Quote Originally Posted by David Lewis View Post
The foam is just to help mold the skin to the right shape. It does not carry any structural load except to resist oil canning and local buckling, which are all small forces.
I don't think that's exactly true. I'm not an engineer, but I'm pretty sure that the foam is indeed loaded in shear as it reacts lift loads out of the skin and into the spar. An engineer like Marc Z. could tell us for sure, and probably exactly how much.

--Bob K.