October 15, 2019

Attached left fuel tank

Fresh back from my work trip to Germany, I was ready to attach the fuel tank to the wing. First, I wanted to check that all the bolts are torqued correctly on the fuel sender cover, but I wasn’t too sure about the correct torque value. The screws provided in the kit are M4 x 16mm hex cap, and the parts list calls them stainless steel, zinc-coated. This doesn’t seem to be a normal alloy/finish combo, so I couldn’t find what torque to use. I chose a value of 20 in-lbs of torque, somewhere between class A2 and class 8.8 from this helpful chart. This seems about right, since M4 is similar in size to an AN3 bolt, which should be torqued 20-25 in-lbs.

After setting the torque, I applied a little dab of paint (nail polish) to each bolt head so that I know they’re already torqued.

Attaching the tank is a little tricky. The z-brackets / channel brackets must bolt to the main spar, but alignment is not guaranteed, and the AN3 bolts don’t self-center. I had to borrow a trick from Craig Maiman, which was to grind down the end of the bolt to give it a taper, so that it could guide itself into its mating nutplate. I think floating nutplates would have been a better design choice here.

Looks are deceiving! It’s actually the skin underneath that’s misaligned.. the fuel tank skin actually lined up pretty well with the main spar cap

Once the tank was attached, I found some pretty bad misalignment of rivet holes on the bottom skin, so I spent quite some time filing and then reaming these holes so that I could get the clecos and rivets in.

Bottom side of the fuel tank, getting ready to rivet the skin onto the main spar cap

The wing is looking pretty good with the tank attached. I’m not quite finished putting in the rivets – tomorrow I’ll finish the bottom side and then flip the wing back over to the top to finish riveting.

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