C85-12 STC - Prop pitch question

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wwiilbird
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C85-12 STC - Prop pitch question

Post by wwiilbird » Sat Feb 02, 2013 07:29

I've read through the postings on prop pitch but haven't found an answer and am seeking user feedback. I have a C85-12 engine going on an Aeronca L3 and it calls for a metal propeller and lists the propellers below however the STC doesn't specify pitch. So I'm looking for feedback. I'm looking for a happy medium between climb and cruise performance. From what I've read I think I would look at a 44 or 45 pitch? At this point I'm leaning toward a new Sensenich propeller because it is hundreds of dollars less expensive than a McCauley. It comes in silver however the company I would be buying it from said they would spray it black for me and rebalance it for free. The fellow said he needs to know what pitch I want. So I would greatly appreciate your feedback on what pitch you've found makes a happy balance. Also, if you have any preference as to manufacturer I would be interested in hearing the reasons for your preference.

Thanks Nick

Sensenich M74CK-2
Max Dia 72" Min Dia 70"

McCauley 1A90CF or 1B90CM
Max Dia 71 Min Dia 69.5"

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rkittine
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Re: C85-12 STC - Prop pitch question

Post by rkittine » Sat Feb 02, 2013 08:35

I would suggest that you call Don Swords at Don's Dream Machine in Atlanta. He is always willing to talk engines and builds some of the best Small Continentals around. He did my C-85-12 Stroker, but it has a Seaplane Prop.

Also, Bill Pancake is another one that loves to talk airplanes and has a wealth of knowledge when it comes to about every form of Aeronca.

I just sent you both of their contact information by PM

Good Luck Bob
Robert P. Kittine, Jr.WA2YDV
West Nyack Aviation, L.L.C.
New York, New York 631-374-9652
rkittine@aol.com

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RRHaldeman
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Re: C85-12 STC - Prop pitch question

Post by RRHaldeman » Sat Feb 02, 2013 09:09

I can recommend the Sensenich 74CK-2-46 Propeller. The pitch is 46. I installed that propellor on my C85-12 with the O-200 conversion and it is a really great combination. I have over 250 hours on the engine and prop and love them both.
Dick Haldeman, RRHaldeman AT aol DOT com
Cell (815) 222-9812
1946 7AC-2407 N83729

jepropst
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Re: C85-12 STC - Prop pitch question

Post by jepropst » Sat Feb 02, 2013 09:26

I have a C85-12 with the O200 modification and I use a McCauley 1A90 71X46. I would suggest that you find someone who has the prop you are considering buying and see if you can borrow it , install it on your plane and check to make sure you can achieve the correct static and red line RPM and that the plane performs the way you like. If you can't achieve the rated RPM then you are giving away HP. I've tried a number of different props on my plane and each one performs differently. The other thing is to have an accurate calibrated tach that you can verify your engine rpm. I find the optical tachs that can pick up the prop speed through the windshield works good. The reason for mentioning this last point is that I found that my mechanical tach appears to have some hysteresis resulting in accurate readings sometimes while being off at other times.
John Propst
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wwiilbird
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Re: C85-12 STC - Prop pitch question

Post by wwiilbird » Mon Feb 04, 2013 10:19

Thanks for the replies. My engine is currently being rebuilt so at this point I can't experiment and I don't have access to multiple props. Having done some reading on the web over the weekend I am changing my mind and going with a McCauley as I've read the Sensenich is limited on repitches. The prop and engine will be shipped to NC where my plane has undergone restoration and flown back to NJ. I'm now considering a 45 or 46 pitch. I'm just not sure how much of difference in performance there is between the 2 pitches. Thanks again, Nick

Paul Agaliotis
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Re: C85-12 STC - Prop pitch question

Post by Paul Agaliotis » Mon Feb 04, 2013 12:36

Nick,
I would put on a pretty flat pitch. You're not going to hurt your speed, it just won't go fast. My TAC had a 45" pitch with an A65 and it's just no ball of fire. Since it won't go fast you might as well have the climb performance.
The L16 has a 1A90 70/38 on the C85 and it goes real good. You need to throttle it back at cruise about 2425 RPM and it scoots right along.
With a C85 on a L3 the wing tanks are a must! I have 12gal with the A65 and some of the legs out West will make you pinch the center out of the seat cushion.
Paul
Mailing Adress : Paul Agaliotis 2060 E. San Martin, San Martin,Calif. 95046

Dennis
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Re: C85-12 STC - Prop pitch question

Post by Dennis » Mon Feb 04, 2013 14:41

nick,

As Paul points out, a change of 1in in pitch has very little effect on speed. The calculated difference between 45 and 46 pitch at 2400 RPMs is only a little over 2 mph. The owner of the local prop shop told me that some shops, when repitching a prop, try to get within +/- 1 in. So when you buy a 46 repitch, you might be getting a 45.25 pitch or a 46.75 pitch. if you ever watch them repitch a prop, you will wonder how they get that close.


Dennis

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