Rough-Trimmed the Canopy Fairing
After more than a little tweaking and alignment, I was more or less finally content with the position of the canopy, and re-clecoed the flange in place. Then I got out some Sharpies and started marking the fairing up. After erasing the marks (lacquer thinner, with the canopy off, of course) and redoing it I decided that it was time for cutting it out.
A die grinder and cutting disk sure use a lot of air, at least my Harbor Freight one does. With both the air compressor and the die grinder working, the noise level was significant. The day was nice and a neighbor abandoned her patio, so I reluctantly closed the garage door and did it without that open. Cutting disks, especially 4Ē ones, donít cut inside radii very well, at least with my current knowledge, so this is only a rough cut. Hereís the fairing and flange. The flange is trimmed.
The next picture shows the cockpit area. You may notice three lines on the side of the fairing about in the middle. Those represent the plans version of where the center of the canopy latch handle goes. Iíll adjust that when I get inside.
Aft of the roll bar, thereís a cross-strip thatís part of the lateral reinforcement. Since this isnít using the standard Vanís canopy frame, I need that for stiffness. Just ahead of that and aft of the cockpit area is a bit of a narrow section. Thatís where a lot of the current flexibility comes from, here and more so on the other side.
In this next one, you can see the panel and the 3.25Ē sunshade the I left. It seems to block about 1/2Ē of the top of the panel, more or less, but thatís preliminary for now.
Aft of the cross-strip mentioned above thereís a bit of a deck or gusset or something, that you can see in the top photo. Since the plane already has an aft deck, I suppose I canít call it that. This is the base for the aft-canopy latch which is still unbuilt. Itíll hold down the aft end of the canopy under air loads, and be latched and unlatched by the same handle that controls the main latches.
I allowed 3/4Ē all around (except at the hinge, of course) for overlap around the cockpit and for blending the flange to the fairing.
After all the rough-cutting and cleaning, I taped the right side of the fairing to the fuselage and opened the canopy fairing. I wanted to make sure that it cleared the roll bar, and it also gave me an opportunity to evaluate its overall stiffness. In this case, itís overall flexibility. I placed the canopy on and lifted the assembly far enough to peek and see the canopy clearance to the roll bar. Itís sufficient.
I really like how that's turning out! I did a similar flange for the FWD section on my -4 to transition onto the aluminum skirt. Are you going to glass it in? I drilled up my glass flange as though it was metal, and riveted it on with Proseal as a bond/seal. All painted, it looks just like a very well fit aluminum flange, similar to the rest of the metal construction.
Stunning work David.
Will the aft end of the frame have any kind of mechanical latching?
The fiberglass assembly that you see is both the fairing and the canopy frame. Or it will be, once a lot more stiffness is added to it. There won't be any aluminum in the frame or fairing except for the latches and the hinge.
The latches will include both the forward and aft latch bars that the plans shows, but I'm adding a new latch at the back end. I suppose that the "aft" latch bar will be the middle one; nomenclature is becoming a bit of an issue here.
The aft aft latch concept is a bit hard to describe, so I won't, but reasonably simple in concept. It'll be operated by a control connection to the latch handle. I haven't decided yet if a pushrod will work or if I need a push-pull cable, but I need to decide that before I glue the canopy down.
That brings up one of the never-ending debates -- how is the canopy to be attached? It'll have an inner and an outer flange and be glued to both with 3M's 2216 epoxy. You can see the outer flange in the photo. The inner flange gets fabricated later.
There won't be any rivets, Sikaflex or other stuff. Just the 2216.
I used is ordinary Hysol 9430, but I think Bryan is now recommending a Loctite product. Anyway, the canopy gets glued to the flange, secured by clecos, and the adhesive squeezes up through the 1/4" holes, forming epoxy "pegs" when cured.
After cure, sand the pegs flush while scuffing the outside surface of the plexi for tooth, wipe flox into the space below the edge of the plexi, and lay up two plies of 9oz or similar to form the outside flange. In my case, that was just West and plain weave. Blend it to desired surface contour with micro, and some high-build blocking at paint time.
Love your frame!
Well, I remember that you'd described that process. Thanks for going over it again with more detail. By the way, I think that Loctite now owns Hysol, so it might be the same product.
This is going to be a little different. I will follow 3M's instructions on preparing the acrylic. There won't be any holes at all in the canopy.
The canopy will bond to the flange and the flange to the fairing in one pass. When cured, I'll tape and lay up the inside flange, remove it, trim it, and bond it to the inside of the canopy and the fairing, again with the 2216.
That's the plan, anyway.
We Got Us a Canopy
Well, for better or worse, this plane has a canopy. After a few lost work sessions deciding if I could form the inner flange before gluing the outer one, and deciding the day I was ready to try, that I couldnít - I glued the outer flange to the canopy.
Iíd planned to glue it to the fairing at the same time but realized that was unnecessary. So at this moment itís taped and clecoed to the fairing. For that matter, there are a few clecoes through both the flange and fairing right into the turtledeck skin. I had no other way to hold things in position.
Hereís the canopy glued with the black electrical tape still on. I removed the black tape shortly after this photo.
For the glue, I used 3Mís industrial glue 2216 B/A. I hadnít used it before, but my mentor is gluing his RV together with it, using rivets also. It wasnít as pleasant to work with as the thickened G/Flex. I made a test batch and found that while it leaves a thick film on a vertical surface, itís only thick by comparison to something like, say, water. It doesnít run but it does seem to creep, before it cures, of course.
The three thickeners I had on hand for use were:
Micro balloons - these do a nice job of thickening epoxy at a significant cost in strength. It is a low-density bulk filler more than anything.
Flox - this is the common structural thickener. It always seems just a hair rough to me, even in small quantities, and I wasnít sure if perhaps it would leave the epoxy too thick.
Cab-o-sil - According to an experienced Materials and Process engineer I used to work with, in small quantities this thickener doesnít affect the epoxy properties significantly, but does thicken it. I used a little of this.
Acrylic is one of the materials that 2216 bonds to, and this is one of the main reasons I chose it. I followed the simple process outlined in the tech sheet: wipe with isopropyl alcohol, sand with up to 180 grit (I used wet or dry, wet) and clean with isopropyl alcohol again.
Iíd taped the mating surfaces of the fuselage because I knew that it was likely that there would be drips inside and I didnít want to get them inside the fuselage.
And thatís where I left it: tape off, clecos in, canopy glued down to cure.
Yes, the elevator tips.
I needed some small jobs for a bit, things I could work on for just an hour at a time, so I pulled out the elevators and stabilizer and in the middle of other things, for a break, have been working on the tips. This was actually part of the plan all along, to hold off on these until I was working on the composite canopy frame/fairing, because then I could do the first batch of the fiberglass stuff all at the same time.
Today, I bonded the left elevator tip to the elevator. Before getting to this point, though, it need a few things. As delivered, the tip was slightly fat. With the flanges nicely in place, the tip shape protruded .040 or .050 above the elevator surface, all over.
1. Drill and cleco the tip in place so that it fairs with the stabilizer tip.
2. Slit the tip along its centerline with an appropriately-thick cutter.
3. Make 1/2Ē squares of .040 for shims, each with a hole for the cleco.
4. Test fit them - okay.
5. Fiberglass over the slit, so that instead of two halves I had a tip again.
6. Drill the holes to #30 and dimple the skin and countersink the shims.
7. Glue the shims to the tip, more for handling than anything.
8. Glue and cleco the tips in to the elevator. Since here the glue is a gap filler rather than structure, it pretty much didnít matter what I used. But I used the thickened G-Flex.
9. Rivet the tips in place.
Right now Iím at step 8 for the left tip, shown, and at step 5 for the right tip.
The stabilizer tips, on the other hand, had the opposite problem. They were too skinny. I followed Wirejockís (Larry Larson) method and heated the tips to 150 F for an hour, then pressed them on to the stabilizer ends. They cooled slightly fat. I forced them into the stabilizer and clecoed them in place. Now they fit well.
Canopy Inner FLange
Back to the regularly unscheduled progress report.
Also, back to the canopy. In areas, the bottom edge of the canopy was too much of a sharp edge to laminate fiberglass around, so I took a two-fold approach to that. I formed a flox bead there and then after it cured, rounded it. There were places that now protruded too much to assemble the fairing on, so I reshaped those with a more gentle radius, blending it into the outer flange. Yes, I went back and smoothed those edges.
In retrospect, flox was the wrong stuff to use here. It would have been better if Iíd used micro, since this was nothing more than a bit of non-structural shaping.
With that out of the way, I taped over the area and prepared the surface to lay up the inner flange. Iím using Aircraft Spruceís crowfoot cloth, p/n 120-38 for this, because it forms better. Since this cloth is only .004 thick, Iím using six plies. And because itís warmer now and Iím still in my busy season, I decided to do it in overlapping sections. Hereís the first. The diagonal white stripes are the ends the short overlapping pieces of peel ply.
I completed the flange, removed it, peeled off the peel ply, trimmed the edges and did a trial fit. It was too thick. After brooding about this overnight, I removed it and am planning to redo it.
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