Mike, here are some of my basic rules of thumb. They are based on my experience and opinion; I have no facts to support them.

Very windy, use a large diameter low pitch prop; 10X4 or 10.5X4.5
Moderate wind, less diameter and a little more pitch; 9.5X 4.5 or 10X5
Calm wind, small diameter max pitch; 9X6 or 9X6.5

Also, when you change props you should adjust your flying style. With lower pitch props you can pull tighter in the turns; with higher pitch props you should not pull as tight. FYI: if you have a pitch gauge, use it; not all props will have the pitch as marked.

We cannot change the humidity or height above sea level but we can play with glow plugs and head shims. So far I have not experimented with head shims but I would think that as humidity goes up so should the head shim.

As for glow plugs, use the one that gives the highest RPM in the weather conditions you have. Medium-Hot or Hot is best because of the idle requirement. Cold plugs do not idle well.


Mike thanks for starting this thread. I would like to see what others have to say.

Bob