Week 8: Right Wing Bottom Skin

I began this week by completing the twist jig installation. Once I had the right size drill bit I was able to open the holes to just allow the 7/16" bolt to fit. This should still be a nice secure joint when the wing is bolted to the carry through spar in the main fuselage.

Once the frame was attached to the jig, I managed to get it flipped over. This was cumbersome with one person so I am going to try to get help the next times I have to do this. With the bottom side up I then did a test fit of the bottom skins. When doing this I noticed that some of the holes I left open on the frame needed to be riveted before the skin was attached. These were not called out on the drawings, so I was not sure if they should be riveted with the skins or not.

After the test fit I removed the skins to prep them for dimpling and priming. I unrolled my scrap carpet to have a large enough scratch free area to work. This worked out well, so I am planning to use the same setup for the other large skins. Once the skins were deburred and scuffed, I dimpled them and then cleaned and primed the mating surfaces.

Then I reattached the skins to the frame and cleco'd them in place. Both of the skins were nice and tight, with no oil canning noticeable between the supports. In the process of attaching the skins I noticed a few other issues.

The main spar hole in the root skin that overlaps with the main bottom skin was sized for a 4.8mm rivet without being dimpled. This lined up with a 4.0mm rivet hole that was dimpled in the main skin and countersunk in the spar. I went ahead and dimpled the hole in the root skin as well, which left it significantly oversized but I am confident it won't be an issue.

The other issues were that one of the rivets for the elevator control bracket access panel lined up perfectly with the reinforcing plate. I had to grind down the end of the flange on the plate to keep the rivet from touching. On the other side of this rib, the end two rivets were hitting the support brace. I shortened these rivets and drilled a clearance hole in the end one to allow the rivets to clear. I let the factory know about all these issues and they said some of them had already been addressed, but would look into the others as well. They seem to be always making a good effort to keep improving the already excellent design and manuals.

With these issues corrected I was able to quickly finish riveting the bottom skins. I am really happy with the results, the skins are nice and tight and the flush rivets create a good smooth surface. With the nice weather this past weekend I was able to catch a neighbor outside who helped me flip the assembly back over, although he seemed a little shocked that I was building an airplane in my garage.

The next step is the right fuel tank. I began prepping those parts and will be working on that in the next week.