Brian - send me your email address if you can - I have a matching car for you plane - send you a pic. Bill ----- Original Message ----- From: Brian Kraut <eng...@earthlink.net> To: KR builders and pilots <kr...@mylist.net> Sent: Monday, October 20, 2003 9:59 PM Subject: Re: KR>paint
> 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 > > > > > > _______________________________________________ > see KRnet list details at http://www.krnet.org/instructions.html >
