Service Ceiling for a C85 powered 415-C?

Thanks Larry!

I was going back and forth internally about the pitch change, but I decided to go 52" because I already had more than enough climb rate but I was losing out in cruise. Vernon thought 52" was a good number based on people he's talked to so I went with that.

With 73/49 I could maintain a solid 700-750 fpm climb to 3000-4000 feet, at which point it starts eroding. But I had to push 2450 RPM to get 105 mph cruising 3000 feet.

Living in the DC area, with all the Bravo airspace and all the restricted areas, I fly below 3000 feet most of the time. Besides, the sightseeing is better down there and I'm not in a hurry for local flying. But I'm hoping this overhaul gets me more speed at altitude - the 73/49 wanted to overspeed above 6000 feet.

I have MAP, Fuel Flow, and a 4-cyl engine monitor in the coupe, so I can collect a good amount of data. The "book numbers" were written for a stock c-75 c-85 so with the stroker there's a need to extrapolate, but at altitude I was getting higher RPM for a given fuel flow/MAP than the book calls for. I think I was leaving some cruise thrust on the table.

52 is kind of way on the cruise side. I’ve had a 7149 for many years and I got 105-115 mph speeds at 2400 and it climbed really great. I used to fly into some shorter runways and that pitch worked out very well. And I had the C-85 with the O-200 crank STC. I think you would be amazed at the increased horsepower you get with the shorter prop. If your prop was really 73 you were basically flying a C-75!

Dropped off the prop at East Coast Propeller Services today. Fortunately that's only a 2 hour drive for me so I didn't have to deal with packaging & shipping.

Fingers crossed for the prop to pass the overhaul measurements & inspections. Once that happens, they'll be trimming it from 73 to 71 inches and increasing the pitch to 52 - seems that's a good set of measurements for the C-85 Stroker.

All remaining fingers crossed for a performance increase after the overhaul.

Larry,

Good catch! The prop hub is definitely marked 73/49 so I will have my A&P look at it. I know I'm meeting the static RPM, the prop was overhauled once (maybe shortened? Definitely was repitched) and I remember someone telling me that there's a trick to measuring the length of rounded tip propellers.

Will report back with findings.

UPDATE: Yup... looks like a visit to the prop shop is in order.

Brooks, if you have a 73 inch propeller on your airplane with a C85 you are illegal! Read the rather convoluted information in TCDS 718. The legal lengths of a McCauley on a C85 range from 69.5 to 71 inches. The 73 was for the C75 only. I believe if you go to a 71 you will see a marked increase in power.

I've been curious for a long time. Since I'm a sport pilot, I'm not allowed above 10,000, except to avoid terrain... and there's nothing tall enough on the east coast to qualify.

I have flown to 9900 (C85 "stroker" with a McCauley 1A90 73/49.) At that point I was still climbing at 250-300 FPM - solo with slightly more than half fuel. It was an interesting flight since it was 97 degrees on the ground, and as I climbed it became more comfortable to close the windows and then to crack open the heater. On the way down, experiencing the return to 97 degree heat was a lot less fun.