Lower cowl sanding and head-scratching

Hello, my name is Philip, and I suffer from analysis paralysis. That’s the main theme for this weekend.

After getting the lower cowl shimmed to my liking, it was time to start fine-tuning the joint between the cowl halves. A ratchet strap around the middle of the cowl helped pull things together to make the gap slightly more reasonable, but not perfect by a long shot. One bit of good news here is that some research indicated that it was best to wait on fine-tuning gaps until the hinges were riveted in place. The reasoning is that clecos aren’t perfect, and some shifting around is likely when the rivets get set. So instead of spending a bunch of time carefully sanding the joint, instead I just focus on rough-sanding it to where I could pull the cowl halves together for a reasonable tight gap with no rubbing or interference.

That led to the more fun and open-ended consideration of laying out the hinges at the joint. This seems deceptively simple, but there are a lot of interrelated issues here that all sort of come into pay at once. The first issue concerns the misalignment I have at the forward edges of the cowl. I have a few different options for addressing this. The first and easiest would be to just slap some micro on the upper cowl to build it up, then contour sand to match the lower cowl. The main concern with that approach is that the inside portion of the cowl there won’t line up at all, which could be a concern for dealing with how I want to cover the hinge pin access points.

What I’ve been wanting to do is to make some nice custom flush covers here – an approach I liked ever since seeing this RV-9 build log. However, to do what that builder did, I’ll need the inside portion of the cowl halves to line up, since it requires laying up an inside flange for the pin cover to mate with. If I want to do it that way, I think what I’ll have to do is lay up actual glass cloth to build up the upper cowl areas, then contour sand that on the outside, then sand the inside of the upper cowl to get the inner surfaces to match.

That’s quite a bit more work, but as of this morning I was still intending to go that route. But as I spent time today trying to work through the process of drawing up my pin cover shape, and laying that shape out against the cowl, and looking at how it would interface with the pins…I’ve come to like it less and less. I’m starting to lean towards a modified version of those pin covers, where the cover only mates with the upper cowl, instead of bridging across both halves.

Because of how I’ll be laying out the hinges, the access hole for them will sit entirely on the upper cowl, so really I only need to cover a hole up there. And if I can only have the cover attach to the upper, cowl, then I remove the need for the inside edges to have similar contours, which would make my life a little easier. I still think I’ll want to build up the upper cowl with actual glass instead of micro, and I’ll still carve some material out of the inside, but all I’ll have to do is get a vaguely uniform thickness up there.

So that’s my working idea for now. I think I need to let the idea bake in my head a little before I commit to it, but I do feel like this approach gives me a more definite path forward – which is something I need. I’ve got to find a way to get my brain past thinking 40-some steps in the future, and instead just be able to, say, go ahead and mark/drill the hinge halves to the lower cowl.

I guess we’ll see how I feel about this idea come tomorrow morning – a good night’s sleep seems to often help with clarity on stuff like this.

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