If you're not aiming for pretty (you never did say if it was stunt), Gorilla Glue works great on foam. Just make sure that there's enough moisture for it to fire off completely, that there's a place for any excess to go when it foams up, and that your clamping system will hold even when the glue tries to push everything apart.
It may even work on a stunt plane -- I've never tried sanding it, so I don't know.