Originally Posted by barit1
OF COURSE the cargo (lower lobe) is pressurized. Otherwise there would be a pressure differential across the flat floor, tending to circularize it (as we saw 33 years ago in the DC-10 cargo door blowouts!)
By maintaining near-zero delta P on the floor -
o Upper lobe skin is in pure tension
o Lower lobe skin is in pure tension
o Floor is in pure tension, preventing the "kink" between the two from bulging out!
OK, a stupid question - why shouldn´t the lower lobe be pressurized to a higher pressure? It has to carry bending loads due to its own weight and the weight of passengers, seats, galleys/lavatories and cargo placed on it... pressurizing the underbelly to a higher pressure would help with that...