Wing Profiling Advice

[Andy Blackburn]

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

[Doug Hoffman]

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

[Udo Rumpf]

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
>
>
>

[Eric Greenwell]

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

[Andre van Niekerk]

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
>
>
>

[Uri Saovray]

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
> >
> >
> >

[OscarCVox]

>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

[Hank Nixon]

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

[John Cochrane]

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)

[TomnKeyLargo]

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.

[Andy Blackburn]

Thanks guys - that helps.

Anyone out there have any experience with heating the
wings to get to a stable post-curing shape? I'm a bit
concerned about being the first person on the planet
to easy-bake my glider.

9B

At 16:48 07 September 2004, Tomnkeylargo wrote:
>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.
>

[Andy Blackburn]

Thanks guys - that helps.

Anyone out there have any experience with heating the
wings to get to a stable post-curing shape? I'm a bit
concerned about being the first person on the planet
to easy-bake my glider. But at the same time I don't
want to make this a bi-annual event for the next half-dozen
years.

At least I have a convenient, lame excuse for my competition
performance this year.

9B


At 16:48 07 September 2004, Tomnkeylargo wrote:
>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.
>

[Bob]

Snip

(John Cochrane) wrote in message >...
>
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)


John

You may need to look into the German or EU warranty rules. It seems to
me that this would be considered a manufacturing problem.

Bob

[Andy Durbin]

Andy Blackburn > wrote in message >...
> Thanks guys - that helps.
>
> Anyone out there have any experience with heating the
> wings to get to a stable post-curing shape? I'm a bit
> concerned about being the first person on the planet
> to easy-bake my glider. But at the same time I don't
> want to make this a bi-annual event for the next half-dozen
> years.


One repair man I know gets the recommended repair cure temperature by
putting black polythene over the trailer.

Just moving back to Arizona may be good enough.


Andy

[Andy Blackburn]

In a similar vein, I was thinking about using a toilet
plunger to pull the dimples out.

It was only 105 in the PHX area today - autumn must
have arrived!

;-)

At 23:18 07 September 2004, Andy Durbin wrote:
>Andy Blackburn wrote in message news:...
>> Thanks guys - that helps.
>>
>> Anyone out there have any experience with heating
>>the
>> wings to get to a stable post-curing shape? I'm a
>>bit
>> concerned about being the first person on the planet
>> to easy-bake my glider. But at the same time I don't
>> want to make this a bi-annual event for the next half-dozen
>> years.
>
>
>One repair man I know gets the recommended repair cure
>temperature by
>putting black polythene over the trailer.
>
>Just moving back to Arizona may be good enough.
>
>
>Andy
>

[Andy Durbin]

(Bob) wrote in message
>
>
> John
>
> You may need to look into the German or EU warranty rules. It seems to
> me that this would be considered a manufacturing problem.
>
> Bob

With enough people pitching in it may be possible to win a class
action. The fix may be worse than the problem though as it could put
Schleicher out of business. I just wish Schleicher would offer an
option for cured sailplanes. I'll be reluctant to buy another "rare"
one.


Andy

[John Cochrane]

(Bob) wrote in message >...
> Snip

> 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)
>
>
> John
>
> You may need to look into the German or EU warranty rules. It seems to
> me that this would be considered a manufacturing problem.
>
> Bob

It sure is a manufacturing problem under anyone's rules. But the cost
of a refinish is a bit below the time, effort, and acrimony it would
cost to sue them, so I sighed, signed the check, and now have a
gorgeous glider and perhaps a bit more goodwill when I want to buy the
next one. Those of us who bought with the Euro at .9 got cheap gliders
in the end anyway!

John Cochrane BB

John Cochrane (BB)

[Lorry Charchian]

(John Cochrane) wrote in message >...
> 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)

Hi John,

I have some issues with my ASW 27A as well however I do not have
dimples in the true sense of the word. Have you or anyone else
measured the depth of the reported dimples? I thought I had dimples
which appeared in regular rows both spanwise and cordwise, however,
they had no depth and could not be felt. They were visible only when
looking at the wing obliquely in the sunlight. I am told they are
produced when the wing is being made. Apparently, when the wing is
made there are vent holes in the jelcoat which are filled with a
somewhat different material and then finished leaving what look like
dimples but are completely smooth. Do you have any depth measurements
of the dimples or further obsevations? By the way my ship was
manufactured in Oct.'98 and has flown about 750 hrs.

Lorry Charchian (LJ)

[John Sinclair]

Larry,
The dimples you see are from holes in the foam core
that allow resin to penetrate the foam and insure a
good bond between the cloth and core. Usually don't
cause a performance problem.

Some ships are perfect and stay that way, others go
to hell in no time at all. Ever wonder why? We have
a 27 here in Northern California that is absolutely
perfect and it shows. It's owner just won the 18 meter
nats with it.

JJ's theory--------------Oh, lets hear yours first.
:>) JJ

[Andy Blackburn]

Thanks to all for the input and theories. I'm going
to go find/build a wave guage and measure the depth
of all these emerging imperfections and report back
here. My ship arrived with perfect skin, the blemishes
didn't arrive until 'puberty' (age 18-20 months --
this year).

Anybody able to point me to a source and/or plans to
make a wing wave guage?

Thanks!

9B

At 18:18 15 September 2004, John Sinclair wrote:
>Larry,
>The dimples you see are from holes in the foam core
>that allow resin to penetrate the foam and insure a
>good bond between the cloth and core. Usually don't
>cause a performance problem.
>
>Some ships are perfect and stay that way, others go
>to hell in no time at all. Ever wonder why? We have
>a 27 here in Northern California that is absolutely
>perfect and it shows. It's owner just won the 18 meter
>nats with it.
>
>JJ's theory--------------Oh, lets hear yours first.
> :>) JJ
>
>
>
>

[Pete Reinhart]

You show me yours first.
Cheers!

"John Sinclair" > wrote in message
...
> Larry,
> The dimples you see are from holes in the foam core
> that allow resin to penetrate the foam and insure a
> good bond between the cloth and core. Usually don't
> cause a performance problem.
>
> Some ships are perfect and stay that way, others go
> to hell in no time at all. Ever wonder why? We have
> a 27 here in Northern California that is absolutely
> perfect and it shows. It's owner just won the 18 meter
> nats with it.
>
> JJ's theory--------------Oh, lets hear yours first.
> :>) JJ
>
>
>

[Gary Evans]

I recall a picture or diagram of the tool for measuring
surface deflection. It may have been in one of Dick
Johnsons articles which are or were available at the
SSA web site. Iif not it was written up in Soaring.



t 18:36 15 September 2004, Andy Blackburn wrote:
>Thanks to all for the input and theories. I'm going
>to go find/build a wave guage and measure the depth
>of all these emerging imperfections and report back
>here. My ship arrived with perfect skin, the blemishes
>didn't arrive until 'puberty' (age 18-20 months --
>this year).
>
>Anybody able to point me to a source and/or plans to
>make a wing wave guage?
>
>Thanks!
>
>9B
>
>At 18:18 15 September 2004, John Sinclair wrote:
>>Larry,
>>The dimples you see are from holes in the foam core
>>that allow resin to penetrate the foam and insure a
>>good bond between the cloth and core. Usually don't
>>cause a performance problem.
>>
>>Some ships are perfect and stay that way, others go
>>to hell in no time at all. Ever wonder why? We have
>>a 27 here in Northern California that is absolutely
>>perfect and it shows. It's owner just won the 18 meter
>>nats with it.
>>
>>JJ's theory--------------Oh, lets hear yours first.
>> :>) JJ
>>
>>
>>
>>
>
>
>
>

[Lorry Charchian]

Andy Blackburn > wrote in message >...
> Thanks to all for the input and theories. I'm going
> to go find/build a wave guage and measure the depth
> of all these emerging imperfections and report back
> here. My ship arrived with perfect skin, the blemishes
> didn't arrive until 'puberty' (age 18-20 months --
> this year).
>
> Anybody able to point me to a source and/or plans to
> make a wing wave guage?
>
> Thanks!
>
> 9B
>
> At 18:18 15 September 2004, John Sinclair wrote:
> >Larry,
> >The dimples you see are from holes in the foam core
> >that allow resin to penetrate the foam and insure a
> >good bond between the cloth and core. Usually don't
> >cause a performance problem.
> >
> >Some ships are perfect and stay that way, others go
> >to hell in no time at all. Ever wonder why? We have
> >a 27 here in Northern California that is absolutely
> >perfect and it shows. It's owner just won the 18 meter
> >nats with it.
> >
> >JJ's theory--------------Oh, lets hear yours first.
> > :>) JJ
> >
> >
> >
> >
Hi Andy,

Apparently I misunderstood what I was told regarding the
spots(dimples) on the wing surface. During the layup of the foam core
onto the outer fabric a roller with spike like protrusions is rolled
against the foam, penetrating it. Follwing the placement of the inner
skins the assembly is vacuum bagged. I am told this is done to help
eliminate excess air. The resuting pressure forces the excess resin
into these depressions in the foam producing little spikes of hardened
resin upon curing. Apparently these spike like discontinuities cause
a non uniform deflection locally about the spikes when the wing flexes
which causes the skin to refect light differently. I am also told
that in time they could produce a slight "pimple" or dimple. At least
in my case I have not seen anything other than a reflective difference
on the surface.

You might give Ed Byars a call for a inexpensive surface gage
employing a dial indicator that he was selling a year or so ago.

I guess I now know more than I really needed to know about this.

Lorry

[Udo Rumpf]

> I recall a picture or diagram of the tool for measuring
> surface deflection. It may have been in one of Dick
> Johnsons articles which are or were available at the
> SSA web site. Iif not it was written up in Soaring.

Use a small block of alu or plastic.
Dimension are 2" Long 1"wide 1/2 thick.
Use three 3/16" round head Nylon machine screws.
Install two screws at each corner and one at the middle on the other end.
Install dial indicator by drilling a hole in the centre of block
as well as cutting a slot for clamping the dial indicator with a screw
or look up 1989 Soaring page 35.
That was a year after I started flying gliders.
Regards
Udo

[Leon McAtee]

Andy Blackburn > wrote in message >...
this year).
>
> Anybody able to point me to a source and/or plans to
> make a wing wave guage?
>
> Thanks!


http://www.oxaero.com/OxAero-WaveGauge.asp

Shouldn't be har to fab one with a dial indicator from Harbor freight,
a hunk of wood/Phenolic and some nylon bolts from the hardware store.
==================
Leon McAtee

[Bob Gibbons]

And kudos to OxAero for not only selling a version of Dick Johnson's
wavegage, but also putting up a pdf format version of Dick's wing wave
measurement article from the 1998 Soaring Magazine.

http://www.oxaero.com/OxAero-WaveGauge.asp

Bob

On 15 Sep 2004 18:55:29 -0700, (Leon McAtee)
wrote:

>Andy Blackburn > wrote in message >...
> this year).
>>
>> Anybody able to point me to a source and/or plans to
>> make a wing wave guage?
>>
>> Thanks!
>
>
>http://www.oxaero.com/OxAero-WaveGauge.asp
>
>Shouldn't be har to fab one with a dial indicator from Harbor freight,
>a hunk of wood/Phenolic and some nylon bolts from the hardware store.
>==================
>Leon McAtee

[Doug Hoffman]

In article >,
(Leon McAtee) wrote:

> Andy Blackburn > wrote in message
> >...
> this year).
> >
> > Anybody able to point me to a source and/or plans to
> > make a wing wave guage?
> >
> > Thanks!
>
>
> http://www.oxaero.com/OxAero-WaveGauge.asp
>
> Shouldn't be har to fab one with a dial indicator from Harbor freight,
> a hunk of wood/Phenolic and some nylon bolts from the hardware store.

Right. I made mine using a block of wood 2" x 3" x 1.25" (laminate if
nec.), an inexpensive dial indicator with 0.5" travel and readable in
..001" increments. Drill a hole just big enough for the barrel of the
indicator, then cut a slot in the wood and cross-drill and install a
small bolt/nut for "clamping the indicator in place. 3 large-ish nylon
bolts installed on the bottom with 2" between 2 at one end and 1 at the
other end provide the contact points on which to slide the device on the
wing surface. Simple, inexpensive to make.

Regards,

-Doug

[John Cochrane]

> Hi John,
>
> I have some issues with my ASW 27A as well however I do not have
> dimples in the true sense of the word. Have you or anyone else
> measured the depth of the reported dimples? I thought I had dimples
> which appeared in regular rows both spanwise and cordwise, however,
> they had no depth and could not be felt. They were visible only when
> looking at the wing obliquely in the sunlight. I am told they are
> produced when the wing is being made. Apparently, when the wing is
> made there are vent holes in the jelcoat which are filled with a
> somewhat different material and then finished leaving what look like
> dimples but are completely smooth. Do you have any depth measurements
> of the dimples or further obsevations? By the way my ship was
> manufactured in Oct.'98 and has flown about 750 hrs.
>
> Lorry Charchian (LJ)

I've seen the same thing on a local A model. It's a totally different
phenomenon. The A's sometimes get these very little dimples on the
top, which as someone else said probably don't do anything. The Bs get
much bigger and deeper dimples along the bottom surface where the spar
is glued to the wing. The ribs also shrink, but that is chordwise
rather than spanwise so probably only esthetic.

John Cochrane

[Doug Hoffman]

In article >,
Gary Evans > wrote:

> I recall a picture or diagram of the tool for measuring
> surface deflection. It may have been in one of Dick
> Johnsons articles which are or were available at the
> SSA web site. Iif not it was written up in Soaring.
>
>
>
> t 18:36 15 September 2004, Andy Blackburn wrote:
> >Thanks to all for the input and theories. I'm going
> >to go find/build a wave guage and measure the depth
> >of all these emerging imperfections and report back
> >here. My ship arrived with perfect skin, the blemishes
> >didn't arrive until 'puberty' (age 18-20 months --
> >this year).
> >
> >Anybody able to point me to a source and/or plans to
> >make a wing wave guage?
> >
> >Thanks!
> >
> >9B

After you've made or purchased the wave gauge, the next question is "How
does one actually use it?".

Be aware that the gauge alone will *not* detect errors in the shape of
the profile or thickness of the wing. For that you need accurate
templates. But I state the obvious.

Since the surface is irregularly curved in the direction of measure
(along the chord) the dial indicator will change its reading when moved
from back to front even on a "perfect" wing as indeed it must. A simple
way to use it is to look for the dial indicator reading to "back-up" in
one spot rather than gradually changing its reading as the device is
moved chordwise. If the "back-up", either bump or depression, is
greater than .003"-.004" in 2" then you should correct the wing there.

I like to use it as follows. I borrow one of my wife's cloth-tape
sewing scales. It easily lays flat on the chord. First I mark spanwise
stations on the wing every foot from root to tip. At each station,
starting from say the flap hingeline to the front of the wing, lay down
the cloth tape. I then use a small tape recorder and speak the readings
of the dial indicator corresponding to every 1 inch location on the
chord. I zero the dial indicator at the flap hingeline. Near the
leading edge the readings become essentially meaningless. I then key
the data from the tape recorder into a spreadsheet. I plot the data at
each station with the X-axis as percent of chord and the Y-axis as the
dial indicator reading. This normalizes the data for differing chord
lengths. (My wings are a constant taper and airfoil so this works well.
A multi-taper wing and/or multi airfoil wing will need to be treated a
bit differently.) The overall shape of the plotted data at each
station, for a constant taper/foil wing, should look about the same.
Inspect the plots for stations with plot shapes that deviate from the
rest. This can indicate a relatively high or low spot on the wing. Of
course also check the data for bumps or depressions that are greater
than .003"-.004" in 2". I'm sure there are other ways to do this, but
this is what I have done.

Regards,

-Doug

[Chip Bearden]

> Be aware that the gauge alone will *not* detect errors in the shape of
> the profile or thickness of the wing. For that you need accurate
> templates.

Actually, it is possible to do *some* profiling of the wing using a
dial gauge. You need the airfoil coordinates and the dimensions of
your dial gauge (the distance between the contact points of the
"feet", and where between the feet is the dial gauge). This assumes
that the thickness is correct and that the very nose of the leading
edge is also correct, two big assumptions.

I believe it was Rudy Alleman who published a paper in Technical
Soaring (early 80s?) on comparing airfoils from one glider to the next
this way. I derived a slightly more elegant (but no more accurate)
solution and wrote a BASIC program to do the number crunching about 20
years ago. Basically for each chord length (spanwise station) in
question, you use three points on the segment of the airfoil spanned
by the dial gauge to calculate radius of curvature (any three points
lie on a circle). Then you can calculate what the dial guage should
read at that position for the correct curvature.

That's a potentially useful number but I found that the easier way is
to calculate how much the dial gauge should change moving from, say 3"
aft of the leading edge to 4" aft on a 28" chord. If it's supposed to
"unwind" (i.e., the curvature is getting flatter) .010" but it
actually drops more than that, then the curvature is getting too flat
too soon, and vice versa. It helps to print out a strip of paper with
the actual readings every inch or so and tape it to the chord line so
you can do the deltas from one point to the next as you slide the dial
gauge along the wing.

I had a little trouble at first visualizing what was wrong when the
actual numbers didn't agree with the calculations. It's especially
difficult when you come to a bad spot that spans more than the dial
gauge itself. Let's see, the needle went clockwise .005" too much
which means that the curvature is too sharp. So the back feet are
sitting in a depression. When the dial gauge slides into the
depression then...what?

I started putting small pieces of tape on the wing to build up the low
points, so the dial gauge feet could rest on the "reprofiled" wing.
Only then did it become obvious there was a large "flat" spot over the
spar cap on my old LS-3 caused by shrinkage. Moving from front to back
there'd be no tape, then .002" of tape, then .004" of tape, then
..006", then .008", then .006", then .004" and so forth back to zero.
Then the two sharp dial gauge needle reversals we had seen made sense
(one was the sharper point at the forward end of the flatter spot and
the other was at the after end of it).

It was too extensive to sand out so we sprayed gel goat over the flat
spot and built up that area, then used the dial gauge to get the
correct contour. The results were dramatic in improved performance.

Templates are a far more accurate way of profiling a wing, but you can
learn a lot, and even make some small adjustments, with a good dial
gauge. It helps tremendously if you have the airfoil coordinates, of
course. That was easier then than now.

Interestingly, when I first ran the program against the Wortmann
series on the LS-3, I found some strange discontinuities (i.e., the
deltas weren't a smooth curve in several spots) even though I had used
the corrections that Dr. Wortmann had published. It wasn't until I
cranked in Dan Somers' subsequent corrections that all the deltas
smoothed out.

Chip Bearden

[Andy Blackburn]

That's pretty impressive Chip.

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.

Since these dial guages are generally only good to
001' or so, it seems like they're best at estimating
surface waviness. I'm not disputing what you did -
I'm just amazed that you were able to do it.

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.

Even if I make my wing .005' thinner overall from sanding,
that's around 1/10 of 1% of the total thickness - I'm
not sure if the design/manufacturing tolerances are
that good to start with and I don't know if the factory
allows for some shrinkage in the initial construction.
Of course if my spar wave is .05' instead of .005'
than maybe the answer changes. At what point does it
start to matter?

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

At 17:54 18 September 2004, Chip Bearden wrote:
>> Be aware that the gauge alone will *not* detect errors
>>in the shape of
>> the profile or thickness of the wing. For that you
>>need accurate
>> templates.
>
>Actually, it is possible to do *some* profiling of
>the wing using a
>dial gauge. You need the airfoil coordinates and the
>dimensions of
>your dial gauge (the distance between the contact points
>of the
>'feet', and where between the feet is the dial gauge).
>This assumes
>that the thickness is correct and that the very nose
>of the leading
>edge is also correct, two big assumptions.
>
>I believe it was Rudy Alleman who published a paper
>in Technical
>Soaring (early 80s?) on comparing airfoils from one
>glider to the next
>this way. I derived a slightly more elegant (but no
>more accurate)
>solution and wrote a BASIC program to do the number
>crunching about 20
>years ago. Basically for each chord length (spanwise
>station) in
>question, you use three points on the segment of the
>airfoil spanned
>by the dial gauge to calculate radius of curvature
>(any three points
>lie on a circle). Then you can calculate what the dial
>guage should
>read at that position for the correct curvature.
>
>That's a potentially useful number but I found that
>the easier way is
>to calculate how much the dial gauge should change
>moving from, say 3'
>aft of the leading edge to 4' aft on a 28' chord. If
>it's supposed to
>'unwind' (i.e., the curvature is getting flatter) .010'
>but it
>actually drops more than that, then the curvature is
>getting too flat
>too soon, and vice versa. It helps to print out a strip
>of paper with
>the actual readings every inch or so and tape it to
>the chord line so
>you can do the deltas from one point to the next as
>you slide the dial
>gauge along the wing.
>
>I had a little trouble at first visualizing what was
>wrong when the
>actual numbers didn't agree with the calculations.
>It's especially
>difficult when you come to a bad spot that spans more
>than the dial
>gauge itself. Let's see, the needle went clockwise
>.005' too much
>which means that the curvature is too sharp. So the
>back feet are
>sitting in a depression. When the dial gauge slides
>into the
>depression then...what?
>
>I started putting small pieces of tape on the wing
>to build up the low
>points, so the dial gauge feet could rest on the 'reprofiled'
>wing.
>Only then did it become obvious there was a large 'flat'
>spot over the
>spar cap on my old LS-3 caused by shrinkage. Moving
>from front to back
>there'd be no tape, then .002' of tape, then .004'
>of tape, then
>..006', then .008', then .006', then .004' and so forth
>back to zero.
>Then the two sharp dial gauge needle reversals we had
>seen made sense
>(one was the sharper point at the forward end of the
>flatter spot and
>the other was at the after end of it).
>
>It was too extensive to sand out so we sprayed gel
>goat over the flat
>spot and built up that area, then used the dial gauge
>to get the
>correct contour. The results were dramatic in improved
>performance.
>
>Templates are a far more accurate way of profiling
>a wing, but you can
>learn a lot, and even make some small adjustments,
>with a good dial
>gauge. It helps tremendously if you have the airfoil
>coordinates, of
>course. That was easier then than now.
>
>Interestingly, when I first ran the program against
>the Wortmann
>series on the LS-3, I found some strange discontinuities
>(i.e., the
>deltas weren't a smooth curve in several spots) even
>though I had used
>the corrections that Dr. Wortmann had published. It
>wasn't until I
>cranked in Dan Somers' subsequent corrections that
>all the deltas
>smoothed out.
>
>Chip Bearden
>

[Chip Bearden]

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

[Bob Kuykendall]

Earlier, Andy Blackburn > wrote:

> Can anyone tell me if it really matters if the overall
> thickness of the wing is off by a few thousandths...

Based on template checks of several top-ranked contest ships, I will
opine that it does not. For a few of the ships, you'd guess on the
basis of the template mismatch that the right and left wings weren't
even for the same aircraft. And yet these were all straight-flying,
go-like-stink gliders.

So you'll find me in the camp that says that waviness below .004" is
first priority, canopy and wing root sealing is second, and fidelity
to profile is a distant third.

Thanks, and best regards to all

Bob K.
http://www.hpaircraft.com/hp-24

[Doug Hoffman]

In article >,
(Chip Bearden) wrote:

> > Be aware that the gauge alone will *not* detect errors in the shape of
> > the profile or thickness of the wing. For that you need accurate
> > templates.
>
> Actually, it is possible to do *some* profiling of the wing using a
> dial gauge. You need the airfoil coordinates and the dimensions of
> your dial gauge (the distance between the contact points of the
> "feet", and where between the feet is the dial gauge). This assumes
> that the thickness is correct and that the very nose of the leading
> edge is also correct, two big assumptions.

Chip, Please accept my apologies for dismissing this idea. After
taking a hard look at my dial indicator readings, comparing them to what
I see on the wings, and thinking more carefully about the method you
describe, I understand what you are saying and see how this could work.
It's actually a pretty clever idea. Sorry again.

Regards,

-Doug

[Chip Bearden]

Doug Hoffman > wrote in message . com>...
> In article >,
> (Chip Bearden) wrote:
>
> > > Be aware that the gauge alone will *not* detect errors in the shape of
> > > the profile or thickness of the wing. For that you need accurate
> > > templates.
> >
> > Actually, it is possible to do *some* profiling of the wing using a
> > dial gauge. You need the airfoil coordinates and the dimensions of
> > your dial gauge (the distance between the contact points of the
> > "feet", and where between the feet is the dial gauge). This assumes
> > that the thickness is correct and that the very nose of the leading
> > edge is also correct, two big assumptions.
>
> Chip, Please accept my apologies for dismissing this idea. After
> taking a hard look at my dial indicator readings, comparing them to what
> I see on the wings, and thinking more carefully about the method you
> describe, I understand what you are saying and see how this could work.
> It's actually a pretty clever idea. Sorry again.
>
> Regards,
>
> -Doug

No apology necessary. In 1985 at the U.S. 15M Nationals, Walter
Schneider (of LS fame) took one look at my dial gauge as I tried to
explain what I'd done and had an even more dismissive reaction. :)

Regarding the idea, as I said earlier, an article in Technical Soaring
provided the basic theory. I just took it a little further and applied
it to profiling.

Also as I said earlier, using templates is a more accurate approach
and is the one I'd recommend. But if you've got the wing profile
coordinates and don't want to go to the trouble of making good
templates for multiple stations on the wing, the dial gauge approach
could be of help beyond just locating localized bumps and depressions.

Chip