Originally Posted by Taildragger67
Isn't a monocoque (egg/oval) cross-section the one which imparts the greatest inbuilt strength, expecially over a pure circle?
I thought that's why all Boeing jets have been oval. I can't recall what cross-section Airbus aircraft have but I'd be surprised if it's perfectly circular.
The fact is that Boeing aircraft since the Stratocruiser (and BTW the Curtiss C-46 before that) have a dual-lobe cross-section. The upper lobe and lower lobe are each circular, and joined at the cabin floor. All elements (skin & floor beams) are thus in pure tension under pressurization loads. Very efficient structural design!
(Blow up a balloon if you don't believe me)
The departure from this practice is in the nose section (e.g. 747), where the fuselage becomes more slab-sided. Here the formers must be heavier to withstand the bending loads in the non-circular area.