On May 19, 6:09*am, JJ Sinclair wrote:

I believe the main purpose of adding Mylar is to reduce drag, but if
you want added control authority, one can think about the combination

I'm arguably the least experienced pilot on this thread, so I'll try
to tread respectfully - but I was under the impression that mylars are
placed over control gaps for three reasons:

1) To prevent (or at least reduce) high pressure air below the wing
from being sucked up through the control gap to the low-pressure air
on top, disturbing or separating the airflow right at the control
surface. If designed to flow properly, such airflow can be beneficial
in certain flight regimes (see "slotted flap") - but for glider
control surfaces its bad news.

2) To lessen the drag as the low-pressure air goes down the top
surface through the pressure-recovery zone and hits a big lip or gap
or sharp angle that might cause the air to separate, tumble, swirl,
etc. In other words, the mylar helps smooth the transition between
the wing and the control surface no matter what angle the control
surface is at (relative to the rest of the wing).

Take care,

--Noel