Upsizing holes in main spar ribs 2, 3, and 4 attachment brackets to correct tolerances to achieve perfect skin alignment

Using the jigs just constructed, the ribs 2, 3 and 4 were secured in the exact locations required to ensure a perfect skin alignment. This was done for both the left and right wings, however the tolerance errors were worst in the left wing - in particular rib 3 - as previously documented. Access was the issue - it was necessary to upsize the middle 4 holes on both ribs 2 and 4 attachment brackets in order to access and correct the issues in the rib 3 attachment brackets, event though in most cases the tolerance issues for the ribs 2 and 4 bracket was minor, and probably by themselves require no remedial action. Tools needed were varied: 30cm 4mm drill bit, right angle chuck, 4.1mm and 4.8mm chuck reamers.

In only one instance was the error so great that there any significant elongation left with the upsized 4.8mm holes. This was for the left hand rib 3 bracket topmost 4.8mm hole, and the elongation was only 0.2 mm or so. A 4.8mm rivet tail would readily expand into this for a secure fastening. In a few instances significant elongation was present in the top and bottom-most holes, which had to be left at 4mm due to insufficient edge clearance (2D-rule). In all cases these top and bottom-most bracket holes were unaltered, but the rib holes suffered elongation in some cases, sometimes by up to 1mm. This reality was deemed acceptable by TAF, and it is likely that the shear load strength of such joins would be unimpaired under the likely load situation encountered Given all the other rivets were upsized, and were free of elongations would more than compensate strength-wise. In any case this overall remedy is in my view superior to the factory-build practice (which is leaving all holes at 4mm, and elongating the rib holes as needed).