Mylar tape wing seals - effect on wing performance

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?

Bill Daniels


"Eric Greenwell" wrote in message
...
Simon Waddell wrote:
Eric,

What you and Herbert appear to be saying is that thee mylar is only a
fairing, rather than a seal. Since the mylar is in turbulent airflow
the
need for a fairing at that point seems limited. At the moment, the seal
is
provided by flexible adhesive tape over the join (upper surface only).

This is sufficient to stop the airflow through the gap. Many gliders use
a single internal tape that works with a "rolling" motion. I believe
this seal is more important than the mylar fairings (I think "fairing"
is a better description, since the real sealing is done by the internal
tape, though the mylar would provide some sealing if there was no
internal tape). I don't know if this internal seal can be done on the
Mini Nimbus. The external seal you describe sounds like it would
interfere with the proper fitting of mylar fairings.

Any of the seals - tape or mylar - must be properly fitted to avoid
control problems. Even the simple external tape can cause problems if it
comes loose on the front edge, or shrinks enough to prevent full control
deflection. The mylar has caused more problems than the simple tape,
however.

Would I be better off (financially, yes!) to forget about mylar and
stick
(not to pun) with the adhesive tape, perhaps on both upper and lower
surfaces?

Probably! There is no need for tape on both sides, as it's job is to
stop the airflow between the wing and control surface. Without clear
evidence of value for the Mini Nimbus, like well done flight tests, I'd
avoid the effort, expense, and potential safety risk of the mylar.

--
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Eric Greenwell
Washington State
USA

"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