I was in the business of recovering Fabric Aircraft. I recovered 35 planes before I retired. On most wings the ribs are only 1/2 ins wide where the fabric touches . The rules as Far as FAA is on most small planes is that the stitching has to be 2'' inside of prop blast and 3 '' else where. It all depends on the Horse power of engine. I recovered a Staggerwing bipe and the rib stiching was every 1" I also recovered 88 wings for local Crop dusters. Because of the big engines the stitching in prop blast was 1" . Look at my site and see the Stearman that I did in 1966-67.