Priming the trim tab skin and rebuilding the bearing assembly4h
July 10, 2022
Today I did two small steps: primed the trim tab skin and made the horizontal stabilizer central bearing assembly.
First, I cleaned, etched, and primed some of the parts for the left elevator. The missing parts are the trim spar and two ribs, which I am replacing. The goal was to prime the trim tab skin, everything else I did just because the parts were ready for priming anyway. Later I realized that I should not have primed the trim tab horns (as they will be painted with the outside). Well, too late. They are scuffed already. Maybe, I'll strip the primer from them once installed and cover them with some temporary corrosion protection?
Also, I forgot to bevel the counter-balance skin, so I'll need to remove the primer from its exterior part, bevel it, and then prime again (with the remaining parts I am waiting for).
Then I rebuilt the central bearing assembly. The story is that I did not like the way it was primed and I think I stripped a bit of the primer accidentally while cleaning it. I tried to disassemble it but scratched the powder coat on the brackets a bit. Also, I did not want to use any solvents to strip the part VA-146, just out of an abundance of caution (if solvents get into the bearing and/or damage the seals). So I ordered new parts.
The tricky moment was to drill them to the horizontal stabilizer (which was already drilled for the previous bearing). Still, brackets are somewhat hard to drill, especially, when guiding through the aluminum. When match-drilling everything, it works fine as you are drilling a new hole. However, when match-drilling to an existing hole, there is a risk of damaging it.
To make sure everything aligns, I used the following process. First, I drilled one hole in the bracket and attached it with the golden cleco. Then I used my bubble level to make sure the bracket is perpendicular to the horizontal stabilizer. Clamped it really well, with the wooden block behind it and drilled with the #12 drill bit, carefully so I don't enlarge the hole. Then I assembled the bearing and drilled the six holes between the brackets using the #31 drill bit.
I used a transfer punch to align the holes on the bracket and the bearing.
After that, I reamed all the holes to #30 and riveted the part. I upsized the rivets from an AN470AD4-5 to an AN470-AD4-6, as I found before that the recommended rivet size is a bit too short. The gauge agrees.
Then I clecoed the assembly back and drilled the remaining two holes. Everything seems to have aligned just fine. I haven't torqued the bolts yet as I did not find an adapter for my torque screwdriver and the socket.