National Aeronca Association Bulletin Board

I have an 11CC Chief that I intend to put on PK 1500 floats. The engine is a continental C85-9 (tapered shaft).

I'm wandering what prop. (pitch) I should be putting on.

The sensenich website indicates that a 74CK-2-40 would be the way to go.

My goal is maximum takeoff performance. I'm not concerned with cruise performance.

Should I go for an even finer pitch like 38?

Any experience out there? Anyone know what model of McCauley prop I should consider?

thanks,


Gord

Looked in my Univair catalog's Sensenich & MacCauley charts.
The seaplane prop for the 11CC (85 horse) is listed as the 74CK-2-40 (72 inch). The landplane prop is the 74CK-2-46. So the recommended seaplane prop is already 6" less pitch than the landplane model. Do you want even less pitch? Hard to tell without flying it first. You can always have it repitched if necesary.
The listed Macauley standard landplane prop is the CM7144 (cruise 7146,climb 7142). For seaplane use they list the 7142 (cruise 7144). Note that Macauley only shows 2" difference in pitch between landplane & seaplane.
Hope that helps.

Eric

My prop. is the McCauley McCauley 1B90CM7142, I'm thinking about re-pitching it back to 40.

Anyone have any idea about how much of a static RPM gain I'll get?

I want to say for every inch you move the pitch, it results in about a 100rpm change. i.e. 7142 = 2300rmp, 7140 = 2500rpm. But I can't seem to find any justification for that statement. Best thing to do is call a prop shop, and ask them how much you can gain.

nkh

FYI: I did come across the Pitch vs. Speed formula.
inches of pitch X RPM X 60 mins / 12 inches / 5280 ft = Airspeed

71x42
42 X 2500 X 60 / 12 / 5280 = 99 MPH in a perfect world

71x38
38 X 2500 X 60 / 12 / 5280 = 90 MPH

I have a Cheif on Edo 1400's and a 100hp O-200 running a 74x38 that works fine. I know a Cub operator with a C-85 running the same prop. My Cheif plows little more than I like to get on the step, but is off quick once up. A little fuel in the aft tank helps to get the CG in the right spot for me. Cruise at 2300 rpm is about 70-75 mph.

You will want all you can get for takeoff, especially on a hot day with a load.

Great floatplane, you'll like it

Charlie

I'm thinking about putting an O200A in my 11CC.

Did you have to modify your cowling at all? I've heard the O200 will sit about 1/2 to 3/4 of an inch forward compared to the C85.

How about the mount? Will the O200A bolt on the same mount?

The STC conversion info is from Wagner Aerial Service, Clark South Dakota 57225. Phone 605 532 3862.

I did not do this myself, but from the drawings I see a new cowl has to be fabricated. The engine mount comes from a later model Champion (P/N 4-1207) or they give drawings to make one yourself.

Looks like a pretty extensive mod, depending on what parts you can scrounge up and how much metal work you want to do.

The STC # is SA57RM it also covers the Lycoming 115 HP engine