Do winglets produce thrust?

Bruce Hoult wrote:
In article ,
ojunk (Bob Salvo) wrote:

Anyone?
Bob


Winglets reduce induced drag by effectively making the wingspan longer.

Perhaps in the past, but maybe not anymo from page 104 of the
Fundamentals of Sailplane Design...

"Subsequently, it has been shown that good results may be obtained with
relatively small winglets. In contrast to early winglets, which were
essentially upward wing extensions, recent winglet designs are optimized
to diffuse the vortex rollup at the wingtip, thus reducing its strength.
There is also evidence that the velocity field induced by the winglets
can improve airfoil aerodynamics in the vicinity of the wing tip by
prolonging laminar flow and delaying separation."


I've never seen anyone argue convincingly that a half a meter of
vertical wingspan does anything that couldn't be done equally well with
an extra half meter of normal wingspan.

Winglets can improve roll rate, while longer tips tend to reduce it.

On the other hand winglets are
worse than span in that they don't produce lift in a useful direction,
and they are harder to make strong and rigid than ordinary span is.

The lift they produced is used to decrease drag, which is a useful
result, and the small ones used on the ASW 27, for example, look pretty
simple to make.


If it wasn't for class rules limiting winspan I don't think anyone would
have winglets.

Much less likely, for sure.

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Eric Greenwell
Washington State
USA