On Tue, 21 Jun 2011 09:09:20 -0700 (PDT), mattm
wrote:

My plane seems to fly about 10-12% worse than the Johnson
measured polar. The gelcoat is in pretty good shape overall
after 33 years though; it looks like a reprofiling is basically
a refinish project, which I'm not planning on doing anytime soon.


Hi Matt,

don't rely too much on Johnson's polars. Dick did an amazing job, but
with his limited resources his polars are off more often than not.

The German Idaflieg polars are usually very precise, but it took ten
times more effort to measure them.

My advice:
Take a close look at the wing and try to find out if there's waviness
in front of the wing spar. The best way is to have a neon lamp over
the wing - by looking at its reflection you can see the slightest
waviness.
If you find serious waviness (which I doubt), come back to this group
and ask for an exchange between help and cash.
If you don't ... be happy and ignore Dick's polar.

In my opinion it is impossible to get a proper airfoil again if you
don't have some experienced guy at hand.


Andreas

p.s.
Do you happen to have a friend with a similar glider (ASW-20, Ventus
1) at hand that you could use to compare your performance to?