wrote in message
ups.com...
Aluminum is stiffer in many cases because for the same weight the
thickness is greater. IIRC aluminum is about 1/3 the weight and 1/3
the stiffness. So if a sheet of steel would need to be .030 inch
thick to provide the strength, the aluminum would be .090 thick and
because it is so much thicker, the aluminum would be stiffer. Since
the aluminum is stiffer, ribs can be further apart.

Dan



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

Also because its thicker it is easier to connect together.
Pat