Dave Jackson said:
Airplane propeller are efficient for propulsion because they have a small disk area and a high induced velocity per sq-ft.
Actually, I thought that most airplane propellers were as large as practical given the size and weight of landing gear. I don't believe that there is an advantage to having a high disk loading, particularly when you've got a variable pitch prop that can cater for the differences between high speed cruise and low take-off speeds.
Daniel