Re-shaping fiberglass parts with heat

On Oct 29, 3:28 pm, JJ Sinclair wrote:
I knew the concept was valid from Schempp-Hirth instructions on how to
heat up an early Cirrus wing and put in the twist that Cirrus's after
s/n 175 had. I have a badly twisted gear door (corner stood proud a
good 5mm), so I thought I'd give it a try on a much smaller scale. I
held the gear door in front of an electric space heater for a good 8
minutes, until it was too hot to leave a finger on the surface. Then I
put it in place on the wheel-well (fuselage inverted) and held the
ends with two 25# shot bags. I slipped in a 5mm shim to achieve over-
twist for the expected spring-back. Let it cool for an hour and it
fits like new!
Anybody else have experience heat-twisting epoxy/fiberglass parts?
What's the yield temp?
JJ

Doesn't seem to work as well on ships made with newer resins like
current production ships
that have been post cured to 50 C or so.
T1(yield) temp is just above whatever it was post cured to from my
experience.
Seems to make sense.
UH

On Oct 29, 1:06 pm, wrote:
On Oct 29, 3:28 pm, JJ Sinclair wrote:

I knew the concept was valid from Schempp-Hirth instructions on how to
heat up an early Cirrus wing and put in the twist that Cirrus's after
s/n 175 had. I have a badly twisted gear door (corner stood proud a
good 5mm), so I thought I'd give it a try on a much smaller scale. I
held the gear door in front of an electric space heater for a good 8
minutes, until it was too hot to leave a finger on the surface. Then I
put it in place on the wheel-well (fuselage inverted) and held the
ends with two 25# shot bags. I slipped in a 5mm shim to achieve over-
twist for the expected spring-back. Let it cool for an hour and it
fits like new!
Anybody else have experience heat-twisting epoxy/fiberglass parts?
What's the yield temp?
JJ

Doesn't seem to work as well on ships made with newer resins like
current production ships
that have been post cured to 50 C or so.
T1(yield) temp is just above whatever it was post cured to from my
experience.
Seems to make sense.
UH

I've used hot tap water to "adjust" fiberglass parts. It conducts the
heat to the part better than air, and I don't think you could over
heat it that way. I maxed out the thermostat on my water heater to do
it. I've been able to do significant "shaping" this way. I've also
gotten scalded more than once.