Fineness ratio

Theoretical ideal fineness ratios in subsonic aircraft fuselages are typically found at about 6:1, however this may be compromised by other design considerations such as seating or freight size requirements.

This is often due to the competing need to place the tail control surfaces at the end of a longer moment arm to increase their effectiveness.

Reducing the length of the fuselage would require larger controls, which would offset the drag savings from using the ideal fineness ratio.

Modern airliners often have fineness ratios much higher than ideal, a side effect of their cylindrical cross-section which is selected for strength, as well as providing a single width to simplify seating layout and air cargo handling.

More technically, the best possible performance for a supersonic design is typified by two "perfect shapes", the Sears-Haack body which is pointed at both ends, or the von Kármán ogive, which has a blunt tail.