Drilling the Flap Tube

Yesterday I installed the oil filter adapter, but didn’t have a socket big enough for the vernatherm. Today I have the socket, so I torqued it to specs and installed safety wire. I welded the aft end of the brace tube for the oil cooler, which will go between the engine case above the number 2 cylinder and the back left baffle.

Oil Cooler Brace Tube

Oil Cooler Brace Tube


I removed the rudder cables and turnbuckles to turn them into flap cables. I wanted to try and get the length of the two cables as close as possible, so I used a rope to tie the triangular junction to the fuselage.
Rope support for flap cable

Rope support for flap cable


The outboard ends of our flap tubes were not drilled yet, so I spent a while looking at the plans. There isn’t a lot of room for error in the geometry of the wing root end, so I measured carefully to get the angle of that inboard horn
correctly. The most accurate dimension that I found to measure was the distance from the center of the hole to the rear spar, measured with a square. I used that method to position the tube angularly, and shifted it left-right to line up with the cable. Then I drilled a small #40 hole at the outboard end of the tube. I installed a cleco and drilled the other side, then enlarged those holes to 3/16″ for the AN3 bolts.
Flap Tube Drilling

Flap Tube Drilling


This is certainly an instance that calls for measurning twice.