Wing Profiling Advice

Andy, see comments below:

I would think that using rate of change of curvature
(or absolute curvature) to estimate the thickness of
the overall airfoil would be really challenging. It's
kind of like using an accelerometer (or variometer)
to estimate your altitude - it's possible if you're
really good at integrating the values, but you need
very accurate measurements to keep the integrated sum
from drifting pretty significantly.

You're right. It's probably poor for profiling the whole wing. But it
worked reasonably well in picking up flaws that were bigger than the
wave gauge but substantially smaller than the chord. If I'd known I
had a significant problem when I started, I'd probably have tried to
make templates. But by the time I finally figured out what the problem
was, I felt like I could go ahead with the dial gauge.

Frankly, an experienced tuner like Hank Nixon would pick up that kind
of problem simply by running his hand over the wing!

Can anyone tell me if it really matters if the overall
thickness of the wing is off by a few thousandths.
This is the difference between sanding down to the
spar wave and building up gelcoat in the spar wave.
I think most people sand down if they can and build
up if they have to.

The main reason we sprayed to build up was that this was the second
time the glider was in for sanding and there simply wasn't enough gel
coat over the leading and trailing edges of the spar cap; I was
already seeing dark spots.

You're right about overall thickness. The later LS-3a wings (I had an
earlier "3") allegedly were as much as 2% thicker than spec in some
places. That's a half inch on, say, a 24" chord!!! From memory, Dick
Johnson found similar things on his PIK-20 and just extrapolated the
airfoil for thicker sections since he had the coordinates for both 15%
and 17% sections.

I thought the main objective of reprofiling these days
was to remove surface waviness - but this adds a new
level of complexity - should I even worry about it?

9B

I sanded/contoured my LS-3 three times in the 12 years I owned it in
addition to extensive sealing and other tuning. The only thing I've
done to my ASW-24 over the past 12 years is add winglets. One reason
is that the '24 wing is amazingly stable over time (maybe one of the
best composite gliders ever). The other reason is that I was single
when I owned the '3 and with a 9 to 5 job. Now I'm married with two
children, and average 60 hour weeks!

If you're really worried about it, I recommend selling your '27 and
buying a PW-5.

Chip Bearden