With the O-200 on my KR I sent a prop back to the manufacturer to have some pitch taken out of the prop as it was turning about 200 rpm slower than desired. Rather than repitching the prop, the prop builder cut 2" off the diameter of the prop. I noticed right away that it took significantly more RPM to taxi and while the engine turned more rpms, it also used more runway for take off and had degraded the climb performance. While the engine could make more PRMs and HP, the prop efficiency dropped way off. I replaced the prop due the the poor performance of the shortened diameter. The prop tips do a great deal of the hard pulling, so cutting down an already short prop almost always has a degrading effect on the taek off and climb performance of the aircraft.
I also experimented with this using an inexpensive Sterba prop on a VW powered Avid Flyer that I had built. The prop was simply too much of a load for the engine. After discussing this approach with Ed Sterba, I marked off the prop tips in 1/8" increments. I spent two days testing the plane then trimming 1/8" off either prop tip, then testing again. With each 1/4" removed from the diameter, the RPMs came up and the climb performance made marginal gains. Then it reached a point where the next 1/8" got me more RPMs, but degraded climb performance, so that's where I stopped. Jeff Scott N1213W ----- Original Message ----- Subject: KR> Change in propeller size from 54" > Aside from the clearance benefit, have any of you made such a change or know > of the results of a smaller prop with the same pitch?
