DuoDiscus Wing

"
I think that people proposing utrasonic quality checks don't have an exact
idea how a wing is constructed. Utrasonic QC basically detects interfaces,
and a composite glider wing is made up from interfaces all over the place.
I'd say that the error rate in an utrasonic QC would be completely through
the roof.

I think it would be more easy (and straightforward) to do just a structural
load test up to 1.5 times max rated load :-)
Bert Willing
************************************************** ********************************
I understand your point about ultrasonic testing. The sound wave
would have to go through the outer skin, foam, inner skin, carbon
fibre rovings spar cap, bonding paste, shear web of differing
compositions. I guess there could be too many interfaces although I
would think that one could find an ultrasonic frequency which didn't
reflect off of the interfaces but did reflect off of voids. Or
reflects different frequencies and giving a picture.
Any idea how composite structures are inspected on large airplanes? I
assume x-ray wouldn't be very sensitive on nonmetallic structures.
How about neutron radiation? Acoustic emission transducers? Ballistic
Recovery Chutes?

Also, if the cotton fibres carry the load, is the repair done with an
epoxy/cotton mixture? How do they get it into a blind air bubble?

In article ,
says...
I understand your point about ultrasonic testing. The sound wave
would have to go through the outer skin, foam, inner skin, carbon
fibre rovings spar cap, bonding paste, shear web of differing
compositions.

Is the spar cap on the Duo Discus bonded to the inner skin or the
outer skin? If it is bonded to the outer skin, it would not have the
foam to go through, which should ease the problem considerably.
--
!Replace DECIMAL.POINT in my e-mail address with just a . to reply
directly

Eric Greenwell
Richland, WA (USA)

On Thu, 16 Oct 2003 08:00:49 -0700, Eric Greenwell
wrote:

In article ,
says...
I understand your point about ultrasonic testing. The sound wave
would have to go through the outer skin, foam, inner skin, carbon
fibre rovings spar cap, bonding paste, shear web of differing
compositions.

Is the spar cap on the Duo Discus bonded to the inner skin or the
outer skin? If it is bonded to the outer skin, it would not have the
foam to go through, which should ease the problem considerably.

The problem is that the bond in question attaches the top spar to the
web. Any problems with this bond will drastically affect the spar
strength by allowing the top spar to peel off the web. In the DG-style
of assembly with carbon cloth between the spar and the web the bond
between the spar and the cloth is equally as critical as that between
the web and the cloth.

In the model world we prevent spar peel failures by assembling both
spars to the web and then wrapping to lot with Kevlar thread or an
epozy-wetted woven carbon tube before building the wing round the
complete spar. This gives a 30G wing. I accept that this is overkill
for full size, but my teeth still itch a bit at the lack of any
binding round both the spars except on the protruding stubs at the
root.

I flat out would not fly a glider with foam between the web and the
top spar and would hope that such a structure has never been made or
flown.

--
martin@ : Martin Gregorie
gregorie : Harlow, UK
demon :
co : Zappa fan & glider pilot
uk :

I wasn't clear enough. The problem I thought would be eased was the
ultrasonic inspection problem. So, is the spar cap attached to the
outer wing skin, or is there actually foam between the outer skin and
the spar cap?

In article ,
ess says...
On Thu, 16 Oct 2003 08:00:49 -0700, Eric Greenwell
wrote:

In article ,
says...
I understand your point about ultrasonic testing. The sound wave
would have to go through the outer skin, foam, inner skin, carbon
fibre rovings spar cap, bonding paste, shear web of differing
compositions.

Is the spar cap on the Duo Discus bonded to the inner skin or the
outer skin? If it is bonded to the outer skin, it would not have the
foam to go through, which should ease the problem considerably.

The problem is that the bond in question attaches the top spar to the
web. Any problems with this bond will drastically affect the spar
strength by allowing the top spar to peel off the web. In the DG-style
of assembly with carbon cloth between the spar and the web the bond
between the spar and the cloth is equally as critical as that between
the web and the cloth.

In the model world we prevent spar peel failures by assembling both
spars to the web and then wrapping to lot with Kevlar thread or an
epozy-wetted woven carbon tube before building the wing round the
complete spar. This gives a 30G wing. I accept that this is overkill
for full size, but my teeth still itch a bit at the lack of any
binding round both the spars except on the protruding stubs at the
root.

I flat out would not fly a glider with foam between the web and the
top spar and would hope that such a structure has never been made or
flown.

--
martin@ : Martin Gregorie
gregorie : Harlow, UK
demon :
co : Zappa fan & glider pilot
uk :



--
!Replace DECIMAL.POINT in my e-mail address with just a . to reply
directly

Eric Greenwell
Richland, WA (USA)

Eric Greenwell wrote in message ...
I wasn't clear enough. The problem I thought would be eased was the
ultrasonic inspection problem. So, is the spar cap attached to the
outer wing skin, or is there actually foam between the outer skin and
the spar cap?



Is the spar cap on the Duo Discus bonded to the inner skin or the
outer skin? If it is bonded to the outer skin, it would not have the
foam to go through, which should ease the problem considerably.

The problem is that the bond in question attaches the top spar to the
web. Any problems with this bond will drastically affect the spar
strength by allowing the top spar to peel off the web. In the DG-style
of assembly with carbon cloth between the spar and the web the bond
between the spar and the cloth is equally as critical as that between
the web and the cloth.

In the model world we prevent spar peel failures by assembling both
spars to the web and then wrapping to lot with Kevlar thread or an
epozy-wetted woven carbon tube before building the wing round the
complete spar. This gives a 30G wing. I accept that this is overkill
for full size, but my teeth still itch a bit at the lack of any
binding round both the spars except on the protruding stubs at the
root.

I flat out would not fly a glider with foam between the web and the
top spar and would hope that such a structure has never been made or
flown.

************************************************** ****************************
I don't think anyone said that there is foam between the spar cap and
shear web. Foam within the shear web adds a great deal of stiffness,
however.

The spar cap of German designs is built into one wing skin while the
spar web
and opposite spar cap is bonded into the other skin. When the two wing
halves are mated the one spar cap is glued to the spar web and cap of
the
other wing half. It's pretty much a blind operation and everything had
better well match or there will be a poor or no bond.

The Genesis 2 and the LAK-17a both have the spar completely built
outside the
wing. The spar is totally wrapped in glass fiber insuring it's
integrity.
It will not debond. Following is a site which has pictures of a
Genesis spar.

http://www.aviation-salvage.com/airc...enesis%202.htm

On the Genesis wing it appears that the spar is bonded to an inner
skin which is a foam sandwich with an outer skin. The Genesis spar in
the picture had a metal fence post cut through it and it looks like
Graphlite rods have been bashed into more of a round shaped bundle. I
believe they are spread out into more of an I-shape than the picture
would suggest. At least with this design, if the spar is not bonded
to the skin there is still a very strong spar.

Earlier, Eric Greenwell wrote:

...So, is the spar cap attached to the
outer wing skin, or is there actually
foam between the outer skin and
the spar cap?

The spar cap is glued to the inner skin, and there is foam between the
spar cap and the outer skin. The diagrams in this tech note pretty
much show it:

http://www.schempp-hirth.com/tmdocs/396-8-489.pdf

(Somehow, when I look at those photos, I smell epoxy resin.)

The big advantage of that method is that the sandwich skins are more
stable, and less prone to mirroring the spar after aging. One of the
disadvantages is that the spar is less stiff than it would be if it
went from outer skin to outer skin, and didn't have its depth reduced
by the sandwich foam.

Bob K.

In article ,
says...
The spar cap is glued to the inner skin, and there is foam between the
spar cap and the outer skin. The diagrams in this tech note pretty
much show it:

http://www.schempp-hirth.com/tmdocs/396-8-489.pdf

(Somehow, when I look at those photos, I smell epoxy resin.)

The big advantage of that method is that the sandwich skins are more
stable, and less prone to mirroring the spar after aging. One of the
disadvantages is that the spar is less stiff than it would be if it
went from outer skin to outer skin, and didn't have its depth reduced
by the sandwich foam.

I don't think this is a disadvantage, but is instead an advantage,
because the wing isn't so stiff, and the pilot enjoys a smoother ride
in turbulence. The disadvantage is it likely takes more material, so
the wing is a bit heavier and more expensive.
--
!Replace DECIMAL.POINT in my e-mail address with just a . to reply
directly

Eric Greenwell
Richland, WA (USA)

The big advantage of that method is that the sandwich skins are more
stable, and less prone to mirroring the spar after aging. One of the
disadvantages is that the spar is less stiff than it would be if it
went from outer skin to outer skin, and didn't have its depth reduced
by the sandwich foam.

I don't think this is a disadvantage, but is instead an advantage,
because the wing isn't so stiff, and the pilot enjoys a smoother ride
in turbulence. The disadvantage is it likely takes more material, so
the wing is a bit heavier and more expensive.
************************************************** ********************************
I don't know Eric, that flexibility and smoother ride might be your
upper spar cap lifting off of the shear web. There is no law which
says the wing has to actually snap. It could be more benign; one wing
a little more flexible than the other or air brakes popping open
during high speed runs in turbulence. Each 4g pop might add another
..010" to the delamination between those two air bubbles in the bonding
paste.

The stiffness, or lack thereof, can still be designed into the wing by
varying the amount of carbon fibre rovings in the spar cap, or
Graphlite rods in the case of the Genesis 2 and LAK 17. I believe the
LAK 17 wing has the externally made spar bonded to the outer skin of
the wing because the designers wanted an extremely thin profile. The
spar is only 3 1/2 inches deep at the wing root of the LAK 17; bonding
it to the outer skin of the wing allows the wing to be extremely thin.
Unfortunately, some of the earlier 17's had that mirroring and the
factory paid to have the wings re-profiled. I believe that happened
to some of the earlier ASW 28 gliders, too. Still, the use of
Graphlite rods instead of carbon fibre rovings, and externally built
spars which are then wrapped in fibreglass cloth and vacuum-bagged is
a method which produces stronger, more durable and longer lasting
wings. As the current fleet of German gliders gets older I'll wager
there will be a lot of speed limiting directives because the "margin
of error" isn't what they thought it would be.
What kind of spar construction methods do the SparrowHawk, Apis and
Russia gliders use?

Is the spar cap on the Duo Discus bonded to the inner skin or the
outer skin? If it is bonded to the outer skin, it would not have the
foam to go through, which should ease the problem considerably.

Modern ultrasonic non-destructive evaluation (NDE) should have no
problem inspecting the joints in question. Rolls-Royce has developed
standoff NDE equipment that must contend with a 20 mm air gap. They
got excellent results detecting defects in carbon fiber samples:

Advances in air coupled NDE for rapid scanning applications
Farlow, R.; Kelly, S.P.; Hayward, G.;
Ultrasonics Symposium, 1994. Proceedings., 1994 IEEE , Volume: 2 , 1-4
Nov. 1994
Page(s): 1099 -1102 vol.2

Applications of through-air ultrasound for rapid NDE scanning in the
aerospace industry
Kelly, S.P.; Farlow, R.; Hayward, G.;
Ultrasonics, Ferroelectrics and Frequency Control, IEEE Transactions
on , Volume: 43 Issue: 4 , July 1996

S-H is just talking to the wrong people.

Tom

"Eric Greenwell" wrote in message
.. .
In article ,
says...

Is the spar cap on the Duo Discus bonded to the inner skin or the
outer skin? If it is bonded to the outer skin, it would not have the
foam to go through, which should ease the problem considerably.
--
The spar caps are bonded to the inter skin of both the upper and lower
skins.
A drawing of this is given in the appendix to the Schempp-Hirth Tech Note
for the inspection of the Duo wing. Of course the Tech Note may be viewed
on the Schempp-Hirth web site: www.schempp-hirth.com

Duane