An interview with Jack Goodman by Mark Frauenfelder

In this third and final piece of our wind cart series, we interview Jack Goodman, the man from Florida who shot a video of a cart he built to find out if a wind-powered vehicle could outrun a tailwind. Goodman’s video (which was posted by the Amateur Yacht Research Society in 2007) seemed to show that it could be done. When the video hit YouTube, it launched a passionate debate between people who thought such a cart was possible and those who thought Goodman was either misguided or a prankster.

In August 2009, I called Jack Goodman to find out a little more about his experiment and about him.Mark Frauenfelder: I saw your video, which really kind of caught the whole web and amateur science movement by storm. How long have you been interested in making a downwind cart like this?

Jack Goodman: Have you heard of AYRS, the Amateur Yacht Research Society?

MF: Only after I started looking into this and then I read your paper that was published in its newsletter a couple of years ago.

JG: OK, I’m a member of that. And they had been arguing for about a year over whether it was possible. The vast majority said no, it wasn’t possible, and they were arguing and arguing, and at first I didn’t think it was possible either, but it came to me how it could work. It’s just a matter of turning your mind around to thinking about it. And once you think about it the right way it’s perfectly clear that it could work.

Once I figured out it could work, they started talking about offering a prize to make one and I thought, “Well, I’m going to be first on that one,” so I made one. I sent them all the data. I did all these load tests and things on the treadmill.

They said no, that wasn’t adequate. That wasn’t good enough. They wanted to see it work, so I had to wait till I went to Florida where it’s flat enough to do it.

Then I had to wait for a month or two to get the right wind because it’s surprisingly difficult to find wind going in the right direction and the right speed. See, at about a 10-mile-an-hour breeze, it starts to come up on the curve, and at 12 or 14 it just hauls ass. I can’t keep up with it.

I strapped my camera to my bicycle and my radio control to the bicycle. My wife had to push it and of course I had left the brake on. I took the brake off, and off we went. The wind kind of died for a little bit and finally came back. All this time I was trying not to fall off the bike, trying to steer it, and trying to keep the camera in the right direction, because the camera was tied to the bike. I had to start it and then I just had to kind of keep the bike in the right place.

It’s a horrible movie and I could have done a much better one but I didn’t think anybody would watch it. I sent it to AYRS as proof and they apparently put it on their website and they got so many hits it closed it down. They’re the ones that put it on YouTube. I didn’t do that.

MF: The cart itself looks really well built and I love the fact that you hooked up some servos and a remote control. Do you have a background in model making?

JG: I’m a consultant and an adventurer. And part of my consulting is I make laboratory instruments. So I mostly made it out of stuff I have in stock. If you’re a model maker you’d go crazy in my basement. I’ve got a milling machine and a lathe and a drill press and I’ve got boxes of Grade A bearings and gears and belts and you’d just go crazy to look at that.

MF: That’s really cool. How do you think the wind cart works? The argument against is it that it’s moving in a headwind so there’s no force being applied from the wind.

JG: The basic thing is there’s a certain amount of energy associated with the disc that the propeller intercepts. It’s got a 32-inch propeller, or about that. It’s just a few watts, but there’s a certain amount of energy available. And difference between the land speed and the air speed — and that’s all. You don’t want to think about the cart moving or the ground moving, it doesn’t matter. The difference in the speed between the two, the ground and the air — it is irrelevant which is moving.

And if you intercept a disc 32 inches in diameter at 10 miles an hour there’s a certain amount of energy available. If you can make a car that’ll go 12 miles an hour with that amount of energy, then it has to work. That’s one way to look at it. It simply has to work.

The other way of looking at is “airplane wings.” You can hold up a 1,000-pound airplane with way under 100 pounds of force pushing the plane forward. Any airplane worth its salt will do 10-to-1. And the airplane wing is just a blade of the propeller. It only takes a tenth of the power to push it forward through the air as you get static lift. The airplane’s not going up or down. It’s staying level.

So if you tilt that airplane vertically then it’s staying stationary in the air. It’s not moving upwind or downwind so you’re not getting anything for nothing here. If it were a 1-to-1 ratio it would create enough lift to push the propeller around.

Well, it’s hard to get a propeller to 10-to-1 but it’s easy to get a propeller to 3-to-1. And it also depends on how fast it’s going, which is another reason why I couldn’t keep up with it. The propellers that are stationary are terrible as far as efficiency goes. The lift-to-drag ratio is terrible but once they start going through new air, accelerating forward, their efficiency goes way up. So once this thing starts going faster than wind speed, it’s — for lack of a better word — processing new air.

And when it starts doing that then it gets way more efficient and at that point it just takes off. Once it starts no longer dealing with what it has just pushed against but working on new air. But anyway the thing [to keep in mind] is the lift-to-drag ratio. The propeller has a better than 1-to-1 lift to drag ratio. And at 1-to-1 it only has to push hard enough against the air behind it.

Now I have to be careful when I say that because all of the aerodynamicists go crazy — you can’t push against air. And if you’ve read any of the blogs, you’ve gone through that. But to understand it — and in fact they’re kind of wrong because if there’s a high pressure on one side and a low pressure on the other, you are clearly pulling air in from the front and you are pushing it out the back. But we get into semantics here and everybody goes crazy and they completely lose sight of the problem, which is why everybody has so much trouble with it.

At any rate, with a 1-to-1 lift to drag ratio, there’s enough energy in the wheels … let’s say the road’s rolling by underneath on a treadmill, turning the propeller. At 1-to-1, a propeller can remain stationary in the wind and create enough … not create. Actually, the wheels are turning the propeller. Bear with me, the propeller never turns the wheels, ever. Not going downwind faster than the wind, it never, ever turns the wheels. The wheels turn the propeller. The force required to turn wheels … you know, you have to hold the thing back so it doesn’t go down the treadmill.

That force, at 1-to-1, is exactly what the propeller will make if there’s a 1-to-1 lift to drag ratio. It’s exactly the same as a propeller makes to hold it stationary.

So at 4 miles an hour on a treadmill, the propeller is making enough force to hold it stationary. Even though the treadmill “wants” it to go backwards. Because the treadmill’s turning the wheels, even though that’s happening, the propeller is still with 1-to-1 — and of course we’re doing this 1-to -1 with all the losses involved: rolling losses and bearing losses, and gear losses but they’re very, very low. This thing is all ball bearing, all roller bearing. I use skateboard wheels because they are the most high-tech, high-efficiency wheels anybody’s every made. They’ve had hundreds of thousands of dollars spent on skateboard wheels, believe it or not, because they have to be efficient.

I have a garage that slopes 1 inch in 10 feet. The cart will start up and roll on its own. That’s how low the drag is. It is all Grade 7 bearings. And the gear belt is extraordinary. They are the most efficient of all the timing belts. They are the most efficient of all the methods of moving power from one place to another, much better gears.

At any rate, so all it has to be is better than 1-to-1, and it turns out my measurements show that at 10 miles an hour it’s about 1½-to-1. It creates more lift … let’s say to turn the propeller it takes 1 pound of force on the cart. But the propeller wasn’t pushing against anything, just to turn at 10 miles an hour the friction drag from the propeller and all that is, let’s say, 1 pound … we’re just using numbers here.


JG: And the propeller generates just about 1½ pounds of thrust at that point. And that a 1½-to-1 ratio in still air. And once it’s moving it probably would go to 2- or 3-to-1.


JG: That’s moving. Stationary is the worst.

MF: OK, OK. So one question I have is, have you been following all these conversations that are on YouTube and physics forums and all over the place? People are talking about this but I don’t think I’ve seen you weigh in anywhere.

JG: I weighed in once on the Discovery Channel [online forum]. Just to put in my two bits, but you know I’d much rather sit back and watch. I’ve had more fun with this. I haven’t made a nickel on it. I’m retired. This is the most fun I’ve had for not having to pay anything.

MF: That’s great. And have you been in touch with Rick Cavallaro, the guy who goes by “spork” online?

JG: Yeah, most of the people that have built them have called me up and asked me advice. There’s several out there. Three or four of them now that people have made that work. And one of them I must say is extraordinarily clever. I’m terribly impressed. It’s the one where they just added two wheels put the gear on it up to the diagonal shaft at the propeller. I am way impressed with that one.

MF: The one that really convinces me — just because it’s really moving in the wind — is this guy who built a circular wind tunnel and put a little cart that rolls around this track of this wind tunnel and …

JG: No, I haven’t seen that one.

MF: I’ll email you the video because you can see it actually start to move faster than the wind vanes that are churning the wind in there. He’s got like a little wind sock in there and that clinched it for me.

The interesting thing is there’s still some debate even between people who have masters and doctorates in physics and aeronautical engineering as to whether or not this can really happen. You know, I have a degree in mechanical engineering, but I was the world’s worst engineer, so I switched over to journalism and I don’t understand why someone just can’t come up with a simple force diagram to show that this thing works or not. Why is it so complex?

JG: It is but it isn’t, and I don’t know how to do a force diagram. I’m not — I’m an engineer, I can’t say I’m an engineer legally. I’ve done engineering all my life. And I’ve been paid extraordinarily well for it. I have two houses on the water, two sailboats. I’ve been extraordinarily lucky.

MF: Good for you.

JG: And I have a high school education, but I do engineering. And I’ve done it, I’ve been in partnership with a guy who invented the laser. I mean, I was — I’ve done very well. I do not have a degree. I cannot put it into a force diagram, but a basic solution is that it’s a lift-to-drag — the wind is lifting more than it takes to move it. And if you think that through, that explains it perfectly. Also the wheels are always turning the propeller.

You see whenever we’re sailing and most people think of sailing, they always think of the wind moving the boat. They cannot imagine that the wind is holding still and the water is moving. It’s a way of looking at it. Like somebody said, if we traveled around at the speed of light, relativity would be simple for us.

That was my turning point, when I was trying to figure out how to do this, was that it occurred to me that the wheels were turning the propeller and not the other way around and as soon as you allow that through your mind it’s all perfectly clear.

MF: Are you done experimenting with this?

MF: I have it. It’s in Florida right now. I’m in Maryland. I go there in the wintertime and if anybody wants to look at it I’ll drag it out of the attic. It’s wrapped up and the propeller is hanging on the wall because the propeller’s a thing of art. It’s a gorgeous piece of work.

MF: Did you make that yourself in your shop?

JG: Yes, and I had to think of a way of making it so I didn’t have to be able to see what I was doing. I’m retired because I don’t see as well as I used to. I had to come up with a method of making it where you did not actually have to see what you were doing.

MF: I think we’ll probably do another article about the wind carts and how your experiment kind of kicked off this renewed interest in a debate that’s been going on for a long time apparently.

JG: Well you know, it’s often referred to as a Bauer machine. It turned out [Andrew Bauer, who made wind carts in the late 1960s] actually never got it to work. [See video here.]

MF: Oh, is that true?

JG: Yeah the one he had, it didn’t work and — he never demonstrated it, let’s put it that way. If it worked, he never demonstrated it.

MF:That’s interesting.

JG: That I can find.

MF: Hmmm.

JG: But he knew it would work. I don’t think he ever got it right. Anyway, I’ve had more fun with this and what actually interests me isn’t the technical aspects of making it go downwind faster than the wind. What really interests me is how it gets people riled up and it gets them thinking and you know the emotional part because I’ve been called a charlatan, which I thoroughly enjoy, I must admit.

MF: [chuckles]

JG: But you know it’s really tweaked everyone’s imagination. To me, that’s what is so neat about it. Technically, once you understand it, it’s really not a big deal. It’s kind of boring.

On the Discovery Channel [forum], one guy wanted to go out in the parking lot and duke it out with someone else. I just got a kick out of all that. That’s why I’ve sort of laid low. I’ve had more fun watching than I have had doing.

MF: Yeah that’s …

JG: But it’s in Florida. If anyone wants to see it, I have an open invitation. What is quite interesting is all the detractors saying it can’t be done and being almost violent — not a soul has wanted to see it. The one’s that knew it could work don’t need to see it. And the ones that are absolutely certain don’t want to look at it. I found that quite curious.

MF: That is very interesting. You know a lot of people just made up their mind about it without even wanting to build something. Well, if I ever find my way in that area and you happen to be in Florida at that time, I’d love to meet you and take a look at it.

JG: I’d be glad to show it to you. It’s southwest Florida.

MF: That sounds good.

JG: Just north of Fort Myers and I’m there when it’s cold up here.


More: Read the rest of the Wind Cart Series

12 thoughts on “The cart that launched a thousand flame wars

  1. Jack might not call himself and engineer, but we know better. There are certainly plenty of engineers that could neither figure this thing out nor build it.

  2. Physically, traveling downwind faster than the wind is equivalent to the following: Imagine three nested threaded tubes, such that the inner interface has steeper threads than the outer interface. Do not allow the inner or outer tubes to rotate. Pull forward on the outer tube. The force diagram is pretty simple. The middle tube moves faster than the outer tube. Wind=outer tube; cart=middle tube; ground=center tube. Pretty cool that you made it work!

    1. I don’t necessarily disagree with anything you said, but I don’t think it would convince many people either. Also, I’m not quite sure how you’d do a force diagram on that arrangement. Would you relate the forces to the masses of the rods? The coeff of friction at the thread interfaces? Or are you really describing a kinematic model?

      I also agree the device will work as you describe (assuming low enough friction at both interfaces), but how would you convince me that it would? Then how would you convince me that this is analogous to the downwind cart?

      Incidentally, I would suggest that a propeller moving along a coarsely threaded shaft might make a better example – or perhaps an example that’s more easily compared to the downwind cart(?)

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Mark Frauenfelder is the founding Editor-in-Chief of Make: magazine, and the founder of the popular Boing Boing blog.

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