Matt's RV-7 Project

Here is what the skirt looked like after being popped off the airplane:

I marked a rough trim line, and then used a cutoff wheel to trim the excess glass to within 1/8" of the real shape of the skirt.

Then I block-sanded all the edges until the overhang was completely gone.

I sprayed another coat of grey primer…

…and sanded most of it back off again. Looking pretty good, only a few very minor low spots left.

I mixed up a big batch of Superfil and squeegeed a thin skim coat across the entire exterior surface of the skirt. Most of this will get sanded off, but what remains will fill the fiberglass weave and become the basis for future efforts to get a smooth surface.

I cleaned up the excess flox on the inside and outside of the doghouse, and then trimmed the slider seal block to a shape approximating what the plans specify. There's no need to be super exact here, especially since I'm not trying to make the seal block fit into a pre-bent aluminum doghouse. As long as it fits beneath the skirt and seals okay, the shape is fine.

I put some packing tape on the fuselage adjacent to the forward end of the canopy track, and followed it with a thin layer of Superfil.

Then I put the canopy skirt back on the airplane, fixed in place with clecoes and held down with buckets of heavy stuff. This is all part of the effort to get a perfect seal and keep out cold air and rain.

Several hours later, I sanded off the excess filler and was left with a nice flat bottom surface that should seal pretty well.

After wiping down the exterior surface in order to get rid of all the sanding dust, I put the skirt back on the airplane, with a fresh new (i.e. hole-free) plastic drop cloth between it and the rest of the airplane.

Then I painted a layer of epoxy onto the skirt, and laid up three plies of 6-oz cloth over it. Afterwards, I spent some time squeegeeing out excess epoxy and making sure the peel-ply was properly adhering everywhere.

The goal of this final layup is to provide a durable outer surface for the skirt that will keep the buildups of filler from cracking or getting dinged. Normally the experts advise you to never lay up glass over micro, but since the canopy skirt is not a structural piece I'm not terribly worried about the reduced strength that results from sandwiching micro in between glass layers. I also made sure to rough up the surface with 80 grit before doing the layup, in order to give the epoxy plenty of surface to grab onto. Considering that the plans call for fiberglass over filler when constructing the fairing for the bottom of the windshield, I judge that the same approach ought to be okay for this application too.

After one last round of sanding, I'm finally happy with the shape of the doghouse:

Remember how I cast a recess out of flox for the plastic slider seal block to perfectly fit inside the doghouse? Yeah, that wasn't such a good idea. Well, it actually was a good idea, just poorly executed. I should never have tried to cast something like that without all the parts in their final positions – when I put it all on the plane, nothing fit together. So, I had to laboriously grind out most of the flox with my Dremel tool.

I put tape down to protect the fuselage, slide track, and seal block, then stuffed a new batch of flox into the open end of the doghouse and set it down over the plastic block. It's only inserted halfway because I haven't trimmed the front end per the plans yet. As long as the exterior surface is cast correctly I can dremel away any excess flox buildup inside the cavity.

While the flox is curing, the skirt is clecoed to the canopy, and the doghouse is weighted down with a bucking bar that I taped in place. This time around, everything should be in its final position while the goop dries.

But just look at the profile of that canopy skirt, eh? Eh?

More sanding, and the slider seal doghouse shape is starting to appear. I like the way Superfil sands – it's a little easier to contour than straight micro.

Another layer of filler to help build up the shape:

I smeared Superfil all along the bottom aft edge of the skirt, so I can sand it down to a nice flat surface for better sealing against the fuselage skin.

While the above was curing, I played with the side skirts a bit, using my shrinker to try to get them to fit the fuselage better at the aft ends. The fit is marginally better now, although since I only have a minimal grasp of what I'm doing with the shrinker I probably wouldn't try this approach again. Still, it seems to fit okay and it looks fine after I buffed out the marks left by the shrinker jaws. There is still a gap of 1/16"-3/32" but I am going to leave it alone and seal it against air leaks using a different method (stay tuned for a future installment).

After 10 hours or so, the filler from this morning was cured enough to sand.

I applied a little more filler in order to fine tune the shape of the doghouse area a little more.

Here's a little detail that may or may not help seal the canopy against leaks, but I think it will at least end up looking cool. I covered the C-679 slide track seal with packing tape, then pressed it down into a bed of flox inside the doghouse:

After letting it cure for an hour, I popped the seal out of there, leaving a perfect impression behind in the flox. Once this is fully cured, I will sand and fill as necessary to give a nice surface. The goal here is to make the C-679 seal perfectly and leave no path for cold air to leak past.