Wing Profiling Advice

I've 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

In article ,
Andy Blackburn wrote:

Do the
dimples hurt performance - how concerned should I be?

According to Richard Johnson waves greater than .004" peak-to-peak (or
+/- .002") will not allow the laminar flow airfoil to perform as
intended.

From your description of the "dimples" I would be inclined to say yes,
you should be concerned, and if I were you I'd have it fixed. Can't
answer your other questions.

Regards,

-Doug

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

Udo Rumpf wrote:
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

I second Udo's suggestions. After 9 years, my ASH 26E had accumulated a
number of dimples and waves, but after flying next to a new ASH 26 E, I
realized the performance difference was imperceptible. So, I'm waiting
for more serious problems before I do anything about the wing imperfections.


--
Change "netto" to "net" to email me directly

Eric Greenwell
Washington State
USA

I suggest leaving as is. Won't gain much by fixing and might regret later. I
agree that temp might have played a role and if so after fixing it will
happen again. Waste of good money.

Andre

"Andy Blackburn" wrote in message
...
I've 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

What does Schleicher have to say about this?
20 months old and exhibits visible shrinkage? I would have had a talk
with them by now.
Uri
"Andre van Niekerk" wrote in message ...
I suggest leaving as is. Won't gain much by fixing and might regret later. I
agree that temp might have played a role and if so after fixing it will
happen again. Waste of good money.

Andre

"Andy Blackburn" wrote in message
...
I've 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

The glider was
manufactured in January of 2003, so it's 20 months
old.

Take it back to your supplier and get them to fix it. It is not of merchantable
quality if it shows such problems after only 20 months

Andy Blackburn wrote in message ...
I've 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

It takes about 5 years to be 90% shrunk from my experience. Seems like
later 27's shrink quicker but no experience with whether this will
continue. My 27 is 7 years old and seems to have stablized.
I suspect the heat your glider sees is accelerating this.
My suggestion is this:
Convince your shop to fill only the spar areas with gelcoat and
contour that.
You will have a slightly different color and sheen but the shape will
be good and it should be much less costly than a full refinish. Then
give it 5 years and see where you are.
If you refinish in Poly, and it continues to shrink, what will you do
then. I strongly suggest you stay with gelcoat.
Good Luck UH

Welcome to the club. Every recent 27B I know of has had this problem
to greater or lesser extent. Mine had awful shrinkage and dimples
after only three months. I gather this is due to curing of the epoxy
gluing the spar to the wing skins, and will happen eventually in hot
or cold weather. I had mine fixed. The decline and then restoration of
the original (amazing) performance was noticeable. I was advised to
wait 3 years so the curing and dimpling is complete before fixing. I
ignored this wise advice and have a little additional shrinkage in the
two years since I had it fixed, but not yet enough to consider doing
it again. It's important to have someone you really trust do this; a
poor job can screw up the entire wing profile. I would advise paying
more to be sure the profiling is done right. BTW, I contacted the
factory under the warranty, but they blew me off. We're on our own
with this. On the good side, once it's done you have a great glider!

John Cochrane (BB)

What BB said happened to mine also. I also got blowen off with no help offered
except bring your checkbook. My bottoms were really bad with waves of great
than .009 or worse. Some approaching .018 to .022. Now, everything is fine and
they are down to .002 or less. Mr. Fidel did mine, he does great work, as do
several others around the country. BUT you have to get it done for the
performance to be where it should be. # 711.