Fitting the right F-684 gusset2h
February 27, 2023
I decided to give F-684 gussets a try and see what edge distances will I get.
The hardest hole to meet the edge distances is the aft hole on the gusset, so I drilled it the first.
Then I drilled the foremost hole on the same edge.
After drilling all the bottom holes, I unclecoed the skin just enough to use an angle drill to drill the holes in the firewall angle. They turned out to be okay. The top hole is slightly less than the 2D edge distance, but still acceptable as per MIL Spec.
The gusset with the holes.
I measured all the edge distances on the bracket (by measuring from the edge of the hole, then adding the radius of the hole) and the one that has the smallest distance was the aft hole.
0.179 plus 0.064 (half of the #30 hole size) is 0.243". It is less than the recommended 2D edge distance, but still more than 0.219" specified by the MIL Spec for -4 rivets.
I don't love it, but I guess I don't hate it as well. All the edge distances are larger than 0.219", and all of them except two have edge distances of more than 0.250".