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Tip-up construction sequence

R

roee

Well Known Member
I'm working on the tip-up canopy frame, and I've got it all fitted (well, the front and sides, not the back). I went to a lot of effort with complicated shims, etc. to get a nice fit to the fuselage, and at this point I'm quite happy with it. The forward skin of the canopy frame is currently held on with clecos, and the whole frame assembly is clamped in place on my fuselage. Now, where I am in the process, it's time to start fitting the plexi, which I haven't touched yet. My dilemma is this: Van's instructions would have you trim and fit the plexi with the forward skin of the frame still held on with clecos, and only rivet the skin to the frame later on. I think it would be advantageous to rivet the skin (and the reinforcement kit) now so that the frame gains better rigidity and keeps its shape as well as possible while I'm screwing around with the plexi. I think it would also be safer for the plexi to not have a bunch of clecos sticking out of the frame everywhere, threatening to scratch it.

I see only two problems with my proposed sequence:

1. The top part of the interface between the front weldment and the sides (i.e. the "tabs") needs to be adjusted to accommodate the contour of the plexi.

2. The "ears" in the skin may need additional trimming for the plexi to pass through, according to other builders' experience.

I can see possible solutions to these, but I'm interested to hear from builders that have been there before.

1. With the tabs, how drastic is this adjustment? Can I just give them a little bit of inboard bend now, rivet them, and do any fine adjustment later by filing?

2. With the ears in the skin, can I just trim away some material now based on what other builders have had to trim, and confidently expect that I'll be able to make it fit? Has anyone done this?

3. Any other possible problems with my proposed sequence that haven't occurred to me?

Thanks!
-Roee
 
A revised plan

After chewing on it for a couple of hours, I've had a moment of clarity and arrived at a revised plan. I'm going to chop those ears completely off (basically from the bottom of the slot, cut straight aft) and just extend the glass fairing further aft to cover the entire area where the ears would have been. I think that's actually a better solution than the aluminum ears, since the aluminum ears just rest on but don't attach to the canopy in any way, whereas the fiberglass will adhere and make a nice robust interface. Reading other threads, it sounds like other builders have opted for this (chopping the ears off I mean), and I think I like that regardless of construction sequence.

But back to construction sequence, I think chopping off the ears completely solves both problems that I described in my previous post, and allows me to rivet the frame/skin before bringing the plexi into the equation. If the ears are completely eliminated, then they obviously don't need to be trimmed to fit the plexi. And as for the "tabs" between the front weldment and sides, they will then be exposed and accessible to be adjusted and riveted at a later time, even after the skin is already riveted on. It was only the ears that would have gotten in the way.

So to summarize, here's my plan:
1. chop the ears off
2. rivet the skin and reinforcement braces to the canopy frame -- makes it nice and sturdy
3. proceed to fitting the plexi
4. once the plexi is a reasonably close fit, adjust and rivet the tabs as needed
5. final fit the plexi

I don't see any problems, sounds almost too good to be true ;-) Anyone see any problems with this?

Thanks!
-Roee
 
I just trimmed the tab back some and that worked well for me. I left out the front screw of the side rail and feel that the tab helps keep some of the pressure off the second screw. I don't have much outward pressure but there is some. Without any tab mine would probably tend to bow out slightly.

Lots of options with the tab, this is just what I did.

tab.jpg
 
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