Wing Profiling Advice

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

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

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

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

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

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

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

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

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

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