Originally Posted by
CONSO
Are you sure about that-?? The ' upper floor' stresses would be significant whereas in a tube, hoop stresses are much easier to handle and uniform ...
Consider that every pressurized low wing aircraft has a big section of fuselage that is not hoop loaded, specifically the area of the center wing tank. The tank structure takes those non hoop pressurization loads. The KC-135 lower lobe has integral fuselage tanks that extend well ahead and well behind the center wing tank. Those tanks take those loads as they are primary structures and not bladder/secondary structures installed in a pressurized section of the lower lobe. In contrast the KC-46's belly tanks are secondary structures, similar to the aux tanks in the bellies of some 737, but of course larger.