Aft Fuse

Today I did a final round of fitting and then drilled the two keeper holes from the aft bulkhead into the tail wheel mount. Then I primed the aft fuse bottom skin and shims.

There is a slight twist in the bulkheads and the tail wheel mount doesn’t quite sit flush against the aft bulkhead. After checking with Vans, this is common and due to the sandwiching of pieces used to make up the bulkheads. With a little hand pressure, I was able to straighten it out and drill the two keeper holes. Then I countersunk them on the drill press. I was disappointed in the quality of the three fluted countersink after using the single fluted sink on the longerons. I need to buy some more countersink cages, and a couple more single fluted sinks.

I decided to prime the outside of the aft bottom skin, as it had been scratched up in the trimming and drilling process. I may regret this at some point in the future, but it seems like the right thing to do for now.

I also cleaned, dried, and primed the inside of the tail wheel mount using some green self-etching rattle-can primer.

The last couple of days I’ve spent a couple of hours trimming the aft most bulkhead. To clear the weld on the tail wheel mount, I had to file down the bulkhead cutout a surprising amount. It now sits flush against the flange of the tail wheel mount, and the bottom skin cutout fits nicely around the mount also. This weekend I’ll drill a couple of holes and countersink then, then touch up the primer.

Today I test fit the aft bottom skin, aft bulkhead, and tail wheel mount. The bottom skin cutout was pretty close, needing just a small enlargement to clear the tail wheel mount. The aft bulkhead needs a bit trim so the skin and contact the bulkhead flanges, and the weld bead can clear the bulkhead. I spent a couple of hours assembling, disassembling, trimming and repeating before it started to fit well. I still have some more work to go before this is final.

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I will need to use some shims to close the gap between bulkhead and mount. Right now the gap is large, almost 1/8th of an inch. This is in part due to the weld pushing on the aft bulkhead, keeping these apart. Will be interesting to see how many shims/spacers I’ll be up needing here.

Today I cut out the aft bottom fuse skin template from the manual, and marked out the areas a needing to be trimmed. I found that taping the template to the outside of the skin resulted in good placement, and some masking tape held it in place while I drew out the area to trim.

I used a variety of tools to make the cut, a handsaw, bandsaw, vixen file and small files like the one in the picture. I was happy with the way this turned out.

Last night and again today I spent a few hours dimpling the side skins. Doing in one session would have been faster, but each time I started I got interrupted. In any case, I rigged up some extensions by placing some sheets of particle board cover with carpet on boxes, and strapping them down with tie downs. I was able to adjust them a little to ensure I had the right support. The holes on the curved edges were the most difficult, but I found a way to make it all work.

Today I primed the side skins. It was quite straightforward, and aside from looking a bit patchy, I’m happy with how things came out.

Tonight I finished countersinking the longerons. Another round of very consistent holes. One more thing I found useful was a countersink drilling table another builder had made by measuring the thickness of the skin to be mated, he came up with a range of hole sizes. This is easier to measure than the depth of a rivet in the countersunk hole.