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Nitrogen molecules in air question

  1. Dec 9, 2012 #1
    hi all. i'm trying to write an article about a molecular perspective on (aircraft) lift. im guessing nitrogen does most of the lift since it's the most abundent in air. how does a nitrogen molecule stick to a steel molecule (plane's)? is there a short term electronic bond between the two molecules? thanks guys
  2. jcsd
  3. Dec 9, 2012 #2
    How do you think airplanes fly?
  4. Dec 10, 2012 #3
    There a few threads around here about how airplanes fly. I would suggest you read a few of them and then repostulate your initial assumptions on what creates lift. Why do you assume that they atmosphere and the wing has to stay together?
  5. Dec 10, 2012 #4


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    Since the air is flowing around the wing during flight, perhaps there is very little sticking going on.
  6. Dec 13, 2012 #5
    if they wouldn't stick (which they do) there would be no interaction at all. i know why planes fly on a macroscopic scale. i was looking for a more quantum explanation. btw they stick because of van der walls forces (at a molecular level). that's how energy is trasnfered between the air and the wing. no molecule knows of eachother
  7. Dec 16, 2012 #6

    An airplane does not require molecular attraction of its wing with a gas to fly. Compared with the forces required lift the airplane, molecular attractions are insignificant.

    There doesn't have to be any attraction. An airplane's wing physically pushes air down so that according to Newton's third law of mass, the reaction force pushes the plane up in the opposite direction. Where did you get the idea of a "stickyness" or attraction of the air to the wing?

    Energy is transferred between the fuel and the engine and the airframe. Any energy used to push the air around is wasted as far as transporting the airplane is concerned.


    P.S. In English, first words of sentences are capitalized. That makes sentences much easier to read.
  8. Dec 16, 2012 #7

    Thanks a lot! Cheers!
  9. Jan 15, 2013 #8
    btw i was reffering to the coanda effect (for the stickiness)
  10. Jan 15, 2013 #9

    also, you can't deny the molecular structure of things. just because we live day to day on a macroscopic world, and base our lives on it, you can't deny the fundamentals of everything
  11. Jan 15, 2013 #10


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    Er... this is empty talk.

    No one is denying anything here. The question here is whether it is RELEVANT or not to the phenomenon! I'm sure when you do your many calculations, you ignore the gravitational field from Alpha Centauri, don't you? Do you think leaving out such a thing affects the accuracy of many of the things you do or calculate?

    Do not go into this line of discussion until you have done a considerable reading on "emergent phenomena".

  12. Jan 15, 2013 #11
    yes it is relevant. it's related to the boundary layer and that is related to the stall limit. and that is related to the plane crashing
  13. Jan 15, 2013 #12


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    Can you please produce a valid reference to back it up?

  14. Jan 15, 2013 #13


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    Nope. It's wrong. The Coanda effect is an aerodynamic phenomena, not a chemical phenomena.
  15. Jan 15, 2013 #14
    Molecular effects are responsible for the Prandl layer aka as no slip condition I suppose. http://en.wikipedia.org/wiki/No-slip_condition Exactly how it works is not important, maybe it's van der Waals, surface roughness, general adhesion, ... relative flow will be very close to zero on the first few layers of molecules. It doesn't really matter if it is not perfectly zero. Changing the surface material of an air plane by coating does not have an effect on flight characteristics afaik. Also the gas doesn't matter. All surfaces make all gases flow slow enough to be approximated by zero relative velocity.
  16. Jan 15, 2013 #15


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    One way of looking at this is "void abhorence" effect. As air flows around a convex surface, what would otherwise be a void near the surface is filled in by the air (else a near zero pressure void would be formed). If the flow is laminar or only mildly turbulent, the air flow tends to follow the curved surface. In a heavily stalled state, what would be a "void" could be filled with one very large vortice.

    Viscosity is also a factor. If visocity is near zero, then adjacent streams of different speeds can flow by each other with almost no interaction, so the "void" could be filled with a stagnant very low visocity gas with almost no movment of that gas, and the stagnant gas would behave as if it were part of the airfoil.
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