Strengthen wing skin 3-4 connection - part 2 - drop rib 12 by 0.8mm

Dropping rib 12 by 0.8mm makes possible inserting the additional 0.8mm strengthening doubler without changing the wing profile or complicating the rivet alignment on the front and rear spar. Of course displacing a curved rib is not the same as creating a concentric curve, so it is expected that some rivet hole misalignment will occur along the existing line of rivets joining the two skins. Estimating the radius of curvature of the skin curve at 2.5m suggests that if the holes are matched at the midpoint of the chord then one can expect about 0.1mm misalignment at the front and rear most holes. This is well within acceptable bounds and in any case there will be additional rows of fully matched drilled (in situ, with the curve) rows of rivets.

I found subsequently the situation proves better than this. A good match all the way from the rear spar to the front two rivets where the mismatch did approach about 0.1mm or so.

The 0.8mm figure is fortuitous as one could upsize and recenter the holes on ribs 12 and the front and rear spar strategically to achieve the desired effect while retaining fully round holes. 4.8mm x 10mm rivets could then be used. To do this accurately, drilling jigs needed to be constructed.

In addition, it was necessary to adjust the front and rear-most flanges of the ribs 12 by hammering down to roll the bend a bit, to bring these into alignment with the spars. This was due to tolerances at manufacture. The correction was about 0.7mm or so. This was done before dropping the rib.

Photo essay follows.