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Another way to achieve lift?

  1. Aug 28, 2008 #1
    I was thinking about Bernouli's principle, which shows how to get lift by creating a difference in air pressure above and below the wings of an aircraft, and became curious as to whether a difference in pressure arrived at by other means might also result in lift. Specifically, if air were chilled below a platform (making it denser) and heated above the platform (making it less dense), would the resulting difference in pressure creaste lift sufficient to raise the platform?
  2. jcsd
  3. Aug 29, 2008 #2
    In the Bernouli principle, the upper and lower air is at the same temperature but differernt density, causing the difference in pressure. I think you might have better luck doing that the other way around, as hot air rises. Hot air also exerts the greater pressure because of the higher energy of the air molecules, same as any gas. The density of the air is not the controlling factor, in this case only the pressure.
  4. Aug 29, 2008 #3
    Thanks shroder! I didn't really expect it to be practical, I was just wondering whether it could provide any lift. I expect that the lift it might provide is less than that needed to generate the cold/hot gradient, since the machinery involved would be fairly heavy, so the lift to weight ratio wouldn't be insufficient to be useful.
  5. Aug 29, 2008 #4


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    Staff: Mentor

    What would really happen is the pressures would just equalize if there is no way to keep the air on the bottom and top surfaces separate.

    Now would you could do is just heat the entire wing, creating and riding your own updraft.
  6. Aug 29, 2008 #5
    I was thinking of something with a disk shape, with a rim around the edge extending above and below the surface, like two frisbees stuck together back to back.
  7. Sep 4, 2008 #6
    if the air is not flowing then the static pressure will be felt on both surfaces, which will be equal to atmospheric. wings utilize dynamic pressure which only exists when the air is flowing.
  8. Nov 11, 2008 #7
    What does exist is a wing, possibly a cylinder, that rotates around the plane's transverse axis so that air is faster above the wing. Also used as a demonstrator sail.

    By the way, forget the tale of faster air because of longer path at the extrados, it's just plain nonsense. Papers, books and teachers who go on telling that just have never seen actual wing profiles.
  9. Nov 18, 2008 #8


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    Gold Member

    It seems to me that you're just reinventing the hot-air balloon in a different shape.
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