Faro From Egypt, joined Aug 2007, 1755 posts, RR: 0 Posted (7 years 1 month 5 days 13 hours ago) and read 7415 times:
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?
Aeroweanie From United States of America, joined Dec 2004, 1612 posts, RR: 51
Reply 1, posted (7 years 1 month 5 days 12 hours ago) and read 7393 times:
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.
Jetlagged From United Kingdom, joined Jan 2005, 2620 posts, RR: 25
Reply 3, posted (7 years 1 month 5 days 8 hours ago) and read 7333 times:
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.
The glass isn't half empty, or half full, it's twice as big as it needs to be.