Shortround6
Major General
For most piston powered aircraft the problem was that they were weight limited, not volume limited.Was aircraft volume a known statistic for an aircraft? I understand the imperative of making the aircraft as small as possible and as light as possible and the conflict of those imperatives with the bulk, center of gravity constraints and ducting of the turbosupercharger that caused the bulbous look of the P-47.
You had more than enough volume to fit stuff into (limited by center of gravity) for most jobs (fresh flower deliveries excepted).
A smooth airflow was more beneficial than limiting the surface area with abrupt changes in cross section that created eddies and drag.
Passenger planes are the general exception. People do not fold well, water weighs about 62lbs per cubic ft, a box 2 ft X 2ft X 4.5 ft (18 cu ft) will hold most humans when seated but even the airlines aren't dumb enough to squeeze people into a space that small.
Jets have a lot more power, they have more automatic systems to move fuel in flight to maintain center of gravity. Jets also suck up a lot more fuel so designers get more creative in moving stuff into out of the way spaces to make space for revenue producing spaces.
Fighters and bombers (really weight limited) are at the other end of the spectrum.