Remanufacture of wing rib bottom skin support angles

Wing ribs 4, 6, 8, and 9 both left and right have a bottom skin support angle. The angles supplied were found during test skin fittings to have their bends very slightly out of position. The anticipated remedy for this was to make shims from 0.64mm 6061-T6 to insert between the angle and the skin, thus avoiding a visible depression in the skin.

Two of the holes in the rib 4 angles were also found to be 1.5-2mm displaced from their correct positions. It was also found that the 4mm holes in the rib 8 angles which match with holes in the rear spar channel were also slightly misplaced owing to the bend error.

Finally, the build manual calls for the builder to form a step of 0.8mm in each angle to allow a smooth transition between the rear spar channel flange (0.8mm thick) and the bottom surface of this angle. The problem occurs when trying to form this step: excessive pinching of the existing fold in these angles result, and a smooth even step is difficult to achieve. The concern is that a crack may form at this pinced bend, a concern also mentioned by builder Pascal Latten.

It was decided to re-manufacture these eight parts, with the aim of solving all three issues. The step could be formed while the bend is being established via nylon hammering, with the help of a custom anvil, shown below. 0.81mm 6061-T6 sheet was employed.

Match drilling of the vertical flange holes is achieved with the help of 0.64mm 6061-T6 acting as a shim to vertically displace the original part.

Mismatch issues with the skin and rear spar channel are avoided by omitting all bottom flange holes, leaving to a future match-drilling procedure with the skin and rear-spar channel

I note that the Sling TSi has changed the design concept of these angles, eliminating the need for builders to form this 0.8mm step.