Checking Prop Pitch

[Dano"T"]

Hi gang,

Can anyone tell me how to measure prop pitch without having to remove the propeller. The stamped numbers are unreadable on the installed prop. I have a C-85-8 motor and a 71" long prop, I want to know for sure if this is a climb prop or not. 71-46 sticks in my mind for some reason...maybe when I bought it 12 years ago the guy mentioned it or something. Nothing written in logs about it. Anyway....can it be measured easily?....and what constitutes a climb prop suitable for seaplane operation on a C-85-8?


P.S.

Static run is about 2450 RPM on the tach for what it's worth.

Dan

[jgerard]

Re: Checking Prop Pitch

I don't think you can mesure a fixed pitch prop's pitch on the plane. The prop shop uses a special bench and rotating fixture. Also to make things worse, McCaulley mesures their props differently than Sensenich. A prop protactor is used on variable pitch props to properly set the end limmits of travel. Fixed pitch props tend to increase in pitch over time so getting the pitch checked is not that bad of an idea.

If your tach is close to accurate, and you can pull redline(and then some)in level flight I would think you have a climb prop.

Jason
N43643

[Forrest Barber]

Re: Checking Prop Pitch

I agree and the 46 pitch is fine . the 71-48 is the correct prop all around...
sounds like a 46 with the static you are getting. Sometimes the seaplanes need the longer prop like a 74-43 maybe the seaplane guys will jump in on this thread. Are you putting her on floats....?

[jgerard]

Re: Checking Prop Pitch

A longer prop will give you a better aspect ratio like a sail plane wing. if "get me off the ground" performance is what you want then allways go for the longest prop available. A friend with a F19 on floats said his seaplane prop (74-43) would let his 0-200 spin up way past the 2750 redline in level flight but sure got the plane off the water fast.

Jason
N43643

[VictorBravo]

Re: Checking Prop Pitch

The C-85/O-200 will stay together for short periods at over 4000 RPM, but not for long. Slightly exceeding 2750 for brief periods won't kill it, AS LONG as you have good oil pressure and the whole mess is balanced.

It WILL greatly reduce the lifespan of major engine components. We got a few hours between overhauls on race engines at best. If it were me, I would say 20 seconds is about it for "takeoff power" when there is a good enough hamburger at stake for the winner. You darned well should be running some extra upper cylinder and valve train lubricant in the fuel, IMHO. You will Marvel at the Mystery of how well this works

Bottom line: Exceeding 2750 is safe so long as you bring the airplane to and from Reno on a trailer Exceeding 2750 makes the suits and clipboards kinda upset, as well as your insurance company.

Bill

[Dano"T"]

Re: Checking Prop Pitch

I checked th FAA Aircraft Specification A-696 for BC12D-85 and is as follows:

Propeller Limits:

Static RPM at maximum permissible throttle setting:
Landplane: not over 2350, not under 2100
Seaplane: not over 2310, not under 2010 (exception: not under 2100 with Edo 60-1320 Floats)

Diameter:
Landplane: not over 72 in., not under 68 in.
Seaplane: not over 72 in., not under 70 in.

So I guess the prop I have should work fine according to this data. I dont know about longer props...acording to this, 72 in. is maximum.


Dan