"CV" wrote in message
...

Another aerodynamic bone to toss around and chew on:

Instead of carefully crafted, expensive winglets, wouldn't
straightforward flat end plates serve nearly as well in
reducing wingtip vortices and improve performance.

Have they ever been tried, and with what results ?
CV



Wing end plates were a big fad in the early 1950's. It was found that the
same or better improvement could be obtained by simply adding the same area
to the wingtip as additional wingspan.

Messing with wingtips has a long and somewhat eccentric history. They have
been bent up and down, swept forward and back, made wider and narrower,
sliced off at an angle or square, slots added and removed. Until Whitcomb
developed winglets, everything else people tried had a huge drag penalty.
Airflow around the wingtip is complicated. You really have to understand it
to extract any gain.

Winglets produce a real gain especially if the glider must remain within a
span-limited competition class. They have the advantage of increasing the
lift inboard of the winglet without increasing the bending force on the wing
as much as additional span would. They also convert some of the energy in
the wingtip vortex into thrust which is seen as a general drag reduction in
the wingtip area. Think of the winglet as a sailboat sail that catches some
of the inward flow on the upper surface and converts it into thrust.

Bill Daniels