Gas Engine's RPM range
 

I am building a KMP 95" B25 with two RCGF 20CC gas engines. I have been breaking these engines in on a Great Planes Revolver. With a 16x6 Zinger wide blade prop the engine and plane fly great at about 7500 RPM on the ground. In the KMP B25 section of Twin Engines Forum flyers are using 3 blade props with great success. Some with Glo and others with gas and are turning between 8000 and 9000 rpms. I tried a 14x7x3 prop on my Revolver at 9000 rpms and the plane flew poorly with the engine over revving. I then used a 15x7x3 prop and with a 7400 rpm reading on the ground the plane flew just as the 16x6x2 prop did. My main question is that I have run a Q52 and a G62 with 10 pitch props at between 5000 and 6000 rpms. I was under the impression that gas engines run at very low rpms compared to glo engines. Do smaller gas engines run at much higher rpms without damaging them? Is the larger prop with less rpms the right choice?

RE: Gas Engine's RPM range
 

Your practical rpm observations for your engines and airframe are correct.

The other stuff you are reading is BS for your situation.

RE: Gas Engine's RPM range
 

These same engines you are using typically turn over 10,000 in industrial applications. Its the propellers tip speed and disk loading that determines the rpm we end up using on model airplanes.