Gelcoat Crazing and Structural Integrity

JJ Sinclair wrote:
On Mar 5, 2:21 pm, "Ken Kochanski (KK)"
wrote:
Hi,

My first glass glider was a cheap, but well-crazed, 15 meter ship that
I flew for 5 years before trading up to a newer model.

Other then potential performance issues (if not sanded smooth) ... do
we have any cases where moderate/heavy crazing led to damage to the
underlying glass ... which grounded the ship at annual - or which
caused an in flight failure.

Hi Ken,
I have been grinding out gelcoat cracks for 35 years and never found
any of them that didn't stop at the fiferglass structure. On ships
with thick gelcoat (DG's) the 'working' back & forth on each side of a
large crack can leave an etched mark in the fiberglass structure, but
examination with a magnification glass shows no broken fibers, just
resin that has flaked away in the emmediate area adjacent to the
crack. I have found that painting on a fresh coat of resin will make
this 'etched' make disappear. I know of no inflight failuers caused
from simple gelcoat cracks. I believe it's a good idea to have your
local glider repair guy take a look to be sure your crack isn't a tell-
tail indicator of underlying structure that has moved (failed).

Schleicher has a "Maintenance Instructions" for paint cracks he

http://www.alexander-schleicher.de/t...ackrisse_E.pdf

Some highlights:
* all cracks should be inspected regularly
* paint cracks, even deep ones going into the resin top skin, may not be
an immediate problem
* steps must be taken to prevent further damage from moisture and UV
* paint cracking is a problem in the USA and Australia, but not in
Europe, and the repair experience accumulated in those countries should
be considered.

It seemed to similar to what JJ was saying, but from the manufacturer's
viewpoint and experience. Perhaps Schmepp-Hirth and DG have similar
instructions, and these might be useful to show an inspector balking at
approving an annual inspection.


--
Eric Greenwell - Washington State, USA
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