Wind powered cart traveling directly down wind faster than the wind

Even the video people that built models didn't show the stupid contraption working in the wind like it's supposed to. Instead they had to demonstrate it on a treadmill because . . .

It's a hoax.
You claim to know about sailing- would you accept Sail Magazine as a reference?
http://sailmagazine.com/racing/running_faster_than_the_wind/

Apparently, the guy that did this got funding from Google- they aren't fools (multiple sources, but here's one):
http://www.physorg.com/news194851568.html

What sort of plane do you fly? I'd like a ride when I get a model working.
 
The problem is (at least the way my mind conceptualizes it) that, once the vehicle is moving at wind speed -i.e. airspeed = 0, the prop can't harness any energy from the wind to drive the wheels.

A sailboat can sail into the wind with an angle as little as 30°. This isn't much different to me other than the "sail" is going round and round (thus making it's travel at a suitable angle to the wind) vs just cutting across in one direction. The key is a resistance to lateral movement in the sailboat and resistance to vertical movement in the car.
 
You claim to know about sailing- would you accept Sail Magazine as a reference?
http://sailmagazine.com/racing/running_faster_than_the_wind/

Apparently, the guy that did this got funding from Google- they aren't fools (multiple sources, but here's one):
http://www.physorg.com/news194851568.html

What sort of plane do you fly? I'd like a ride when I get a model working.

At your second link, one of the designers/builders posts this link to a mathematical analysis of its operation:

http://www.mediafire.com/?gnznnd3dwct

His analysis is pretty complex, and I don't know if I'm going to be able and/or have time to figure out whether it's valid or not, but it's interesting that as he describes the design, it sounds like a mechanical (geared) linkage, whereas at the second link in post #22 (which I discussed in post #39), a member of the same design team describes a vehicle with an electromechanical linkage (an electric generator connected to an electric motor). I'm puzzled by the apparent discrepancy.
 
I'm puzzled by the apparent discrepancy.
None of these links work well for me but I just wanted to point out the type of linkage is only an implementation detail - either one would probably work and is only an engineering choice, not something that alters fundamental physics.
 
You claim to know about sailing- would you accept Sail Magazine as a reference?
http://sailmagazine.com/racing/running_faster_than_the_wind/

Apparently, the guy that did this got funding from Google- they aren't fools (multiple sources, but here's one):
http://www.physorg.com/news194851568.html

What sort of plane do you fly? I'd like a ride when I get a model working.


I'm with the first comment in the Sailing magazine article. The one that says it's a hoax.

As for getting funding from Google, there is no evidence of that. All that there is is a Google logo on the car and the guy's statement. Also, note that all of the activity on the purported car happened during a brief period in 2010. It's possible that Google sent a cease and desist letter to the car owners because it's a hoax.

That makes more sense than a bogus free body diagram that magically omits friction once the car starts going faster than the wind.

IMO the video of the actual car shows it going into the wind. My recollection of the video is that there is no wind vane on the car so you can't see its relative wind. The hoaxsters did this to hide critical data. Also the wind vanes on the chase cars are never in the same video frame with the car.

Note that the car designer has numerous patents...in video editing.

Back to the sailing issue. Sailors know that when you are going dead down wind the relative wind goes to zero once the boat speed equals the wind speed. This can happen when you are already at max forward speed, say 0.9x wind, and a wave hits the stern and gives just one brief nudge. The relative wind then becomes dead calm and the sails hang like towels on a clothes line. There is no more relative power to harness between the wind and the surface of the sea (or roadbed for a car). At that point the guy manning the spinnaker sheet needs to trim in so that the sail repowers as quickly as possible when the boat speed bleeds off. This is critical during sailboat racing when every split second of error adds up over a course of several miles, or several hundreds or thousands of miles.

Changing the sail to a propeller with a supposed angle of attack similar to a reach (at an angle to the wind) does not change the fact that the relative wind speed is zero. Again, there is no more energy to harness from the wind.

That's my story and I'm sticking to it. :D
 
Here is a frame from the beginning of the video. It ends up that there is a wind vane (tape) on a pole that projects from the nose of the car.

The wind tape clearly shows that the car is pointing into the wind before it starts moving. The claim that they are pointing downwind is a hoax.
 

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I'm with the first comment in the Sailing magazine article. The one that says it's a hoax.
...snip...
That's my story and I'm sticking to it. :D

After 40 years of sailing real boats in real winds, I gotta agree. :yesnod:

Sailing teaches one to use nothing but pure, natural physics to achieve a goal (getting there from here) and do it without the application of external power. You become very intimate with Sir Newton's legacy.
 
After 40 years of sailing real boats in real winds, I gotta agree. :yesnod:

Sailing teaches one to use nothing but pure, natural physics to achieve a goal (getting there from here) and do it without the application of external power. You become very intimate with Sir Newton's legacy.

Sailing is beautiful.

Another thing that it helps with is appreciating centers of lift. We talk about it with airplanes and we do CG calculations, but that doesn't really drive home how massive those forces are and how carefully they are balanced to define the CG envelope.

To appreciate that it helps to ride out a broaching sailboat and then, after changing underwear, figure how a nice multi-ton yacht turned into a bucking bronco seemingly without notice. Yeeee-haaaaaah! :eek::rofl:
 
This is the one that "blows" my mind ... how can it be? ;)

I suspect that the fan blowing into the sail acts a lot like thrust reversers on a jet but the bottom line is that if you create a higher pressure behind the sail than in front of it, the sail will experience a force (pressure delta times sail area) towards the low pressure. And as long as that force exceeds that generated by the fan in the opposite direction the net force will move the boat forward.
 
Unfortunately, those figures don't really explain anything. In particular, Figure 4 doesn't explain why the red arrow next to the propeller is drawn pointing to the left (thrust) instead of to the right (drag). I also don't understand why the relative wind is still stated as zero knots when the cart is alleged to be traveling faster than the wind.

I'll try the words part again and save it in notepad this time.

In box 1: the cart is stationary. The 10kn wind begins pushing the cart foreward, because there is drag which acts in the direction of the relative wind. This part happens whether there is a propeller strapped to the back or not.

In box 2: the cart begins to move (because the wind pushes the cart). When the wheels start turning, they mechanically drive the pusher prop to create thrust. At this point, the cart is still traveling slower than the wind, so the drag force is still an accelerating force, as well as the thrust created by the prop which is only turning because it is mechanically connected to the wheels.

In box 3: the cart is traveling exactly as fast as the wind. Because the relative wind is 0, there is no drag, but the propeller is still producing thrust accelerating the cart. The cart does not get stuck at this point or begin to slow down because if you sum the forces, the only force acting on the cart is the thrust from the propeller. The propeller does not stop turning because it is mechanically driven by the wheels, NOT turned by the relative wind. There is no drag therefore no force equal and opposite to the thrust therefore sum of forces says the cart must continue to accelerate.

In box 4: the cart accelerates faster than the wind. There is now relative wind acting against the motion of the cart, so now there is drag acting as a decelerating force. I can't tell you exactly what speed it will happen, but it must happen at a cart speed that is greater than the wind speed in order to create any decelerating drag force, let alone a drag force that is equal and opposite the thrust created by the propeller.

Richard, you said "Figure 4 doesn't explain why the red arrow next to the propeller is drawn pointing to the left (thrust) instead of to the right (drag)." - Its the same as an airplane. When you're flying, there is a relative headwind equal to your airspeed acting against the direction of travel (airspeed indicator), which does create drag on the airplane, but because the prop is being turned by the motor, it continues to produce thrust (the thrust vector points in the direction of travel). In the cart, the propeller is not being turned by the wind, its being mechanically driven by the wheels, and no matter which way the wind is blowing, if the wheels are turning, the propeller is producing thrust.

You also said: "I also don't understand why the relative wind is still stated as zero knots when the cart is alleged to be traveling faster than the wind." - you didn't examine the figure closely enough. In box 4, the relative wind is stated to be greater than zero left to right, or against the direction of travel. I didn't put a number there because I can't tell you exactly what speed the cart will have to be traveling, only that it must be greater than the speed of the wind in order to produce drag equal and opposite to the thrust.


Here is a thought experiment. Suppose there is no propeller, and you have a very light cart with wheels that produce little friction (negligible). There is a tail wind. The tailwind creates drag and pushes the cart forward. As long as there is a relative wind, there will be drag pushing the cart forward. Drag is the only force acting on the cart. The cart will continue to accelerate until sum of forces equals 0. Since drag is the only force, the cart will continue to accelerate until there is no drag, or until the relative wind is 0. That happens when the speed of the cart equals the speed of the wind. Therefore, a cart with no propeller will be pushed exactly as fast as the wind.

With that in mind, take the cart with no prop traveling exactly as fast as the wind, and add on the propeller mechanically driven by the spinning wheels of the cart. The cart was at steady state, wheels spinning, traveling exactly as fast as the wind, now turn on thrust from the prop and what happens? The cart must speed up because sum of forces no longer equals 0.
 

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Only possible issue is the drag on the drive wheels caused by powering the prop.
 
I could build a vehicle that would sail downwind at an average speed faster than the wind. It isn't that hard to envision and I imagine most of us could come up with two or three variations that would work.

Simply put, the vehicle would have a very large collector (wind turbine or similar) that charged a storage device (e.g. a flywheel or battery) while it accelerated (and had a relative tail wind). Once the relative wind was zero the collector may need to be configured to minimize drag (turbine blades feather) or maybe the drag isn't significant...in either case the vehicle would use the stored energy to sprint ahead by driving the wheels. If it had a big enough turbine and the storage was efficient enough it could go really fast or cruise a surprising distance at that point. Once the sprint energy was depleted it would drop back down to having a relative tail wind and collect energy for the next sprint.

As for continuously sailing faster than the wind, if one part of a machine powers another part which in turn powers the first part, the system needs energy added to keep going. A relative headwind caused by forward motion is not an energy addition, it is an energy transfer from one part of the system to another. There is always an energy loss when transferring energy. As such, claims of continuously sailing downwind faster than the wind are extremely dubious. I'm not sure they are making that claim though.

Oscillating at an average well above wind speed is no problem.
 
Here is a thought experiment. Suppose there is no propeller, and you have a very light cart with wheels that produce little friction (negligible). There is a tail wind. The tailwind creates drag and pushes the cart forward. As long as there is a relative wind, there will be drag pushing the cart forward. Drag is the only force acting on the cart. The cart will continue to accelerate until sum of forces equals 0. Since drag is the only force, the cart will continue to accelerate until there is no drag, or until the relative wind is 0. That happens when the speed of the cart equals the speed of the wind. Therefore, a cart with no propeller will be pushed exactly as fast as the wind.

With that in mind, take the cart with no prop traveling exactly as fast as the wind, and add on the propeller mechanically driven by the spinning wheels of the cart. The cart was at steady state, wheels spinning, traveling exactly as fast as the wind, now turn on thrust from the prop and what happens? The cart must speed up because sum of forces no longer equals 0.

I think the disconnect here is that you're missing two drag forces: the rolling resistance of the wheels and the resistance in the propeller gearing. Ordinarily we could say these are negligible, but because the energy from the propeller comes from these two sources we need to make sure by quantitative analysis that the extra thrust provided by the propeller is greater than the drag inherent in the system. It could very well be that the drag in the gearing system negates the speed gained from the propeller's thrust, which would mean that the cart would either reach only the wind speed, or even fall short of the wind speed.

PS: I'm not sure if drag is the right word for what I'm talking about. What I mean is that because of the gearing of the propeller, it's going to take a significant amount of energy to get it moving, and that energy has to come from somewhere.
 
I think the disconnect here is that you're missing two drag forces: the rolling resistance of the wheels and the resistance in the propeller gearing. Ordinarily we could say these are negligible, but because the energy from the propeller comes from these two sources we need to make sure by quantitative analysis that the extra thrust provided by the propeller is greater than the drag inherent in the system. It could very well be that the drag in the gearing system negates the speed gained from the propeller's thrust, which would mean that the cart would either reach only the wind speed, or even fall short of the wind speed.

PS: I'm not sure if drag is the right word for what I'm talking about. What I mean is that because of the gearing of the propeller, it's going to take a significant amount of energy to get it moving, and that energy has to come from somewhere.

I understand what your saying. I haven't forgotten those forces, I just didn't think we were at that point yet. If thats the point where at, then we're no longer arguing the physics of the problem, but have moved on to the details. If people don't understand the theoretical FBD, then adding in addition forces only makes it more confusing. In other words, if I understand what people are saying, those additional forces aren't the reason why people are claiming the cart is a hoax.


To sort of address what your saying, its all about torque at the wheel, and you can optimize the cart for maximum mechanical advantage. For example, before the cart starts moving, there is a drag trying to push the cart foreward, but the wind is also trying to windmill the prop in the wrong direction (inefficiently, I might add, since the trailing edge would be the leading edge in this instance), which would tend to spin the wheels backwards and thus move the cart backwards. These 2 forces are in direct competition with each other. Who wins? Well, the drag force times the radius of the wheel is the torque trying to spin the wheel foreward, and the wind force trying to windmill the prop creates a constant torque value trying to spin the wheels backwards.

So you end up with something that looks like:

force * radius > torque

or said with words, drag force times wheel radius must be greater than the windmill torque if the cart is going to move foreward. If they're equal, the cart won't move at all. If the windmill torque is greater, the cart will actually start tractoring into the wind. With constant wind speed, the drag force is constant. With constant air speed, the windmill torque is constant. But you can change the radius of the tire, and you can change the gearing between the prop and the wheels to reduce the torque at the wheels produced by the windmill torque. In other words, really big wheels and the correct gearing will ensure that drag wins.

Utilizing the same principals as DDWFTTW, you can also create a cart that works backwards in order to tractor directly into the wind. In the tractoring into the wind version, the wind will spin the prop as a windmill, which spins the wheels driving the cart into the wind, which increases the realitive headwind and speeds up the windmill, which drives the cart faster, etc until the torque created by the drag force acting at the wheel equals the torque produced by the windmilling propeller. In order for that to happen, the inequality at the just starting out time must be reversed (torque > drag * radius).
 
As such, claims of continuously sailing downwind faster than the wind are extremely dubious. I'm not sure they are making that claim though.

That is precisely the claim they made, and accomplished. This is from the preamble at the top of their web site:

"Can a vehicle be built which can go directly downwind, faster than the wind (DDWFTTW), powered only by the wind, steady state? Thin Air Designs, in collaboration with the San Jose State University Aero department, along with generous corporate sponsors set out to definitively answer this question. On 3 July 2010 we established a world record by going directly downwind at 2.8 times the true wind speed. "

http://www.fasterthanthewind.org/
 
That is precisely the claim they made, and accomplished. This is from the preamble at the top of their web site:

"Can a vehicle be built which can go directly downwind, faster than the wind (DDWFTTW), powered only by the wind, steady state? Thin Air Designs, in collaboration with the San Jose State University Aero department, along with generous corporate sponsors set out to definitively answer this question. On 3 July 2010 we established a world record by going directly downwind at 2.8 times the true wind speed. "

http://www.fasterthanthewind.org/


They made the claim but the sanctioning body didn't give it to them.

It doesn't mean much when a person gives himself a prize.
 
Here is a frame from the beginning of the video. It ends up that there is a wind vane (tape) on a pole that projects from the nose of the car.

The wind tape clearly shows that the car is pointing into the wind before it starts moving. The claim that they are pointing downwind is a hoax.

Whatever that is, it is barely visible, even at 480p. When the video pans to the anemometer mounted on the pace car, it definitely shows the wind from the right at the height of the prop hub. You're stuck on believing it is all a vast conspiracy and looking for evidence to support that theory and basically disregarding everything else.
 
Whatever that is, it is barely visible, even at 480p. When the video pans to the anemometer mounted on the pace car, it definitely shows the wind from the right at the height of the prop hub. You're stuck on believing it is all a vast conspiracy and looking for evidence to support that theory and basically disregarding everything else.

It's a wind tape and it's small to reduce drag. Here is an example:

http://www.apsltd.com/c-4713-telltalesshrouds.aspx

Teh anemometer on the pace car isn't worth sh*t for the simple reason that it's on the pace car. WTF does the pace car have to do with operation of the wind cart? The pace car is a distraction, part of the ruse, a red herring . . .

The only instrument that matters is the instrument on the wind car and that instrument says that the car is pointed into the wind at all times. Given that that's what the instrument says, and that's what science says is the only way the car will work, then I believe it to be true.

You're stuck on believing the video. :D
 
I understand the physics and mechanics and you simply do not. A pity for you. :wink2: (There is more than one video; here are a couple more:)

At least I can learn. You're ugly and there's no cure for that.

Seriously dude, if your best argument boils down to implying that your challenger is stupid then you're done. You're out of ammo and have hung yourself.

All the purported data posted in this thread supports that this is a hoax:

* The wind tape on the car proves that the car is always pointing into the wind (this alone is conclusive)

* The person that made the video and designed the car holds on the order of twenty five patents in video editing and special effects

* The four free body diagrams magicly convert friction to thrust (this alone is a joke -- there is only one car so there is only one valid free body diagram, not two, three, or four)

* The sanctioning body did not award a prize

* No one has reproduced the results using wind power
 
At least I can learn. You're ugly and there's no cure for that.

Seriously dude, if your best argument boils down to implying that your challenger is stupid then you're done. You're out of ammo and have hung yourself.

All the purported data posted in this thread supports that this is a hoax:

* The wind tape on the car proves that the car is always pointing into the wind (this alone is conclusive)

* The person that made the video and designed the car holds on the order of twenty five patents in video editing and special effects

* The four free body diagrams magicly convert friction to thrust (this alone is a joke -- there is only one car so there is only one valid free body diagram, not two, three, or four)

* The sanctioning body did not award a prize

* No one has reproduced the results using wind power
Yep- the editors of Sail Magazine are dummies. They didn't disbelieve it.

I noted you never answered my question about the type of plane you'll fly to Nebraska to see a working model in operation.
 
Yep- the editors of Sail Magazine are dummies. They didn't disbelieve it.

I noted you never answered my question about the type of plane you'll fly to Nebraska to see a working model in operation.

The author of the Sail magazine article didn't say whether he believed or disbelieved anything. All he did was report a story.

What I fly isn't your business. Nor is it material to the wind cart.
 
That is precisely the claim they made, and accomplished. This is from the preamble at the top of their web site:

Thinking about it a little more... they are just circularly tacking on a broad reach. No big deal there.
 
I just got off the phone with the Sailing editor. He does believe the story but he has not seen the car. He is basing his info on the same stuff we are plus his character knowledge of one or two of the people involved.

I'm still not sold. People with great character are also capable of great pranks. :lol:
 
The author of the Sail magazine article didn't say whether he believed or disbelieved anything. All he did was report a story.

What I fly isn't your business. Nor is it material to the wind cart.
Didn't you say you'd fly to where ever a working model was located? That does make it material.

I just got off the phone with the Sailing editor. He does believe the story but he has not seen the car. He is basing his info on the same stuff we are plus his character knowledge of one or two of the people involved.

I'm still not sold. People with great character are also capable of great pranks. :lol:
I'm sure the editor of Sail magazine knows more than most of us about what can be done with the wind, including you.
 
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At least I can learn. You're ugly and there's no cure for that.

I look even uglier without the hat.

Seriously dude, if your best argument boils down to implying that your challenger is stupid then you're done. You're out of ammo and have hung yourself.
Dang! I hate when that happens!

All the purported data posted in this thread supports that this is a hoax:

* The wind tape on the car proves that the car is always pointing into the wind (this alone is conclusive)
Good point - but so conclusive that it proves other indicators - and all other replications - false?

* The person that made the video and designed the car holds on the order of twenty five patents in video editing and special effects
And that he has a BS and MS in aeronautical engineering. But clearly his patents make him a patent fraud. Good catch.

* The four free body diagrams magicly convert friction to thrust (this alone is a joke -- there is only one car so there is only one valid free body diagram, not two, three, or four)
I wish I knew what you were claiming here, but since it is all a fraud I guess it doesn't matter.

* The sanctioning body did not award a prize
Rats - another proof it is a fraud. NALSA merely proclaimed it a record - something (it seems) they do for everyone, fraud or not.

* No one has reproduced the results using wind power
True - so long as you ignore the reproduction about 1 minute 20 seconds into the first video of post 62 of this thread. And so long as we all accept that Galilean transformation is a fraud, all those reproductions using treadmills must also be considered fraud.
 
What happens when you put the device on a treadmill?

At 3:19 into the video, you'll find out. Starting at 3:45, anybody who thinks a plane could not takeoff from a treadmill whose speed matches the aircraft's wheel speed should get their questions answered.

 
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I'm not an engineer, but I just can't see it. Intuition is sometimes wrong, but it seems to violate some fundamental laws of physics.

I can see how it could work of there was a side wind component and the prop could redirect the vector to thrust, but for a direct tailwind I just don't see it.
 
I was there at the dry lake bed for their NALSA record runs. It's real. It goes a LOT faster than windspeed, for as long as you like until you run out of lakebed. No tomfoolery with pedals, gusts or batteries.

During steady state operation at > windspeed, the prop is a prop. It's producing thrust. It's driven by the wheels. In fact there is a freewheel gear so that it can only be driven by the wheels, it cannot drive them.

Consider an iceboat or land yacht tacking downwind. The downwind component of its velocity can be > windspeed. Same principle.

The energy input comes from the differential velocity between the wind and the ground.

Good explanations:
http://blueplanettimes.com/?p=3922
https://docs.google.com/View?docID=0AdRsKX7aaZTPZGRnbjhkajdfMTY0aGRzNWtnaGM&revision=_latest&hgd=1
http://www.wired.com/autopia/2010/08/ddwfttw/all/1

Don't feel bad for not getting it at first. It's quite counterintuitive.
 
The energy input comes from the differential velocity between the wind and the ground.
...
Don't feel bad for not getting it at first. It's quite counterintuitive.

The Wired article actually made the most sense. Props to the author (no pun intended).

I actually does make sense. Rolling resistance changes minimally with speed, aerodynamic drag is the biggest eater of kinetic energy. With the tailwind, drag is reduced far below it's calm wind state, plus propeller efficiency is far higher with very low airspeeds.

The the wheels are turning far faster than the airspeed would indicate, and the lack of aerodynamic drag (due to the tailwind) allows you to syphon off some kinetic energy (in the form of momentum) and transfer that to the air which is moving far more slowly (in the form of thrust).

Everything comes apart if the wind direction changes. But in that one specific regime, it works.

Thanks for helping me get it.
 
Yeah, the wired article comparing it to two sailboats tacking around the world was a good example
 
All the purported data posted in this thread supports that this is a hoax:

Having designed, built, and operated the cart, I can tell you it's definitely not a hoax. What it is is a brain teaser that no one was willing to accept the correct answer to - so we built it.

The wind tape on the car proves that the car is always pointing into the wind (this alone is conclusive)

What!? It is pointing directly downwind. I will be happy to post videos that make that quite clear.

The person that made the video and designed the car holds on the order of twenty five patents in video editing and special effects

I have patents on enhancing live sports broadcasts. This means using technology to track things like baseballs and race cars, and then render relevant graphics over the live video. None of my patents prevent me from designing and building a cart that goes DDWFTTW steady-state.

* The four free body diagrams magicly convert friction to thrust (this alone is a joke

I was very careful not to employ any magic at all in designing this vehicle. I think that would be considered cheating.

* The sanctioning body did not award a prize

Why do you insist on making and repeating this lie. I think you'll find all the relevant data on their website: www.NALSA.org

No one has reproduced the results using wind power

Many have. I have posted a series of detailed build videos on youtube so that anyone can reproduce our results with a small working model. I'll be happy to post the links if you like.
 
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