Lexan question

[bret]

Looking for some expertise on polycarbonate. I see the data that it is good from -40 to 260ish F. wondering how this would hold up as a plenum lid? I know the CHT can be 400+ but the lid will be seeing outside air temp till shutdown, heat soak? I see that some lower temp rated epoxy has been used in FG layups and do fine. Is this worth exploring or NO? I have a new sheet in the garage and I heard it say it wanted to get cut up and fly real fast ;-)

[F1R]

I am thinking after a shut down after a long slow taxi on hot day you might soon have a shrink wrapped Lycoming. But let us know how it turns out.

[lr172]

In no wind conditions, I would expect that a plenum cover could hit 225 and possibly 250. I know several posting here have temp sensors in various places under the cowl. They should have good numbers. It should be an easy test. Turn your EMS on 2-3 minutes after shutdown. By that time the aluminum cylinder head should match the ambient under the cowl.

I would be concerned with the temp at which polycarbonate maintains it primary rigidity. Your talking about a decent span and I would be concerned that, like some plastics, above a certain temp there is a somewhat linear relationship between temp and structural stability. It doesn't go from a firm solid directly to liquid. I have seen some plastics easily bend long before they are hot enough to become noticeably soft. I just don't know what those temps are. I suspect it would be easy to find those properties on the web.

Resin-based products (epoxy, FG, etc) are cured and not thermo-set (I know Acrylic is thermo-set and assume polycarbonate is, but not sure) and exhibit very different properties as they increase in temp.

EDIT: apparently polycarbonates are amorphous and therefore they exhibit different properties than plastics. Here is a quote from wikipedia:

Polycarbonate has a glass transition temperature of about 147 °C (297 °F),[6] so it softens gradually above this point and flows above about 155 °C (311 °F)

Larry