As for a comment, I was not at all enthusiastic about the mixing of military and civilian airspace in EADS, not to mention in Airbus itself. *Lunatic*, n. One whose delusions are out of fashion.
Wiki gives this explanation. You can't be me, I'm taken
A further consideration is the number and the shape of the blades used. Increasing the aspect ratio of the blades reduces drag but the amount of thrust produced depends on blade area, so using high aspect blades can lead to the need for a propeller diameter which is unusable. A further balance is that using a smaller number of blades reduces interference effects between the blades, but to have sufficient blade area to transmit the available power within a set diameter means a compromise is needed. Increasing the number of blades also decreases the amount of work each blade is required to perform, limiting the local Mach number - a significant performance limit on propellers.
