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Low Pressure Air?

  1. Nov 1, 2009 #1
    I know that low pressure air is created when air moves fast, but what other ways are low pressure air made?
     
  2. jcsd
  3. Nov 1, 2009 #2
    Can someone correct me if I'm wrong about something. Also, is there even any other way to create low pressure air?
     
  4. Nov 1, 2009 #3

    FredGarvin

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    Increase the volume the air is contained in or drop the temperature.
     
  5. Nov 1, 2009 #4
    So can these strategies be applied to create lift on a surface? For example, you create low pressure air at the top of the surface and high pressure air at the bottom and you can create lift, like in a plane?
     
  6. Nov 1, 2009 #5

    Redbelly98

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    No, since FredGarvin's suggestions apply to air inside a sealed container.
     
  7. Nov 1, 2009 #6

    russ_watters

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    Punch holes in the upper surface of the wing and suck air through them.
     
  8. Nov 1, 2009 #7

    OmCheeto

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    Or just get a whole bunch of vacuum cleaners. One can pick up a bowling ball. I'll bet 10,000 could lift an airplane.

    [PLAIN][PLAIN]http://www.carlson-store-fixtures.com/Portals/3/aspdnsf/images/Category/icon/798.jpg [Broken] [Broken] [Broken][PLAIN][PLAIN]http://www.carlson-store-fixtures.com/Portals/3/aspdnsf/images/Category/icon/798.jpg [Broken] [Broken] [Broken][PLAIN][PLAIN]http://www.carlson-store-fixtures.com/Portals/3/aspdnsf/images/Category/icon/798.jpg [Broken] [Broken] [Broken][PLAIN][PLAIN]http://www.carlson-store-fixtures.com/Portals/3/aspdnsf/images/Category/icon/798.jpg [Broken] [Broken] [Broken]
     
    Last edited by a moderator: May 4, 2017
  9. Nov 1, 2009 #8
    How does a windmill work...seems like a change in air pressure as it flows over the curveature is at "work" (pun).
     
  10. Nov 1, 2009 #9
    I don't want to lift a plane. I want to create lift.
     
    Last edited by a moderator: May 4, 2017
  11. Nov 1, 2009 #10
    So you're telling me that if someone we're to punch holes through the wing of an airplane and use vacuums at the top of them, it would create lift?

    I know it's not practical but in theory might it be possible?
     
  12. Nov 1, 2009 #11

    russ_watters

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    I don't know if there are any production aircraft that have used the technique, but it is well documented to work - not just in theory.
    http://www.dfrc.nasa.gov/gallery/Photo/F-16XL2/index.html
     
    Last edited by a moderator: Apr 24, 2017
  13. Nov 1, 2009 #12
    I think heating the air on top of the wing is one way to go. We should probably put a cover over the top to keep the hot air from getting away. The wing don't have to be moving though the air anymore so we'll just call the wing the 'bottom surface', and the entire contraption a balloon.
     
  14. Nov 1, 2009 #13
    Alternatively high pressure can be develped on bottom surfaces of a craft. A ballistic parachute comes to mind.

    While in mid-air or on the ground, fire the parachute high into the air on a long cable. A wench reels in the cable more quickly than the parachute falls. Upon reaching the vehicle the parachute is repacked and the next balistic charge loaded, whereupon the cycle begins again.
     
  15. Nov 2, 2009 #14
    So is there a way we can take all these ideas and create vertical lift. For example, we can "blow" air across the top of a surface and heat air at the bottom of the surface. I understand that it would be hard to stabilize the surface but again in theory.
     
  16. Nov 2, 2009 #15

    russ_watters

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    It can certainly be done......Why you would want to do that is another question....
     
  17. Nov 2, 2009 #16
    The intent of this system is to reduce drag by suctioning off the turbulent boundary layer, rather than provide lower pressure--apparently. Although it's still something that can be considered as a means of providing or enhancing lift.

    How this is supposed to work, according to the link, is something of a mystery to me. Normally one wants to encourage a turbulent boundary layer to reduce the drag, inherent toward the trailing part of the upper surface, as the boundary separates on encountering an adverse pressure gradient. A turbulent flow will remain attached further along the cord.

    1) The article seems to be advertising something useful in supersonic flight, though. 2) With enough suction it may be possible to move the adverse pressure gradient rearward from where it would otherwise detach.
     
    Last edited by a moderator: Apr 24, 2017
  18. Nov 3, 2009 #17

    Redbelly98

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    What if you took the energy that is required for creating the suction, or heating the wing, and instead used it to provide more thrust to the engines? That would create additional lift as well, and be much simpler to implement.
     
  19. Nov 3, 2009 #18
    It might be the start of a new type of transportation. Can it?
     
  20. Nov 3, 2009 #19
    ......no.
     
  21. Nov 3, 2009 #20

    rcgldr

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    Depends why the air is moving fast. Take the simple case of a propeller, as the air passes through the virtual disk formed by the rotating prop it's speed isn't changed much, but the pressure is. The air ahead of the prop accelerates into the low pressure zone in front of the prop, then the pressure is increased, and the air continues to accelerate as it's pressure is reduced back to ambient.

    When solids interact with fluids or gasses, both pressure and speed can be changed by that interaction. The exhaust from a jet engine is both high pressure and high speed.

    For the fluid or gas flow outside of the region of interaction with a solid, that fluid or gas accelerate from higher pressure zones to lower pressure zones, and the relationship between the change in pressure versus change in speed can be converted into a relationship between static pressure and speed, and this relationship can be approximated by Bernoulli equation (Bernoulli doesn't take turbulent factors into account).

    There are man made "flying saucer" type aircraft that use a set of propellers (vertical axis) located in holes around the aircraft. One of these was demoed at the 1984 Los Angeles Olympics.
     
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