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Homework Help: Help needed with airplane question

  1. May 3, 2009 #1
    Hi guys, new here just wanted to say hello and I stumbled across this site while studying for my final, great site, now onto my question...

    1. The problem statement, all variables and given/known data
    A small plane of mass 3000 kg is flying in air of density 1.0 kg/m3. Air moves over the top and
    bottom of the surface of the wings at velocities of 160 m/s and 130 m/s, respectively. What is
    the minimum wing area needed, to keep the plane in air?

    2. Relevant equations
    Bernoullis equation and Area = Force/Pressure

    3. The attempt at a solution
    Ive found change in pressure to be 4350N/m2 but I cant find the force, nor am I sure how much pressure is needed to keep the plane in the air, any help would be appreciated, thanks in advance =/
  2. jcsd
  3. May 3, 2009 #2
    Well you have half the problem solved then. This pressure will cause an upward force on the wings. If you remember your pressure equation [tex]P=F/A[/tex] then you can get the upward force knowing the surface area of the wings.

    Then you ask yourself why does it need an upward force. Well what could be causing the plane to go down? And you remember that gravity has a downward force. So look up the force of gravity equation.

    Then equate the two forces and solve for the surface area needed.

    P.S.: A plane has 2 wings, so be sure to divide this surface area in half for the area needed on one wing.
  4. May 3, 2009 #3
    The first thing that a lot of people forget to think about is to equilibrate the forces.

    To just keep the plane in the air Force up = Force down.

    Force down is mg......

    Think about where you might get force up from....
  5. May 3, 2009 #4
    awesome guys, thanks a bunch! i figured it out, 6.75m2, or 3.37 per wing
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