First lower cowl trim

Haven’t had a ton of time for the project this weekend, but I still got some work done. Yesterday I pulled the lower cowl off and got to work fitting the attachment hinges. I actually ended up cutting a new piece for one of the hinges on the bottom of the cowl – because the eyes weren’t lined up like I want. What I want is to always be able to start the attach pin in the fuselage-attached hinge half, before putting the cowl in place – this will make things a tiny bit easier.

After doing that, I just spent the time to clamp each of the four hinges in place on the fuselage and drilling through the rivet holes into the hinges. Today I picked up by removing those hinges and deburring and countersinking the holes as required. Once they were back in place on the fuselage, it was time to move on to trimming the aft end of the cowl.

First, though, I had to finish laying out the trim line. Doing this is a little more complicated on the lower cowl, because it doesn’t sit flush to the fuselage all around like the upper. There’s the cowl exit area, where the cowl itself dips down – there’s no way to easily measure from a guide line on the fuselage to mark this area. What I needed to do was to find some way to take the marked cut lines and extend the plane they represented across the cowl exit area.

The method I settled on for this involved using my laser level again. I just set the cowling on the table on end, set the level diagonally off of the cowl corner, and adjusted it until the line was following my cut marks. At that point, I could be sure it was following the desire cut plane, and so I marked more hashes around the exit area:

I repeated this exercise from the other bottom corner of the cowl, so I essentially brought the cut line in from both sides. It was encouraging to see that the resulting marks joined in the same spot. Next, as with other cuts, I laid masking tape all along the marks to create a continuous cut line, then got to work with the oscillating saw. This was mostly rote work, but the inside corners at the edge of the exit were a little interesting to do…I could just make the cut all the way from the outside, so I ended up making it as deep as I could, then finishing the cut from inside the cowl.

After a bit of basic cleanup sanding of the edge, it was time to hang everything back on the fuselage. I was a little worried that I might have cut too close to my trim line, but as it turns out I did pretty well, and there shouldn’t be nearly as much sanding to fine-tune the cut line as with the upper cowl.

Better yet, it looked like sanding this also won’t be as tedious as I thought it might. Mounting and dismounting the lower cowl in the current configuration is kind of a pain – It has to be lifted in place, the aft end rested on some strategically-stacked boxes, then I hang the front end in place with my cleco + string setup, then I put ratchet straps around the aft end to cinch it in place, then I go back up front and cleco the temporary join plates, and finally the thing is hung.

I really didn’t want to have to repeat that exercise over and over again. But it turns out that with the join plates in place up front, if I loosen the ratchet strap, the aft end will drop down just enough so I can sand it with my little popsicle stick setup. There will still be plenty of trial-and-error, but it’ll be a little more tolerable.

I did start on sanding that edge down a bit today, but there’s still plenty of work to be done…I’ll have to pick back up on that another night.

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