Gelcoat sag?

Andy wrote:
On Dec 15, 1:19 pm, wrote:

Experienced racers have long known about the dreaded sag.


I know this reply was in jest but at Hobbs years ago I got into
conversation with a DG owner. I forget who it was or what the glider
type was. He told me that the gell coat on his wings had sagged. He
also told me the factory had told him it was due to being stored in
the trailer above a maximum temperature approved by the factory. He
seemed upset enough about the problem that I assumed it was true. I
have never heard of this happening to anyone else and don't pretend
to understand the physics that could allow it to happen.

Way back when the CIBA-Geigy 24 hour Araldite was a new wonder glue,
i.e. the mid 60s, we soon discovered that it had to be cured at or above
the design operating temperature for the completed assembly. If you
cured it at a lower temperature the epoxy would soften when its
temperature was raised above the cure temperature, even if this was
quite some time after the glue had set up.

I have no knowledge whether this applied to other contemporary epoxies
by CIBA-Geigy and other manufacturers, except that the Standard Libelle
Owners Manual (which was written around the same time), says explicitly
that storing the glider in a hot trailer will not warp or soften it
provided that the parts are not under stress. It adds that this will
"temper" the structure, which may even increase its strength slightly.

HTH


--
martin@ | Martin Gregorie
gregorie. | Essex, UK
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