Brief Description: Tail Spring Mount Final Fitting
After I finished drilling the aft fuselage I did the final fitting of the tail spring mount. I wanted to get both the 711 and 712 bulkheads drilled in their final position before performing this step. I removed the 712 from the assembly and located the keeper rivet holes on a lateral line even with the top of the bulkhead tab just below the end of the bottom J-channel, and 1/2" either side of the vertical centerline per DWG 27. After reinstalling the bulkhead I match drilled the keeper rivet holes through the tail spring mount and countersunk them for -3 rivets.
Due to slight interference with the F-779 bottom tail skin I had to trim about 1/32" of the bottom edge of the long vertical flanges on the 712. On reinstallation, I bent one of the narrow tabs that sits over the end of a bottom J-channel. It cracked when I tried to straighten it, so I'll have to remove that tab and fabricate a patch with a replacement tab. I'll have to be careful that the patch not interfere with the tail spring mount.
Note in photo 2 that there are slight gaps (0.035 on the right, and 0.027 on the left according to my feeler gauges) between the outboard portions of the tail spring mount and the forward face of the 712 bulkhead. The very bottom of the mount at the tube, and the center of the aft flange both contact the bulkhead, so the bulkhead is bowed slightly. I don't know if I'll have to fab shims for this, or if it will pull in when I mount the vertical stab.
Final shape of the mount clearance hole, and keeper rivet holes drilled.