By Mark Frauenfelder
In 2007, MAKE projects editor Paul Spinrad sent me a link to a YouTube video of a wind-powered cart, made by a Floridian named Jack Goodman, that seemed to be able travel directly downwind faster than the wind. How could a wind-powered cart outrun a tailwind, we wondered? Intrigued, Paul and I asked contributing editor Charles Platt to repeat the experiment and report on the results for MAKE.
Charles built a small cart, but was unable to get it to outrun the wind. Charles wrote in his article (which appeared in MAKE Volume 11 in August 2007), “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.” In the end, Charles suspected Goodman had played a prank.
As soon as the issue hit the newsstands, our message boards (here, here, here, and here) began to boil with impassioned arguments over the theoretical and practical possibility of travel “DDWFTTW” (Directly Downwind Faster Than The Wind). Several people emailed me, including a fellow named Rick Cavallaro, about errors in MAKE’s wind cart design. I soon came to the conclusion that we had likely misunderstood the design of Jack Goodman’s cart. I told Rick I would like to publish a follow-up article (authored by him) in MAKE, but not until I’d conducted more research, and not until Rick had developed a convincing DDWFTTW demonstration. Rick happily obliged, and in the months to follow, he kept me apprised of his impressive research efforts.
Meanwhile, I began corresponding with wind cart enthusiasts, skeptics, physicists, and Jack Goodman. There was no clear consensus — even some physicists told me DDWFTTW was impossible — but I was starting to side up with the proponents.
Then, 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). It was very convincing, and I asked Rick to write an article about it, which you can read below.
Is DDWFTTW possible? In 2007 I didn’t think so. In 2010, I think so!
—Mark Frauenfelder, editor-in-chief of MAKE
The Little Cart That Did
By Rick Cavallaro
Is it possible to build a wind-powered vehicle that travels directly downwind, faster than the wind, powered only by the wind, continuously?
This is a question I asked myself several years ago. After working out a few vectors, I decided it should work just fine. But since this is pretty clearly counterintuitive, I figured I’d pose the question as a brainteaser on a kitesurfing forum and a radio-controlled helicopter forum.
To my surprise, very few people believed my claimed answer was correct. They simply didn’t accept my vector analysis.
But more surprises were in store. It turns out that an aeronautical engineer by the name of Andrew Bauer built exactly such a vehicle in the 1960s. There exist a few still photos of Bauer standing next to his cart, but little other evidence. There’s no compelling documentation beyond Bauer’s own claim that he beat the wind speed briefly, and by a modest amount.
The next surprise came when a man by the name of Jack Goodman built a working model of such a cart to settle the now raging debates taking place across the internet. Goodman intended only to prove to his sailing buddies that the feat was possible, but one of those buddies posted Goodman’s proof (in the way of a video) on the internet.
This only fanned the flames. The video went viral. There were claims it was a hoax — that it was being pulled by a string, that it was going downhill, the wind wasn’t directly at its back, the wind wasn’t steady, and on and on. Goodman could have made additional videos addressing these concerns but, as we learned the hard way, doing so would not be trivial, and still few would be convinced.
In 2007, MAKE published an article titled “The Little Cart That Couldn’t” by Charles Platt. This article specifically addressed Goodman’s video, and concluded that Goodman had hoaxed us all.
Small demonstration wind cart. Photo: Rick Cavallaro
Learning the Hard Way
After more than a couple of years debating this on the internet, my old hang gliding buddy, John “JB” Borton, convinced me we would have to build our own cart and address the skeptic’s concerns if we hoped to convince them. And so we did.
To address the issues of whether the road was level, the wind was constant, the cart was going downhill, or being pulled by a string, we decided to perform (and document) carefully controlled tests. If this were an airplane, we’d use a wind tunnel. But since this vehicle is intended to go downwind — rather than into the wind — the appropriate instrument for our tests was a garden-variety treadmill.
Rather than move the air over the road, we’d move the road beneath the air. Galileo, Newton, and Einstein have assured us (and it’s now one of the most basic and accepted principles in physics) that these two situations should be identical from the point of view of the cart.
If our cart could hold its ground on a level, moving treadmill, it would be a demonstration of going directly downwind at exactly wind speed. If it could advance, against the motion of the belt, it would be an ideal demonstration of going directly downwind faster than the wind.
Of course there are those that argue there’s no wind in the room, so the treadmill test is not valid. But it’s really just a matter of looking at it from the cart’s point of view. If you ride your bike downwind at exactly wind speed you won’t feel any wind either.
Video footage of the first run of the two days spent on the lakebed in Ivanpah, NV
So, the little cart did as we predicted. Not only did it hold its own on a level treadmill, but it advanced against the belt consistently. In fact, we inclined the treadmill to its maximum angle, and the cart climbed the treadmill against the motion of the belt.
Still, most of the skeptics remained … skeptical. So we invited them to submit tests they’d like to see. We panned the camera to show there were no fans or strings. We hung streamers over the belt, in front of the cart, and behind. We placed a fan in front of the cart to create a headwind (as requested). But still the doubters (including Platt as well as some noted physicists and aero engineers) remained unconvinced.
Ultimately, we posted a detailed set of build videos (watch part 1 | part 2 | part 3) so that anyone could build their own working model of our cart and prove it to themselves for about $40 in parts. In Texas, group of high school students on a budget followed our plans and improvised them to keep the price below $20! The result? They won the science fair with their demonstration.
But with the skeptics still unconvinced, and the hang gliding and kitesurfing seasons winding to a close, JB convinced me we’d have to build a full-scale, manned cart that could operate outdoors in “natural” wind and be witnessed by trustworthy experts. And so we did.
With funding from Joby Energy and Google, we proceeded to build a cart that weighs 450 lbs and stands 23′ tall to the top of its 17′ propeller. We approached the North American Land Sailing Association (NALSA) to develop a record category specifically for wind-powered vehicles designed to go directly downwind faster than the wind. We worked with NALSA over the next several months, and ultimately established a world record by going 2.8 times the wind speed directly downwind on the 2nd of July 2, 2010 on the El Mirage Dry Lake Bed in California’s Mojave Desert.
Blackbird wind cart. Photo: Emilio Castaño Graff
Some skeptics still remain, but then there are still those who believe the Earth is flat and man never stepped foot on the moon. So we’ve decided to be satisfied with the evidence we’ve produced and the minds we’ve changed. And we’d certainly like to thank MAKE magazine for giving us the chance to set the record straight regarding “the little cart that did.”
Blackbird wind cart. Photo: Steve Morris
In the spirit of MAKE and the scientific method, we truly hope some of you will follow our build videos and make one of these carts for yourselves. It’s not difficult to do, and if you have a hard time accepting that a wind-powered vehicle can go directly downwind faster than the wind, you owe it to yourself to see it firsthand.
Up next: On Monday, Make: Online will run my piece about wind carts and their proponents and detractors, and on Tuesday, you can read my interview with Jack Goodman, the wind cart designer who captured the attention of so many people. –Mark Frauenfelder
Editor’s note: We gave Charles Platt, the author of the wind cart article in MAKE Volume 11, the opportunity to respond. His response is below. Rick Cavallaro asked to respond to Charle’s statement, which is also below.
I have never denied that a vehicle may be designed that will move into a headwind if the propeller is geared appropriately. What I do not believe is that this vehicle can start from rest with the wind behind it, accelerate until it is moving at the same speed as the wind, and then continue to accelerate faster than the wind, i.e. into a net headwind, without any fluctuations in wind speed, and without any gear-shifting along the way. That is what the original video from Florida purported to demonstrate, and is where all the arguments began. I have always suspected that the Florida video was faked.
I know very little about Rick Cavallaro’s cart, and am not very interested, partly because Rick has been extremely abusive, obnoxious, and condescending to me, and partly because, as I say above, I am quite willing to believe that his vehicle can move into a headwind. Indeed, the very primitive cart that I built for my original MAKE article did succeed in edging forward into a strong blast from a large fan. Again, what I do not believe is that his vehicle or any other can start with a steady wind behind it, accelerate to a speed equal to that of the wind, and then continue to accelerate so that it is moving faster than the wind, in one uninterrupted process.
I have repeated myself in an effort to make this clear. — Charles Platt
Mr. Platt seems to suggest that he refuses to consider real-world evidence because he feels I’ve been “abusive, obnoxious, and condescending” to him. This strikes me as being ironically similar to our differing position on reference frames. From where I stand, Platt established the pattern of abuse and condescension in his emails to me. Perhaps we’re both right (or wrong) on that count.
Unfortunately, Platt wrote an article presenting an unfair attack on an honest man (Jack Goodman), without even contacting Goodman or making any reasonable attempt to reproduce Goodman’s results. To me this seemed unfair. My only hope here is to set the record straight. I can live with the fact that Platt, and many others, may never accept these results that have been ratified by NALSA (a qualified, independent, and disinterested organization). I hope that we can agree to leave it at that, and not attack each other in public any further. — Rick Cavallaro