Brief Description: Drill lower VS spar to fuselage.
Time to drill the lower VS spar to the fuselage. I deviated from the plans here. Behind the aft most fuselage bulkhead is the tie down bracket. The 4 lower VS holes go through the bulkhead and then through the tie down bracket . The plans have you first drill the 4 holes in the tie down bracket. Then match drill outward through the bulkhead and VS. Two problems with this method. First, the holes in the tie down are not critical, but where they exit the VS is very critical because they exit on top of a rudder hinge bracket. Get these wrong and your screwed.. You will be blind drilling the VS aft bulk head if you match drill through the tie down bracket.. Second, it’s a very tight spot in the aft fuselage to match drill outward through the tie down bracket holes.
I didn’t drill those 4 holes in the tie down bracket way back when building the fuselage because I had planned all along I would match drill them through the VS. The challenge was locating the 4 holes on the VS aft spar from the dimensions given on the tie down bracket. Take pause and work through it. Take measurements several ways to cross check your VS spar hole locations. The tie down bracket is held on by 8 fasteners. 4 rivets through the tie down and bulkhead. And 4 that we are about to drill through the VS. I didn’t rivet the tie down to the bulk head because I want a chance to debur these 4 holes I’m about to drill. So, I put the 4 rivets in to locate the tie down bracket but did not buck them. And I plan to just hold the tie down bracket against the bulkhead by hand when I drill the 4 holes from the outside through the VS main spar. After the holes are drilled I can debur the bulk head and tie down bracket and then finally rivet the tie down bracket to the fuselage bulkhead.
These images show how I use various ways to assure I was drilling straight. The red bar height was adjusted to assure I was drilling straight up and down. The clamped square helped assure I was drilling straight left and right.
