ORIGINAL: Tall Paul
I've seen an large electric B-717 which uses fluted corrugated cardboard for the fuselage.. With a few formers and maybe some longerons, it's about as stiiff and light as needed.
The large diameter all by itself results in a stiff fuselage.
Stiff maybe, but slope aircraft also have to be tough and resilient for when they hit trees, rocks or other planes. Still, corrugated cardboard (or even better, corrugated plastic - Coroplast) might be just the material I should use. I'm surprised I didn't think of that myself, as I used to fly a SPAD Dart before a marsh swallowed it up. It would be pretty easy to form an airliner fuselage with, too. Thanks for the idea! Now I just need to buy up all the Coroplast in my area.