DuoDiscus Wing

"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
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"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.