ORIGINAL: av8tor1977
Pitch can make a pretty big difference on static rpms. This is because when a higher pitch prop is not moving through the air, a good portion of the blade is stalled and causing a ton of drag. This is also why lower pitch props are used for 3D flying, as lower pitches are more efficient at lower, or zero, airspeeds. As an aside, this is also why high performance full size airplanes use variable pitch props.
I don't think, at the prop speeds and pitches we are considering here, we have a problem with cavitation at static conditions. Cavitation unloads the power system. Sure the drag of the prop increase in those areas that are cavitated but the fact that there is no lift in those sections causes a net decrease in the power system load.
If we went to an 8in pitch prop from a 6in pitch prop, from the same manufacturer and model prop, and saw no decrease or if we saw an increase in prop speed one might suspect some cavitation. But based on my back to back test of the APC 18x6W and 18x8W props the results are as expected. You move more air at the higher pitch, it loads the power system down and there is a decrease in prop speed.
diceco