re talking about a cart like the
    >cart on the video, let’s assume that the
    >spinny thing is a propeller. In that case,
    >the sailboat wind angle thing is irrelevant,
    >right?

    I take it from the above statement that the reason you feel it would be “irrelevant” is because you hold a belief that a sail acts only as a turbine — correct?

    While I await your answer on that, I will address one other thing from that post:

    You say:
    >I really really don’t think that the
    >downwind component of a sailboat’s
    >velocity exceeds the wind speed,

    Since hull drag dominates in waterborne craft, sailboats that can achieve VMGs over 1.0 are not common, but not totally rare either. PlayStation/Cheyenne and Phillips were two that could regularly achieve this.

    Great discussion among boat designers here:
    http://www.boatdesign.net/forums/sailboats/tacking-downwind-faster-than-wind-24761.html

    However, far easier to demonstrate are land yachts and ice-boats — same sailing rigs with a lot less hull friction.

    Discussion among land yacht racers here:
    http://sports.groups.yahoo.com/group/2nalsa/message/161

    JB

  415. FoetusNail says:

    Airshowfan, you are making a mistake when you fail to see the video of the cart on a powered treadmill as anything other than a cart with a motor. Instead of the motor being mounted to the frame and a belt going from the motor to the wheel to power the propeller, the video is of cart sitting on a belt powered by a motor. This video means nothing. Tell them to take the thing outside and prove what they claim this video proves they say it proves, but which they do not now want to prove with out placing our bets.

  416. FoetusNail says:

    And now more condescending name calling.

  417. GregLondon says:

    As the parachute pulls the wagon along, the turning of the axle will slowly reel in the thread, pulling the wagon closer to the parachute, i.e., moving the wagon faster than the parachute

    Ooooooohhhh, crap.

    I think I just saw how it might work.

    If you have a lever on a fulcrum, and if you push the short end of the lever down an inch, the long end of the lever might go up three inches. You have to use more force, but you get more speed.

    Now, change it around to gears instead of a lever.

    If you put the propeller stationary in a 1 mph wind, but you then gear it to the wheels so that it turns the wheels at 3 miles per hour, then as long as the force the wind exerts on the propeller is large enough that when you gear it down its still enough to move the thing forward, then maybe, maybe, you could get something weird happening.

    The thing is, this isn’t like an airplane taxiing on the tarmac. An airplane uses its propeller to push air back and that moves teh plane forward. The wheels on a plane spin freely, you just steer the nose, and you have brakes for the back wheels. And a plane can never taxi forward faster than the air moving backward is going.

    But this isn’t like a plane taxiing on teh ground. The “engine” is replaced by the wind. The wind turns the propeller, and the propeller is geared to the wheels. If you gear it up enough, and if you have a light enough widget so that the friction is extremely low, then you might have enough force to move the thing forward faster than the wind is moving backward.

    At least for a while.

    Say you gear it so that a 10 mph airflow over the prop makes the wheels spin at 100 mph (with the wheels off the ground). And say you’ve got a light enough widget adn low enough friction that whatever force turning the prop can be divided by 10 and still turn the wheels and make the thing go forward. So, you put the machine down on the ground in a 10 mph wind. it accelerates.

    you get up to 5 mph. The prop still feels a 5 mph tailwind. The gearbox to the wheels make the wheels want to turn at 50 mph. so you keep accelerating.

    you get up to 8 mph. The prop feels a 2 mph tailwind. The gearbox wants to spin the wheels at 20 mph. so you accelerate.

    You get up to 9 mph. The prop feels a 1 mph tailwind. The gearbox spins the wheels at 10 mph. So you accelerate.

    You get up to 9.1. teh prop feels 0.9 mph. the gearbox wants to spin the wheels at 9 mph, so you decelerate.

    You’ve just found steady state at 9 mph. You have a 10 mph tailwind. the prop feels 1 mph draft over it.

    All you’ve got to do is add an occaisional gust of wind and you’ve suddenly injected enough energy to get your machine above the 10 mph tailwind. if the wind gusts to 14 mph, and you’re moving at 9 mph steady state, the prop will feel a 5 mph tail wind, and the wheels will want to spin at 50 mph. so you accelerate. You should quickly get up to just under the gust speed of 14 mph. The wind drops back to 10 mph, and now you’re going faster than the wind.

    I can see this working up to a point. But I think if you did this in a controlled windtunnel, you’d never get above the windspeed. If you have a gust, you could easily get it up to speed, then the gust could drop, but the machine is already moving with more inertia, with nearly frictionless wheels, on a completely smooth surface, that speed will take a long time to bleed off, so it seems like you’re moving faster than the air. But you’re only moving faster than instantaneous air. you’re still moving slower than the airspeed over time.

  418. tomtheblacksmith says:

    Chris,

    The expanding air behind the propeller is the “endless string” component needed for the PYYM to work, but it actually takes the form of “an endless rope that you can actually push upon” against the air coming up from behind.

    Good grief, I need to come up with better analogies.

    G’night.

    Tom the Blacksmith

  419. tomtheblacksmith says:

    Chris,

    This is a good description, and I will reply with my thoughts. The computer was gone for a couple of days, but I’ll be back soon. Thanks for writing.

    Tom the Blacksmith

  420. Anonymous says:

    surely bindun : with the device as referencial, if it goes towards the wind, with his acceleration, doesn’t the wind go faster too ? then if you’re sitting on the cart, with a wind blowing at 10kmh and the cart going towards it at 3kmh, you feel a 13kmh breeze, and keep accelerating. thx

  421. GregLondon says:

    That’s correct, but tape yourself to the prop and tell me you don’t feel any wind on your face.

    Look, just say you don’t know how it works and at least you’ll be honest about it.

    What you’re yapping about here though is pure pseudoscience.

    Seriously. Are you an aeronautical engineer?

  422. Anonymous says:

    @Foetus:

    Actually, the spool/paper demonstration spork linked (http://www.youtube.com/watch?v=E7vcQcIaWSQ) does indeed show the principle. The paper tape is the wind, the spool is the cart, and the spool travels faster than the “wind” driving it. No principles are violated. If you’d like to claim that the paper driven spool is possible, but it’s impossible using air instead of paper, you’ll need to provide a lot more detail in your proof of impossibility.

  423. HUDMAN says:

    “”Subductionzone, no sailboat, NO SAIL POWERED boat, cart, vehicle of any kind sails directly into the wind.””

    Sure about that?
    http://www.youtube.com/watch?v=NNbNNSDljGI

    “”The cart in the video is no different than a motorized cart traveling on a motorized belt. You turn on the motor wait for it to get up to speed, then match the wheel speed with the belt speed and set it down.””

    Dude! I think you’re starting to get it. It is no different! Except the part where the cart has no motor that is, and yet it still has to do what the motorized cart does.

  424. GregLondon says:

    I think I saw Wiley Coyote use one of these to chase the Road Runner one time.

  425. ThinAirDesigns says:

    CMPalmer:
    >As long as the wind is blowing faster that
    >the cart, you could use a wind vane on the
    >vehicle to automate the steering. When the
    >wind speed drops below the effective range
    >of the wind vane, you just keep going straight.

    Certainly what you say above it true, but consider two things:

    A: the desire is to get the vehicle at or above TWS as quickly as possible.

    B: the vehicle performs the feat of getting at or above TWS damn fast.

    I don’t think when you take “A” and “B” into account there is much point in building a vehicle that self steers only when well below TWS.

    I guess the question that could be asked is “are we attempting to solve an admittedly cool control problem, or are we attempting to test a vehicle that goes DDWFTTW?”

    I fall more into the latter, but everyone has their own interests.

    JB

  426. FoetusNail says:

    – as demonstrated by the fact that our cart works *without* a flat sail.

    This is how you know they are full of it, they claim they have proved their cart works, but then say they want money to prove their cart works.

    Is everyone alright with this?

  427. codesuidae says:

    ThinAirDesigns:

    LOL, nice. True, the tests cannot easily determine whether the town is on a stack of treadmills (or, perhaps, if it is turtles all the way down), but the question to be answered was whether the air was still and the town was moving south at 10mph or if there was a 10MPH wind from the south and the town was still.

    If the sextant measurements indicate that the street has a relationship to the stars that is consistent with the previously determined relationship between what we deem to be the stationary land and the stars, then one can reasonably infer that the street is not traveling south at 10MPH.

    Of course it could be that in your deviousness you have previously contrived to install a massive display screen above the town to foil stellar measurement, and have cleverly arranged for the entire town to be placed inside a rocket in deep space, accelerating at 9.8M/s/s, thereby foiling gravimetric readings. The rocket of course has a constant southward component to it’s movement, thereby satisfying the conditions, at least for the first 790 hours.

  428. spork says:

    “The wind turns the propeller, and the propeller is geared to the wheels”

    Nope, the wind “pushes” the prop forward. The wheels apply the torque that turns the prop.

    “But I think if you did this in a controlled windtunnel, you’d never get above the windspeed”

    And that’s precisely why I offer the standing bet.

  429. GregLondon says:

    arkizzle@245, the bit that seems to attempt to directly explain the input of energy is this piece:

    The energy to continue to push this machine past ambient wind speed does indeed still come from the wind (in the outdoors model) at the interface of the thrust air with the wind air. They make for an action-reaction pair. While the thrust air is keeping the cart ahead of the wall of wind, that wall also keeps pushing the thrust cushion ahead. The wind is not gonna give up, it keeps advancing, and provides a squishy but implacable wall for the thrust air to push off of.

    And I’ve read it several times and I still don’t get it as energy. Ground speed is 10 mph. 10 mph tailwind, gives me an airstream of 0 mph over the prop. The prop is still turning so it pushes air back, which can accelerate the craft forward. However, I don’t see how the zero mph relative wind induces energy into the system.

    Especially when I’m doing 11 mph groundspeed and am runing into a 1 mph relative headwind.

    I’m not saying there isn’t something going on here, I’m saying no one has explained it to any degree that says “the energy comes from blah”, where blah is obvious the direct cause of the observable effect. “the wind” isn’t specific enough. And while AlpinWolf appears to be pointing to something more specific than , when I parse it down, I still get “the wind”, which doesn’t do it for me.

    Energy isn’t that hard. you should be able to point to something and say “energy continuously enters the system here” and go, yeah, that’s it.

    Here’s what I’ve been trying to visualize lately. Imagine two 2×4′s set soem distance apart. In between them, you put some machien that has wheels between the two boards. one board is stationary. The other board starts moving. Would it be possible to have the machine between the two boards extract the energy of the motion of the two boards and move faster than the boards are moving?

    I wish I had a gear/pulley simulator I’d set something up. Two belts, one above the other. In between them, you suspend this thing that connects between both belts, but floats in some way. Then you start moving one belt releative to the other. And the question is if the belts are moving at 10 mph difference, is it possible for something like a simple pulley mechanism between these two belts to move at something faster than 10 mph?

    If it can, then that might be the way to look at this propeller/cycle. The prop is like a pulley touching the top belt. The drive-wheel is like the pulley touching the bottom belt. The bottom belt is stationary. The top belt is moving at 10 mph. Can the machine move at 11 mph relative to the bottom belt?

    I can’t visualize how it could be done, but that doesn’t mean it can’t be done. Anyone know of a really good belt/pulley simulator online somewhere?

  430. misterfricative says:

    What Daneel said (#254)

    Spork’s treadmill minicart and the magnified downwind velocity component of iceboats are both counter-intuitive — at least, they are to me! — but if you consider the forces at equilibrium (ie at stable terminal velocity) then it’s possible to see how they work.

    In the case of the treadmill minicart, there’s a backward force being applied to the wheels by the belt of the treadmill. A small component of this force acts to push the minicart backwards, but most of the force is applied to rotating the wheels. This wheel rotation drives the prop via the gearing, and the prop generates a forward thrust that is slightly greater than the backwards force from the belt. Consequently the cart moves forward. The force differential is great enough that the minicart will even move uphill if you tilt the treadmill slightly.

    The force vectors for ice boats are more complex, but they basically work in a similar way, except that the continuous source of energy comes not from a treadmill, but from the wind, and the leveraging is effected not by gears but by an airfoil/keel (or sail/blade) system.

    The more complex DWFTTW thought experiment system described by Thinairdesigns (#280) also works for the same reasons that a single iceboat works.

    But the free-running Jack Goodman cart is problematic. If the wheels are powering the prop, then the treadmill model applies. But on the treadmill at equilibrium, there’s still a force being applied to the wheels via the moving belt; whereas in the JG road cart, the pushing force of the wind on the wheels drops to zero when cart velocity equals wind velocity. Thus the cart will slow down, not speed up.

    Conversely, if the prop is in fact acting as a turbine which is being used to power the wheels, then you have something closer to the iceboat model. But unlike an iceboat airfoil, which is configured to magnify the downwind component, the airfoils of an airscrew turbine are designed to generate a rotational force from the air flowing past its blades. This rotational force can be harnessed to power the wheels, but once the whole system is moving at downwind velocity, there’s no longer any external airflow being applied to power the turbine’s blades. Again, the system will slow down, not speed up.

    Also consider this: the evidence for JG’s DWFTTW road cart appears to consist of one (1) YouTube video with — please correct me if I’m wrong — not so much as a followup comment, never mind a followup demonstration. (Although heaven knows it would be easy enough to fake something out if anyone were so inclined.)

    So, yes, iceboats work as advertised, and so does Spork’s experimentally verifiable and repeatable treadmill minicart. The essential point is that at equilibrium, both of these systems still have access to a continuous source of energy. But JG’s DWFTTW road cart? Not so much — unless you count the off-screen bicycle that’s pulling it down the road.

    (And doing a Mythbusters on the treadmill system won’t prove anything about the viability of JG’s DWFTTW cart because the two systems aren’t equivalent. If Mythbusters are going to get involved — and hey, why not! — then they should approach the question directly and test JG’s DWFTTW cart.)

  431. FoetusNail says:

    We all agree the only energy propelling this thing over the ground is wind energy, once we remove the cart from its motor. However, some of believe we are going to magically create enough energy at the ground/air interface to turn a prop, which would then create enough added thrust to propel this cart ahead of the wind energy used to propel the cart. And this is all going to be done without anymore sail area than a couple of plastic straws. You really don’t understand this do you? Do you understand the ratio of sail area to weight necessary to get a boat to overcome its drag and perform this trick? The Laser dinghy mentioned above needs 75 square feet of sail and a stiff breeze to propel its 130 lb hull and its 150 lb skipper. And let me tell you this, when you are riding one of these things in these conditions you hiking out as far as you can to control the heel of that boat.

    They offer no data on weight and drag of the vehicle or the thrust and drag of its propeller.

  432. Anonymous says:

    Haven’t read all the comments (too many!), but spent a few minutes thinking on this. It’s a cute problem.

    First, my creds, just to convince you to read on: undergrad & grad physics, a modest but not stellar research publication record, and a current research career not really in physics. That’s not worth much, though, I’ve been wrong before, and surprisingly often.

    Second: it’s very easy to get confused, even for experts, by seemingly reasonable arguments that are in fact wrong. Eg, the energy conservation arguments don’t apply (at least in any trivial, perpetual motion machine sense) to an open system. Some problems are called counterintuitive for a reason. Just because what I write below seems reasonable to me doesn’t mean that it is correct.

    So: we have an energy source available, in the relative motion of the wind and ground. Let’s look at a few simple cases. Case 1) we take advantage of the energy by fixing a windmill to the ground, extracting energy, and storing it in a battery. No laws of physics are violated, this matches our intuition and experience, and a nonnegligible fraction of the grid power comes from this mechanism. We can call this wind power. Case 2) we take advantage of the energy by fixing a machine to the wind, as best as possible, with a large sail/balloon, and extract a small amount of energy by putting a roller connected to a generator on the ground going by. We can call this ground powered, but it’s really analogous to the previous case. There may be some slight slippage, just as the Case 1) windmill may slip if poorly anchored to the ground, but it’s not essential. If you like, imagine the wind as a hard medium with a relative velocity to the hard medium of the ground. (If you don’t like, your proof of impossibility will need to rely on the wind’s fluid nature. See below.) No laws are violated, and extracting a tiny bit of power by sticking a roller out of the balloon seems unusual, but not impossible. Case 3) Put the windmill from Case 1) on wheels, and attach the wheels to the generator. It’s clear we can roll the windmill around slowly in arbitrary directions. If we go downwind, we’ll lose some amount of power since the apparent wind speed drops, but if we’re going slow, not much, and wind drag will help push us along. If we go upwind, we have to work harder. In no case is energy conservation violated. Force balance is not violated either, the wheels on the ground provide all the counterforce to the wind that is required. Case 4) is to Case 2) just like case 3) is to case 1): we’ve attached our roller generator to a fan to push our balloon around, relative to the wind. We won’t go fast, but we can move in an arbitrary direction. If we go against the direction of the ground motion, we’ll look like we’re going faster than the apparent wind speed to an observer on the ground. Counterintuitive, but no laws of physics are violated.

    The basic idea is to think of the ground and air as symmetric. If the ceiling was moving at a constant rate, and the floor was fixed, you wouldn’t find much trouble in building cars that used that power to move in any desired direction. I think I have a use for my son’s lego tonight :-)

    Now, consider the fluid case. This is more complicated, because fluids and solids seem different, and breaks the symmetry. The central question, I think, is that our prop needs to provide enough thrust to not just counteract its drag, but also the drag of its roller power source. Force on the roller gets transmitted through the mechanism to force on the airfoil. Every newton of force driving the airfoil costs more than a newton of drag on the vehicle from the roller, and has to be overcome by more than a newton of lift from the airfoil. I think the right way to pose this question is therefore whether it’s possible to build an airfoil with a lift-to-drag coefficient larger than 1, or whether that’s a physical impossibility. The book answer is that L/D can be surprisingly large, >100 for a glider wing. The experimental answer is to try it out. From the YouTube videos, it looks like someone has, and it works.

    Bottom line: This does not appear to violate any laws of physics to me, and appears to be aerodynamically reasonable. I suspect the problem is well known, if you look in the right place (Flying Circus of Physics, maybe): if not, it’d be worth a note in an educational journal like Am J Phys. And oh yeah: don’t bet money you can’t afford to lose.

  433. HUDMAN says:

    “”You really have no idea what mechanical advantage is do you.””

    LOL – You have no idea what happens when an airplane flies in a tailwind!

    Let me ask you, when a plane flies in a tailwind, is the tailwind pushing on the frame of the plane or on the thrust from the propeller?

    Before you answer, I must let you know… Of the choices I gave, neither are the correct answer. The tailwind pushes on NOTHING. The plane is flying in the “medium” of the tailwind. Now, any thrust provided in this “medium” allows the plane to exceed the speed of the medium it is in. Kinda like the prop cart…

    If you can’t figure that out, don’t get all upset and try to piss people off. Just think it through, and when you have questions, just ask.

  434. HUDMAN says:

    I will make an attempt to explain this.

    The cart is immersed in a medium of wind. (The tailwind) The prop is producing thrust in this medium much the same way a plane produces thrust and flies in a tailwind. For a plane, ground speed = plane speed (air speed) + tailwind speed. But with the cart, there are losses due to friction & drag, because as it moves forward, the wheels are geared to turn the prop. So with the cart, the ground speed = cart speed + tailwind speed – drag.

    The secret is in making a cart that is efficient enough that the thrust is greater than the drag. In the treadmill tests in spork & JB’s (ThinAirDesigns) video, the cart obviously accomplishes that.

    There’s no perpetual motion here, as the wind is the power source. Remove the wind, and the cart stops moving. Add the wind, which pushes the cart, turning the wheels, which turn the prop, generating thrust, and the cart will catch, then surpass the speed of the wind in a direct downwind configuration.

    For those that don’t understand the treadmill test, think about it. Zero wind, with a moving ground that turns the wheels, generating thrust. If the cart goes backwards, then it is slower than the wind. Doesn’t go forward or backwards, and it is matching the wind’s speed. If it is going forward, (as it does) then it is outrunning the wind and now has a relative headwind, albeit a small one. Given a long treadmill, and if the cart is efficient enough, it should reach a speed of about 1.5 times the wind’s speed. If one can find a perfectly consistant, constant and straight wind outdoors, with a long, smooth, flat surface, the same results will be achieved.

  435. deejayqueue says:

    Ok, there are about 7,000 comments here and I read about the first hundred or so. If this has already been covered I apologize but I have a short attention span this late in the afternoon ;)

    The challenge is to build a machine powered by wind blowing from behind it that can go faster than the wind, correct?

    If yes, then the treadmill vids are not a valid way of testing how this machine works. It’s like saying I can ride a bike that’s got a propeller geared to the back of it and the propeller will give me an extra boost of speed. In this case, “me” is replaced by the motor of the treadmill.

    So, the propeller is working in reverse, using energy from the wind to generate mechanical force to move the wheels, correct? In that case, as soon as the vehicle reaches the speed of the air that’s pushing it, it will stop accelerating. If the vehicle were to move faster than the air that is driving the propeller, it would begin pushing air backwards against the wind. Since no other force is acting on the vehicle to keep its momentum or acceleration, once air started pushing back against the only source of power, the tailwind, the vehicle would stop accelerating.

    Now, the other part of this is the question of whether the propeller can be geared to the wheels such that a smaller windspeed can generate more wheelspeed, which could make the vehicle travel faster than the air driving it. I believe you most certainly can gear a propeller to a wheel such that it will move faster than the air which drives the propeller. When it’s not on the ground. As soon as you put it down, I don’t believe there’d be enough energy in the wind to get the vehicle started, unless there were some sort of conical transmission system which would adjust the gearing of the wheels as groundspeed increased to take advantage of momentum, but nothing like that is mentioned here.

  436. Anonymous says:

    Greg, your tumbleweed isn’t going to work. The principle is fine, but you neglect to take into account that when the metal trough pieces are passing over the top, they’ll be creating a disproportionate amount of drag due to how fast they’ll be moving at that point. By making them asymmetrical, you’ve attempted to reduce this effect, but it’s not going to be enough. In the real world, they’ll have to be feathered, which requires moving parts, and is actually pretty hairy with this design. It’s great for explaining the principle, but much less practical than using a propeller.

    spork and JB do completely understand how their cart works, and they never claimed to have invented it. Bauer had a big one working years ago, and Goodman more recently did the outdoor test that many people request. Posting a video (particularly an outdoor one) will never really satisfy people, because there will always be claims of strings, non-level roads, gusts, etc. The indoor treadmill demo is the most controlled way to do it.

    The reason why the carts you’ve seen demonstrated all look similar is the same reason why all airplanes look similar. There are features of this design that work particularly well, and you might as well use the best design. Why does everybody use propellers? The same reason why all non-jet airplanes use propellers, and why all modern powerboats use propellers — paddle wheel boats are a thing of the past, because props work better once you figure out how to use them.

    What a real scientist does is to publish how he achieved his results so that others can attempt to replicate them, and spork and JB have done precisely that. There are now other youtube videos showing other people running DDWFTTW carts, and they have made public the complete parts list and plans for their cart.

    There’s no magic here. It is interesting to see what kinds of explanations help people understand the physics. No matter what speed you’re moving at, if there’s wind, you can tap off of either the ground, or the air, or both, to get energy, and there’s a tremendous amount of energy available, far more than adequate to make some puny device move in an arbitrary direction.

    jjcote

  437. Matthew Mastracci says:

    It’s been a long time since my engineering degree, but I’ll admit it looks feasible. It’s not perpetual motion – it seems to sap energy from the relative motion of air and ground (slowing down the wind in the reality case, slowing down the treadmill in the controlled test). The biggest problem it has is that it’s totally unintuitive. :)

    In theory, this thing should propel itself downstream faster than the flow of water too. I look forward to further investigations of this device, in any case.

  438. RedShirt77 says:

    What does make any sense to me is how this vehicle can work both ways. Outside, the wind pushed the blades which push the wheels faster then the wind. So lets say that’s true and pwehaps there is some sort or presure differential and moves the cart forward in the same way that a swimmer can move faster then the water it pushes around it. But then how the heck does it work in reverse on the treadmill? If the treadmill is pushing the wheels which turn the blades that works to push the cart like a fan, then there shouldn’t be any wind or pressure differences that push the cart in the way a larger system. It can’t create energy going both ways or the forces would counter act each other in both circumstances. (i do think the pushing with the spork is part of the problem on the treadmill, it ads speet to the blades and increases the push).

    Wind tunnel, track. Only real test.

    I just hope the mythbusters turn it up to hurricane speed at the end of the show. I would love to see this think perform at 200+mph.

  439. Oliver says:

    Just some simple question…

    If the car would go faster that the wind and thus the relative windspeed would go to “minus carspeed-windspeed” shouldnt the propeller start running in the other direction, thus turning the wheels in reverse?!

    To the treadmill: The energy put into the setup is.. electricity. The treadmill is set up to run at some predefined speed. So for a first view we’ll leave friction, inertia and such aside. The car would stand still relative to the outside of the treadmill and the weels would go at the same speed then the tredmill, this speed is transfered to the prop and this provides additional thrust, so the thing is moving.

    Unfortunatly there IS friction, inertia and such, you CAN’T simply CAN’T erase it, simply moving the beltdrive, gear, whatever takes energy. So the treadmill will slow down marginally by loosing energy to the cart. But hey, it will simply draw more energy from the outlet and increase it’s force. TADDDAAAA… running…

    But not with ‘myhstix’ but with an input of additional energy!

  440. GregLondon says:

    Hm, so say you have a 10 to 1 gear ratio. then you put the gizmo on a treadmill moving at 10 mph. The wheels instantly spin at 10 mph. Which makes the prop spin at 1 mph.

    The machine is sitting in perfercly calm air. So the prop pulls the machine forward.

    Because the air isn’t moving around the treadmill, and because you hold the machine in place until the wheels spin up, you get the prop to pull the machine forward.

    so, teh machine moves forward until it hits your spork. You hold it in place. the treadmill is spinning at 10 mph. THe wheels turn at 10 mph. The propeller is spinning at 1 mph. That keeps pulling it forward.

    I think as soon as you take it off the treadmill, and subject it to a 10 mph wind over the prop, rather than a 10 mph ground speed under the wheels, you’ll find that you can’t move faster than the wind.

    This would have to be an indoor, controlled environment, no gusting winds, nothing outside, a 4 mph gust would make you suddenly go 4 mph faster, and low friction wheels/axles on a flat smooth surface would mean you’d maintain that speed for a long time.

    Here’s a test for you. Take the prop off your gizmo. Get it moving at whatever speed your treadmill is set at (3 mph is regular walking speed, 18 mph is a good run), push your widget that fast on the ground, then let go and see how far it coasts. That’s how long the energy from a gust could take to bleed out. Which means your average ground speed might be above your average windspeed, but only because the gusts spike in and speed you up, then the windspeed drops back to normal.

    Put it in a wind tunnel with very exact controlled wind speed, and I think you’ll see you can’t exceed the wind.

    I don’t think the treadmill is a valid experiment. you get the wheels turning at ground speed, which spins the prop and creates a forward force, which pushes it forward because the air around the treadmill isn’t moving.

    If the ground is stationary and you have to move the wind, I think you’ll see the wheels don’t move as fast as the wind.

    I’d be willing to wager $50 to the charity of your choice on that. Not the treadmill. stationary ground with a controlled wind blowing over the prop.

  441. Anonymous says:

    Hello Tom,

    as said, it was an oversimplified model.

    As for the prop in “still” air, keep in mind that the prop rotates, and that it’s blades have an angle which moves through the air. So it really is equivalent of a sailboat tacking through the wind to achieve a speed greater than the windspeed.

    While my model is simplified, the more correct one would be to look at the thrust the prop generates. So, the speed of the cart would be the velocity of the wind plus the velocity that the prop generates. Also, it not only generates thrust, on the other side of the prop it tries to produce a vacuum, trying to “suck” the cart into forward direction.

    As the builders said, it is quite unintuitive, but nothing impossible.

    Keep in mind that when the cart is at windspeed, the prop still rotates and thus, at the prop’s blade tip’s you still have air moving, while relative to the cart you have not. Otherwise we would have a hard time using regular fans in rooms without wind ;)

    Greetings,

    Chris

  442. LaserRage says:

    JB:

    So what you’re saying is that the body of the vehicle acts as a sail and the motion over the ground drives the propeller?

    I might be able to go for that. And once you’re over wind speed, though, the prop would just be coasting on the momentum, thus eventually dropping back to wind speed and not breaking any physical laws. Right?

  443. GregLondon says:

    spork: I’m amazed at the folks here that admit they don’t understand how this thing works, but somehow they’re sure we don’t either.

    I seriously starting to doubt that youre an aeronautical engineer. By all means, correct me if I’m wrong. The reason I say that is because when I studied engineering at the university, almost every class I was in was covering some topic I didn’t understand at first. And yet, it became crystal clear which instructors were bluffing their way through the material and which instructors really knew their stuff.

    If you have a masters in aeronautical engineering, I’d assume you’d recognize this experience, but maybe every instructor you had really knew their stuff?

    Anyway, I don’t know how this thing does what you claim it does. You claim it can go 11 mph ground speed with a 10 mph tailwind. I don’t know how it does that. Thing is, it seems to me that you don’t know how it does it either.

    Now, that doesn’t mean you haven’t been a rigorous observer in whatever experiments you’ve been doing. Maybe you’ve been able to get 11 mph ground speed in a 10 mph wind. I don’t know. I’m not the only one who has doubts (I know, I know. Bet me. Whatever.) But the more you and your cohorts try to explain this, the more I get the feeling that I’m in a physics lecture, the professor is on vacation, and the teachers assistant is filling in.

    It seems fairly clear that you guys don’t know how this thing works. Or if you do, you can’t explain it very well. I’ll assume enough good faith that you guys aren’t deliberately commiting a hoax here, but that doesn’t mean whatever you think is going on is what’s really going on.

    But shouting “bet me” to every question isn’t telling me anything other than that you’re more interested in being right than in explaining it, or that you can’t explain it. One or the other.

  444. farkinga says:

    Although I heard the plans for building this thing were “all over the Internet” I couldn’t find them…

    So, I grabbed Spork’s parts list and combined it with pictures of the completed product here:

    http://www.rtfa.net/2008/12/02/downwind-faster-than-the-wind-dwfttw-parts-list

    I can’t afford to make this right now, but I want to make it easier for someone else to get the job done. Please keep me updated!

  445. HUDMAN says:

    “”Airshowfan, you are making a mistake when you fail to see the video of the cart on a powered treadmill as anything other than a cart with a motor.””

    So, let’s all pitch in, waste thousands of dollars, build a giant wind tunnel, PROVE again that it outruns the wind, so then you can run along and say, “This is crap! The electric fan is powering the damn thing! This proves nothing!”

  446. Ahoj says:

    @68, after much much thought, your right I’m wrong, the treadmill does prove it works. I jumped too fast on my badger comment.

    and @71, I shouldn’t ask for the money back, because I had the answer and didn’t know it, and didn’t know all it meant when I said it. I wasn’t asking for funding, I wasn’t saying it was final. I just like the idea of slapping someone with a wet badger. is that so wrong?

    you shouldn’t be so hubris to jump on the first part of what I said when the second part was dead on. you got to be willing to be wrong to be certain you are right in the end.

  447. airshowfan says:

    Oh my god. This is so frustrating. (It’s like that XKCD where the guy won’t go to bed while “here are people being wrong on the internet”…)

    #73: No. The prop is a propeller, not a turbine. It is powered by the wheels, it does not power them.

    #74 (of all people ;]), be careful. When you say “The wind pushes the prop” that sounds like “The wind spins the prop” which makes it sound like a turbine. I think “The prop pushes the wind” is much clearer (although, yes, it’s the same thing).

    #77: The only difference between a treadmill test and a wind-tunnel test is which inertial frame of reference you’re on, i.e. no difference at all.

    #80: That’s what I said (#66).

    #81, read my #60. It might be more useful to think of it as “treadmill-powered” than “wind-powered” from the point of view of the wind (i.e. when you watch it from a balloon or when you do the treadmill experiment). It’s only useful to think of it as “wind-powered” from the point of view of the “road” (wind-tunnel test, outdoors test).

    #82: The treadmill experiment IS valid BECAUSE you’re injecting energy into the wheels. If DWFTTW works at all, then that’s how it works.

    #87: On the treadmill the vehicle IS moving faster than the wind, since you can see it move forward through still air. And when you describe an outdoors experiment, remember that we are not debating whether/how the vehicle accelerates to wind speed, just whether/how the vehicle stays AT wind speed or accelerates beyond that.

    #89: They do at the end of the video, although I will admit it’s hard to see whether the thing really is going faster than the wind (it might not be). So the answer to your question is: The performance of the device might be so marginal that in order to work it might require a wind that is more steady than any wind actually found outside in nature (at least in the vicinity of the experimenters’ homes).

    #92: I don’t think anyone is claiming that this is USEFUL ;)

    #94: It is not true that “the only force in the system is that supplied by the wind”; there is also thrust from the prop.

    #95; No. It’s a propeller, not a turbine.

    #97: The treadmill moves at EXACTLY wind speed, by definition. I.e. in a treadmill test, the wind speed is the relative speed between the (still) air and the (moving) treadmill. If the cart moves forward at all, it is seeing a headwind, and thus is going DWFTTW. Inertial reference frames, inertial reference frames.

    #105: The cart DOES move forward, relative to the air! So it is going DWFTTW!

    #107: A peer-reviewed publication would realize that a treadmill test is just as valid “proof” (well, “evidence” might be the better word) as a wind-tunnel test.

    #111: Remember that the propeller is a propeller, not a turbine or a sail. The wheels are what make the prop spin, not the wind. As for the validity of the treadmill: Say someone does an outdoors DWFTTW experiment (cart going down the street, wind blowing) and you watch from a balloon. How is that ANY different from watching the treadmill experiment?

    #112: See #60. From the point of view of the air or from a balloon or when watching the treadmill experiment, the vehicle can be better described as treadmill-powered. Or, rather, the prop is powered by the treadmill (via the wheels) and that’s what pushes the cart forwards.

    #117: The question of whether this device can GET UP TO wind speed it not the point (besides, anything with a big sail can get up to wind speed, pretty much). It’s what the vehicle does FROM THERE that’s interesting. And please keep in mind that the vehicle might be so marginal that it requires a steadier wind than what you’d experience out on the street.

    #119: A moving treadmill is equivalent to a wind tunnel, the only difference is your reference frame… (And as #129 points out, the thing is supposed to move relative to the ground faster than it moves relative to the wind, so a treadmill is much more practical than a really long wind tunnel).

    #120: It’s not perpetual motion. It takes energy from the difference in velocity between the air and the ground. After the vehicle passes, the air is moving at a speed closer to that of the ground.

    #103: I might start accepting Paypal donations soon ;)

  448. davidglover says:

    #171 Greg, what understood law of physics is being violated? The problem is, in this case, you don’t understand the physics involved.

  449. toilet says:

    This is my new favorite topic. I love how spork and thinair have the zeal for coming to every site and enduring the same slew of comments and attitude. Lol at “go build a reverse wind tunnel otherwise you’re wasting my time… while surfing.” Keep up the good fight guys!

  450. Nelson.C says:

    ThinAirDesigns @244: Like it or not the onus is on you to provide a proof to anyone who asks it, same as any other scientist or engineer, regardless of whether the claims are extraordinary or not. Darwin wrote a couple of books about his extraordinary claims; why do you find it so hard to copy and paste previous explanations, or provide links to them, and so easy to provide obfuscating, detail-less answers?

  451. tkaraszewski says:

    Here’s my opinion, which at this stage in the conversation, seems that it should echo many previous opinions, yet I haven’t seen it expressed yet (there will be 50 more replies by the time I finish writing this, I’m sure).

    The fact that the vehicle can get up to wind speed is not being debated. Everyone agrees that a sufficiently-efficient vehicle can travel at (or very nearly at wind speed), powered solely by the wind, heading directly downwind.

    Once the vehicle reaches wind speed, the wind behind the vehicle is no longer accelerating the vehicle. If it wasn’t for the wheels being attached to the propeller, the vehicle would stop accelerating at this point, and continue coasting along at the speed of the wind.

    However, the wheels *are* attached to the propeller, and being that the ground is still moving under the car at the speed of the wind, this means that energy is being put into the system such that you could potentially go faster than the wind.

    At the point in time where the vehicles speed equals the wind speed, there is zero relative wind over the vehicle, yet there *is* energy being input to the system by the wheels. If the wind is 10mph, the vehicle is moving across the ground at 10mph, and so the wheels are spinning the propeller at some speed, determined by the gearing with the wheels.

    Assume a more complicated vehicle, such that it has a sail as well as the propeller, and a clutch that engages and disengages the propeller to the drive wheels.

    Assume the vehicle is set in motion using the sail to accelerate it up to wind speed the same way a sailboat works.
    when the car hits windspeed, the relative wind is zero, and the propeller is engaged. now, with the propeller turning it produces some force pushing the vehicle forward.

    At this point, relative to the vehicle, you have zero wind, and the ground moving 10mph in the negative direction. this motion of the ground past your car is used to produce thrust via the propeller. This accelerates the car up to 11mph, at which point the propeller has accelerated as well, due to the increased speed of the road past the wheels, however, now the speed of the relative wind is 1mph, coming from the front, which brings with it an amount of drag.

    The car will continue to accelerate until the friction due to the now positive relative wind combined with the friction from the wheels exceeds the amount of thrust generated by the propeller.

    I don’t see why it *wouldn’t* be possible in theory. There are a few things that are definitely questionable:

    The friction on the wheels seems like it would be quite high. They’re not simply free-turning wheels, they’re geared to the propeller and as such, as the propeller speed increases, the amount of drag they create increases, due to the propeller having to move more air around it.

    Getting the car up to speed with the single, fixed-gear propeller, as seen in the videos, seems impossible. As the vehicle accelerates up through windspeed, and the relative wind shifts from the rear of the vehicle to the front, the propeller would have to change directions. This may not be a factor in the model with it being so light, that even with the counter-rotation of the propeller as caused by the wheels, the back of the propeller has enough surface area to act like a sail to get the car up to speed.

    When I started writing this post, I was thinking of offering $1,000 towards the 10:1 bet to see it proved that it actually works, but now that I’ve been thinking about it, I’m not so sure. It seems that in the right conditions, especially with such light cars like these models, where an ambient wind of 5mph provides a huge amount of energy considering their mass of a few ounces (as compared to a 1000lb sailboat in the same wind), it may be possible.

    Given a realistic “vehicle” say a 100lb tricycle-like contraption, with orders of magnitude more friction with the ground and the air from the front of the vehicle, you may need to have the wheels spinning at 50mph before the propeller is moving fast enough to generate enough force to overcome it’s inertia and friction with the ground and get the vehicle moving. With a tiny vehicle, you need a much lower amount of power to get the vehicle over that hump in the first place, and a 5mph treadmill or a moderately windy day is more feasible to get the thing moving.

    Note that the reason it doesn’t work with no wind (such as one commenter mentioned inside a gymnasium or other large space) is because, at an relative wind of 0 (when the vehicle is moving at wind speed) the wheels have to be spinning the propeller fast enough to overcome the friction that they are generating. At a speed of zero, the propeller wont be spinning.

    I don’t know, It doesn’t sound impossible, maybe impractical for a 300lb vehicle with an actual person riding in it in wind speeds under hurricane force (at which point you probably don’t want to be going faster than the wind, anyway), but I’m not convinced that the model wouldn’t work on a small scale.

  452. gpomputius says:

    #202: I don’t understand how your comment counters the proof. If anything it supports it.

    “..is this equivalent to the craft moving at 1mph, and the wind moving at 0 mph?”

    “And the ground moving backwards at 10mph. (treadmill)

    QED Fail.”

    So you modify my equivalent model by noting that the ground moves backwards (upwind) at 10 mph and this makes the proof fail how? Friction does not speed things up, it slows them down. Think physics vectors from back in high school, forces applied in a direction opposite its forward velocity i.e. from friction. If anything, a craft moving constantly at 1 mph, with 0 mph wind and the ground moving backwards at 10 mph requires an even greater violation of thermodynamics than one where the ground moved backwards at 0 or 1 mph (relative to the craft).

    QED success (for now).

    Also: what is the magical property of this propeller that it generates forward motion by having wind blown at it / running into wind moving slower than the craft.

    Here’s a link that should help you understand propellers http://www.grc.nasa.gov/WWW/K-12/airplane/propth.html

  453. dustbuster7000 says:

    OK, so now I see the cause of the problem. The ‘spinny thing’ is causing people confusion, since they are used to thinking of a propeller as a source of thrust. And Airshowfan is right, is cannot be both turbine (collector of energy from the air) and propeller (outputer of energy to the air. In this design, the ‘spinny thing’ can only be a turbine. If, as has been said many time in this thread, the source of power is the wind (and that’s the only source of power), then the ‘spinny thing’ is only ever a turbine, collecting wind energy and turning it into mechanical work. If at any point the ‘spinny thing’ started providing energy to the air, i.e. being propeller, then that energy can only come from the wheels, since thats the only thing it connected to. Taking energy from the wheels must slow the cart down, i.e. force of thrust from the spinny thing acting as a propeller will at best equal the force lost to the wheels.

    So neglecting the apparently trivial and unimportant initial stages of acceleration, we assume that the device is moving at the same speed as the air, now there is no apparently wind over the blades of the ‘spinny thing’.

    (BTW if you think I’mm being pedantic about calling it a ‘spinny thing’, I not, the main source of confusion seems to be what this thing does, so a neutral name avoids any preconceived ideas about the purpose of the ‘spinny thing’).

    So, no apparent wind, just a cart rolling at some speed, equal to the wind speed. Now what? The cart can’t accelerate, since the source of its power, the ‘spinny thing’, can’t derive any energy from the no existant wind. The spinny thing is spinning, since it connected to the wheels and they are turning, but it isn’t providing thrust at this point, since we already stated that it can’t do that, its working to collect energy from the air, any energy imparted by the blades is robbed form the wheels, and in our friction free thought experiment, nothing is lost. But nothing is gained either. So no faster than wind stuff happens in this scenario.

    If you want to start talking about all that troublesome initial acceleration stuff now, I’m all ears

  454. PharSyght says:

    OK watched it again and it is a hoax. Even if what you are all discussing is somehow possible, these guys didn’t achieve or even really try to. They are faking the whole thing.

    Pay attention to the video…

    When they take it off the treadmill to show that it still runs for 7 seconds, it slows down. I thought the wind was powering it. ??? It should keep spinning regardless of the treadmill. From what I can tell, on the treadmill it is spinning because of the treadmill. That makes the propeller spin, in this case it is a propeller, if you watch it closely when it slows down and look at the angle of the blades, they are spinning to add to the forward motion, not like it is being powered from wind behind as they insinuate (a windmill type turbine). Even if it was a legit experiment with a fan, why don’t they show the fan, and who says the treadmill is set to exactly the same speed as the “wind” which they show us nothing about. It would be darn hard to measure windspeed in a closed room and set a treadmill to exactly that speed.
    They only need enough power from the gear box to overcome the friction of the wheels by a little and they get forward motion on the treadmill. If it were frictionless, it would stay in one place on the level treadmill, even without the propeller and gears.

    In the outdoor version they show, the propeller again is spinning the wrong way. It acts as a large fly wheel, so when he pushes it, it starts spinning and that helps keep it going, almost like a little windup toy which you pull back 6” but it goes for 15’. It could be a big disk or round bars instead of blades. There is no new science and no myth to disprove. Mythbusters shouldn’t waste our time with this BS.

  455. airshowfan says:

    #166: Where do we get the energy from? From the fact that the air is not at rest relative to the ground. The air is “going by” the cart at a slow speed (which – if this helps you think about it – helps the propeller get “a better grip” on it), while the ground is going by at a faster speed. The cart’s wheel-prop setup is like a gear that “connects” the air to the ground, and takes energy from the difference in velocity between the air and the ground. So after the vehicle goes by, the air at that spot is moving at a speed that is closer to that of the ground, and the vehicle moves forward to grab the next bit of air and push that towards the back (as the ground passes, towards the back, even faster) as it pushes itself forwards.

  456. codesuidae says:

    ThinAirDesigns @365

    I’m sorry Code, but that was NOT the question to be answered. Following is the question taken verbatim from that post #351

    Well, that was the question that was asked, but as a software developer I’ve learned clients do not always (or even usually) ask the question that they are really interested in. A pedant who enjoys letting others founder in their inadequacies may answer exactly and only the question asked (and in addition to being entertaining it can help to train the questioner to ask better questions), but to provide maximally useful answers one ought (IMO) attempt to understand why they question is being asked in order to provide an answer that both answers the specific question and also goes beyond to address the source of the question.

    Of course, whether one intends to produce a useful answer can determine how one approaches the question. It is often very useful to answer the ‘letter of the question’ rather than the ‘spirit of the question’.

    In this case the context of the question is provided and while the query has to do with determining if there is a treadmill, it seems to me that the real question is whether the town is moving, or perhaps whether a treadmill is moving the town (though it seems to me that that is two distinct lines of inquiry; is it moving, and what moves it). Since the question has to do with the origin of the wind, the mere existence of a treadmill is not of primary concern when answering the central question.

    Regarding the barometer; I love that story! My high school physics teacher would have appreciated it; I went to great pains to always avoid answering her questions the way she intended them.

    But yes, we are in agreement regarding the validity of treadmill testing, though I think of it as an engineering model and test rig; to me the most pleasing proof would be a vehicle that demonstrates the principle while carrying a person.

  457. GregLondon says:

    me: “The wind turns the propeller, and the propeller is geared to the wheels”

    spork: Nope, the wind “pushes” the prop forward. The wheels apply the torque that turns the prop.

    Dude. You just created energy out of nothing with that explanation. The only energy you’ve got is the wind. That’s it. Everything else is a closed system. The wind is like a bunsen burner, it cna add energy. The prop and wheel mobile is like a sealed flask with water/vapor etc in it. the flask completely conserves energy.

    The only thing that can make anything move is teh wind. The wind goes over the prop. The prop turns, the shaft is geared to the wheels, which turns the wheels.

    If the wheels turn the prop, where did the energy come from to make the wheels turn??? It had to have been the prop. If not, you just created energy from nothing. The only thing that can add energy to the system is the wind, and the only thing the wind can affect is the prop. The only way the wheels can get energy is if the prop turns.

    The wheels can’t get more energy than the wind is moving except if there is a gust, or if you push the vehicle faster than the wind (or put it on a treadmill when the wind is stationary).

    This is why the treadmill experiment is invalid. You’re injecting energy via the wheels. And that doesn’t work. The only way you can get energy into the system is from the wind into the prop. And if you have a perfectly consistent wind, then the wheels will never go faster than the wind.

    If you inject energy into the wheels via a treadmill, then yeah, the wheels turn the prop, and all sorts of weird things happen, but none of it is like what happens when the energy is injected via the prop.

    “But I think if you did this in a controlled windtunnel, you’d never get above the windspeed”

    And that’s precisely why I offer the standing bet.

    I said I’ll wager $50 to the charity of your choice. But the vehicle has to be on stationary groudn with a fixed wind blowing over it. No tread mills.

  458. FoetusNail says:

    HUDman, that is a boat powered by a windmill which powers a propeller, not a sail powered boat. Kinda fun, but the opposite of what these guys are claiming.

  459. spork says:

    “Although I heard the plans for building this thing were “all over the Internet” I couldn’t find them… ”

    I guess the internet is bigger than I realized. Here are the high points…. As you said, buy the listed parts and assemble them in the way you see in the photos (thanks for posting).

    The important thing is to get absolutely minimal friction and the correct advance ratio. This means you should definitely start with exactly the prop, gears, and wheels specified. There is a big gear and a little gear. The little gear goes on the axle and the big gear goes on the prop shaft. I sand the shoulder off the back of each gear to give a very loose gear mesh.

    Make sure the prop spins clockwise from behind when the cart is pushed forward.

    We’ve used rubber bands on our wheels for better traction – when needed.

    It works fine on our treadmill without.

    To get it to steer straight can be sort of fidgety. Bend the aluminum tube very slightly to turn the rear wheel until it doesn’t veer off either side of the treadmill.

    Initially you should run your treadmill at full speed (10 mph in our case) and make sure the bed is dead level (I have to put a phone book under the rear end of our bed to get it level.

    Once you have it working well (steering straight and all friction minimized) you should find it will climb a fairly steep incline (it will climb the steepest setting on my treadmill easily).

    If you’re pretty sure this can’t work, be sitting down when you put it on the treadmill.

  460. FoetusNail says:

    No you just aren’t remembering the only reason that plane is exceeding that tailwind is because of a 100 hp engine, does this cart have an engine once removed from the treadmill?

  461. HarveyBoing says:

    The forces acting on the cart are:
    1) Gravity
    2) A reaction to gravity perpendicular to the treadmill
    3) The contact points of the wheels are stationary with respect to the treadmill, so the the friction acts on the cart at the bearing, i.e. where the axle meets the wheel. The direction will point somewhere between “down the treadmill” and “behind the cart (parallel to the ground)”.
    4) A reaction to the momentum that’s being given the the air that’s being pumped backwards by the propellor.

    The counter-intuitive thing is that (3) can be made pretty small – I don’t think that there’s a theoretical minimum to how small friction in a bearing can be made.

    The thing is, you’ve left out a force. In the above, you’ve basically got the classic “four forces of flight”: gravity (1), lift (2), drag (3), and thrust (4).

    But, you left out a major component of drag. That is, the energy to use the propeller to move the air has to come from somewhere. It comes from the wheels, and adds to the drag generated by the wheels.

    So, your #3 item is not solely the friction in the wheels. In fact, the friction is probably a very small part of the total drag. Most of the drag comes from the load of the propeller, and conservation of energy tells us that whatever work is coming out of the propeller cannot exceed the work being put into it (and in practice, cannot even equal it).

    It’s true that gears and levers and whatnot allow you to have unequal force, but the work has to remain the same. Triple the force, you have to cut the distance over which you can apply the force to a third. There’s nothing in this system that allows for that kind of tradeoff (the force coming in is applied over the same distance as the force coming out), so with work being equal, the forces are at best equal too.

    In other words, no matter how much thrust you get from the propeller, you have to get at least as much drag just to power the propeller. TAANSTAAFL.

  462. arkizzle says:

    So, the propeller is working in reverse, using energy from the wind to generate mechanical force to move the wheels, correct?

    Nope. Wind pushes the cart, wheels turn, prop turns, prop gives extra push.

  463. Anonymous says:

    Hello Tom,

    “Ok, did I get it right? That took several hours to figure out.”

    Yes, from what i can see, and given my limited and simple understanding of the cart, you got it right.

    The cart in the Goodman video did indeed get a small push initially, but at the same time it was trying to self-start already. The amount of wind needed depends on the frictions inside the cart-system, so a bigger cart (as Goodman’s is) might need more wind or a push, compared to the smaller cart that Spork and JB built. Their small car can indeed self-start. in a light wind.

    Yea, the analogies. Many ways to somewhat explain it. The important thing is just to keep in mind that there is a surface on the cart that moves slower (or “backward”) relative to the cart moving (or at standstill). This is, i guess, what many people overlook initially, and instead assume the cart to be one static object pushed by the wind.

    Greetings,

    Chris

  464. Anonymous says:

    There is one way to travel downwind faster than the wind, powered only by the wind. Imagine an electric train powered by a stationary wind turbine (bolted to the ground). For example: http://gadgets.boingboing.net/2008/11/07/electric-bullet-trai.html

  465. spork says:

    “The essential point is that at equilibrium, both of these systems still have access to a continuous source of energy. But JG’s DWFTTW road cart? Not so much — unless you count the off-screen bicycle that’s pulling it down the road.”

    Jack’s cart works exactly like ours, and for the same reason. It exploits the energy available at the ground/air interface. In his case it’s a tailwind over a “stationary” road, while we move the road under a stationary wind. While it might not “feel” right, Newton, Galileo, and Einstein tell us through the principle of equivalence of inertial frames that the two situations ARE in fact one and the same.

    Also, keep in mind – Jack didn’t post that vid (a friend of his did). He has nothing to prove to any of us and didn’t ask to be a part of this circus. I’m always amazed at how willing people are to question his integrity, even in a published article, with absolutely no basis at all, and without even contacting him for comment.

  466. ThinAirDesigns says:

    Nelson:
    >Why are ThinAirDesigns and Spork working
    >so hard to make me disbelieve them?

    Perhaps it’s because you exhibit classic troll behaviors. Following is a perfect example:

    In my last few post exchanges with you I have stated:

    Me:
    >I encourage folks to put our claim
    >to the test.

    and

    Me:
    >If you wish to build one and test one,
    >I’ll give you my personal contact
    >information and help you in any way
    >you wish.

    and

    Me:
    >All I’ve ask is that the individual
    >video document a good faith effort to
    >make it work, post the results and
    >return the craft to me.

    The above can’t be confused by any rational being as saying “take my word for it”.

    On the contrary, it’s clearly stated that I encourage people to test our claims, I offer to personally help people build the device to test our claims and have even gone so far as to offer certain critics the access to ready made device so they can test our claims.

    Your classic Troll response to my ‘please, don’t take my word for it — test it” missive? Here it is:

    >Well, science is like that, full of
    >scurrilous rogues who won’t take a
    >gentleman on his word, the scoundrels!

    In what manner to you expect me to interact with you when you make insinuations falsifiable by the thread record? There’s no honesty in that above statement, intellectual or otherwise.

    If you’re truly serious, stop acting the dishonest troll and tell me you would like to build one — Let me know what information you need that hasn’t already been posted on this tread.

    If you still have issues I’ll tell you how you can contact me and I’ll make sure you have any help you wish. (still no plans though — they don’t exist and for at least the time being won’t be produced by me.)

    If you want it done another way, find another DDWFTTW builder who’s willing to do it your way. I won’t mind at all.

    JB

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