I have a question about the multi-blade props also. I've run a little over a gal. of fuel through my 120SP with a Master Airscrew 18x12. I followed the manual supplied with the engine and I've been able to consistently get 5500 rpm. It idles nicely at 1400-1500 rpm. It does not sag at full throttle. I then added a Zinger 18x12 3-blade thinking that I would loose maybe 500 rpm. Well, the engine only turns the Zinger at 4300 rpm! My plane is heavy for a .60 size plane (12+ lbs.) because I installed lots of goodies that added weight, plus the extra weight of that 120SP. At this point, I'm afraid the the Zinger will not fly this heavy plane at that rpm. If I switch to the recomended APC 15.75 3-blade prop, what rpm should I expect from the 120SP engine? Am I getting the proper output from this engine? If not, do I need to run it some more on the bench to increase performance? Keith, what do you suggest?

In the mean time I've contacted Biela Propellers. Check them out at www.smigla.com. They will custom-make me some 17x12 composite scale props later this year that I will test on the engine. They also will be offering 16x10 and 18x10 scale props available later this year.