McCauley Propeller question

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matthewhinmann120cm
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McCauley Propeller question

Post by matthewhinmann120cm »

Hello all,

I installed Randy’s O-200 conversion STC, I’m currently looking for a legal prop. I found a 1A101/DCM6948, but the STC wants a 6952.

My question is, can I install the 48 pitched prop? Or do I need to have it repitched per STC.

Learning lots here. Thanks!
Matt H.
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Re: McCauley Propeller question

Post by 6643 »

Give Randy a call. I know he has been working on getting other props approved. That said, I think a 48 pitch would give you lots of noise and not so much thrust. Probably climb pretty good, though.
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Re: McCauley Propeller question

Post by 8434 »

I can tell you that changing 4" in prop pitch is quite significant. I have C90 and had a 7152, my static RPM was in the 2050. I changed to a 7150 and now have a static of 2350.
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Re: McCauley Propeller question

Post by 6643 »

I don't think it should be that big of a change. I seem to recall someone stating as a guideline 50 RPM per inch, or maybe 2 inches, of change. There are other factors that figure into static RPM, too. for example, a 71 inch prop can be cut down to 69.5" and still be called a 71. Also, when the blades are overhauled material is removed from the blade. The thickness and chord are reduced, so even if the pitch (blade angles) is the same, the static RPM will be higher,.
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Re: McCauley Propeller question

Post by phil123 »

I have the same prop and a 50 pitch will get you up to 2750 +- rpm in a slight decent at around 115/120mph indicated.
The STC should give the prop model # requirements, the pitch range is optional.
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Re: McCauley Propeller question

Post by 6298 »

There are various pitches approved for each propeller authorized by my STC. You will find them on the Installation Instructions pages. Item 10. The Static RPMs are in the Airplane Flight Manual Supplement. I use the McCauley 1A101 69/48 on my airplane.
Randy Thompson A&P IA Pilot
Hold STC SA547EA for installation of O-200 engine in Cessna 120/140 and 140A"s
Overhaul small Continentals
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Re: McCauley Propeller question

Post by matthewhinmann120cm »

Thank you for all the replies. After posting I read the STC again and found the limits… :oops: Thanks Randy. I think I’m going to try for a 6948 prop. I would like the ability to climb out a little faster, and not necessarily faster cruise speed.
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Re: McCauley Propeller question

Post by 4004 »

Randy,
Which plane? :D There goes that devil again!
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Re: McCauley Propeller question

Post by 8413 »

6643 wrote: Sat Jun 04, 2022 8:18 pm I don't think it should be that big of a change. I seem to recall someone stating as a guideline 50 RPM per inch, or maybe 2 inches, of change. There are other factors that figure into static RPM, too. for example, a 71 inch prop can be cut down to 69.5" and still be called a 71. Also, when the blades are overhauled material is removed from the blade. The thickness and chord are reduced, so even if the pitch (blade angles) is the same, the static RPM will be higher,.
I've been kicking around the idea of possibly re-pitching the prop on my 140A when I take it in for a static balance at the prop shop. I have a C90 and McCauley 7152 prop. Static rpm is about 2050. Full throttle straight and level I get 2375-2400rpm and about 115-118mph indicated at about 1500'MSL and 60F. My thoughts are to decrease pitch just enough to get redline rpm at full throttle straight and level or an increase of 75rpm over what I get now. My goal is to pitch it to get max available horsepower straight and level which I'm hoping might increase speed and climb since I feel the prop is a little over pitched at this time. Seems like the prop should be pitched to just barely be able to get to redline straight and level...is that good thinking? Assuming this is a good plan, how much pitch do you all think I should ask the prop shop to remove? John...you indicate 1" in your above comment would get about 50rpm...I'd be happy with that. If I do have it re-pitched...do they re-stamp the new pitch on the hub or is it only noted in the logbook?

On the other hand (sorry if this is too much wandering thought), my engine is far from fresh. Last overhaul was in 1987. It has about 1100SMOH and about 800hrs on Millenium cylinders. Is it even a smart idea to start repitching the prop to make up for an older and theoretically less powerful engine? This is why I'm "kicking" around the idea. Hate to re-pitch the prop to "band-aid" fix a tired engine. The engine seems to be pretty healthy though. Burns about 1/2 qt every 15hrs, oil pressure comes up quick and stays in the 40-45psi range in flight...about 30-35psi at idle when fully warmed up. As far as whether it puts out good power...hard to say...it seems to put out the same static rpm as I hear other C90's and 7152 prop's do.

Any advice is welcome.
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Re: McCauley Propeller question

Post by 6643 »

Josh - First thing to do is to verify the tach reading. See if you can borrow an optical tach and check the RPM at full throttle level flight. Go from there. OTOH, your problem could be a tired engine. Your RPM vs. Airspeed readings are pretty close to mine, IIRC. What are you getting for compression readings?
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