Dave,

Can you crunch the numbers for the Yellow F-16? It's got two solid carbon rods for spars. The front one is 6mm and only extends into the wing about 4", the aft one is 10mm (I'm pretty sure--this is off the top of my head) and extends about 5.5" into the wing. The wing is relatively thin, but has carbon cloth laminated between the foam and balsa skin. Both spars extend into the fuse about 3.75" into clamps.

Thanks...