Over a year ago on Boing Boing, I linked to this video from a guy who made a propeller-powered vehicle that he claimed could travel downwind faster than the wind. Some people think it was a hoax, and some don't.
In Make Vol. 11, 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.
Now there's a new video on YouTube (above) that claims it is possible to sail directly downwind faster than the wind (aka DDFTTW). You can read heated discussions about the video and its claims at Makezine, the Mythbusters Fan Club discussion board, and Randi.org. The creator of the video, spork33, hopes that the Mythbusters folks will attempt to replicate the experiment.
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.
UPDATE: Charles says: "You might make it clear to readers that the argument is strictly confined to the behavior of vehicles in a direct tail wind. A cross wind can indeed create a force-multiplying effect when it blows against an angled sail."
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.
Clearly these plastic spork wielding scientists have got me convinced! Did you all see how many mississippi's that thing kept going for?!
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.
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.
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?
Aaaannnddd.... it's self steering?
I'm going to make a giant version of this in space so that photons can push me faster than the speed of light!
No! NO! NOOO! The sky can't be blue! It's not blue until you prove it in a double blind study!
Helpful?
http://www.physclips.unsw.edu.au/jw/sailing.html
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.
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.
(for more: http://letmegooglethatforyou.com/?q=can+you+sail+faster+than+the+wind )
I don't think there is anything wrong with sailing faster than the wind if you want to.
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.
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.
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.
Any Smart People who might like to weigh in, per chance? Someone who may have gone to college?
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.
Because nothing engenders trust like the username "spork33".
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.
From the original creator's PDF:
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.
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)
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.
Would this discovery not lend a little more weight to wind power as a way to generate electricity?
"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?
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
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.
>>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.
plane takes off.
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.
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.
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...
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
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
>>
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.
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.
Manners, please.
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.
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."
"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.
http://www.grc.nasa.gov/WWW/K-12/airplane/wrong3.html
http://www.grc.nasa.gov/WWW/K-12/airplane/right2.html
Madness on the water! http://www.youtube.com/watch?v=Nljxi4E4-4Y
49er's are complete small boat madness.
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
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.
BTW, note the heavily reefed mainsail. Those guys are fukin crazy!
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.
>>
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.
@43.
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.
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.
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.
Lay out your terms for the bet. I might be interested in taking it.
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.
Ah, Occam's Bludgeon. If I don't believe it, it must be fake.
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.
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.
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?
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.
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.
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.
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
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.
"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.
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.
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!!!
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.
#60 - okay, "air currents created by eddies".
#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.
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?
#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).
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).
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.
"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.
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.
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.
"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.
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.
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.
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.
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!
@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.
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.
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.
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.
"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.
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.
@#53 joelphillips:
Re 3), I think you're forgetting Rolling Resistance.
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.
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.
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.
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?
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.
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?
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.
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.
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.
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?
"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.
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.
I smell longhorse manure. Does anyone else smell longhorse manure around here?
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.
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.
"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.
Screw your wager! Smoke screen! Prove your claim or go home, this ain't youtube.
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 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.
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.
"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.
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.
the whole thing was addressed back in post 97.
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.
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.
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.
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
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.
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.
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.
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
"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.
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?
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! :)
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.
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.
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.
#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.
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
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
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.
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).
>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
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!).
Bill, are effin' insane?
Try the science on before you put down $10k (eg, build your own for $40, first).
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
God I hope sure Bill follows through. Expensive high school physics lesson though.
JB
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.
I find it beneficial to imagine this experiment taking place submerged inside a giant stream of molasses instead of air.
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.
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
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
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.
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
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.
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 ;)
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!
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
Please remember not to resort to name calling or insults while discussing this. Let's all be civil.
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.
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
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.
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.
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.
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.
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.
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?
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?
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.
#148: It doesn't, the whole thing is a scam...
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?
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.
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
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.
wow Cool video
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.
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
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 :)
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.
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.
#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.
#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.
"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.
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.
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.
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.
"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.
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
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).
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.
I think I saw Wiley Coyote use one of these to chase the Road Runner one time.
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!
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?
#171 Greg, what understood law of physics is being violated? The problem is, in this case, you don't understand the physics involved.
#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.
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?
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
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.
Thanks JB, that cleared it up for me.
#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? ;)
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.
#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.
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
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.
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.
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.
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.
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
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.
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.
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.
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.
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.
I know, I was being inclusive :)
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.
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
"..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.
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?