Archive for the ‘Canopy’ Category

Fiberglass canopy skirts part XVI

Sunday, August 26th, 2007

Overnight I figured out how to fix the misalignment of the canopy skirt mounting holes. The nice thing about fiberglass is that you can usually fix your mistakes with enough patience and sandng.

I applied a layer of packing tape over the holes on the exterior surface of the skirt:

From the inside, I used a popsicle stick to force a thin epoxy/flox mixture into the holes. After I took this photo, I came back and squeegeed off the excess flox.

Once that was cured, I removed the tape and did the same thing from the exterior side, to fill both sides of each hole. When that was cured, I sanded it all flush. Here's the result – no more holes:

Then I put the skirt back on the plane, and after a great amount of measurement and double-checking I re-drilled the holes. This time it came out straight.

In some places, yesterday's holes were okay, but in others they were substantially off:

Since the alignment of the skirt to the plexiglass and frame was now acceptable, I went ahead and drilled most of the holes that attach the rear skirt to the C-660 side skirts. There are still a couple holes on either side that need to be drilled (where the obvious gap is in this photo) but I wanted to finalize the alignment before I removed the skirt again.

Without removing the skirt from the plane or otherwise disturbing the alignment, I drilled straight through the skirt, canopy, and steel frame with a 1/8" plexiglass drill, enlarging the holes in the skirt and frame to the final size (note copper clecoes in this photo). The holes in the canopy were already at 1/8", and will be enlarged to their final size of 3/16" soon.

Back on the worktable for more surface preparation and pinhole filling:

Fiberglass canopy skirts part XV

Saturday, August 25th, 2007

Yet more sanding… this time down to 400 grit.

I didn't like the blunt shape of the leading edge of the skirt up in the thickest part of the middle where the glass layers were doubled up, so I sanded it to get a gentler slope. Of course this means I'll have to do more pinhole filling here.

I re-drilled the skirt to the canopy using a hole finder, since the previous pilot holes got closed up by fiberglass filler. I think it must have slipped a little bit this time, though, since the alignment is ever so slightly skewed. It still fits and nobody but me will know it's crooked, but I may yet try to fix it. Not sure what I'll do about this yet.

I clecoed the C-653 cover strip in place and marked a line where the rear skirt overlapped it. Later I trimmed the cover strip so it ends just at the leading edge of the skirt. In retrospect, it would have been cool to mold the fiberglass skirt to fit over the cover strip perfectly, but I didn't think of it until it was too late. Oh well, a simple trim works just as well.

Also, my propeller governor arrived today. It's a PCU-5000 that I picked up for a good price through the VAF group buy that was organized a few months back.

Fiberglass canopy skirts part XIV

Sunday, August 19th, 2007

I spent an hour sanding off the previous application of Superfil. Does this sound familiar? Anyway, this time I went all the way down to 220 grit paper – previously I'd been staying at 80 grit.

Now that the shape is basically how I want it, it's time to start preparing the surface by making it smooth and filling pinholes. For this job I'm using DuPont 210S, a single-part surface primer.

You're supposed to spray this stuff on, but it was too windy outside to spray effectively, and I didn't feel like getting out my spray gun and trying to mess with painting inside the garage. So, I just brushed the surface primer onto the skirt with a cheap foam brush. I'd never do that for a finish coat, of course, but for a filler coat it actually worked pretty well.

I put one one heavy coat, sanded with 400 grit, then applied two additional lighter coats without sanding in between. No rhyme or reason, I'm just winging it based on what seems reasonable as I go.

I kept the skirt up off the table with little balls of aluminum foil, to prevent the surface primer from getting all blobbed up along the bottom edge.

This is a picture of the third coat dying. The brush marks should sand right out.

It's starting to get smooth and look pretty good… is that the light at the end of the tunnel I see up ahead?

Fiberglass canopy skirts part XIII

Thursday, August 16th, 2007

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.

Fiberglass canopy skirts part XII

Sunday, August 12th, 2007

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.