> I have a 0200 that I will be installing on my KR2S that I removed >from my Citabria, I was using a 69X48 McCaully prop. I could get 2610 RPM >static, 2700 90 mph climb, 2750 redline 120mph cruise. The way I understand >it the higher the expected cruise speed the shorter the prop needs to be, >but at the same time it needs more angle >Jim Raleigh ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
Jim, I didn't realize they ever ran an 0-200 in a Citabria. Anyway, according to the chart in Tony Bingelis' book " Firewall Forward", 2750 rpm with a 48 inch pitch prop at 90% efficiency would put you right in the 120 mph range. My 64 inch pitch prop at 2700 rpm puts me in the 160 mph cruise range which is pretty close to where I'm at. More diameter is good as you will see in the notes below but with increased diameter comes increased tip speed and TOO MUCH of that is not good. An interesting note on one of his formulas, with my 64 inch pitch prop at 90% efficiency and 2800 rpm I should only be getting 153 mph. Three possibilities: A. my prop is more than 90% efficient. B. I'm turning 2800+rpm C. I actually have more than 64 inch pitch in the prop. I'm guessing it's voo doo science at work. :-) See notes below. Larry Flesner Some notes on propellers from the same book: The speed of sound at sea level is 741 mph (approx 1,100 fps) The tip speed of a propeller should not exceed the speed of sound. . Above a tip speed of approx 850fps (950fps for metal props) propellers suffer a loss of efficiency and produce a marked increase in noise level. A blade angle change of one degree will change the engine speed approx 50 to 100 rpm. Additionally, clipping one inch off the diameter (1/2 inch on each end) will cause an increase in engine speed of 50 to 100 rpm. About static rpm, (aircraft stationary on the ground with throttle wide open) a propeller should allow an engine to turn approx 80 percent of it's rated rpm. Your propeller's efficiency increases as the airspeed increases. It also increases with additional diameter - up to the critical tip speed range (speed of sound). Propeller efficiency is rarely above 90%.
