Thursday, September 25, 2008

Whatever happened to that canopy fairing?


Yes, I know, I haven't put another post up about sanding the canopy fairing I've been working on for at least -- what? -- two days.

I went out to the hangar last night and have done some more sanding on the top edge after -- following the directions -- putting a coat of epoxy on the edge onto the electrical tape that marks the top edge. The directions say to then sand the epoxy off the tape, revealing a nice edge. Later in the instructions, however, it says the top edge consists of "two or three coats of epoxy." So I was confused -- my natural state. Should I put a few coats on and sand or put on one coat and then sand, then put on another?

Joe Blank, who is easily the best technical support dude at Van's Aircraft set me straight:

Hi Bob,

Usually multiple coats of brushed on epoxy filler works in this area to finish off the fairing, and sand between coats. Here is the way I prefer to finish out the fiberglass strip on either the slider or the tip-up style canopy.

Once the multiple layer glass cloth/epoxy layup is completed/molded and set, if you haven't defined the strip width already using tape, do that now. I prefer to use black electrical tape. You can make nicer curves and contours, and the epoxy won't wick under the tape edge. You can vary the width of the fairing a bit around the corners to make it look more esthetically pleasing to the eye. Lightly sand the area to eliminate any high zones. Next, mix up a baseball sized amount of either micro-balloons (glass beads) or a product called "Superfill" (from Spruce).

I prefer the Superfill, as it's light, the right consistency, and is very predicable. Using a 4x6" piece of plastic or cardboard as kind of a squeegee, apply the filler to the taped off area. You can start in the middle and work to the outer edge or start on one side and work to the other, as it really doesn't matter. (I call this arts and crafts at this point ;-) Symmetry is the name of the game here, to simply make both sides look the same. If an area looks too low, then add a bit more material. If an area looks to high, then use a bit more pressure on your squeegee to scrape it down. Use the squeegee action to form a nice smooth surface. Once you have enough material on and are reasonably happy with the results, step away from the work! Let it set up for a day or so.

The next day, come back and inspect the work and determine if there are any high/low spots that need to be addressed. Circle these with a sharpie so that you only try to repair these spots. Once everything else looks acceptable, it's time to sand. Fabricate 3 sanding blocks from wood that approximate the shape of the fairing in the center, halfway to the outboard edge, and at the outboard edge. I simple cut several pieces of cardboard that mimicked the shape and held them up to the the fairing.

Using progressively finer grits of sandpaper and the blocks, lightly sand each zone until you get the exact contour you like. Once that looks acceptable, paint the fairing with a filler/primer (rattle can works fine). Once primed, the painted surface will highlight any other defects or contours so that you couldn't see otherwise. If everything looks acceptable, then peel the tapes off and clean up any areas that need it.

Hope this helps.....

This is one of those times I wish I'd talked to Joe beforehand because this isn't the way I did it. I did one layer of fiberglass at a time (I don't have that much time at the hangar that I can do it all at once) and I tended to shape as I went along. I like Joe's method better, however, but it's too late now.

That next RV I build is going to be really nice!

2 comments:

  1. I am getting ready to do my canopy and windscreen fairing on an RV-8. I have always used micro balloons and epoxy with good success. The only part I really dislike is the dust produced during sanding. No matter how good the quality of the dust mask I use I still seen to have a dust cough for a day after sanding. It was never a problem in my youth, but alas...
    Joe Blank's instructions are pretty much the same as in the instructions. One thing I have found is hotel/motel key cards or used up credit cards make a great squeege for applying the goop.

    On a slightly different note... will you be hosting a bar-b-que at next years Oshkosh? John and I had a great time at last years! (I'm not GMCJETPILOT).

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  2. I'm kind of wondering about the baseball-sized glob of SuperFil. Once you've sanded the fairing into shape, aren't you pretty much just filling pinholes at this point. I used SuperFil to feather the fiberglass to the canopy skin, but used epoxy/balloons with black dye near the tape on the plexi.

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