Propellers

Maintenance, parts and services related to Cessna 120/140's

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Propellers

Postby Doug Corrigan » Sat Jan 01, 2005 8:09 pm

As long as I'm getting the engine overhauled (should be back on the airplane soon), I'm considering getting a new prop for my 0-200. The one on the engine now is an MCM6950 however, there is a 4 stamped in the center of the 0. Checked the logs and there is no entry for a pitch change anywhere. :?: Several props (standard) are listed for the 0-200. McCauly - MCM6950, DCM6948, and OCM6948. Sensenich lists 69CK-0-50L and 69CKS12-0-52L. So, does anybody know what the difference is between these props as far as design and performance?
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Re: Propellers

Postby 5095 » Sat Jan 01, 2005 8:23 pm

Don't know about the design, but the 6948 would give you better climb and the 6950 would give better cruse. The 69CKS12-0-52L would give the fastest cruse but lest climb. Charles Wright in TN has a 7154 on his C-90. He runs off and leaves my 7148 on my C-85 and climbs about the same as I do. With the 0200 if you don't have to deal with hills or short runways I would go with the 69CKS12-0-52L. JMO worth what you paid for it. :)
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Re: Propellers

Postby Mike Smith » Sat Jan 01, 2005 8:36 pm

Doug,

You haven't mentioned how the 0-200 was installed in your airplane - 337 field approval or through an STC.

Not trying to bust your hopes for a new propeller here, but have you checked the installation paperwork for your aircraft to see which propeller can legally be installed before you go out an buy a new one?

My aircraft with an 0-200 was converted with a 337 field approval, and on the 337 it lists for my aircraft to have a 6950. Doesn't mean that a 6948 wouldn't work, just says that if I'm to operate with that engine installed it must be the 6950. Your paperwork may say something else, but to make sure, check. You may be able to use other propellers.
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Re: Propellers

Postby Paul Domeier » Sat Jan 01, 2005 9:17 pm

I have a MCM69/50 on my O200. Seems like the perfect match for the engine. With 1/2 fuel and no passenger in cool weather, I climb 1100 fpm (75 mph @2600 rpm, cruise is 113 mph at 2550 rpm, and my plane is fat (1018 lbs)

On hot days with a full load the 69/50 gets about 350 fpm. I wouldn't to want try that with a 69/54.

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Re: Propellers

Postby Doug Corrigan » Sat Jan 01, 2005 10:05 pm

It's installed with an STC which lists the MCM6950. I was just curious. Aircraft Spruce has a price of 3 grand :shock: for that prop.
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Re: Propellers

Postby 5095 » Sat Jan 01, 2005 11:09 pm

I have heard of people buying used props around here at prop overhaul shops for as little as $600.00. They may also have a 4 stamped on them.
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Re: Propellers

Postby Joe Henrich » Sat Jan 01, 2005 11:58 pm

Carl what prop shops are near you? I need a 6950 for my ongoing O200 conversion and I sure can't spring for a new one.
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Re: Propellers

Postby 5095 » Sun Jan 02, 2005 1:17 am

There is one in Mc minnville TN KRNC and another in Clark Co Ind KJVY. We had a guy from here go to KRNC and buy a used one a couple years ago for his C150.
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Re: Propellers

Postby Victor G » Sun Jan 02, 2005 1:33 pm

Doug,

I wouldn't sweat this one. The last two digits are your "pitch". Of all the things that would negate an STC that would be about the last one. It appears you have the Gary Rice STC?

That STC lists The 1A100 MCM 6950 prop. Also listed is the static RPM of 2425 + or - 50 RPM. If you don't like the numbers you're getting you could always have the prop "re-pitched" at any prop shop to either match the 6950 bit or to get you inside the static RPM limit. Either way you'd be covered.


I don't know about yours, but my FAA guy wouldn't get excited if your pitch was "off" the listed STC number, especially if it made Static RPM.

Edit;
Ugh, I oghta read better. I see you're thinking about replacing a prop, not making yours "right". I have the Emmet STC, which I believe is now owned by Randy Thompson out of CA. I installed the 1A101DCM prop. The DCM was a later and improved (according to the McCauley guy I talked to at the time) blade design. Which is why the pitch I guess for the 0-200 and C-150 went to 48 instead of 50? I've also heard the McCauleys are more efficient on the 0-200 than the Sensenich, but that just may be the old Ford vs Chevy debate, not sure on that one.
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Re: Propellers

Postby Paul Domeier » Sun Jan 02, 2005 4:23 pm

Victor Grahn wrote: Also listed is the static RPM of 2425 + or - 50 RPM.


I dug out the Randy Thompson STC, and it actually does specify pitch, 6950 - 6954. It specs max static @ 2450 rpm. I wonder if this number reflects the 24 degree timing AD for old style cylinders? I see 2550 at full power static with 6950, but I have new style cylinders so timing is back up to 28/28.

Anyone know the max static rpm for a C-150?

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Re: Propellers

Postby Paul Domeier » Sun Jan 02, 2005 4:49 pm

Found a neat little site where some geeks tested an O-200 on a homemade dyno. The geeks were only getting 76 hp @2750 rpm out of an O-200 that turned max static - what gives?

http://www.flycorvair.com/thrust.html


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Re: Propellers

Postby Matt Lahti » Sun Jan 02, 2005 5:27 pm

One of those guys is a member here and also has a 120.....
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Re: Propellers

Postby Randy Thompson » Sun Jan 02, 2005 7:53 pm

My STC, SA547EA, allows the use of the McCauley 1A100 or 1A101, MCM or DCM 6950 to 6954. Like Paul says. The static RPM limitations are Not More than 2450 and Not Less than 2200. I prefer the lower pitch as the engine produces closer to the 100 HP is is rated at with the lower pitch.
The 24 degree timing came along after the STC was created. The timing then was 28 on both mags. Since props vary with the same markings the static RPM varies. I use an electronic tach to check static as the mechanical tachs usually read low or at least incorrectly.
I have a brand new 1A101DCM6950 for sale on eBay at the moment. I keep one on hand in case someone wants a 3 day changeover from their 85. I also have mounts on hand for the same reason.
My take on the difference between the MCM and the DCM is the same as Pauls. The blade design on the DCM is more substantial and it is a newer design. I have a request in to add the Sensenich 69CK to the STC but it has been slow in coming.
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Re: Propellers

Postby David Sbur » Mon Jan 03, 2005 12:06 am

I have Randy's 0-200 STC back when it was the Lucas/Emmett issue (dated 12/17/87 for my installation). However, I have a McCauley 1B90-CM pitched 7142 installed. It has a letter to go with it from Witchita Aircraft Certification Office/FAA. The RPM limits from Wichita wants: static not over 2400 and not under 2100, which differs from Randy's STC. I have the original letter from Wichita, plus the 337 if that interests you. It's a pretty good combination, great climber and average cruiser.

My STC paperwork has no specifications on pitch, just min/max diameters of the 1A101 and 1A100 props.

I think the original story I was told is that the prop came from a C-85 (140 installation?) and rather than buy a different prop for the 0-200 installation an old owner got this approval done to save $$. Randy might know the story better (Hal Thompson's old N110V).

I have always wondered that the 42 pitch was awfully shallow yet experience in my case tells me it's just fine. I can red-line it easily in cruise if I don't throttle back.
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Re: Propellers

Postby Ray Davidowski » Mon Jan 03, 2005 9:47 am

Paul Domeier wrote:I have a MCM69/50 on my O200. Seems like the perfect match for the engine. With 1/2 fuel and no passenger in cool weather, I climb 1100 fpm (75 mph @2600 rpm, cruise is 113 mph at 2550 rpm, and my plane is fat (1018 lbs)

On hot days with a full load the 69/50 gets about 350 fpm. I wouldn't to want try that with a 69/54.

Paul Domeier
N1940V


Paul, do you have metal or fabric wings? Our plane is fat too, and we have a 1A101DCM6948 on our O-200 and indicate 90 mph in cruise at 2450 RPM on a 70*F day at 3000'. Summer climb performance is comparable, getting about 300 fpm on a 90*F day fully loaded with the power back to 2550.

Our static RPM is closer to 2600 (over 100 more than the 2425 +/- 50 in Gary Rice's STC), so our prop might be pitched so low it's more or less spinning free and not grabbing much air. Wrinkly, metalized wings wouldn't help, either.


BTW, add us to the list of straight-leg 140s without extenders! We removed the ugly things last week, flew it January 1st. I don't see how people were flipping them over, the tail is still plenty heavy. Just give the brakes a break!
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Re: Propellers

Postby Randy Thompson » Mon Jan 03, 2005 11:06 am

I checked the Type Certificate Data Sheet the Cessna 150 thru the Aerobat and they specify the 1A101DCM Propeller set at a static RPM not to exceed 2600. The 1A100 has a limitation of 2475 RPM.
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Re: Propellers

Postby N1940V » Mon Jan 03, 2005 12:50 pm

Ray Davidowski wrote: Paul, do you have metal or fabric wings?


Ugly, wrinkly metal. I'd sure like to have fabric, but you go to war with the secretary of defense you have, not the one you want...

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Re: Propellers

Postby Steve Dold » Mon Jan 03, 2005 2:01 pm

Take out the wash-in, maybe the wrinkles would go away.
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Re: Propellers

Postby N1940V » Mon Jan 03, 2005 11:07 pm

Steve Dold wrote:Take out the wash-in, maybe the wrinkles would go away.


A person hasn't lived his life to the fullest potential until they've had the honor of Steve Dold applying the patented, trademarked New & Improved Super Doldomatic Wing Checkerizer to his plane's wings.

Steve, you really should post a photo of that scientific contraption.

I'd like to readjust the struts based on the Doldomatic readings. Maybe when it warms up, you and Rick could give me a hand. I'll buy the hot dogs.

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