Physics debate settled: faster than the wind is possible

A wind-powered car has reached a top speed of 38.61 miles per hour (62 kilometers per hour). By itself that might not sound impressive, but it appears to answer a long-running physics question: can a wind powered vehicle travel downwind at a speed faster than said wind.

The main argument against such a possibility is that it would create perpetual motion, meaning that once the vehicle started it would never stop. It’s generally held that this would violate the laws of thermodynamics. However, supporters of the “downwind faster than the wind” idea have argued it is not perpetual motion.

In the past, there have been no full-scale demonstrations that the theory holds up in reality. Instead there have been a variety of demonstrations using small models on a treadmill. The treadmill isn’t cheating, but rather a way to recreate a “perfectly straight road that’s perfectly aligned with a perfectly steady wind”, which is easy to assume in physics theory, but trickier to achieve in the real world.

That is until a project run by Rick Cavallero, the chief scientist at Sportvision Inc. His team received funding from Google and wind turbine firm Joby Energy, and worked with San Jose State University’s aero department.

They’ve now built a vehicle known as Blackbird and repeatedly achieved speeds of 2.85 times faster than the wind which was powering the car.

The key to this achievement is that the wind doesn’t directly turn the propeller. Instead the wind pushes the vehicle and the wheels turn the propeller (in the opposite direction to normal wind-powered vehicles). This pushes the wind backwards and thus creates more forward momentum for the vehicle.

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21 Responses to Physics debate settled: faster than the wind is possible

  1. That demonstration proves nothing because the wind velocity is not relative to the treadmill. It's relative to the standing observer. So it still provides thrust.

    If the model car was actually traveling at exactly the speed of the wind, its propeller would stand still, because there would be no effective wind velocity.

    The propeller on the model is actually quite inefficient. The car would travel considerably quicker "uphill" if it had a sail instead. But of course, if you did that, then it would be much more obvious why the demo is rigged.

    Incidentally, there's a related "Mythbuster's" Myth that says an airplane can't take off if it's standing on a carpet moving backwards. This was Busted, and the reason is that the propeller of an airplane doesn't push against the ground, it pushes against the air.

    Sorry guys – if you aren't just doing this as a physics troll, the joke's on you.

  2. That demonstration proves nothing because the wind velocity is not relative to the treadmill. It’s relative to the standing observer. So it still provides thrust.

    If the model car was actually traveling at exactly the speed of the wind, its propeller would stand still, because there would be no effective wind velocity.

    The propeller on the model is actually quite inefficient. The car would travel considerably quicker “uphill” if it had a sail instead. But of course, if you did that, then it would be much more obvious why the demo is rigged.

    Incidentally, there’s a related “Mythbuster’s” Myth that says an airplane can’t take off if it’s standing on a carpet moving backwards. This was Busted, and the reason is that the propeller of an airplane doesn’t push against the ground, it pushes against the air.

    Sorry guys – if you aren’t just doing this as a physics troll, the joke’s on you.

  3. So where is the video of the 'Blackbird' car?

    The video of the toy on the treadmill proves nothing. Instead of using a treadmill they should be using a wind tunnel. Then let's see what the toy does.

    • @Astro:

      Search Youtube for these two terms:

      "BUFC very first run"

      "BUFC second run"

      I would post the links to those Blackbird videos here, but I don't know if links are considered spam on this site.

  4. So where is the video of the ‘Blackbird’ car?
    The video of the toy on the treadmill proves nothing. Instead of using a treadmill they should be using a wind tunnel. Then let’s see what the toy does.

    • @Astro:

      Search Youtube for these two terms:

      “BUFC very first run”
      “BUFC second run”

      I would post the links to those Blackbird videos here, but I don’t know if links are considered spam on this site.

  5. >> "Sorry guys – if you aren’t just doing this as a physics troll, the joke’s on you."

    I assure you we're not physics trolls, we just enjoy really big brain-teasers. And I assure you the joke is not on us. If you care to understand what's happening here just ask. We're happy to explain it.

  6. >> “Sorry guys – if you aren’t just doing this as a physics troll, the joke’s on you.”

    I assure you we’re not physics trolls, we just enjoy really big brain-teasers. And I assure you the joke is not on us. If you care to understand what’s happening here just ask. We’re happy to explain it.

  7. So if you had two opposing offset propellers connected by a belt, would the same priciple apply?
    One propeller would act as the wheels and one as the propeller. If you had the rotors for the propellers spinning a magnet and the magnet was inside a coil you could then produce electricity even when the wind was not blowing?

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