Matt's RV-7 Project

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.

I spent the morning sanding Thursday's application of filler, then sprayed it with another guide coat of primer and sanded that off too. The result was pretty good – the light grey areas shown in this photo are actually historic low spots that are now filled and sanded level. The dark grey spots are the only remaining low areas still needing filler. Most of these are in the area of the slider seal "doghouse" which I have yet to do much with.

Since I am running low on micro, I mixed up a batch of Superfil from a quart kit that I'd bought a while back. I've never used this stuff, but people seem to rave about it. Each of the two components is the consistency of peanut butter, and you mix them 2:1 by weight or volume. I eyeballed three plastic spoonfulls of blue goo to one and a half of tan goo.

Since I had a little extra mixed up, I started applying filler to some of the more egregious areas on the underside of the canopy skirt. I don't intend to go for a perfect finish on the bottom, since it will be hard to see from inside, but I do want to at least fill in the voids.

I finished sanding off all the high spots on the canopy skirt:

Then I smeared on more micro filler, thus making more high spots to be sanded off later.

Hopefully the remaining low spots will become smaller after each fill/sand cycle. Eventually this should converge on a nice-looking surface, but there's a lot of work between now and then…