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C145/ 7649 Static RPM
Posted: Thu Aug 22, 2002 3:56 pm
by Psmith
I recently purchased a 51 Model A with a McCauley 7653 prop. This is my first experience with a 170. I live in MT where field DA in the summer is usually in excess of 6500'. Because of low static RPM, 2100, I had the prop flattened to 49 in pitch. Static is now ~ 2200 with climb of 2400 @ 75mph ind. Level at 8000' DA, full throttle, yields 2650 and about 118mph ind. Does this sound normal?
Static RPM
Posted: Thu Aug 22, 2002 6:05 pm
by N2218B
You should be able to get the static RPM listed in the type certificate data sheet with your 7653 prop. I don't have one handy here but I think it is in the neighborhood of 2230 rpm. Over here in Bozeman where we are roughly 300 feet higher than you are I get very close to the spec'd rpm. I would think the 49 inch prop would turn a lot faster than 2200. Have you had your tach checked?
Posted: Thu Aug 22, 2002 7:50 pm
by Psmith
Annual is coming up and I plan on checking the tach as well as timing and compression.
Posted: Thu Aug 22, 2002 10:13 pm
by Bill Venohr
We should have talked about 6 months ago--I had my 49 prop taken to a 53! Anyway, I think your static is too low (I could get 2350) and my airspeed was around 115 mph at about 2600. This is at 1000 msl.
Prop Pitch Vs RPM Vs Mph
Posted: Thu Aug 22, 2002 10:38 pm
by N1277D
A simple way to approximate and check if things look OK for the tach and airspeed indicator is to use the following formula:
Mph = (Pitch x Rpm)/1056 - ~ true airspeed
This should be your approximate true airspeed. You need to correct for altitude and temperature to find the indicated airspeed.
A 49 inch pitch should provide about 120 mph true airspeed at 2600 Rpm . At 1,000 agl and 75F the indicated airspeed should be around 115.