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Need help understanding a lift coefficient formula

  1. Jan 21, 2016 #1
    Please go to this Wikipedia article on Lift Coefficients, and behold the first formula. The last part of the equation has a "S" which is supposed to stand for "relevant plan area". Now, there was no explanation of what this "relevant plan area" is or means. I was guessing that it means the surface area of the airfoil, but this cannot be so, because as "S" is in the denominator of the formula, thus as the surface area increases, there is a diminished lift coefficient, and hence a diminished lift power (so my reasoning goes). I would write down the formula here, but for some reason Latex isn't working.

    So: what is the "relevant plan area" referred to?
     
  2. jcsd
  3. Jan 21, 2016 #2

    fresh_42

    Staff: Mentor

    "As relevant area is considered the wing area on profiles and the front area on vehicles."
     
  4. Jan 21, 2016 #3

    boneh3ad

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    Gold Member

    For a given amount of lift, if you increase the area required to generate it the lift coefficient goes down. That's precisely what is written in the article with S in the denominator.
     
  5. Jan 23, 2016 #4

    David Lewis

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    Gold Member

    Relevant plan area refers to the area that significantly contributes to lift. On a normal airplane, S would just be wing area plus the area of the fuselage between the wing roots. But it also lets the formula apply to lifting bodies, airplanes with wide fuselages, chines, strakes, lifting stabilizer, etc.
     
  6. Jan 23, 2016 #5
    See if this image helps.
     
  7. Jan 30, 2016 #6
    It does. Thanks spamanon.
     
  8. Jan 30, 2016 #7

    David Lewis

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    There is a lift coefficient for the wing, and a lift coefficient for the whole airplane (a.k.a. total lift coefficient). Total CL will be less than wing CL when the horizontal stabilizer generates a down force.
     
  9. Jan 30, 2016 #8
    is anyone else having trouble with Latex? For some reason I don't have it anymore.
     
  10. Jan 30, 2016 #9
    is a lift coefficient in units of meters/second^2?

    Anyone?

    I had performed a calculation of lifting force, and in order to be in Newtons, the lift coefficient would need to have these units...
     
  11. Jan 30, 2016 #10

    fresh_42

    Staff: Mentor

    The definition I found is dimensionless.
     
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