Wind powered cart traveling directly down wind faster than the wind

spork said:
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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please do!:yesnod:
 
Okay, I'm no engineer either, just a lowly gas plant operator with a high school diploma from podunk. Since this concept obviously works, we need a practical use. Here's my thought. Tell me what you think.

Take a front wheel drive car. Use the axles and diff from a rear wheel drive car on the back wheels, but turned around backward. Connect the rear facing drive shaft to a propeller, maybe using some kind of gear accelerator. So you have the front engine driving the front wheels, making the car go and making the rear wheels roll. The rear wheels turn the propeller at a higher rpm, and create some amount of thrust over that of the engine that can help push/pull the car. I'm thinkin once you get the car moving, and thus the propeller spinning, the engine will have to do way less work, which would translate into much better fuel economy. My question is, once the propeller starts producing thrust greater than the engine, does the engine become a braking force that will defeat the purpose?

Does that make any sense? I know it's not really DDWFTTW, but it got me thinking.

Pardon the three minute drawing :wink2:
 

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Good idea but it seems it would only work when driving directly downwind and at other angles into the wind the extra drag and weight would far outweigh any benifits when driving downwind,
 
I think I'm beginning to understand this. I wish someone would post the math that made the "record" possible. I hate "brain experiments" and much prefer math explanations (even when I don't understand the math, I know people who do).

I see it as a really cool special circumstance. Being able to sail downwind only brings us back millennium to days when "sailing" was not much more than advanced "drifting". This narrow sailing angle makes for very little advantage over other designs. It is a single purpose built vehicle.

Spork, send more info. Find some math on the working record holder or we will never stop arguing.
 
OkieFlyer said:
Take a front wheel drive car. Use the axles and diff from a rear wheel drive car on the back wheels, but turned around backward. Connect the rear facing drive shaft to a propeller, maybe using some kind of gear accelerator. So you have the front engine driving the front wheels, making the car go and making the rear wheels roll. The rear wheels turn the propeller at a higher rpm, and create some amount of thrust over that of the engine that can help push/pull the car. I'm thinkin once you get the car moving, and thus the propeller spinning, the engine will have to do way less work, which would translate into much better fuel economy. My question is, once the propeller starts producing thrust greater than the engine, does the engine become a braking force that will defeat the purpose?

Does that make any sense? I know it's not really DDWFTTW, but it got me thinking.
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Keep in mind that this is still a wind powered vehicle, even though it outpaces the wind. What it does is to exploit the energy available at the ground/air interface (i.e. the wind). When the cart passes by, it leaves *slower* moving wind in its wake - because it has taken a large portion of the energy from that wind. Your car idea would work, but only in a wind. If we could make the entire propeller arrangement pivot on a vertical axis, and vary it's pitch, it would be possible to make that car work in any wind direction. But it will be tough to get through the drive-thru.

Dart said:
I think I'm beginning to understand this. I wish someone would post the math that made the "record" possible. I hate "brain experiments" and much prefer math explanations (even when I don't understand the math, I know people who do).
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How about if I explain the math in a way that you will understand... If you don't like it, I'll be happy to post something that looks way more mathy.

Basically it comes down to a simple power balance. As you may know, energy (or work) is simply force x distance. Because power is work/time, that means power is force x speed. So...

Keeping in mind that the wheels turn the prop (never the other way around), let's not worry just yet about how we get the thing up to speed. Instead we'll tow it up to twice wind speed, and then cut the tow rope. The question is then whether it can maintain that speed or even accelerate.

Now, let's remove the drive chain and replace it with a generator on the wheels, and an electric motor driving the prop. Wind speed is 15 mph, and we tow the cart up to 30 mph. At this point the cart is going over the ground at 30 mph, and there is a retarding force on the wheels because they're turning the electric generator. If we want to know how much power we're generating it's simply going to be that retarding force multiplied by 30 mph (remember, power is force x speed).

Now let's see how much power we need our prop to put out in order to keep us going at that speed - or accelerate. If we produce a thrust equal to the retarding force, we will maintain our speed (ignoring losses for the moment). So our prop is only moving through the air at 15 mph (30 mph - 15 mph tailwind). The work it does is thrust x 15 mph.

So the work the prop needs to do in this case is only one half of the work available from the generator. But in real life we will have aerodynamic drag, rolling resistance, and transmission losses. The secret is to keep the overall efficiency above 50%. If we can do that, we can accelerate after cutting the tow rope.

A simpler way to look at it is as a simple lever. Any lever can trade a large force over a small distance for a smaller force over a larger distance. That's all we do with the cart. And we do it by having the wheels work on one medium (the road) while the prop works on another medium (the air). As pilots, you're probably aware that you can produce more static thrust at full power than you can when flying at cruise. We're doing the same thing here. We're taking advantage of the fact that the prop is going through the air much more slowly than the cart is going over the ground.

I see it as a really cool special circumstance. Being able to sail downwind only brings us back millennium to days when "sailing" was not much more than advanced "drifting". This narrow sailing angle makes for very little advantage over other designs. It is a single purpose built vehicle.
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It was designed with only one purpose - as a brain-teaser. It's worked wonders in that regard.

Spork, send more info. Find some math on the working record holder or we will never stop arguing.
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No need to find more math. I am the record holder. I'll post more math or alternative descriptions if you'd like.
 
I still like my "mic, amp, and feedback" explanation the best :) :P :P :P
 
ebacon said:
It's a hoax. :rofl:
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ebacon said:
If you think the garbage works then build a car yerself, tell us when it's done, and I'll fly over and check it out.
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When I build a working model car like the ones you claim is a hoax- you said you'll fly over & check it out. Maybe you could fly over Spork's place and see the real thing! Assuming you really have a plane. :)
 
I'm game.

Spork, you in?

I apologize for making a mistake about your NALSA certification. After more research I agree that you did get it. I'm still not persuaded that the car works, though. IMO this car situation is a group of guys having fun with a brain teaser. On another board I've actually played devil's advocate and argued that the car works. Admittedly it can be fun game to play. :D
 
Cap'n Jack said:
When I build a working model car like the ones you claim is a hoax- you said you'll fly over & check it out. Maybe you could fly over Spork's place and see the real thing! Assuming you really have a plane. :)
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I've invited a whole bunch of people to witness it for themselves. Very few have. But none have witnessed it and failed to be convinced.

ebacon said:
I'm game.

Spork, you in?
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For demonstrating it? Sure.

I apologize for making a mistake about your NALSA certification
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Thanks. I didn't realize it was a mistake. I apologize for that.

After more research I agree that you did get it. I'm still not persuaded that the car works, though.
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Do you think we fooled NALSA (and NASA) and many many others? Would you believe it if you saw an analysis by the foremost aerodynamic authority today? Tell me what it would take to convince you and I'll bet I can provide it.
 
ebacon said:
The most certain way to convince me would be for me to inspect the cart and then witness it...
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If you built your own cart from the build videos, you could do that in the comfort of your own home for about $45. Surely much cheaper than flying out here - and should be even more convincing than inspecting ours.

...going faster than the wind in the wind, not a treadmill.
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Operating on a treadmill IS the wind. Wind is the relative movement of air over a surface. There's no such thing as a "stationary" surface. We think of the ground as stationary since we live on it, plant trees on it, build houses on it, etc. But the ground (near the equator) is moving at about 1000 mph as the earth rotates, much faster as it revolves around the sun, faster still as our solar system revolves around the Milky Way galaxy, etc.

Einstein and Galileo tell us there is no way to distinguish between a wind moving over a surface vs. a surface moving under the wind - because "moving" is strictly relative. That's why people test planes in wind tunnels.

Like a wind tunnel, the treadmill makes it much easier to create the carefully controlled conditions that should convince you it works. No gusts, and no questions about wind direction.

I am willing to fly out (at my expense of course) for such an experience.
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We're currently working on the modifications to make the cart go directly UP wind faster than the wind. If you'd like to fly out to see that, we'd love to have you. Not sure when and if we'll do more downwind runs with the cart. We promised the prop blades to a researcher that's doing low-wind turbine research.

Absent that, the next best thing would be seeing full screen HD versions of the following videos:
http://www.youtube.com/watch?v=5CcgmpBGSCI&feature=player_embedded#at=21
http://www.youtube.com/watch?v=xHsXcHoJu-A
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I don't think the first one was taken in HD. I know the second one was taken with my little pocket digital camera (not HD). The first one was taken by a somewhat noteworthy skeptic who DID fly down to see for himself. Richard Jenkins is the holder of the world land sailing speed record at 126.2 mph. He thought we were nutcases. Look for that same video on our blog here:
http://www.fasterthanthewind.org/

followed by Richard's statement:

A guest Blog from Richard Jenkins;

"So, one night, I was happily drinking my beer and tending to my inbox of endless boring emails that had be answered but were of no real consequence, when Lester, my landsailing buddy texted me a link to fasterthanthewind.org. Lester knows a lot, and if he says this needs my attention, then it gets it. I am not sure if it was how many beers I had had, or simply the inane nature of the quest, but I laughed enough to email all my friends to share the absurdity of their mission. My heart is split between belittling idiots, and saluting eccentrics, and this downwind quest lay somewhere in the middle. These loonies were pursuing a pointless goal, doomed to failure, but there was some genuine merit in the myth and their enthusiasm.

I dismissed it as utterly impossible. Traveling through zero apparent wind, with no stored power? Impossible. Why would you even attempt it? (Though I'm no stranger to that question myself!) But had I been asked to bet at that moment, I would have just lost a lot of money.

A few months later I actually met the idiots in question and, to my surprise and concern we not only have a few mutual friends, but they seemed to be rather technically credible. But, everyone makes mistakes, and I let them off as decent people with a blinkered view of fundamentally flawed engineering....

A few months later they were claiming success and if it was not for another great friend, Bob Dill, advising that they were actually correct, I would have discarded their claim as an April fool. I thought about the possibility that I was wrong, and then considered that as Bob was getting on a bit and had a bit of a shake with his stopwatch finger, maybe it was he who was mistaken. There was, however, a growing momentum of technical people (who should have known better), saying that these idiots have actually proven that it is possible to travel faster than the wind going directly down wind.

Not content, I had to witness this myself. When I heard it was on for the official record at El Mirage, I jumped on a plane and went to check it out.

The video speaks for itself. These guys are not idiots, but sincere, genuine, technical people who took a myth and made it real. It works. It starts from rest, trundles to true wind speed, then powers to a multiple of about 3 times the true wind speed. Bob will confirm the final number I am sure.

To all fellow skeptics, start baking that humble pie, or eat your hat. Your choice."

Richard Jenkins - Greenbird - 126.2mph
 
Spork,

I was talking about witnessing the little model cart, not Blackbird. I was already aware from your web page Blackbird is being reconfigured and the original prop is gone.

As for building a model cart, I don't have the inclination as I'm confident it's a hoax. Travel money is not an issue. We all fly airplanes and we all know that that can easily make first class commercial travel look like a bargain.

It appears the onus is falling back on the Cap'n to build one. He tried to shirk his duty and fell flat. :tongue:

Absent either of those options, I'll wait for a MythBusters episode which, IMO, all of this is viral advertising for anyway. It's all good fun. :D
 
You're welcome to come out to inspect the small model and watch it operate, both on the treadmill and in the wind. You may have to be a bit patient to wait for a wind day that suits your requirements of course. The treadmill on the other hand works every day.

Did you happen to read the submission report for the NALSA record - or NALSA's observer report?

What makes you think it's a hoax? Do you not understand the math?
 
There's no reason to wait for wind. All it takes is to set the cart on the floor and blow a fan at the back of it. If the cart moves forward then walk behind it with the fan.

I read the NALSA stuff but that can be falsified. A report is not a cart. I'm interested in the cart in the wind. Not the cart on a belt. Not the cart in the rain. Not on a bus, not on a train. I will not eat those with a spork, I will not eat those Cap'n Dork. :D

I'm not calling you a liar. I'm calling you a damn good hoaxster with friends that enjoy a good practical joke. That's a good thing.
 
ebacon said:
There's no reason to wait for wind. All it takes is to set the cart on the floor and blow a fan at the back of it. If the cart moves forward then walk behind it with the fan.
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You are invited out to inspect and experiment with the small cart. I'll provide a fan - and a long extension cord. You can walk behind it with the fan. If you're able to convince yourself with that method - great. I'll be surprised if you can convince anyone else that way.

I read the NALSA stuff but that can be falsified.
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You think maybe I hacked the North American Land Sailing Association's website - and they can't remove it!?

I'm interested in the cart in the wind. Not the cart on a belt.
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As a pilot I would hope you'd understand that the cart on a belt IS a cart in the wind. They are not similar - they are two instances of exactly the same thing. Would you trust the cart in the wind on MY street? How about yours? Just two different instances of the same thing - a cart in the wind.

I'm not calling you a liar. I'm calling you a damn good hoaxster...
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Actually, you're calling me a liar since I've told you this is not a hoax. But that's fine. Fly on out here and do whatever tests you like. I hope you don't mind if I take video of the tests and post them.
 
ebacon said:
Spork,

I was talking about witnessing the little model cart, not Blackbird. I was already aware from your web page Blackbird is being reconfigured and the original prop is gone.

As for building a model cart, I don't have the inclination as I'm confident it's a hoax. Travel money is not an issue. We all fly airplanes and we all know that that can easily make first class commercial travel look like a bargain.

It appears the onus is falling back on the Cap'n to build one. He tried to shirk his duty and fell flat. :tongue:

Absent either of those options, I'll wait for a MythBusters episode which, IMO, all of this is viral advertising for anyway. It's all good fun. :D
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Nope, not trying to shirk anything. I'd think a man-carrying vehicle would trump a model for a variety of reasons:

- More fun. Most of us that frequent this forum prefer to see a full size plane flying rather than a model.

- You get to talk to someone that has already made both models and a full-size version and undoubedly knows how they function better than I.

- The man-carrying version is more efficient- bigger wheels are generally reduced rolling resistance. Thay's why muscle-powered vehicles tend to have much larger wheels for their size than mechanically powered vehicles. Even small potholes matter much more to a bicyclist than to the same person in a car.

I'm reading that you might think the model is a hoax and the full size version isn't now? Or do you think they all are a hoax?

If the first case, why would you think the model is a hoax and large one isn't? The physics are the same.
 
ebacon said:
There's no reason to wait for wind. All it takes is to set the cart on the floor and blow a fan at the back of it. If the cart moves forward then walk behind it with the fan.
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Wouldn't this prevent the cart from ever going faster than the wind because in chasing the cart with the fan won't the wind speed keep increasing as the car accelerates:dunno:
 
spork said:
As a pilot I would hope you'd understand that the cart on a belt IS a cart in the wind. They are not similar - they are two instances of exactly the same thing. Would you trust the cart in the wind on MY street? How about yours? Just two different instances of the same thing - a cart in the wind.
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Just need a difference in airspeed vs ground speed...
 
Skylane81E said:
Wouldn't this prevent the cart from ever going faster than the wind because in chasing the cart with the fan won't the wind speed keep increasing as the car accelerates:dunno:
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I don't care. My analysis says that the steady state velocity of the cart will be toward the fan (i.e. backwards) or zero, but not away from the fan. If the cart goes forward steady state I will be amazed and could give two craps if it goes faster than the wind or not. I won't burden spork with that kind of instrumentation detail on a model cart.

I expect to only take fifteen minutes or so of his time.

Of course the cart must be geared such as it is shown in the force vector diagrams in this thread. If it is geared in reverse of that then the cart will move with wind no problem, but not faster than the wind.
 
ebacon said:
I don't care. My analysis says that the steady state velocity of the cart will be toward the fan (i.e. backwards) or zero, but not away from the fan. If the cart goes forward steady state I will be amazed and could give two craps if it goes faster than the wind or not. I won't burden spork with that kind of instrumentation detail on a model cart.

I expect to only take fifteen minutes or so of his time.

Of course the cart must be geared such as it is shown in the force vector diagrams in this thread. If it is geared in reverse of that then the cart will move with wind no problem, but not faster than the wind.
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Gottcha, you're thinking the wind will turn the prop and spin the wheels backwards.

I think they actually had it set up so the prop couldn't turn the wheels
 
ebacon said:
You're on.

Let's work out the details in PM. I've never been to California.

http://www.youtube.com/watch?v=ZuXxy8cjZQA
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Sounds good. Bob Dill of NALSA will be visiting here toward the end of July. We're hoping to be ready to do our upwind runs at that time. If you make it out while he's here, you can meet with him as well. But you're welcome to come out any time.
 
Skylane81E said:
Gottcha, you're thinking the wind will turn the prop and spin the wheels backwards.

I think they actually had it set up so the prop couldn't turn the wheels
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The Blackbird web page shows the ratchets. They are simple ratchets in the axles that let the cart be pushed in a tight circle. The ratchets are useful for maneuvering Blackbird around the shop, etc. At least that's my understanding.

As far as I know the model cart has no ratchet anywhere.
 
Skylane81E said:
Gottcha, you're thinking the wind will turn the prop and spin the wheels backwards.

I think they actually had it set up so the prop couldn't turn the wheels
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No ratchets on the small cart.

 
spork said:
Sounds good. Bob Dill of NALSA will be visiting here toward the end of July. We're hoping to be ready to do our upwind runs at that time. If you make it out while he's here, you can meet with him as well. But you're welcome to come out any time.
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Roger. I appreciate this opportunity.
 
Cap'n Jack said:
Nope, not trying to shirk anything. I'd think a man-carrying vehicle would trump a model for a variety of reasons:

- More fun. Most of us that frequent this forum prefer to see a full size plane flying rather than a model.

- You get to talk to someone that has already made both models and a full-size version and undoubedly knows how they function better than I.

- The man-carrying version is more efficient- bigger wheels are generally reduced rolling resistance. Thay's why muscle-powered vehicles tend to have much larger wheels for their size than mechanically powered vehicles. Even small potholes matter much more to a bicyclist than to the same person in a car.

I'm reading that you might think the model is a hoax and the full size version isn't now? Or do you think they all are a hoax?

If the first case, why would you think the model is a hoax and large one isn't? The physics are the same.
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Cap'n,

The man-sized version no longer exists. It is being retrofitted for a different challenge. The model is all there is wrt to the free body diagrams in this thread.
 
Skylane81E said:
I was thinking big one,
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The big one has ratchets, the small one doesn't. It would be tough to chase the big on around with a fan though.


ebacon said:
Cap'n,
The man-sized version no longer exists. It is being retrofitted for a different challenge. The model is all there is wrt to the free body diagrams in this thread.
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It still exists, but it's a big deal to take it out to the runway, assemble it, instrument it, and test it. Then you need to repeat until you get a day with wind that will satisfy a skeptic. The plan is to loan the prop to a researcher that has asked for it. On our build blog you can see the new turbine taking shape.

ebacon, I've got a paragliding friend that swore up and down I was nuts. He simply wouldn't accept this thing could possibly do as we claimed. But he showed up at the New Jerusalem runway to see for himself. He rode on the trailer behind the chase vehicle. I was driving the downwind cart. But from where I was, I could see his jaw drop when I accelerated past wind speed. Hopefully I'll get to film a similar reaction when you visit.
 
Here are some videos of our first tests at Ivanpah dry lake. This is before we make the prop variable pitch and before we added the aerodynamic fairing and extended left axle.


First Ivanpah run:

Second Ivanpah run:

Last Ivanpah run:

Opposed streamer and flag (at 2:14):

Onboard footage from DDWFTTW vehicle:

Opposed Streamer and flag (at 0:36):

Slo-Mo of “the money shot”
 
spork said:
If need be I suppose I could mount the paramotor for my powered paraglider on a truck and give it a try.
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I imagine it would work but my brain keeps saying that it taks a healthy wind to overcome the static momentum of the cart.
 
spork said:
So what's the status? Did I convince you this is not a hoax, or are you planning to come out and see for yourself?
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Spork,

Sorry for the pause. I spent the weekend canoeing in Canada.

I would like to come out and witness the upwind version of Blackbird and play with the model downwind car. Please let me know (or know where to watch) for a schedule.

As for whether the downwind is a hoax IMO FTTW is a hoax for sure. Whether the cart can go downwind at all is something I need to witness. It seems to me that reverse direction torque from the prop would overpower or at least cancel out forward thrust from the wind. If it doesn't then I'll just admit I don't know WTF is going on. :D

Thanks
 
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