Eric R Snow wrote:
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

I'm just guessing, but my guess is that there are several reasons. The
first that comes to mind is galvanic corrosion where a steel frame meets an
aluminum skin due to contact of dissimilar metals. The second is thing that
comes to me is that an airplane has to heat and cool just like any ship and
they may want the metals to have similar temperature properties so they don't
overstress any rivets. Planes go into very hot and very cold places. If the
skin stretched a lot but the airframe only a little maybe it would shear
rivets. It also may be something to do with the way their shops are tooled,
maybe they only want to work with aluminum ..

GWE