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Aerospace Airplane and Helicopter Lift

  1. Jan 2, 2012 #1
    I came to know that Fixed wing as well as propeller lift equations are same [Am I right]?

    Anyways I have question.

    What's total lift for fixed wing plane with Wing length of 4 m, 1 m width, Angle of attack = 16 degree, and Wind/plane speed of 6 m/s?

    Secondly, what's total lift for Helicopter with propeller diameter of 4 m, width of 1 m and Rpm of 420? Considering angle of attack = 16 degrees?

    Any one care to explain in detail?

    Surely, I will have follow up questions but let's divide and conquer :)
  2. jcsd
  3. Jan 2, 2012 #2


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    It also depends on the air properties and the airfoil shape...
  4. Jan 3, 2012 #3
    This is a difficult question to answer. Like russ said it depends on airfoil shape but it will also depend on whether or not certain parts of the wing are stalled. For a wing with a chord of 1m and velocity of 6m/s in air the Reynolds number is approximately 380000 which is pretty low. At this low Reynolds number and and angle of attack of 16 degrees there will almost certainly be regions of separated flow over the wing. The entire wing may even be stalled.

    For a wing, the easiest way to get an estimate of the lift is lifting line theory. Unfortunately LLT assumes the flow is inviscid, which is a poor assumption in your case since there will be regions of separated flow. However it is possible to get decent estimates with this method by using experimental data for the airfoil as opposed to the thin airfoil theory result which determines the sectional lift coefficient assuming inviscid flow.
  5. Jan 3, 2012 #4
    Thank you for your replies. Lets consider it's quite air. Air Not flowing, but wings are in speed. No stalling. Wings are in perfect or ideal shape for max lift.

    I'm just setting hypothetical envioronment saying everything is ideal as it should be :)

    Second question for wing's width in both cases. Having more width at lower speed is'nt benefitial (contributing factor) for more lift?
  6. Jan 3, 2012 #5
    If you want an upper bound on your lift the easiest thing to do would be to treat your wing as an airfoil and then use thin airfoil theory.
  7. Jan 8, 2012 #6
    What would be equation in either case for Thin Foil Theory?
  8. Jan 8, 2012 #7


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    There is no standard equation for lift or any sort of general case for any sort of aerodynamic force. The situation is much more complicated than that.
  9. Jan 22, 2012 #8


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    Gold Member

    One simple observation: A helicopter's lift is generated by its "Rotary Wing", and NOT its propeller.
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