Hi noname. First you must define "thrust." Static measurements are misleading, since a prop is stalled when airspeed is zero. Recent studies indicate that propeller "slippage" is actually much less than the ten percent rule-of-thumb that was taught when I studied aeronautical engineering.

My experience has been similar to yours. I found by experiment that a 12-10 Master Airscrew (electric) prop flies my sport-aerobatic model much better than the 12-8 indicated by the "MotoCalc" program for my Aveox 1409-2Y motor with 3.68:1 reduction gear. The increase in pitch reduced RPM by 400, while the load increased by two amps (static). Contrary to the rule that more pitch produces more speed at the expense of low-speed or vertical performance, I found that with the higher pitch I gained not only more speed but was able to complete three or four vertical rolls instead of two before losing airspeed.

Jim; I don't agree with your formulas. In my experience I have found that a change in pitch has much more effect on actual flying performance than a change in diameter. Recent full-scale propeller tests indicated that when pitch x RPM equals airspeed, the slippage measures only one to two percent!

Ideally pitch should be matched to the cruising speed of the aircraft, and that is what we do by trying different props and observing the results.