Originally posted by SHenion
A a lot depends on the plane. A slow, fat airfoil has a lot of drag at high speeds.
Depends on what you are looking for.
Go to higher pitch if you want more speed.
Go to bigger diameter, lower pitch for more pull.
High pitch props tend to have less of a pitch-factor. Will require less rudder input on take-offs.
Try going one step in each direction. I.e from 10-6 try 10-7 and 11-6 or 11-5.
A tach is a good tip. You want to be within the range. For example the best prop on my 91FX gave 12400 rpm on the gound. It would hit close to the max (16k) at full speed. If RPM on the ground is too low, it may not reach the ideal power band. If too high, it will max out the engine in the air and will be hard on the engine.
Pitch factor? I'll assume you're talking about propellor factor, or p-factor. This is a VERY VERY small effect regardless of what prop you use. This is nothing to worry about...A larger prop will have a bigger gyroscopic effect though causing gyroscopic precession. Again, that is not a big deal. A larger diameter prop also causes a larger slipstream which also causes a yaw to the right with high angle of attack. This sort of matters, but is nothing to worry about. Torque is something to worry about!
You make a good point about props unloading in the air... A longer flatter prop will not unload nearly as much as a short curved type...