ORIGINAL: alexedit
Hi - I just checked the specs of the OS91FX on the OS website and it says 16,000 RPM did I read it wrong?
Practical rpm: 2,000-16,000
Output: 2.8 hp @ 15,000 rpm
Recommended Props: 13x8, 13x9
Using ThrustHP as a calculator, it would take
2.754 horsepower to turn a 13x4 prop at 15,000 rpm.
5.508 horsepower to turn a 13x8 prop at 15,000 rpm.
3.999 horsepower to turn a 12x8 prop at 15,000 rpm.
I do not know if these numbers are exact, but, I do think they show that you'll never see the "advertised" rpm using a prop that is in the recommended range.
For at least one "real world" number for a 91FX, here is the text from the link I posted:
"12x8 APC - 11,700 peak, idle around 2200-2300 after a gallon of break in.
- stock muffler, powermaster 15%, OS #8 plug, 75F and humid at around 500ft ASL"