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Are you sure that is correct, that the wheels are powering the propeller at some point? The article explained it completely differently. The article said that

Are you sure that is correct, that the wheels are powering the propeller at some point? The article explained it completely differently. The article said that the effect is similar to when a sailboat tacks downwind sharply, they can briefly accelerate beyond wind speed. The propeller is essentially shaped as if each side is a sail continuously tacking, so the force from each of the two "sails" drives the propeller in a circular motion. I don't believe the wheels are providing any energy into the process, but I could be wrong. I think it is the shape of the propeller that causes the effect. The article also said it could most likely work on water as well. The wind energy applications of this propeller design are intriguing.

stygianguest 16y ago
Yes, the wheels drive the propeller directly. Read the articles posted in the first comment. They will explain it. Very short summary: The prop creates an air cushion that acts as a virtual sail.
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JoachimSchipper 16y ago
The interesting part is not that they can briefly go faster than the wind, but rather that they can keep this speed up. It's easy to briefly go faster than the wind: use some gears to connect a windmill to a heavy piece of metal rotating on the end of a long pole. Assuming a strong wind, low-friction gears, and that you've chosen the gears such that the metal rotates faster than the windmill, the machinery will soon be spinning quite rapidly. Now, just put a hapless pig in the way of the rotating piece of metal, and you suddenly have a slightly-dented pig flying at greater-than-wind speed. ("With sufficient thrust, pigs fly just fine", although this will definitely annoy the pig.) I'm sure you can think of other ways to store the wind's energy and use it for a speed boost; the interesting thing is that this vehicle can consistently outrun the wind. Also note that my explanation does not require the vehicle to be on the ground instead of in the water - think "water wheel". With respect to "tacking": you'll find that Chu-Caroll's article, which smanek linked to, provides the same explanation as I did (skip the initial part where he explains his error and start reading after "let's look at a new diagram"), and mentions the similarity to "tacking" (start at "Once it's moving, what's going on can be described in a bunch of different ways.") However, note that not even the "perfect" sail that Terence Tao assumes in the article linked above achieves more than 2x wind speed; clearly, there is something about this real-world vehicle that makes it move faster than even theoretical (fixed-)sail-powered cars. I think my comment above is a plausible explanation for how this can happen.
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barrkel 16y ago
It's the difference between the wind speed and the ground speed that's driving the vehicle. The wheels are always driving the propeller against the wind; and when the vehicle is travelling at wind speed (so that relatively speaking, the wind should be dead air), the propeller is pushing against the wind, making it go faster.

stygianguest 16y ago

Yes, the wheels drive the propeller directly. Read the articles posted in the first comment. They will explain it. Very short summary: The prop creates an air cushion that acts as a virtual sail.

deleted 16y ago
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JoachimSchipper 16y ago

The interesting part is not that they can briefly go faster than the wind, but rather that they can keep this speed up. It's easy to briefly go faster than the wind: use some gears to connect a windmill to a heavy piece of metal rotating on the end of a long pole. Assuming a strong wind, low-friction gears, and that you've chosen the gears such that the metal rotates faster than the windmill, the machinery will soon be spinning quite rapidly. Now, just put a hapless pig in the way of the rotating piece of metal, and you suddenly have a slightly-dented pig flying at greater-than-wind speed. ("With sufficient thrust, pigs fly just fine", although this will definitely annoy the pig.) I'm sure you can think of other ways to store the wind's energy and use it for a speed boost; the interesting thing is that this vehicle can consistently outrun the wind. Also note that my explanation does not require the vehicle to be on the ground instead of in the water - think "water wheel". With respect to "tacking": you'll find that Chu-Caroll's article, which smanek linked to, provides the same explanation as I did (skip the initial part where he explains his error and start reading after "let's look at a new diagram"), and mentions the similarity to "tacking" (start at "Once it's moving, what's going on can be described in a bunch of different ways.") However, note that not even the "perfect" sail that Terence Tao assumes in the article linked above achieves more than 2x wind speed; clearly, there is something about this real-world vehicle that makes it move faster than even theoretical (fixed-)sail-powered cars. I think my comment above is a plausible explanation for how this can happen.

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barrkel 16y ago

It's the difference between the wind speed and the ground speed that's driving the vehicle. The wheels are always driving the propeller against the wind; and when the vehicle is travelling at wind speed (so that relatively speaking, the wind should be dead air), the propeller is pushing against the wind, making it go faster.