By Mark Frauenfelder


Rick Cavallaro demonstrates his treadmill wind cart.

In February 2007, MAKE’s project editor, Paul Spinrad, emailed me a link to a YouTube video shot by a man named Jack Goodman. The video opens with a woman in a pink shirt and blue shorts standing in the middle of an asphalt road somewhere in Florida. She’s holding onto a 2-foot-high, three-wheeled, unmanned cart with a large propeller mounted on the back. There’s no motor on the cart, but the propeller is connected to the back wheels with pulleys and a belt.

A man’s voice offscreen says, “OK, April 13. Wind light and variable, about 5 or 6 knots.” A small mast with a windsock attached to the cart shows that the wind is blowing from the back to the front of the cart — in other words, the cart is pointed downwind. The man instructs the woman to “give it a shove,” and she pushes it lightly down the road. It rolls for several feet, making a clicking sound, then slows down and comes to a rest.

“Oh,” says the unseen man. “I had the brake on again. Give it a push.” The woman pushes it again and the cart takes off down the road, this time picking up considerable speed.

The video camera continues to tape the cart as it rolls down the road. The camera operator is on a bicycle, shooting the video while pedaling along the rural road. After a moment, the windsock stops pointing downwind and changes direction. It’s now pointing toward the back of the cart. This means the cart is traveling downwind faster than the wind.

For the next three minutes, the cart rolls down the road. The man says, “I’m going 10 miles an hour, the wind is about 6 knots.” The cart races ahead, and the man says, “Up to 13 miles an hour.” A minute or so later he says, “Brake on.” The vehicle stops and the video abruptly ends.

Jack Goodman’s three-minute video has been the subject of an intense, hotly-contested speculation ever since it was uploaded to YouTube on November 30, 2006. In an article for Catalyst: Journal of the Amateur Yacht Research Society, Goodman explained that he built his curious cart to settle an ancient debate among sailing enthusiasts: Is it possible to for a wind-powered vehicle to travel directly downwind faster than the wind?

The intuitive answer to this question is “of course not.” Imagine tossing a balloon into a steady breeze. It will go along at the speed of the wind (or slightly less, due to drag) but it’s inconceivable that it could go faster than the wind. How could it? If it were to go faster than the wind, it would be outrunning its source of power and move into a headwind, which would slow it down.

Think of a sailboat moving downwind. Once it gains enough speed to be moving at the speed of the wind, the sail will go slack, because the wind speed relative to the boat is zero. With no wind in the sails, how in the world could the sailboat go any faster? To claim that it could go faster than the wind is the same as claiming it could move forward with no wind at all!

People immediately began attacking Goodman’s video, saying it was a fake. The video doesn’t have a clear shot of the road ahead, so many commenters accused Goodman of towing the cart behind a car or bike with a piece of fishing line. Some said the cart was moving downhill; others said Goodman was deluding himself — the windsock changed direction because of propwash, not because it was moving faster than the wind.

Defenders of Goodman’s video said that detractors weren’t thinking about the problem properly. It wasn’t the propeller that was driving the wheels — it was the wheels that were making the propeller spin, and this critical bit of information made all the difference. The energy, said the defenders, came from the net motion of the air over the ground, not the net motion of the air past the vehicle. Unlike a sail that goes slack when a boat moves directly downwind, the propeller will continue to turn, because the wheels are driving it.

As Goodman wrote in his article, “The key to understanding DWFTTW [Downwind Faster Than The Wind], is that the wheels are turning the propeller and the the propeller need only produce enough lift in still air to overcome the forces required to turn it.”

The naysayers weren’t buying it. One critic said “Yeah, every time I sit in a calm, wind-free room, the floor rushes by underneath me too.”

After having digested more than 100 comments on YouTube and other online forums on the matter, I didn’t know what to think. Some of the pro-DWFTTW arguments were quite persuasive, and they’d almost convince me that Goodman was right. But then I’d read a convincing counterargument from a naysayer that would make me doubt again.

Paul, the MAKE editor who sent me the video, thought it plausible. He said, “It’s taken me a while to put my brain around how this works — for me, the key point is that the propeller is a propeller, not a wind vane, and when the cart is rolling, the wheels are powering the propeller, not the other way around. With the right gearing, the propeller will always push backwards against the air, whether or not the air is moving forwards or backwards relative to the cart. The tailwind and the propeller action combine to make the wheels spin fast enough to keep the whole system rolling faster than the wind. Definitely counterintuitive, or a hoax I’ve fallen for.” He too, was on the fence, but leaning over on the side of the believers.

If Goodman wasn’t perpetrating a hoax, I had a lot of admiration for him for actually building something and trying it out. It was a great example of a DIY science experiment. I showed the video to my friend, Charles Platt, who’s written many excellent how-to articles for MAKE. His solid knowledge of math, physics, and electronics, coupled with decades of hands-on experience making models, medical equipment prototypes, games, and electronic circuits has made him one of the magazine’s star contributors.

Charles watched the video and emailed me back saying he thought the video was bogus. The reason the cart can’t work, said Charles, is that as the cart goes faster, the wind force on the cart is diminished. “If it’s a 10mph wind and the cart gets up to 8mph there is now only a 2mph push behind it. Really it should slow down, but, no, it accelerates! When it is running equal with the wind, it is like a sailing ship ‘becalmed.’ No net force from air behind or in front. Yet still it runs faster!”

Even though Charles’ experience-informed intuition told him the cart couldn’t work, he decided to build his own cart. He constructed a tabletop model of the cart out of wood and attached model airplane wheels. He built a propeller and connected it to the rear axle with a rubber belt. Making sure the moving parts were thoroughly lubricated with WD-40, Charles placed the cart on his workbench, put a 15-inch fan behind it, and turned the fan on.

“The cart barely moved in response to the fan,” explained Charles in his write-up about the experiment for MAKE (Volume 11, page 58).

He then used a massive 38-inch warehouse ventilation fan and ran it at its highest speed. “[T]he cart ignored it and did nothing.” After building a shroud to channel the wind onto the cart, he observed a forward motion of 2 inches per second. At least it was moving, but the wind propelling it was traveling at 30 feet per second.

Charles’ conclusion was that the cart didn’t work, and that the Goodman video was highly suspicious. He wrote, “Perhaps Jack Goodman has some clever explanation for this. Perhaps I didn’t build my version exactly the same way that he built his. Perhaps you should build your own, just to make sure. Building a prototype that doesn’t work is always educational, provided, of course, that you are willing to face facts and admit that it doesn’t work.”

I agreed with Charles’ conclusion, figuring Goodman had pulled an excellent prank on his yachtie friends, and that now that his cart had been debunked, the story was over.

But shortly after the article ran, a number of believers started chiming in on the Make: Online forums, claiming that Platt was wrong, and Goodman was right. Charles patiently answered each comment. He defended his article and his cart, and even offered one believer, who used the screen name pelesl, “$1,000 cash of my own money if he can prove that [a cart of Charles’ design] will start by running slower than a constant wind, will accelerate to equal the wind speed, and will then accelerate further to exceed the speed of the wind, without any outside interference, on a flat surface,” just as Goodman’s appeared to do in the video.

Soon, people began posting YouTube videos of their homemade wind carts. Instead of running them outside in the wind, though, they placed the carts on exercise treadmills. The videos showed the carts, their propellers spinning furiously, move in the opposite direction of the treadmill belt. This was impressive, but was it the same as testing a cart on stationary ground with wind pushing it? The DDWFTTW proponents argued that the two scenarios — “moving ground and still air” versus “still ground and moving air” — were equivalent for the purposes of proving DDWFTTW, but I wasn’t sure. (The phenomenon is also called Directly Downwind Faster Than The Wind, to eliminate the possibility of tacking or angling into the wind.)

Rick Cavallaro (known on message boards as both spork and spork33) was the most impassioned defender of wind carts. He said that the treadmill videos (many of which he shot and uploaded himself) proved Charles wrong and that he should pay the $1,000 to pelesl. Charles responded that he’d said the test had to be conducted with wind, not a treadmill. Cavallaro raised the stakes, writing: “I will do exactly what you suggest both indoors and out. But it won’t be an open challenge. It will be a bet. Your $10K against my $100K. But we’ll both put the funds in a joint escrow account to be awarded to the winner. I will then pay pelesl from my winnings.”

I wondered what a physics professor would make of all this, so I emailed Dr. Paul J. Camp, a professor in the physics department at Spelman College in Atlanta, Ga. Camp had helped me with other physics brain-teasers in the past and I appreciated his clear explanations. I asked him to take a look at Goodman’s video, as well as Charles Platt’s article, and the treadmill cart videos. “What do you say?” I asked.

“Impossible,” replied Camp. “Would violate conservation of momentum and conservation of energy … In fact, we can state this in pretty bare terms — for a car moving downwind at wind speed to go a little faster is physically indistinguishable from a car at rest on the ground in stationary air to suddenly leap into motion. What can be done in one inertial frame can be done in any other inertial frame with the same physical circumstances.”

Camp’s explanation, which was the same as Platt’s, made sense to me. But I couldn’t stop thinking about those wind cart enthusiasts’ videos, which clearly showed the carts moving up the spinning belts of treadmills.

I contacted Rick Cavallaro. He’s the chief scientist for a Silicon Valley company called Sportvision Inc., which creates systems that overlay computer-generated visual effects onto televised sporting events. He has a B.S. in aerospace engineering from Georgia Tech and an M.S. in dynamics and controls from UCLA.

Cavallaro told me he’d started making kits for wind cart enthusiasts to put together and try out on their own. I PayPaled him $40 and, a few days later, a FedEx tube arrived with all the parts I needed to make my own cart: three plastic wheels, a pre-bent aluminum tube, a plastic propeller, and some gears. It only took a few minutes to assemble the cart, which looked quite sleek.

dwfttw_2_rtfa.jpg

A DWFTTW model that can be built from plans found here

.

There wasn’t a lot of wind that day, so I used an electric fan and tried the cart indoors, in a long hallway. I turned the fan on full blast and held the cart, off the floor, in front of it. The propeller spun counterclockwise, making the wheels spin backward.

Then I set the cart on the floor, with the fan pointed behind it. It started moving forward and the propeller spun clockwise. This meant that the wheels were driving the propeller, as the Goodman defenders claimed it would, and not the other way around, as many detractors insisted that it would. So the cart proponents were correct on that count.

The cart picked up speed, but then slowed and bumped into the wall at the end of the hallway. This, of course, was not a good environment to conduct the test, but at least I learned that the cart could indeed move in a tailwind.

While I waited for a day in Los Angeles with a steady wind so I could take the cart outside, I checked out various message boards, and found that the debate was raging even more than before. The doubters said the treadmill was not an accurate simulation of a cart in the wind, while the believers insisted it was. At times, the debates would get highly emotional, with name-calling and slurs. (My favorite: “I am more than physically capable of taking that little cart and shoving it up your ass, sideways.”)

One of the doubters, whose screen name was swerdna123, wrote that only a wind tunnel demonstration would satisfy him. But there were no takers. Apparently, it was too difficult for anyone to rise to the challenge of making one. So swerdna123 took it upon himself. His intention, like Charles Platt’s, was to show the believers that the cart wouldn’t go downwind faster than the wind.

Swerdna123’s design was clever — a circular wind tunnel, made from a cardboard drum that had a rotating spindle with a motor that drove wind-making flaps around in a circle. He designed and built a tiny propeller cart to roll around the drum on a circular track. After he built the setup, he posted several videos to YouTube. The cart had a stiff wire coming off it, like a radio antenna, with a small paper flag. This small paper flag was to indicate the direction of the wind speed relative to the cart, just like the wind sock on Goodman’s much larger cart.

As the rotating flaps picked up speed and created wind the cart started moving. At first, the flag pointed in the direction of the cart’s rotation, meaning it was traveling slower than the wind inside the setup. After a few seconds, the flag hung straight down, meaning the car was traveling at exactly the speed of the wind. Then, to my surprise (and delight) the flag began to tilt in the opposite direction of the motion, and the cart was rolling faster than the flaps. It really was outrunning the wind!

I contacted swerdna123 and learned that his real name is Tony Andrews. He’s a 58-year-old website developer and self-described “backyard inventor” from Christchurch, New Zealand. (He’s also a former New Zealand and World silver medal finalist Monopoly champion.) Like a lot of other wind cart skeptics, Andrews didn’t think the cart-on-treadmill demonstrations were adequate to prove the DDWFTTW theory. In addition, he was annoyed by the nasty tempers of the treadmill crowd: “Their main purpose seemed to be to insult and incite argument.”

Andrews wanted to see a wind cart move from the wind, not from a treadmill. And since no one else was stepping up to the challenge, he had to take it on himself. “Although I was very busy with other things at the time,” he said, “I couldn’t resist building and testing my own DDWFTTW equipment.” He said he possesses “natural mechanical abilities,” and has “invented and built many weird and wonderful mechanical things like rotary motors/pumps, constant velocity transmission systems, toys, games, and puzzles.”

Andrews said he has several ideas on how to improve the wind cart test, like a better wind tunnel and a camera that moves with the cart so it would be easier to compare its speed with those of the wind vanes, but that he probably won’t get around to building them, as his interests have shifted. Besides, he said he felt that his experiment shows that continuous DDWFTTW travel is possible.

How does the cart do it? I asked him. His theory is that the cart uses “some of the force of the wind to continuously push back against the wind.”

I felt confident that Andrews had settled the matter. But to make sure, I sent links of Andrews’ videos to Paul Camp, the physicist at Spelman College. He immediately began poking holes in Andrews’ test apparatus. Camp’s main beef was that the fan blades that created the wind were so close to the cart itself, that the cart was being subjected to turbulent air flow.

The viscosity of air, Camp explained, produces velocity gradients when air flows past an edge. “The behavior would also be very peculiar next to the fan blades in a linear wind tunnel. In that case, to see the effect of wind alone, you get far enough from the fan blades for viscosity to damp out turbulent flow. In this case, it is impossible to get that far away. What we would really like to see is smoke trails in his wind tunnel to see how the fluid is actually flowing.”

Once again, I’d been lured over to one side of the fence, only to be pulled back to the middle. I started wondering what Jack Goodman thought about this particular DIY science movement he had kick-started. Apart from one or two comments early on, he’d been quiet for the last two years.

In August 2009 I got Goodman on the phone and learned that he was a retired consultant/inventor living in Maryland. As a member of the Amateur Yacht Research Society, he’d been interested in the concept of DDWFTTW for a number of years. The members of the society frequently argued about whether or not DDWFTTW was possible. Goodman didn’t see how it was possible, but he had a nice model shop in his basement with a lathe, milling machine, and other shop tools, so he decided he’d try to settle the matter once and for all by making a wind cart.

Goodman initially tested his cart on a treadmill, and found that it could move in the opposite direction of the treadmill, which encouraged him. But he wanted to try it out in the wind. The wind and terrain in Maryland weren’t right to test it, so he brought it with him to his winter home in Florida and scouted around until he found a level road with wind conditions suitable for the experiment he wanted to run. He waited a “long time” for the wind to blow in the right direction before he was able to conduct the experiment, which he videotaped and posted online.

Goodman said he never expected his video to cause such an uproar (he didn’t post it to YouTube; someone else from the Amateur Yacht Research Society did that) and that he has gotten a tremendous kick out of reading the thousands of posts about it. He even gets a chuckle out of being called a charlatan and a fake.

I was even more convinced that DDWFTTW was real when I learned that Mark Drela, a world-renowned aerodynamicist at MIT, says it’s possible. Drela is the designer and maker of a variety of amazing human-powered, propeller-driven vehicles. In 1998, Drela designed a human-powered airplane called the Daedalus, which set a world record when it island-hopped more than 72 miles from Crete to Santorini.

Drela is also the developer of a computational aerodynamic analysis system called XFOIL, which allows aircraft designs to be tested before they’re built. An article in MIT’s Aero-Astro magazine reports that Drela has “engineered aircraft for Boeing, the wing for the Predator UAV, the keel of America’s Cup yachts, and experimental aircraft used by NASA. In addition to XFOIL, he has written design programs for rotorcraft, machinery blading, and axisymmetric bodies such as zeppelins.”

In other words, Drela knows his stuff. And so what does his analysis conclude?

“Although DDWFTTW seems like it violates physics, it really does not,” Drela explained to me via email. “The various analyses show this, and the cart experiments on YouTube are definitive proof. In my view, the most closely controlled and unambiguous DDWFTTW demo is the cart climbing up the tilted treadmill. The main problem is then convincing some people that this is equivalent to DDWFFTW. But whoever tries to argue against that equivalence is really arguing against Galilean relativity, which is unassailable. So that secondary argument is a complete waste of time.”

So Goodman, Andrews, and Cavallaro have been vindicated. DDWFTTW is possible.

But even with Drela’s analysis floating around the web forums, the debate won’t die. Last year, Cavallaro and his colleagues demonstrated the wind cart to the aeronautics and mechanical engineering departments at San Jose State University and Stanford. After those presentations, Cavallaro said, a UC Berkeley Ph.D. student contacted him about demonstrating the cart at Berkeley. She asked her professor, Dan Kammen (an Obama advisor and Nobel Peace Prize winner) about having Cavallaro present the wind cart to his students.

“He decided DDWFTTW is not possible,” said Cavallaro. “So it does fool some pretty sharp people.”

In July 2010, Rick informed me that he and his colleagues had taken a downwind cart they’d built onto the El Mirage Dry Lake Bed in southern California and had achieved a speed 2.8 times faster than the wind. They carried out the test in front of authorized representatives of the North American Land Sailing Association (NALSA). You can read Rick’s article about it here.

Mark Frauenfelder is editor-in-chief of MAKE.

Mark Frauenfelder

Mark Frauenfelder

Mark Frauenfelder is the editor-in-chief of Make magazine, and the founder of the popular Boing Boing blog.


  • Mikec

    I am not an engineer but I would like to offer the following brief comment. If the craft that was to be tested consisted of only a flat sail at right angles to the wind , I would confidently say that it could not go faster than the wind. All sailing vessels that sail faster than the wind do so at some angle to the wind (“reaching”).

    It appears that the craft that have been shown in the various videos do not contradict the above. The blades of the propeller are indeed angled to the wind and therefore could go faster than the wind and provided the propeller was big enough could supply enough force through the gearbox to propel the craft at a speed faster than the wind.

    I don’t wish to kick off another world war 3 on this topic but I do think the angle of the propeller blades is of relevance.

    • buddyhollyclone

      The passionate voices in this debate have been very surprising to me as well! re/ the previous comment: important to note that the blades are not acting like a sail (being pushed by the wind and turning in response), but as a propeller (pushing against the air – in response to being driven by the gearbox).

      I am an engineer, and at first this thing looked like a sham – reminded me of the crackpots who make “perpetual motion” machines with the magic of rare-earth magnets… but I think that the mechanics are fairly straightforward, and if one truly seeks to discover the truth, it will be revealed.

      • ThinAirDesigns

        @buddyhollyclone: “… important to note that the blades are not acting like a sail (being pushed by the wind and turning in response), but as a propeller (pushing against the air – in response to being driven by the gearbox).”

        Buddy, while what you say above in parenthesis is absolutely correct, part of what you say outside the parens is not correct. It’s likely that you have a complete understanding and have just worded it a bit loosely, but I will add something so others don’t get confused.

        You say: “it’s important to note that the blades are not acting like a sail” (and then go on to correctly clarify)

        Interstingly enough, the blades are acting *exactly* like a sail — it’s just that most folk aren’t aware of how a sail actually acts some of the time.

        Most folk think a sail always works as a turbine works — the air hits it and make it move. While that is often true (and always true when the boat is going upwind), it is also true that a traditional (non square rigger) boat sail often works in the opposite manner … it acts as a propeller and *accelerates* the air relative to itself rather than slows it.

        If one compares the properly trimmed sail of a traditionally equipped boat on a broad reach, one will find that in an aerodynamic sense it is acting identically to the blades of the traditional propeller mounted on the Blackbird.

        As Mikec correctly points out, the blades on the Blackbird are on one long, continuous, helical broad reach – the same angled reach as the sailboat. The only difference between the Blackbird blade and the sailboat sail is that the airfoil on the boat must go all the way around the world to complete one circle while the Blackbird airfoil takes a significantly smaller diameter and thus shorter path.

        JB

        • buddyhollyclone

          Very interesting – thanks for the clarification re/sails. I do better with gear trains ;)

          But very true – I was trying to just make the distinction between a geartrain-powered propeller and a wind-powered impeller. And even though I’m pretty sure I’ve convinced myself that it works, it may take a weekend prototype to re-set my intuition.

  • Rick Cavallaro

    Kudos to Mark Frauenfelder, and Make magazine for a great piece, for sticking with this story, and for really doing the homework.

  • mightor

    or maybe Drela could demonstrate it occurring (or not) in XFOIL, under simulated perfect conditions

  • DavidGlover

    Do you think Charles lost the bet? Is he still a unbeliever? Should he pay the $1000?

    • Mark Frauenfelder

      I don’t have an opinion about the bet, because I’m not really interested in it. The science is much more interesting to me. I now think that a wind-powered vehicle can indeed outrun a tailwind, and I’m very impressed by the people who have invested their own time to build vehicles to learn about wind carts. The betting and personal arguments are an unimportant side issue.

  • Rick Cavallaro

    I’m a giant fan of the Mythbusters. But do you honestly think they’re going to settle an issue better than a live test judged by the North American Land Sailing Association?

    For what it’s worth, JB and I tried every way we could to get the Mythbusters to take this up. I’m honestly not sure why they didn’t. Possibly because they concluded there was no winning after they did “Airplane on a treadmill”. Maybe because it doesn’t explode. Perhaps its a bigger build than they wanted to take on. Perhaps because they think this is obviously internet woo. I rather suspect (and hope) it was the latter. That would make it an even better brainteaser. Just think – it’s so *obviously* impossible that even the Mythbusters won’t attack it.

    >> or maybe Drela could demonstrate it occurring (or not) in XFOIL, under simulated perfect conditions

    So you have all the analysis, all the real world evidence, on the treadmill under controlled conditions and on the lake bed witnessed by experts, and finally the ability to build your own and test it for yourself for about $40 – and you figure you’ll be convinced by a simulation!?

    One day I’m going to get to the bottom of the Mythbusters mystery. I’m just dying to know if there’s a story there.

    • Alsee

      I think Mythbusters would be vastly more effective than the North American Land Sailing Association(NALSA) test. The reason is that most people have never heard of NALSA, and when told about it they don’t even bother going to the relevant webpage to look at their results. It’s just more internet Woo from an unknown nobody.

      People know Mythbusters. Mythbusters have a reputation for being reliable at independently debunking or confirming things. People would be far more likely to click to watch a Mythbusters video. Even without watching the episode a lot of people will put a lot of confidence in the easily verifiable fact that Mythbusters did an episode on it and confirmed it.

      Often 95% of the battle is just getting people to accept it’s possible at all. Once they have an open mind it’s much easier to explain how it works.

  • migpics

    When I was in school our engineering teacher showed us that a screw was basically a ramp that was rolled around a tube. By spinning it, you create a forward motion due to the pitch of the screw.
    In looking at this, I’m thinking that first of all, the propeller is acting like a sail. Just the way a sail boat tacks back and forth against the wind. What happens though, is when a sail is going with the wind, and reaches the speed of the wind, it goes flat, well in this case, the propeller, because it’s in a constant rotation, never goes flat, it is constantly tacking against the wind. By pushing the cart, you allow the momentum of the cart to create this constant tacking, which initially is started by the movement of the wheels, but then keeps going with the wind. If you could visualize a plan view of a sail boat tacking across the wind, now take that line of action, and coil it, basically like a spinning propeller, now you have constant tacking, but without having the vessel have to move at a diagonal to the wind.
    Another way to visualize it is a sail boat tacking in the wind back and forth. If you allow your distances between your tacking to approach zero, you effectively travel in a straight line.
    The prop does that by constantly switching the angle of attack to the wind, in essence, tacking back and forth very quickly.
    That’s what I’m thinking anyway. Sorry for the late comment, just read this!

    • RocketGuy

      I was about to post essentially the same thing.

      As I understand it, the force between the wind and wheels is similar to a boat reaching but just folded differently around the drive and propeller.

      Oddly, I have no trouble seeing how this works once I saw the blackbird video. But then, I’m a little weird.

  • gregb

    Of course this is possible energetically. Velocity and energy are not the same thing. Imagine the cart sits on its brakes and lets the propeller and a few gears wind up a rubber band (storing energy). Then the brakes are released and the card darts downstream (energy converted to velocity). Its downstream velocity is limited only by air friction- not the wind. With no air friction, it travels downstream forever at whatever speed the rubber band can produce.

    Unlike the thought experiment above, the wind cart tries to convert wind energy to motion on a continuous basis, balancing frictional losses against harvested wind energy. This is much harder, because the propeller adds a lot of drag, and that drag will tend to bring the car’s speed into sympathy with the wind speed. But a light, low friction, aerodynamically optimized cart (preferably with a variable speed transmission to optimally match ground speed to propeller RPMs, and thus to the apparent air velocity over the blades) should be able to travel faster than the wind.

    Simple toy wind carts generally have fixed gears between the wheels and propellers, which means there is only one speed where the terminal downstream cart velocity perfectly matches the propeller optimal drag conditions.

    Would challenge even the Mythbusters.

    • ThinAirDesigns

      @Gregb
      >> “But a light, low friction, aerodynamically optimized cart (preferably with a variable speed transmission to optimally match ground speed to propeller RPMs, and thus to the apparent air velocity over the blades) should be able to travel faster than the wind.”

      Turns out a light, low friction, rather crudely aerodynamically optimized, cart (without variable speed transmission) *can, did and does* travel faster than the wind (directly downwind).

      JB

  • gregb

    Hmm, the Mythbusters should race a properly designed wind cart against a simple square sail cart- which will definitely move at the wind’s speed. The sail cart should gather speed more quickly, but then the wind cart will pass it in the stretch…

    If they build the wind cart out of bicycle parts, Nuvinci makes a nice continuously variable transmission.

  • Rick Cavallaro

    We went one better than that with our model carts. We raced a turbine cart against a prop cart to satisfy some of the skeptics. As predicted the turbine cart took off like a shot – then the prop cart whipped its butt to the finish line.

  • Subduction Zone

    If this ever does get to be on Mythbusters there are better things to use than a square rigged cart or a turbine cart, both of which would be slower than the wind. They could even have a theme. For the Fourth of July they could release about a hundred neutral buoyancy balloons when the cart got to wind speed, the cart does take a while to get to wind speed after all. Or they could use a mixture of red white and blue smoke. Either of these could be carried by chase vehicles paralleling the path of the cart.

    Of all of the videos of the Blackbird, actually it was the BUFC when this shot was taken, was on their first weekend on Ivanpah. JB was driving the chase vehicle and passed the cart. As they shot back towards the cart you could see the cart charging through the cloud of dust raised by the pickup truck. I always like to ask the deniers what ratio of the speed of the wind does a cloud of dust travel at. Not one has answered to date.

  • Miguel Angelo

    If you can’t get to Mythbusters, the use the next best thing which are the many variants of Maker Faire around the world.

    Build a transparent tunnel of say 30 feet length with about 1 or 2 square feet section (to reduce costs wood frame and 6 mill plastic with a plywood base – 5 or 10 feet modules that you can clamp together – similar to those power tool races previously seen on the Make blog) and rails for the 3 wheels in the model shown above.

    Place a fan at one end of it and an Arduino with lights sensors (also as shown in the Make blog) at the start and end of the last tunnel section to measure the time of travel and therefore the speed. Maybe another tunnel module may be needed for good measure.

    Block the fan as you place the little cart in the tunnel at a precisely marked spot and close the tunnel up. Hold the cart in place (from the outside of the tunnel – with some blockage that prevents it from moving and spinning the blades) as the wind stabilizes and after a few seconds let it go. Measure the speed it reached.

    Do the experiment with the cart with the blades locked and not connected to the wheels. This will give you the “sailing speed” – just the wind on the non moving blades. Next let the blades move but do not connect it to the wheels – this will give you the “gyro-copter” speed (I have no idea if it’s better or worse). Lastly repeat it with the blades and wheels connected to demonstrate the additional speed above the wind speed.

    An additional test that can be done is to try different flat sails on the little cart(properly sized) to see the wind speed down the tunnel as another sort of reference that takes into account the friction between the wheels and the track.

    All in all, I find the debate very interesting and a sign of our times. Imagine how would this happen just 20 years ago!

    Thanks to Make Magazine for creating the opportunity to discuss it.

    • Subduction Zone

      I am sorry, but this would not convince the deniers. The treadmill test is a definitive test. It uses the 400 year old concept of a Galilean Transformation. They would come up with some other complaint, for example you would probably here some nonsense about how an enclosed wind tunnel is not the same as the air.

      • vf

        >> They would come up with some other complaint, for example you would probably here some nonsense about how an enclosed wind tunnel is not the same as the air.

        Oh, I know what they would say. The same problem as with the treadmill: “The wind tunnel uses fan with a motor to move the air. So the carts in the tunnel are not wind powered, but motor-driven.”

    • buddyhollyclone

      Seems to me that the dearth of level-headed discussion is what separates hobbyists from actual scientists or experimentalists. Real science is about answering interesting questions – not boosting egos, making financial wagers, or “whipping butts”.

      Miguel brings up a great point. There must be some satisfactory testbed apparatus that will transparently show the mechanism of propulsion. Or at the very least provide a real measure of acceleration and terminal velocity that will vary with a few controlled parameters. Interesting questions are: What effect does the propeller pitch/design have on terminal velocity? What about gear ratio? Air speed? Is the terminal velocity simply a unitless function of wind speed?

      A straight wind tunnel is a great idea, as many folks are not able to intuitively translate a “still-air moving-ground” coordinate system to a “moving-air still-ground” system. It has the unfortunate burden of taking up more space and materials, but is satisfyingly transparent and accessible. The addition of a controlled environment and electronic timer would be a major plus. Shaky video and gusty wind just doesn’t convince.

      Also, suggesting to move this to a Maker Faire is a great idea! This could be like the modern-day pinewood derby. Your cart must meet certain size and weight requirements, and will be propelled by a steady and predetermined flowrate of air through a CreativeCommons licensed air tunnel design.

      Let’s not try to squash the nonbelievers — they’ll just go and form their own religion ;)

      Instead, let’s encourage eachother to be inquisitive, patient, and methodical. Group hug, anyone?

      • Rick Cavallaro

        >> Seems to me that the dearth of level-headed discussion is what separates hobbyists from actual scientists…

        If only that were so. Some of the greatest abuse came my way from the scientific community. If you don’t think scientists act childish and let their egos get wrapped up in their arguments you should hang out with paleontologists for a bit (although I’m sure others are just as bad). Check out Bryson’s “A Short History of Nearly Everything”.

        >> Interesting questions are: What effect does the propeller pitch/design have on terminal velocity? What about gear ratio? Air speed? Is the terminal velocity simply a unitless function of wind speed?

        All easily answered. But what’s the point if people refuse to accept all analysis and all real-world evidence?

        >> A straight wind tunnel is a great idea…

        I’ll make you a deal. You build me a transparent, instrumented, straight wind tunnel long enough for the job, and I’ll provide the cart of the experiments. By the way, make sure the diameter is large enough (say 10X the prop diameter) so people don’t question the issue of air being accelerated as it flows between the vehicle and the wall (and I assure you they still will).

        >> Also, suggesting to move this to a Maker Faire is a great idea!

        Look for us there in 2011

        • buddyhollyclone

          Rick, I can only imagine the irritation you’ve had to put up with from the “deniers” and abusive comments. I applaud you for sticking to it and manufacturing evidence and documentation. I am reminded of Galileo: “… All the disputes that for so many generations have vexed philosophers are destroyed by visible certainty, and we are liberated from wordy arguments”. But obviously your documentation is not sufficient for a certain proportion of the community — what, like 20 percent? Difficult to believe, I know, especially considering the full-scale blackbird wind racer vids posted by you and others.

          Thus my interest in encouraging an agreement regarding the apparatus.

          Point well taken about the wind tunnel. Probably infeasible on a “hobby-scale”, but maybe folks could iterate a few times and think up something satisfactory. Long indoor hallway and large movie-industry hurricane machine, perhaps. Surely some maker has a wind machine in his garage. Mostly, I propose the wind-tunnel idea because it’s more fun than a treadmill.

          • Rick Cavallaro

            >> I can only imagine the irritation you’ve had to put up with from the “deniers” and abusive comments.

            It’s such a mixed bag. I presented it as a brain-teaser, so half the fun is having people get it wrong. But the other half of the fun is supposed to come with explaining it and having them get it all of a sudden.

            What I hadn’t counted on was all of the fun of being called an idiot and much worse. But I’m getting over it.

            >> I applaud you for sticking to it and manufacturing evidence…

            We prefer not to think of it as “manufacturing evidence”. : )

            >> obviously your documentation is not sufficient for a certain proportion of the community

            I put forth the following challenge: I’d like anyone to describe a test or demonstration that would satisfy the greatest skeptic. Be as bold as you like. Put the skeptic in the cart. Give him instrumentation calibrated by NASA before during and after the run. Do the test in a wind tunnel. Have Galileo, Einstein, and Newton on hand to explain, verify, and witness.

            I will then give you three reasons for any such demonstration that skeptics would give to deny it.

            >> maybe folks could iterate a few times and think up something satisfactory.

            See above.

            We’ve done this on paper, on treadmills, outdoors, established a world record, and have one of noted aerodynamicists of our times explaining it both mathematically and in plain english. It’s time to stick a fork in it. Next plan… up wind faster than the wind.

  • Subduction Zone

    At about 2:15 you can see the BUFC (the unfinished Blackbird) charge through a cloud of dust made by the chase vehicle. I always like to ask deniers, what is the ratio of the speed of the wind of a cloud of dust blown by the wind. None have answered to date. It is obvious, even to the most ardent denier, that fine dust will have a speed almost identical to that of the wind.

  • SaskView

    Once the car is traveling faster than the wind, the propeller ‘should’ start turning backwards, slowing the car down.

    • Subduction Zone

      Why do you believe that? The wheels drive the propeller, not the other way around. The propeller is always slowing down the speed of the wind that it interacts with relative to the ground. That air had energy. Where did it go to?

  • migpics

    I want to throw this question out there because I think it would help give us a reference point as to what is happening here.
    If you define a DWFTWV as the vessel as whole, then it is obvious from the many tests and physical experiments that yes, the vehicle is travelling faster than the wind.

    But what if you define it as from the perspective of the actual point of contact with the wind? In the case I had mentioned above of a boat tacking back an forth and the tack distance aproaching zero, would give the perception that you’re moving in a straight line, when in fact, you’re zig zagging back and forth in very small increments.

    If you’re ‘sail’ is perpendicular to the wind, it will eventually reach the speed of the wind and then go flat, thereby bringing about the idea that faster than down wind vehicle is impossible.

    So in the case of the cart, you have a dynamic sail and just like a boat that tacks back and forth, you can achieve faster than wind speed, but pushing the vehicle in a straight line rather than back and forth like a boat, but the sail is actually doing the tacking!

    So to prove the efficacy of the sail, I propose the following (if you have resources in Norway to do this I’d love to meet you and we can work on it together!)

    Create your standard cart with the propeller on it but do not attach it to the wheels.
    Put a fan on it and see what happens. I anticipate the prop will spin but the cart will not move.
    Now, attach a motor to the prop. Have the motor rotate the prop at such a speed that it cannot propel the cart forward on it’s own.
    Turn the fan on and see what happens. I anticipate that the cart will move forward slowly increasing speed because now you have a constant change in the angle of attack of the wind, and the friction from the motor gives a certain amount of resistance which allows the vehicle to be pushed forward. It may even go faster than the fan blowing it because like I mentioned before, it’s really in a continuos tacking.
    Last, attach the prop to the wheels just to check it.
    So, going back to the definition of things, if this vehicle is really just a boat with a sail that is constantly and tacking against the wind, then no, downwind faster than wind vehicle has not been proven. But if you assume that the propeller as a whole is a sail and disregard the angle of attack to the blades, then yes, you now have a downwind faster than wind vehicle.

    • Rick Cavallaro

      >> Put a fan on it and see what happens. I anticipate the prop will spin but the cart will not move.

      The prop will spin, and will create significant lift. This is called autorotation. It’s how a helicopter gets safely back to the ground if its engine quits.

      >>if you assume that the propeller as a whole is a sail and disregard the angle of attack to the blades, then yes, you now have a downwind faster than wind vehicle.

      Each propeller blade is a sail. Each blade is on a continuous spiralling downwind tack. The propeller as a whole is going directly downwind faster than the wind – while spinning.

  • vivi

    I’ve been following the debate on Make the last few days with a lot of interest.

    When I heard about the problem the first time I immediately thought that it was impossible. My intuition told me so. However I know from experience that if intuition can often help the scientist by allowing him to skip reasoning to get a glimpse of what’s ahead, it can also quite often be his worst enemy by disabling rational thought. So I watched the video, and well, you can’t deny such material proof.

    So two questions come to mind, first why am I wrong to think that you can’t go faster that what’s pushing you, and second how does this machine work. The answer to the first question is quite obvious, once intuition has been pushed aside and reasoning has taken its place. In fact it happens all the time. For example the output of a gear train can spin faster than its input. I saw a good example that you can try at home to convince yourself in one of the comments : stand a bike wheel and push forward on the middle of the bottom-most spoke : the wheel will go forward twice as fast as your finger. No replace your finger by a small sail, you have a vehicle that can go faster than the wind (for a small rotation, after which you’d have to come up with a mechanism to deploy the sail on the next spoke).

    The second question, how it works, is a bit more difficult. I’m by no means a competent aeronautician but I think I’ve come up with a reasonable answer. My first understanding is that the propeller does not quite work like a regular propeller, like in a plane for example. In a plane the propeller transfers some backwards momentum to the air, and per Newton’s second lay this pushes the plane forward. Some people when trying to explain faster than the wind motion, give the explanation that the wheels power the propeller, which makes the vehicle go forward, which makes the wheels go faster, etc… And I understand the skeptics at this point because this explanation *alone*, is clearly impossible and against the laws of conservation of energy. However (I believe) this is not how this works. The vehicle is simply pushed forward by the wind. But what happens when you reach wind speed, you ask? At this point surely the speed differential is zero, so there can be no thrust. But what matters is the *relative speed* between the wind and the propeller. Since the propeller is rotating, and angled, you must add the effect of the rotation to the speed differential. That’s how you can still extract momentum from the wind even if the cart is going faster than the wind; because the propeller, due to its rotation, is in fact going slower than the wind along the wind direction axis.

    At this point I’m pretty sure this would be quite easy to put into equations, and figure out the max speed, optimal blade angle, best wheel to propeller ratio etc. Intuitively (*this time* I think I’m right) I think speed is limited only by drag and losses.

    I wrote this mostly to see if it was clear enough in my mind to articulate it into words. This is usually a good test. It might also help others to understand it better.

    • gregb

      Vivi-

      Your observation about the bicycle wheel is absolutely correct. In fact, I’ve built such a device and will film and post on youtube. The issue, of course, remains– convincing people the device is ACTUALLY moving faster than the wind. But it does.

      In the case of the wind cart, the propeller first acts like a simple drag plate and pushes the cart along. Even though its rotating and blowing air in the “wrong” direction, at low speed the “fan” effect is too weak compared to the downstream wind forces. (imagine a 10 mph wind and the cart is just off the starting line- the rotation speed is irrelevant compared to the drag. So there is more pressure on the rear of the cart than the front). But as it draws energy from the wind, it continues to rotate in the same direction, partially reducing the pressure on the front (downstream) side of the cart, so the upstream wind will continue to drive it forward. More pressure on the back of the blades than the front. Basically, its cutting a hole into the pile of wind created as the cart speeds up. Only works if the propeller dominates the drag- the cart must be nearly invisible by comparison.

      • Rick Cavallaro

        >> Only works if the propeller dominates the drag- the cart must be nearly invisible by comparison.

        Actually it can work exactly the other way around. Then you’ll only go a little faster than the wind.

    • Rick Cavallaro

      >> My first understanding is that the propeller does not quite work like a regular propeller, like in a plane for example.

      That’s a common assumption, but the propeller does in fact act exactly as the propeller on a plane.

      >> Some people when trying to explain faster than the wind motion, give the explanation that the wheels power the propeller, which makes the vehicle go forward, which makes the wheels go faster, etc…

      And that explanation is correct.

      >> And I understand the skeptics at this point because this explanation *alone*, is clearly impossible and against the laws of conservation of energy.

      It doesn’t violate the law of conservation of energy because the propeller is operating in a different medium than the wheels. The wheels move faster over the ground than the cart moves through the air. The wind powers that little feedback loop. Take away the wind and it all comes to a stop.

      >> the propeller, due to its rotation, is in fact going slower than the wind along the wind direction axis.

      Nope. The prop is going faster than the wind.

      >> Intuitively (*this time* I think I’m right) I think speed is limited only by drag and losses.

      Right – and chosen prop pitch and gear ratio.

  • gunter

    So if it can go faster than the wind, then shouldn’t it move into the wind at very slow windspeeds, then reverse at higher windspeeds moving downwind? The reversing speed would be roughly the speed that the cart can go faster than the downwind? (essentially moving into the wind, as it is going faster than the wind)?

    Just a thought.

  • Mikec

    When I first posted the initial comment on this article, I had not done much research on the available information on the web and was still trying to work it through in my head.
    I have now done that research and am comfortable in my own mind that it is possible and has been proved. As I said in my original post it was not my intention to kick off WWIII and from reading the majority of the posts I can see that the debate seems to have moved on from the original days of derision and abuse to a well structured debate.

    I think that questions/problems like this tends to unite the hobbyists and scientists/engineers with the hobbyists asking the questions/posing hypothesis and the scientists/engineers providing an explanation of the relevant theories and correcting misinformation and both groups learning from each other.

    Out of these sort of debates there seems to emerge three distinct groups. The first is those who immediately take a position without giving it too much thought and then proceed to to discredit/abuse anyone who dares disagree with them. The second will retreat into their minds and onto the web and try and rationalise the problem and arrive at a position that they are comfortable with and also attempt to rationally explain their thoughts to others by analogy and theoretical argument. The third group emerges out of the second group and builds the bloody thing and conducts rigorous tests/experiments to prove their position. I have no time for the first group – learn a lot from the second group and are in awe of the third.

    May there be many more of these conundrums and may the groups 2 and 3 prevail.

    By the way does any one have any thoughts on which way the water goes down the plughole in the southern hemisphere?… (Just joking!!!!!!!!).

  • Miguel Angelo

    Who says 2.8 times the wind speed is good enough?

    How fast can you really go down wind?

    How would you tweak the original cart design to make it faster or to prove it wrong?

    Let’s put our thinking hats one and compete for the Faster than the Wind World Title at the Maker faire next year!

    Non-believers can come to prove that it is a hoax and have fun. Believers will compete and have fun. The general public will have no clue but will have fun too!!!

    Those that cannot attend can send their carts in (let’s make them small so they are cheap and light and so will the real wind tunnel to test them) and a Maker Faire volunteer can place them at the spot – timed races can be broadcasted live on-line across the globe for anyone to see. The cart may not be returned though :( (unless you pay for shipping & handling ;) ).

    The more eyes we have on this the better it will get.

  • Jack Goodman

    I want to thank Rick Cavallaro for his persistance and Mark Frauenfelder for this great history lesson. This is the best article on DDWFTTW yet. There is only one thing I would like to add. When I first read about downwind faster than the wind in AYRS, my gut reaction was, how could it be possible? After turning the problem upside down, the question changed from, how can you get energy from the wind if there is no wind, to, what to do with the energy from the moving ground. Armed with that and a little knowledge of propeller lift to drag ratios, it was relatively easy to make a propeller and come up with the right gear ratio. Except for the radio control for steering and brakes, the cart remains unchanged from the first treadmill test. I always knew it would work, but then and even now, it still suprises me when it advances up the treadmill.

    • Mark Frauenfelder

      Thanks for your comment, Jack! I appreciate it. For those of you who don’t know, Jack Goodman is the fellow who got this whole thing, er, rolling, when he made a DDWFTTW cart for an Amateur Yacht Research Society challenge. He took a video of his cart, and the AYRS posted it to YouTube.

      Later this week we will run a very informative interview I conducted with Jack last year.

      • Rick Cavallaro

        I *think* Jack built his cart in response to the internet battle I inadvertently started with the brain-teaser I posted earlier that year – but I could be wrong.

  • Rick Cavallaro

    And we’d like to thank you Jack. It’s good you didn’t know it can’t work. : )

  • vf

    Quote from the article, by Dr. Paul J. Camp, a professor in the physics department at Spelman College in Atlanta, Ga. Camp: “In fact, we can state this in pretty bare terms — for a car moving downwind at wind speed to go a little faster is physically indistinguishable from a car at rest on the ground in stationary air to suddenly leap into motion.”

    Does the professor finally see the difference, between:

    air speed < ground speed

    and:

    air speed = ground speed

    Or does he still make excuses like Charles Platt?

  • Patrick Willgohs

    I know it’s a fun thing to wrap your mind around, but it’s been done full scale. I thought it was old news considering the team sponsored by Google and Joby made initials attempts back in mid summer and the North American Land Sailing Association (NALSA) announced their place in the official record books in September. It’s one thing for a group to announce “it’s not possible” which merely opens the door for someone else to come back and say “yes it is, look we just did it.” but the fact is that these guys succeeded.

    Here’s a Wired column from july:
    http://www.wired.com/autopia/2010/07/downwind-faster-than-the-wind-possible-and-theyll-prove-it/
    The team’s own blog covering construction and various attempts (along with the most recent post about the progenitor of this topic, Andrew Bauer, passing away):
    http://www.fasterthanthewind.org/
    And here is the NALSA page announcing their record setting success:
    http://www.nalsa.org/DownWind.html

    I know, there’s still plenty of interesting stuff to learn and discuss about the topic, but debates over the impossibility of it are should all now be unceremoniously settled.

  • Rick Cavallaro

    @vf

    >> What does professor Camp say now, BTW?

    Good question. It got me wondering as well – so I gave him a call. He felt that he hadn’t heard a sufficiently complete explanation to make a determination at this point, but he had a few minutes to hear me out (he had a student in his office at the time). After discussing it for a few minutes he now wants to consider it further.

    He agreed that the above characterization is accurate when I asked if he’d mind my posting it. Additionally, I understood him to say that the treadmill is a valid experiment that represents the same thing as a car going downwind on the road. His final questions related to self-starting in a tail-wind, and I briefly explained how that happens. I believe he’s considering that as well. I’ll follow up with an email to him and encourage him to post here as well. This paragraph contains my interpretation of our discussion. I think he’d agree this is accurate as well, but I didn’t run this part by him.

    • vf

      Cool, make sure he has links to Drela’s analysis, videos, this article etc.

  • Rick Cavallaro

    I sent him links to this article and to Drela’s analyses. He indicated that he’d seen the videos. We discussed both the treadmill and playa videos. He was clearly quite skeptical initially, but also open-minded. I think he’s quite close to having it sorted out. I told him the readers here would love to here from him in these comments either way. So I’m really hoping he has the time and inclination to join us here.

  • Jack Goodman

    Rick, to some people it may seem your machine runs on a wind that blows nobody any good.

  • Jack Goodman

    Rick, to some people it may seem that your machine is powered by an ill wind that blows nobody any good.

    • Rick Cavallaro

      Indeed it sometimes seems that way, but certainly a lot of people have had fun with the topic too.

      Mark Frauenfelder is promising us an interview he did with you. I’ve been following every day eager to read it. Crossing my fingers that it’s posted tomorrow.

  • http://www.facebook.com/jonas.alexis Jonas Alexis

    Fascinerande! trodde inte detta var möjligt.

  • http://www.facebook.com/jonas.alexis Jonas Alexis

    Fascinerande, trodde inte detta var möjligt.

  • Pete Metcalfe

    Guys , I haven’t told many this as when i have it hasn’t gone down well and I know I’ve been put in the loony catagory . In reading & viewing the videos on your wonderfull down wind machine I was reminded of my experiences while sailing my canoe in the tidal river on my boundry. Namely , with a slight push to start it [ reads paddle ] the canoe [ with no wind – other than the now apparent] accelerates at times quite rapidly against the tidal flow ! . this I believe to be analgeous to your wind cart ,only my wheels – where the power comes from – is the high aspect foil which is getting lift from the water current .
    OK , it dosen’t seem to make sence to me rereading what I just wrote so let me try to rephrase that .
    with little to no wind I am able to tack up against the tidal flow by useing the canoe/leeboard/foil to gain lift from the same current .That combined with the apparent wind is enough to overcome the waters flow and I progress up stream . I need to say that I need to start the canoe moving to get the required lift — much in the same way that I saw mr Goodwin’s [ was that right?] wife push start the infamous cart on it’s downwind trip .at times I would paddle hard out on a given angle of attack only to feel the canoe accelerate rapidly ahead , but after having to turn to avoid pranging into the river bank , the lift was lost . It seemed to me for every dollar in [ a paddle ] I got two dollars back . Hmmm seems to me I can’t explain myself enough ! . Ok, I finish by saying that time and time again while reading of the down wind cart I was reminded of things like , well how weird it was to feel acceleration when there was no apparen’t wind — Rick , when you get to wind speed , that is , there is no apparent wind , how weird/amazing is it to feel your cart accelerate Given there is no wind ??

    • Pete Metcalfe

      I should have reread that last post to qualify one comment I made . when I ” paddle hard out” I only do that to get the boat up to a certain speed [ I don’t keep paddling – which is how it read] — I guess at that speed the lift outweighs the drag — after which it accelerates rapidly until I need to turn to avoid the river bank. was always hopeing to find time to make a hibrid – electric motor to get the craft to lifting speed , then pem magnet dc motor becomes gen set to replace the power for the next time I required it , etc etc .

  • http://www.facebook.com/morey.ladini Morey Ladini

    “…DDWFTTW is not possible…”
    decided
    “Dan Kammen (…an OBAMA advisor…)….”

    “…It does fool some pretty sharp people…”

    Say no more….

  • $4330198

    Landsailors go faster than the wind on a daily basis around the world, sometimes twice the speed of the wind. Ice sailors have been going faster than the wind for a long time.

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