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Wing Span Efficiency Factor

  1. Nov 28, 2013 #1
    Hello Everybody,

    Span efficiency factor appears in the lifting-line theory of Prandtl describing Lift and vortex drag of a finite wing. According to this theory, the most efficient wing is an elliptical one and, roughly speaking, the span efficiency factor defines an efficiency of a given wing planform relatively to elliptic wing.

    In the framework of the lifting line theory the span efficiency cannot exceed 1.

    My question is: can this efficiency factor be more than 1, when going beyound lifting-line approximation ? (sorry for abusing notion of efficiency which supposed to be less <= 1).

    In other words: does it exist such a wing whose induced drag is less than that of estimate for elliptic wing in the lifting-line theory (provided aspect ratios and lift coefficients are the same and viscous effects, such as skin friction and boundary layer, are neglected).

    Last edited: Nov 28, 2013
  2. jcsd
  3. Dec 9, 2013 #2
    Short answer is yes, you can have a >1 efficiency factor. But you have to cheat. It's accomplished by using tandem wings or boxed wings. Winglets also allow for a >1 factor.
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