Mark Langford's KR2S Project

Mark Langford's KR2S Bodywork and Paint

created August 24, 2003

updated October 27, 2003

Earlier, I showed y'all a photo that proved that I am "nowhere near flying". This week, I am a little more hopeful. I shot a coat of DuPont Ultimate2K urethane primer at the whole thing. Now that it's all one color, I can see how bad the body work is. But you know what? I DON'T CARE! If I was painting a Lancair that came out of factory molds, it'd be one thing, but I built every piece of this critter from scratch, so whatdya expect? I'm not going to spend the rest of my life building a show plane. If it has something to do with improving aerodynamics, I'll do it, but if it's just an appearance thing, it's off the radar screen. Painting the cowling something other than "carbon fiber black" has allowed me to see how wavy it is. Oh well, it sure is nicely faired in to the fuselage, and it'll get the job done!

I really like this view. Maybe somebody will take a picture at this angle at next year's KR Gathering for me.

Having this coat of primer on it means I could fly it just like it is, but I'll probably go ahead and paint the bottom, at least, and will probably paint the whole thing, but I may wait until spring to do that. Now I need to clean up my wings and install my nav lights and strobes, then prime and paint. Right now I'm thinking about painting the bottom and stubwings metallic red, the same color as my GTI, and the top and outer wings silver, the color of Jeanie's Audi.

What's a golf cart have to do with anything? Since I bought a whole gallon of paint, and only needed a half a gallon, I painted my buddy's golf cart at the same time I painted the bottom of my plane. I took this picture to show what the color's going to look like on my plane.

I had to paint the thing outside, so I could raise the tail high enough to get up under it. Not ideal, but it's painted and done!

This is after only one coat, and before I applied the clearcoat, so it looks sort of dull at this stage, but it got a lot nicer looking after the clearcoat was applied.

I'm using DuPont's "cheap" stuff, Nason. It's equivalent to PPG's cheap stuff, Omni. If you walk in and ask for basecoat/clearcoat, they'll sell you the expensive stuff. But I'm told by the paint store guys that REAL painters only use the premium "ChromaBase" for repairs, where color matching is critical. For an overall repaint (that's us), the inexpensive Nason product is almost every bit as good. The big difference is color matching and coverage is not quite as good, but I don't have much to cover anyway, since it's all just the same color primer. By inexpensive, I'm talking 1/3 or 1/4 the price of the good stuff. A quart of Nason is 20-30 bucks, a quart of the same color of ChromaBase can run up to $140!

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.

Jeanie thought that painting the entire bottom of the fuselage (which includes the sides and stub wings) would just be "too much red in any one place", so we decided gray would look nice. I put 8 ounces of gray base coat on, and in the process could see a few areas that really weren't ready for paint. And the more I stared at it, the less I liked the dark gray.

So I sanded it all off again, which was amazingly easy. It turns out that base coat is very weak stuff without the clearcoat on top. Alcohol wiped it right off! So, since I knew I was going to have to reprime anyway, I went ahead and block sanded it another time. As you can see from the photo, it could probably use another round, but it's a lot better than it was.

I also sanded the stub wings again, and got them fairly smooth. After that, I put another coat of Ultimate 2K two-part epoxy primer on the whole thing...and the look started growing on me.

I have to admit that the color is kinda neat, and goes nicely the spruce and mahogony, and with the red on the bottom. I'm seriously considering adding a red stripe between the top decks and the fuselage, and clearcoating the whole thing and calling it done! But if nothing else, I can fly the thing this way, so I'm not going to worry about paint for a while now. Eventually I plan to build a paint booth into my house, so I'll worry about it when I'm better equipped to do something about it. One neat thing about primer is that you can shoot it without worrying about dust, since you have to sand it before topcoating anyway, so I can make modifications to wingtips or whatever and easily blend it back in. When I'm pretty sure I'm done, I can paint it then...

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