Sunday, March 08, 2009

Sealing the trailing edge

The stripper arrived about a week ago. I put the traling edge wedge from the rudder in the portable spray booth, now pressed into service as a fume hood. (As it turns out, the the stripper doesn't seem to give off a lot of fumes, but I was taking no chances with stuff capable of removing epoxy.) I didn't need to strip the rudder's skins because the epoxy adhered much better to the trailing edge than it did to the skins.

Stripping was a matter of brushing the epoxy on, using a disposable paintbrush, waiting a while for it to bubble or show signs of softening, and then cleaning it off. The stripper dissolves in water, but it took a while to find a suitable scraper. I eventually settled on a green Scotchbrite pad, which did a pretty good job of taking off epoxy without itself dissolving. I went through three coats of stripper. The epoxy came off just fine--in fact, it came off pretty well with the first coat--but I'd also primed the wedge. To make sure the fuel tank sealant adhered well, I also wanted to strip as much of the primer as possible, so the sealant would be gripping aluminum on both sides of the bond. Except for a couple small patches, almost all the primer came off with a combination of the stripper, scrubbing with the Scotchbrite pad, and a bit of wet/dry sandpaper.

The intervening week was a busy one with no opportunity for workshop time, and we were out of town this weekend. When we returned this evening, I mixed up the batch of sealant. If you've never seen the stuff, looks like sticky, somewhat runny black tar that gets into absolutely every place it shouldn't. You can remove it with MEK or acetone, at least before it cures, but it's a challenge to keep it under control. It won't stick to the non-sticky side of packing tape, though, so I put a piece of packing tape the length of the aluminum angle. After squirting sealant between wedge and skin on top and bottom, assembling the trailing edge, and clecoing it to the aluminum angle, I spent a fair bit of time with paper towels cleaning up all the sealant that oozed out and trying mighty hard to get the sealant off the aluminum instead of spreading it further.

Also, to ensure the trailing edge came together fairly tightly (without the wide gap I ended up with before), I decided to clamp a second piece of aluminum angle along the narrow space between the rivet holes and the very trailing edge of the rudder. You can see that here.

The next step is to wait. The sealant has a 30 minute working time, but it'll need to stay there at least 48 hours to cure properly before I can mess with trying to rivet the trailing edge.
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Joe said...
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