With work, vacation and cars that needed attention, I haven't spent a lot of time working on the plane. I've done a lot of head scratching and staring, moving something 1/4" here 1/4" there, but no progress worthy of pictures. This weekend I finally got a good chunk of time to work on the cowling. I had the whole thing on and off a good 20 times, so at least I'm getting good at doing that!
The next step in the fit was to get the horizontal cowl edges matched up and the hinges drilled. The hinge gets attached to the lower cowl first. In order to make inserting the pin easier, the hinge is supposed to rise slightly as it goes aft. Unfortunately, that means that you can't just draw a line parallel to the edge and use that for the drill line. I cut the hinge stock to the right length and clamped it in place to check the fit.
It was too hard to drill the hinge with the cowl in place, so I pulled it off. I first drilled the hinge on its own (1" rivet spacing), then clamped it back on the cowl and match drilled through the fiberglass. The front of the cowl near the air inlet has a slight curve to it. I thought I was in trouble because the pin was hard to get past the curve into the straight section, but I found that once the other half of the hinge was in place, the addition of the other eyes made guiding the pin through a non-issue.
I did the same to the other side, after putting the cowl back on to tweak the fit to the top cowl. For now, I sanded the edges so they meet perfectly. Eventually I'll have to sand a little more off to provide enough of a gap to allow for paint and some wiggle/vibration room.
I went around and wrote notes on the cowl to help me remember where I eventually need to add fiberglass. It's going to take a lot of work!
Now for the difficult part - match drilling the hinges to the top cowl. I inserted the pin into the hinge to hold the top hinge half tightly in place. I secured the top cowl and pulled the edge down so it mated up with the lower cowl.
There isn't much room to drill the top cowl with it in place, but it's super important to do as much as possible with it attached to the lower hinge half. There's no way it would be the right fit if I tried to do them separately. I've read a lot of stories about horribly difficult cowls to take on and off because of how the hinges are fit. They need to be lined up in a natural position with no preload one way or the other. I measured very carefully up from the lower hinge rivet holes I'd drilled (3/4" up from those holes puts the top holes in the middle of the hinge material) and, using a block of wood to reach in and hold the top hinge half against the top cowl, I drilled and clecoed a couple of holes. My hope was that would be enough to keep the hinge in place once I pulled the cowl off to finish up. It ended up working fine, and made for a nice tight fit. I did the right side the same way, although it was much easier because I could reach in through the oil door to do a few of the aft holes before taking it all apart to finish up on the bench.
With the hinges done, the cowl sits nice and solid. Now all that is left is the aesthetic part, which is going to take quite a bit of effort. I'll tackle that after I've gone back and fit the baffles and finished the rest of the firewall forward stuff though.
I had done all of this fitting using my jig that kept the cowl consistently placed relative to the engine center. This whole time I had my fingers crossed that my original math was right and the front part of the cowl would be the right distance to the spinner back plate. Thankfully, my math was right! However, the horrible shape of the cowl is going to make it require a lot of surgery regardless. The gap behind the spinner is about right at the top, but the cowl is far from vertical and opens up a lot towards the bottom. I'll have to add a bunch of fiberglass to get it all parallel. You can see that the spinner sets a little bit above the cowl. That is by design, since the engine will sag a little over time as the engine mounts compress.
