Quote:
Originally Posted by freebeard
Interesting. Could the ring duct be reduced to upturned winglets at the tips similar to what they use on airliners to reduce vortexes forming at the wingtips?
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Yes, that can be done, although it seldom is. Wingtip fences are most popular on cars. They raise skin friction, may cause complications in crosswinds and turbulence, and reduce the effective span due to the build up of stagnant air in the corners where a wing-root fillet would look familiar.
The Whitcomb winglets on airliners are interesting. They "sail" on the induced vortex to recover some thrust, but they would do just as much good as increased wingspan, and be easier to build. However, more wingspan means higher rent at airports.
The "best" wingtip is also subject to construction considerations, but the debate over the best shape has come down for the one shown, the "Finch Tip" which tapers finely to a straight trailing edge to minimize the tip vortex.