The performance will be reduced, if the indentation is more than the
allowable tolerance, which can vary a little from airfoil to airfoil.
Just look at the top surface for now only.
If you would assume an indentation of, for example, of .004"
over a distance of 1/4", a transition from laminar to turbulent flow would
follow.
The same .004" over 2 or 3 three inches may not have any negative effect.
In case of a spar shrinkage, the imperfection would be located
approximately at
40% chord. Your glider in optimum climb has a laminar transition at
approx. 65%
on the top surface. If this early transition happens at 40% due to the
imperfections,
the climb will be negatively affected.
Since pressure and friction drag values in climb are relatively small,
compared to induced and interference drag, the difference in climb between
a perfect wing and one that has imperfections may not show up readily.

In fast cruise the bottom surface becomes very important.
The ASW27 wing is designed to have laminar flow to 90% chord.
If the same imperfection holds true as above on the bottom surface,
over half of the bottom wing becomes a turbulent boundary layer wing
and your performance will suffer substantially.
The drag relationship in fast cruise changes and the pressure and
friction drag become dominant and induced drag is a much smaller portion
of the total. Now laminar flow will show its stuff and the airfoil of the
ASW27 will shine.

Make comparison flights with an other ASW27 which is known to perform well.
Also read Dick Johnson's articles on laminar flow.
I hope this helps to make a decision.
Regards
Udo






got my ASW-27B in the shop to have some cosmetic
work done - building up the tip skids and fixing some
minor scrapes.

At the same time I'm wondering if a profiling job is
in order as I can now see spar and rib dimples top
and bottom all along both wings. The shop tells me
that it's going to need filling, priming, maybe microbaloons
- it's shrunk that much while curing. The glider was
manufactured in January of 2003, so it's 20 months
old. I am surprised at how visibly dimpled it is.
It's always been kept in the trailer in a hanger -
but it does live and fly in the Western deserts so
maybe the heat has something to do with it.

I need to tap into some collective experience and advice:

Is it too soon for this? When does all the shrinking
stop? I don't want to go through this twice. Do the
dimples hurt performance - how concerned should I be?

The shop tells me they can bake the wings to accelerate
whatever remaining curing/shrinkage remains prior to
profiling. Is this recommended or to be avoided. I
wasn't quoted a temperature.

In terms of materials - what are the tradeoffs with
Urethane versus Prestec versus the Schleicher factory
stuff?

What should I expect to pay for a full top/bottom filling,
profiling and resurfacing/polishing? I've heard numbers
that are all over the map.

Thanks!

9B