I tried something new on the Ki84. In studying Greebo's Ki43 and Hirricane defaults, I noticed that he mimics the stitching of the fabric over the ribs by using a row of white pixels, each white pixel separated from the next in line by a blank pixel. This row faces the light source. Beside the white pixel line is another row done in black pixels with the same spacing. The black pixels are aligned with the blank spaces in the white row. This gives both the textured and shading effects to the ribs after this layer's opacity is reduced to about 10%. Next add some faint shading to the fabric between the ribs. There are two layers at play; the stiching and the shading. Each is about 10% opacity, but keep the layers separate so you can fine tune to best suit the scheme.
Here's a pic of my Ki84 rudder showing how the effects come together:
