Hello,

I have a new thunder tiger .15 GP, what rpm may I expext with a 7/6 prop and 10% nitro ?

I never ran that small of a prop on my TT GP .15. It will spin an APC 8x5 @ 13,000 RPM burning 10% nitro/20% lube fuel though. Being a bushed engine I didn't think it was a good idea to run it any faster...as it definitely would with a 7x6.

With an 8-4 it will turn over 14,000. Why wouldn't you turn a bushed engine over 13,000? Cox engines are steel crank through a bored aluminum case, some of them turn over 20,000 with no problems. IMO there is more worry of a ball bearing going bad at those speeds. A grit of dirt at those speeds can ruin them in an instant. A bushing will just have a large scratch and reduced life.

ok, I finished the breaking in, it peak at 13100 with the 7/6 and start like a dream at the first chicken stick hit !

Sport-Pilot...I never thought of a bushed engine in that respect. Actually, if the shaft/bushing fit was right and there was the right lube and enough of it, I would think it would almost present less friction than BB's at very high speeds.

...I might just have to try a smaller prop on my TT GP .15...might get a bit more speed out of the plane.