DuoDiscus Wing

"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

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?

In any case you will have a blind bonding applied to one side, be is spar
web to spar cap, or spar cap to wing skin - that's the backdraw of using
negative moulds.

Now if you produce voids in one case, you might as well produce voids in
the other case, no? And, by the way, how much would you allow the price of a
glider to increase in case the the manufacturer goes for x-ray or ultrasonic
QC?

--
Bert Willing

ASW20 "TW"


"Slingsby" a écrit dans le message de
om...
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?

Earlier, "Bert Willing"
wrote:

In any case you will have a blind
bonding applied to one side, be is spar
web to spar cap, or spar cap to wing
skin - that's the backdraw of using
negative moulds.

Now if you produce voids in one case,
you might as well produce voids in
the other case, no?...

Well, no, I don't see it that way.

The loads between the skin and the spar are far lower than the loads
between the shear webs and the spar caps. Also, the stiffening of the
spar caps against buckling is absolutely critical to the itegrity of
the spar. Voids between the shear web and the spar cap leave the cap
much more vulnerable to buckling.

Bob K.





And, by the way,
how much would you allow the price of a
glider to increase in case the the
manufacturer goes for x-ray or ultrasonic
QC?

--
Bert Willing

ASW20 "TW"


"Slingsby" a écrit dans le message de
om...
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?

"Bert Willing" wrote in message ...
In any case you will have a blind bonding applied to one side, be is spar
web to spar cap, or spar cap to wing skin - that's the backdraw of using
negative moulds.

Now if you produce voids in one case, you might as well produce voids in
the other case, no? And, by the way, how much would you allow the price of a
glider to increase in case the the manufacturer goes for x-ray or ultrasonic
QC?

--
Bert Willing
************************************************** *******************************
"During operation the bonding areas carry high loads, but after
closing
the wing they become inaccessible forever. Therefore these "blind
bonds", as they are called, must be carefully prepared and executed
with
great precision. To achieve this, we developed a simple but very
reliable procedu

Small strips of play dough ("Plastilin") are applied to all areas
where the upper and lower wing halves will get in contact. These are
special areas on the leading and trailing edge, the spars and ribs.
Adhesive tape protects the bonding surfaces from grease contamination
by the play dough. When the the upper and lower molds are put
together, the play dough is compressed and reflects a very accurate
image of the bonding gap. A similar technique is used for the spars: A
series of cloth pins are inserted into the foam of the shear web.
These pins are then pushed in when the molds are closed, providing an
accurate meassure of the bonding gap.

After re-seperating the molds, our quality controller inspects the
visualized thicknes of the bonding gap, which has to stay within very
tight tollerances to guarantee a long-term reliable bonding.

Before permanently closing the wing, the quality controller checks all
elements which will become inaccessible. Each individual nut of the
control linkage is verified, secured, marked and signed off on a
detailed checklist.

"Mumpe" call our workers the glue to close the wing. It is a mixture
of epoxy resin and cotton flakes, which gives it a consistency like
cookie dough. After all bonding areas have been thoroughly cleaned and
roughed, the mumpe is applied with a squeeze bag, similar as for icing
cake. The thickness of the mumpe layer reflects exactly the gap height
as previously meassured with the play dough or cloth pins, plus
additional two millimeters. The long experience of our workers shows
in the "artwork" of optimally trapezoid-shaped mumpe layers they
create with squeeze bag and wooden spates.

The right area, exact thickness and correct processing of the bonding
layer is crucial for long-term reliability. Any attempt to save weight
or cost here would compromize relaibility and safety.

The lower wing half is put onto the upper half, adjusted exactly to
the guide pins, and then compressed with many vise clamps. Both halves
must fit exactly in all places, or the profile will not be correct.

The force of the vise clamps squeezes the excess epoxy mixture out
between the wing halves. The glued wing is tempered overnight at 35
degrees Celsius. The next morning the wing is taken out of the mould,
using the crane and usually with a loud crack. In the sanding room the
excess epoxy is removed. After the moulds have been cleaned and waxed,
the whole process starts over again."

The above is copied from the DG website. The process requires a great
deal of skill, experience, attention to detail and craftsmanship.

It's not a matter of how much I will allow the price to increase. The
more important consideration for the manufacturer is whether I will
ever consider pruchasing or flying in a German designed and built
glider. I realize that Shemp Hirth is having the problem and the
broken wings are limited to Czech. manufactured SH gliders.
Nevertheless the process of blindly assembling the spar while also
blindly assembling the wing is a process which requires a great deal
of faith that it is done correctly.

In article ,
says...

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?

I just finished speaking to Greg Cole, the designer of the
SparrowHawk, and he told me it's spar is completely laid up in a mold,
then oven cured (like the rest of the glider). An advantage of this
method, he said, it that even if there are spar to wing skin voids in
the final wing assembly, the strength is very little affected, as the
spar has all of it's strength.

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

Eric Greenwell
Richland, WA (USA)