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This question already has an answer here:

Has anyone done any research about the upwind vehicle http://www.popsci.com/cars/article/2012-07/wind-powered-car-travels-upwind-twice-speed-wind?

I think it is impossible but get a surprising number of disputes from some pretty educated people. It seems to me that if it were possible for a wind powered vehicle to go into the wind at greater than the speed of the wind X, then it would follow that on a windless day, a Ford F-150 towing the same vehicle at speed X (equaling the relative wind), would allow the vehicle to accelerate and pass the Ford, which is absurd, especially considering that the towed vehicle only needs to overcome the rolling coefficient of friction while the self starting vehicle must overcome the static coefficient of friction.

Am I overlooking something?

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marked as duplicate by Kyle Kanos, DavePhD, Brandon Enright, ja72, BebopButUnsteady May 1 '14 at 1:06

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There no hard theoretical upper limit on the true wind multiple a wind-powered vehicle can achieve. It's just a matter of practically achievable efficiency. This applies to all directions, including directly upwind and directly downwind.

The mechanical principle can be demonstrated with a simple gear-toy, where the air mass is replaced with a strip of paper, and the rotor with another set of wheels. Note that by changing the gear ratios you can achieve speeds greater than the paper-speed in both directions:

http://www.youtube.com/watch?v=pw_B2MnMqZs

Dealing with a fluid like air adds slippage making it less efficient and more difficult to achieve. But that is just an engineering challenge. Nothing in physics prevents it from working. Here some theory on the subject:

Theory and Design of Flow Driven Vehicles Using Rotors for Energy Conversion Mac Gaunaa, Stig Øye, Robert Mikkelsen

http://orbit.dtu.dk/fedora/objects/orbit:55484/datastreams/file_3748519/content

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