When I painted my wing tips and rudder blue I figured that if I wound up destroying the glass after a few years from the heat I could easily strip off the glass with an orbital sander and reglass them. The fusalage sides and bottom are plywood and if there is glass on them it isn't needed anyway. The turtledeck isn't structural and Mark has made so many of them that it would be no big deal to remake one if the heat ruined it.
Mark Langford wrote: >Y'all can just go ahead and call me stupid, but my airplane's gonna be red. >Again, I'll say that when the plane is sitting on gear, there are no >stresses on any composites, other than the Scotchply 3M gear legs. My wings >are covered with two layers of carbon fiber (three on the leading edge), >which you might remember, are supported by 3/8 to 1/2" of urethane foam, >which is supported by an inner layer of fiberglass. > >So let's just say my composite skin gets up to Tg, the temperature at which >the strength of the epoxy is significantly reduced. For Aeropoxy, that's >194 degrees F for layups cured at room temperature. It's normally good for >something like 45,000 psi. I'd call "significant" something like 75%, but >lets just be conservative and say that the strength is cut in half. Now >it's down to ONLY 22,500 psi. But wait, I have a half inch layer of foam >being supporting by another layer of fiberglass that's at least 30 degrees >cooler (my inner skin). And don't forget, there is absolutely no external >influence on this surface, other than gravity pulling down on something that >weighs just about nothing. > >I actually called myself "post curing" my stub wings right after they were >constructed, by parking the plane out in the sun one hot day that summer, >shortly after construction. I taped (using clear tape) a Fluke 52 digital >recording thermometer's thermocouple to the black, unpainted surface, and >the best I can remember, the highest temperature I ever saw was 128 degrees >F. Don't forget, it's "air-cooled", just sitting there! > >Given the rule of thumb that your Tg will be raised to 50 degrees over the >post cure temp, I was probably wasting my time at that "low" temperature. >So when is it going to see 194 degrees? Never. And what effect would it >have if it DID see 194 degrees? None. And how much strength is required >of the skin, just sitting there on the tarmac? Absolutely none. And how >long does it take something as thin and massless as a .020" thick layer of >carbon fiber layup to cool off with a 30 mph breeze blowing on it during >takeoff? About 5 seconds. > >The few horror stories you hear about planes "melting" in the sun are >referring to airplanes with composite parts such as spars and stressed skins >supporting the load while parked. Neither of these apply to my plane. > >Sorry, but I have a bad habit of getting the facts, considering all aspects >of the situation, and making my own decisions. It's gonna be red, and if >y'all don't like it, you can just get over it... > >http://home.hiwaay.net/~langford/03101703m.jpg > >Mark Langford, Huntsville, AL >N56ML "at" hiwaay.net >see KR2S project at http://home.hiwaay.net/~langford > > > >_______________________________________________ >see KRnet list details at http://www.krnet.org/instructions.html >
