West System epoxy/fiberglass service limits

[Freemasm]

The title is a bit misleading. Sorry.

I’m about to candy coat my fiberglass plenum. Been using some hobby dye in the epoxy candy coat with good results.

There’s plenty of FG plenums out there.

Question to the masses. Is the extra absorbed energy from black color (dye or paint) on the glass gonna exceed the epoxy’s limits? Please let me know if you have direct knowledge. Much thx.

 

[scsmith]

It would certainly be a problem for parts that are out in full sunlight.

Under the cowl, black parts will come up to equilibrium temperature faster, because of the radiative heat input. The equilibrium temperature is where all the heat flows in and out balance. For a plenum cover, most of the heat input is probably radiative, with only a little bit of convective and conductive heat addition. The black color will also reject heat from the outside surface of the plenum cover to the upper cowl.

So if it is all black, it will probably run hotter than a clear epoxy+fiberglass cover. A lot of people have epoxy+carbon fiber plenums that are black and don't seem to have problems. So you are probably OK.

A cool set-up (pun intended) would be to paint the inside of your plenum cover gloss white, and have the outside surface black (a matt finish would be best, but not as pretty). That gives you the least heat input from the cylinders on the inside, and the most heat output to the surroundings.

 

[Freemasm]

I had thought about the two color approach. It’s not primary structure and if you’ve seen it applied successfully, screw Kirschhoff. Never liked him/therm/heat xfer anyway. Black candy coat it is. Thanks.

 

[wirejock]

Black plenum

Sure hope it's not a problem. Carbon fiber layer over fiberglass. Carbon fiber has West 207. Inside is a brushed seal coat of West 206 with black epoxy pigment.

 

[PilotjohnS]

Glass transition temperature

The concern with black pigment is the West System Epoxy has the lowest glass transition temperature of all the other resins out there. I would be concern because you are using West Epoxy (made for Boats). I used Aeroepoxy for all my fiberglass, but even then it is about 194F, I think West 105/206 is like 139F.

I would paint it white if using West Epoxy to keep it from getting soft in the heat, but that is just me. JMHO

 

[Bill Boyd]

I had thought about the two color approach. It’s not primary structure and if you’ve seen it applied successfully, screw Kirschhoff. Never liked him/therm/heat xfer anyway. Black candy coat it is. Thanks.

Just when I thought I'd seen all the pronouns

 

[Stewbronco]

White

I used a west system white dye and brushed two coats on inside …

 

[BillL]

West Tg is on the bottom end of what might be a recommendation, but many have used it and it seems to hold its shape. I had no data so used a higher temperature specification for my plenums, and baked them up to 350F to ensure full specification. Hot landing, taxi- sitting in the sun after for heat soak is the worst condition and no reported sagging of 105 based resin.

When in operation there is plenty of air to keep the temps much lower (measured).

 

[Freemasm]

Thanks to all. This was a case where fleet experience matters; probably more than most of the threads here. "Been using xxx in my yyy for 100 hours now. No problems." I cringe at most of those. As most service limits are for some xx% of strength at some condition, this was a tough one. There's no loading except supporting its own weight when active cooling isn't present. Then it won't matter. I did add a center support a' la Mooney, JIC.

So, sometime in the future I'll be the guy that makes the cringey statement or someone will state, "My hangar neighbor did that on his aircraft and he used to work on the Space Shuttle"

@ Mr. Boyd. Yep. Anybody that knows me knows I'm a big disciple of such "stuff": or, I got auto-corrected. I do think I'll change my pronouns.

Sincerely,
Scott Freeman (Hey you/therm)