From what I've read the stiffness, by weight, of steel and aluminum is
almost equal. So when building a tubular space frame there's really no
advantage, from a weight standpoint, to using aluminum over steel. But
modern aircraft are built using aluminum almost exclusively for the
frame and skin. Is the reason this makes sense due to the skin? By how
much does making the skin a structural component favor aluminum? And
what are the other factors that favor aluminum over steel for the
frame? Is this because of the frame shape?
Thanks,
Eric