"Bill Daniels" wrote:

Direct question to the group.

My Nimbus 2C has Mylar on both the upper and lower aileron gaps plus an
internal seal. The lower gap Mylar "fairing" is in only fair condition.
Should I just remove it?

An airfoil expert of greatest fame once told me that the smoothness of
the underside of the wing is most important for achieving minimum
drag. More so than upper surface...
Thus I would assume a Mylar fairing, if correctly installed, is most
significant on the lower surface: you should replace it with a new one
if it's not perfectly attached or shaped.
Whether a Mylar fairing is truly beneficial to a Wortmann airfoil I
don't know, but I guess the aerodinamic noise of an aircraft could be
a good indicator of low drag; if your friend will report of a lower
noise level during high speed finishes, I think you may be pretty sure
drag has been reduced. (?)

My limited experience relates only to normal adhesive tape used to
seal the gap on the lower surface of my former DG400. When, in very
hot wather, the tape on the left wing started to slide backward (from
the tape's leading edge towards the aileron) creating a vertical bump
(about 3 to 5 mm high), the glider was more and more steering to the
right. Anxiety about landing grew as I needed 2 hands on the stick to
just keep the glider straight and level.
It all finished before landing (good!) as the tape eventually fell
off.
The effect on the behaviour of the glider was opposite to what I would
have expected (should have been: bump=drag=left wing down and back...)
Maybe it has had something to do with the principle of "Guerney
flaps"?

Aldo Cernezzi