Canopy Heat Treating

[Lucky Aviation]

My friend who is an engineer and in the industrial plastics business guided me with heat treating my canopy to reduce stress.
I carefully measured the frame when installed on the airplane track and installed temporary bracing on the frame to keep things exactly where they need to be. We placed the canopy in an oven which is designed to anneal plastics. We brought the temperature up slowly to 190 degrees, maintained it for 2 hours and brought the temperature down very slowly.
I removed the clecos and the plastic fits the canopy frame perfectly with zero stress.
After going through this process, I believe that a simple homemade oven can be made up with some basic materials to accomplish this without spending a ton of money.
I was just lucky to know a guy who knows what he is doing and has a set up already.
I thought that it may help someone who is worried about too much stress on the plastic when riveting it to the frame, which may invite cracks.

[scsmith]

It is indeed quite easy to make an oven to do this kind of thing.

We made an oven for post-curing carbon-epoxy composite parts, primarily wing tips made with epoxy that requires a 150F post-cure.

The "oven" is just a box made from 2" styrofoam insulation available at home improvement stores. We pin the panels that form the box together with bamboo shish kabob skewers. Then we tape all the seams with 2" wide aluminum foil tape.

The heat source for the oven is an electric hot plate from Goodwill, and a 6" desktop circulating fan. We use a couple of oven thermometers stuck through the foam to the interior to monitor the temperature.

With the big L-39 "CEllipse" racing tips in the oven, it takes about 2--3 hours to get up to 150F, which is what we want for the post-cure cycle. Adding another hot plate would bring the temperature up faster obviously.

[RhinoDrvr]

I wonder if a completed canopy assembly could be heat treated this way after it was already attached to the frame, or if the differential expansion would just make the assembly more likely to crack during the process?

[Paul 5r4]

EXCELLENT thread. Canopy cracks is one of the things i worry about the most. Especially in cold weather. I thankfully live in the south. I would love to fly up to Massachusetts to visit my son sometimes in the winter but the super cold temps keep me from it.

I would almost rather have a canopy that's in smaller sections or something to eliminate cracking issues. Thankfully none in the 11 years mine has been flying.

I wish I had known about this "stress relief" before installing mine.