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Homework Help: Airplane Weight

  1. Dec 7, 2004 #1
    ----An airplane has an effective wing surface area of 15.9m^2 that is generating the lift force. In level flight the air speed over the top of the wings is 61.5m/s, while the air speed beneath the wings is 52.2m/s. What is the weight of the plane?----

    I tried looking through my textbook and lecture notes, but nothing is really discussed about how to solve a problem like this. Would anyone be able to help me figure this out? Thanks.
  2. jcsd
  3. Dec 7, 2004 #2
    Bernoulli's equation may be applicable :)
  4. Dec 7, 2004 #3
    mm that makes sense...but i'm not sure how i could come up with the weight from that equation. is there another equation i could use with bernoulli's to get the weight?
    thanks so far :)
  5. Dec 7, 2004 #4


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    No,it's just that u need to know the air's density (assumed constant,of course).It's about [itex] 1,29 kg m^{-3} [/itex] under normal conditions of pressure and temperature.
    The gravity should be balanced perfectly by the aerodynamic force.From this eqality you'll find your answer.
  6. Dec 8, 2004 #5
    I have a modified version of Bernoulli's equation that seems to apply : P1-P2= 1/2 p (V2^2-V1^2) ....and I know how to plug in all the numbers, but I'm still not seeing how I can derive weight from that...even with the regular equation I still don't see how weight can be found. Sorry to sound so clueless; I'm not sure what I'm missing...
  7. Dec 8, 2004 #6

    Doc Al

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    Bernoulli's equation allows you to find the pressure difference. Combine that with the effective surface area to get the lift force. As dextercioby says, that will balance the weight of the plane.
  8. Dec 8, 2004 #7
    ah I see it now! Thanks so much :D
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