Dave said:
I suspect that there is an optimal propeller diameter. However, what you say is correct because in most cases the diameter is physically limited before it can reach this optimal size.
I think you'll find that momentum theory will tell you that larger is always better.
The limits that determine "optimal" are likely to be related to:
- Tip speed and compressibility effects - however this is more of a limitation for helicopters as the advancing blade has a higher tip velocity in translational flight
- Structural limitations - how heavy is the structure of the rotor/propellor.
Daniel