C145/ 7649 Static RPM

[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?

[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?

[Psmith]

Annual is coming up and I plan on checking the tach as well as timing and compression.

[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.

[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.