Rounding of rib tabs

All rib tabs contacting the skin, and which would be pulled tight against the skin by a rivet were rounded. This was prompted by the idea that a tab corner being pulled against the skin would press against it in a pointlike region and therefore create an interior corner in the skin. This interior corner could then become a region of stress concentration within the skin.

Note that the only tabs that are rounded off are those that are likely to apply pressure at a point when they are pulled by a rivet. This means that tabs contacting internal spar channels are not rounded, as there nominal contact is flat. Also some tabs make contact with the skin almost in a nominally flat manner. Such is the case with the elevator ribs. These skin contacting tabs will not be rounded.

Exterior corners in general will not be rounded - they are not themselves subject to stress concentration. Only when such corners press into other surfaces thus forming an internal corner (however nearly flat) in that other surface, and a stress concentration in that other surface - will that corner be rounded.