This was an answer from an expert re post curing. Gary is crew chief for
Pushy Galor. I thought it might be worth reading here.
Graham
Message text written by "Hunter GA (Gary) at MSXSCC"
>Terry Lamp wrote: If I may ask you a couple of questions about post
curing.<
Thank you and YES, ask away....
> How hot and how long?>
140-150F for as long as possible within reason. Slowly heat the part
over a period of about 4 hrs. Then hold it at temperature for no less
than 4 hrs. and as much as 12-24 hrs. After the first 4 hrs at 140F,
and if you have the capability to accurately control the temperature, it
would be good to slowly increase the temperature to 170F for another 4
hrs. and then slowly cool it down in the oven. Don't just open the
door and yank the parts out. They will be a little susceptible to
distortion at 170F (depending on the resin you use). More so from
uneven cooling and coefficient of thermal expansion factors than from
being too hot. Remember, the foam core cannot cool as quickly as the
skins and its expansion coefficient is far greater. Thus, we want to
EVENLY heat and cool slowly.
If you look around, you should be able to find a automotive paint shop
that has a heated paint booth you can rent on a weekend. Put a couple
of box fans inside with the airplane to help circulate the air for even
heating rates. Load everything up Saturday morning, cook all day, and
cool all night, unload Sunday morning.
> Should the part be held in the perfect alignment or flatness or what ever
> for the post cure period?
>
YES. Although the post cure schedule outlined above is slow and gentle
with intention to prevent distortion, every little bit of precaution to
keep things straight is cheap insurance for the same.
> Does it matter at what point in time after the initial cure that you post
> cure?
>
NO.
> If it had been say, 6 months for instance. And say we are talking about
> the wing, should it be placed back in the jigs to post cure?
>
After one week - YES, 6 months, NO - it isn't necessary to go to that
extreme for supporting the wings. Simply position them leading edge
down on a flat surface and support the winglet so the wing waterline is
vertical. Same for the canard. Fuselage inverted on two level saw
horses would be nice. If it is already on the gear and the floor is
level, it will be level. Cowlings should be in place on the plane if
possible. If not, stand them up on the floor with the forward edges
down.
> Sorry for all of the questions, but I have been saving up.
> I hope I'm not imposing.
Gary Hunter
EAA Technical Counselor
Incidentally, the EAA doesn't "officially" recognize what I do here on
the internet. If any of you have the desire, please send a note to the
EAA Technical Counselor Program - Ben Owen recently retired and do not
know who his replacement is yet.
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