The top of the wing needs to be sheeted ~9" back from the leading edge in order to help maintain the airfoil between the ribs.
I used 1/16" mahogany ply. Probably overkill, and definitely too pretty for something that is going to be covered, but it is what I had, so we used it. We couldn't figure out a good way to clamp the sheet to the curved ribs, so we used a less than ideal method... we nailed the ply to the ribs. There is some discussion about using nails on surfaces that are to be covered, primarily due to the fact that rust could show through trhe covering, but these will be sealed under two layers of polyeurethane and a layer of felt. I think it will be ok, but I have a while to think about it before we cover. Once the epoxy cures the nails won't be necessary, so I may just pull them.
