>>1576617Real answer, since you haven’t gotten one yet.
The primary issue with square airplanes is that you cannot efficiently pressurize a box shape, as the internal pressure causes the sides of the box to bulge out. This is the same reason why you don’t see square soda bottles.
If you don’t pressurize an airplane, it can’t fly as high without risking damage to the cargo. Flying low increases drag, and therefore increases flight times and fuel costs.
There are definitely square airplanes, but they are to my knowledge all unpressurized. The photo is a Shorts Sherpa, they’re still used by the US forest service to airdrop firefighters.
Source: 7-year ATP.
