Corner rivet doublers for wing ribs 4, 6, 8, and 9

I have never liked how a rivet sits right between the bottom skin attachment bracket and the rear spar channel attachment bracket. I have not tried it but I would expect the metal pieces to be forced apart slightly when setting the rivet, except perhaps they were full rivetted down prior to setting this final rivet. I have not tried it. I see another perhaps theoretical possibility of the part jumping out from under the rivet tail under some exceptional stress situation. I say theoretical, because I would have expected this to show up in a service bulletin by now if this were a real problem.

Simple washers could address the first issue, but I could not find anything suitable (they would preferably be 6061-T6, and approach 20mm diameter)

Here I fabricate washer-doublers that sit right on top of this junction, and the two adjacent rivets on each side, make from 0.8mm 6061-T6. This part will address both of the above concerns, particularly the first which is more substantial. It may also address the second, as it prevents one of the edges to jump out from under the rivet tail. I see no downside to this modification.

The 1/2" hole in each bracket is to reduce the chance of rubbish or moisture building up in the slot so formed, and to allow some inspection. The outer edges are slightly chamfered to ensure clearance with the bend radii while providing plenty of rivet centre-to-edge distance.

(Edit 29 Jan) TAF have just approved this addition, pointing out the need for priming (since done) and appropriate grip-range rivets (4.8x15mm will do)