Jon Meyer wrote in message ...
Bernhard's diagrams are spot on, but whether you call
it thrust or a reduction in drag is up to you. My Aeronautical
Engineering textbook uses both as alternative ways
of describing it. It all depends on how you choose
your frame of reference. The winglet produces a vorce
vector which consists of drag and lift, but when this
force vector is considered with the sailplane as the
frame of reference then its components could be considered
as a thrust force and a lateral force. I feel that
this is the easier way to describe the way they reduce
overall drag, but if you want to be pedantic........

If there is only drag and no thrust you'll eventually be
flying backwards, right?

Suppose you raise your glider up into the air under a balloon and
drop it. If the wings (nor anything else) generate only lift and
no thrust then you'll just move in the verticle direction only,
or hover.

If a wing can generate thrust then so can a winglet depending on
geometry, AOA etc. It will also generate drag and weight.

--

FF