On May 19, 9:53*am, "noel.wade" wrote:

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.

Not primarily - seals are used for that. Either tape (for top or
bottom hinged) or rolling seals (for center-hinged) control surfaces.
Mylar without seals will probably slow the crossflow, but probably not
completely stop it. My LS6 manual specifically shows how and where to
install both rolling seals and Mylar gap covers on all control
surfaces.

Mylar without the rolling seals made my LS6 sound like an RC airplane
at full throttle at about 130 knots - I figure the crossflow was
"buzzing" the mylar on the flaperons. Could turn it on or off within
a couple of knots. Made sneaky low passes a bit difficult! Quickly
fixed by properly installing seals, BTW!

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).


What was #3? ;)


Cheers,

Kirk