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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Eric Greenwell schrieb:

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.

LOL - sorry for the "lol", but when i hear that paint cracking is no problem in
Europe... then Germany must be on the moon.
Most older ASK-21s (ours are from 198x and 1990) are showing bad cracks. The
first got already a new gelcoat and the 1990 one is due any year now.

Not for cosmetic reasons but for protection against moisture - here in Germany
it sometimes rains..... :-)

The old Mini-Nimbus we have (one of the last ones build) did get a new gel-coat
in 2000. And that was REALLY neccessary. You were nearly able to hurt yourself
on the cracks.

So Schleicher is telling total BS there.

just my 2c... had to get that out....

CU
Markus

Schleicher has a "Maintenance Instructions" for paint cracks he
http://www.alexander-schleicher.de/t...ackrisse_E.pdf

another interesting tidbit:

" we suggest to spray the sanded surfaces first with polyester
fillers, to sand then again, and to respray them finally with a white
paint system on a polyurethane basis.."

i.e. ditch the gel-coat.

John Cochrane