Miscellaneous wrote:Anyone able to explain the detail of why a prop designed for climbing (tugging) may not be suitably adjusted to give a sensible cruise close to that achieved on the same aircraft with conventional props?
Is it simply a case of the amount of adjustment required being beyond what is possible given the original design?
Well it is all about angle of attack, of the prop blades. The blade of a prop works like a wing, it creates lift based, mostly, by its AoA.
You can change the AoA two ways, by literally changing the angle, the pitch of the blade, or by changing the direction of the wind that strikes the blade.
As the aeroplane speeds up the AoA reduces and so the prop doesn’t create as much lift, and so doesn’t pull as hard.
So ideally you want a coarse pitch when you are going fast and a finer pitch when you are going slow to achieve an optimal AoA.
So no fixed-pitch prop is optimal at all speeds, they are all a compromise. You simply choose at which speed you want maximum efficiency.
A c/s prop works by changing the pitch to be optimal for whatever rpm you choose. The mechanism tries to keep the rpm constant whatever the speed.
The prop on the tug is optimised for low speed, climbing, and so is less efficient in the, faster, cruise, by definition.
Is that what you meant?