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Faro
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Elliptic Wing-Tips Vs Winglets

Wed Apr 22, 2009 1:10 pm

If winglets minimise wing-tip vortex drag by effectively extending wingspan and hence aspect ratio, why not simply do this by having ellipse-shaped wingtips (à la Spitfire) instead?

In this case, the wing-tip tapers off to a diminutive length which should not generate as much vortex drag because the wing-tip section which is -more or less- parallel to the airstream is reduced. Indeed what benefit is there in systematically having airliner wing-tips which are parallel to the airstream?

Faro
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aeroweanie
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RE: Elliptic Wing-Tips Vs Winglets

Wed Apr 22, 2009 2:37 pm



Quoting Faro (Thread starter):
If winglets minimise wing-tip vortex drag by effectively extending wingspan and hence aspect ratio, why not simply do this by having ellipse-shaped wingtips (à la Spitfire) instead?

Having an elliptical tip is not enough - the whole wing must be elliptical to get minimum induced drag. The Spitfire's wing had twist, to produce a good stall, so it did not have the lift distribution necessary to get minimum induced drag. The main reason that the Spitfire wing was elliptical was to provide the depth necessary outboard to house the ammunition trays, without having to use high thickness to chord ratio airfoils.
 
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Faro
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RE: Elliptic Wing-Tips Vs Winglets

Wed Apr 22, 2009 2:45 pm



Quoting Aeroweanie (Reply 1):

Having an elliptical tip is not enough - the whole wing must be elliptical to get minimum induced drag.

Is a fully-elliptical wing an economically viable solution for modern airliners? Is it compatible with wing sweep notably?

Faro
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RE: Elliptic Wing-Tips Vs Winglets

Wed Apr 22, 2009 6:18 pm

Elliptical wings are harder to make due to the complex curvature required. Perhaps less of a problem with composites. The advantage of an ideal elliptical lift distribution over the near elliptical distribution you get from straight taper aren't great in comparison with savings due to simpler manufacture.

Elliptical planform would also make it much harder to design complex high lift devices as the leading and trailing edges are continuous curves.
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