The International Cessna 170 Association

I will need a different prop for my "new" engine as it has the 6 bolt flange and my old prop is the 8 bolt pattern.

I am leaning heavily toward a climb prop but apparently have a choice to make. There is the EM 76/53, the standard climb prop for this engine or the Kenmore stc for the 80/42 prop.

My question is: Can anybody tell me the difference in cruise speed between the two climb props?

5 knots slower in cruise is negligible to me.... 20 knots is not negligible. Everybody I have talked to only speaks in general terms so it's been tough to figure out just how much effect each prop will have on the cruise speed.

Any significant difference between the EM 76/53 and the 80/42?

Thanks,
Keith

I don't have any experience with the 80/42, but I did have a 76/53 on my plane when it had the stock motor. The 76/53 was nice at lower altitudes, however the higher I flew the less it pulled (obviously) and every summer when the density altitude was high I would consider having it pitched up to a 76/55. I would cruise about 105mph indicated with it turning about 2500rpm. I could make it go a bit faster but it just burned more gas and felt like I was flogging the motor, 115mph indicated was about the most I could get out of it but of course that varied a little bit depending on conditions.

My plane isn't the cleanest around for top cruise speed, so I bet you could bump those numbers up a bit if you plane is slicker, but I doubt you will be able to cruise as fast with the 80/42.

Hi,

The Kenmore STC does not cover the six bolt propellers. It only covers the 1A175DM propeller. I just installed a 1A175DM8042 propeller on my taildragger 172 and the speed decreased 15 mph. The climb rate increased 300 fpm.

Hope this helps!

I had my 6 bolt, EM 76 53 prop, re-pitched to 49 pitch,
it cost my about 5 or 6 mph and it cost about $300 at the prop shop.

It gave me about 300ft/min better climb.

53B wrote:Hi,

The Kenmore STC does not cover the six bolt propellers. It only covers the 1A175DM propeller. I just installed a 1A175DM8042 propeller on my taildragger 172 and the speed decreased 15 mph. The climb rate increased 300 fpm.

Hope this helps!

Well.... that answers my question. I should have called Kenmore before giving it this much consideration. The engine shop that is overhauling my engine has a prop shop attached to the same building and they did offer to find a prop for me and pitch it any way I wanted it.

Thank you.
Keith

Keith, the STC for the six bolt prop (STC #SA7441SW) includes a seaplane prop 1A175SFC 8040 prop. you might have trouble putting it on a land plane?? Ron

Keith,
Despite the "hairy" video you posted...I guess I'll still help you out with your UN-original question. (Actually, thought that video was pretty funny....never realized you could make me look like Ron Massicot!)

I have the EM7655 prop. The ORIGINAL prop was a DM 7653. The cruise DM prop was the 7655. BUT (I was incorrect on this for a long time) the EM series of prop has a slightly different, more efficient profile than the DM series, and saves weight due to a lighter hub as well. The C-172 with the O-300-C/D engines had as STANDARD the EM7655 prop. The EM7653 was a CLIMB prop in that installation.

My EM7655 seems to suffer (in my singular-experience) as regards takeoff/climb...but it does very well indeed at cruise. I have a EM7653 hanging on the wall, and as soon as I have a couple days in the next week or two I hope to take careful measurements and inflight readings and determine the takeoff-run and climb and cruise comparisons of the two props. (I've been wanting to do this for 3 months...just haven't had a chance to get with a friend to help observe the TO distance excersizes at a paved runway. Hopefully I can put this project on the front burner for a report in the 170 News soon.

I'll keep you posted here, also.

George

Sorry about that George. It was meant to be all in good fun.......

As you can tell, I had an afternoon without much to do and started playing around with the internet.... amazing what is out there!

Anyway... that would be some good info if you can do a proper analysis of the two props.

My old engine with the cruise prop left me skimming the tops of the trees a couple of times taking off from a 2000 ft strip. Partly due to my old, tired engine but certainly also a function of the cruise prop. I like squirrel nests. I just don't feel the need to see them up close.

My engine shop has a prop shop attached. My engine guy said he could get a prop and pitch it any way I want it. Maybe get the EM and have it pitched to 76/54 as a compromise? I'll have to decide soon as, with any luck, my engine will be ready in less than two weeks.

Thanks,
Keith

Keith,
I have both a 80/46 and a 80/42 for my 53 170B with 180 gear, 8:00 tires and a 0-300A. The 80/42 gives me a cruise speed of 90/95 mph at 2450/ 2500 RPM which is where I've run it for years. The climb performance is excellent. I use the prop, not for extended climbs, but for get up and go. It allows you to break free and rotate much faster than the 76/53 which I used previously. It will also get you over the trees with more margin.
A couple words of caution however. 1. The long prop is sensitive to a tailwind while taxiing, causing the airplane to shutter. Absolutely avoid a downwind run up. 2. The 80/42 will allow the airplane to rotate when you only have marginal control. Use caution in a gusty wind. 3. The 80/42 will allow you to climb at too steep of an angle for safety. 4. You could easily overspeed the 80/42 in a slight descent.
A side benefit of the long prop is the static pulling power. Nothing beats it for moving the airplane on a soft surface. Unfortunately, only a few 8 bolts are made every year and they are pricey. Also, the prop balance and 3 inch station pitch from the factory are terrible. You wil have to have a new one tweeked. Jake

I have ordered the STC to install the O300D in my airplane but Jan said she is out of town and it will be next week before she sends it. That will be soon enough for my engine installation but I am needing to order a propeller and my man at the prop shop wants me to get the specific model numbers that are authorized by the STC so we can decided on which one to order.

Do any of you have a copy of STC #SA7441SW that I can refer to for the options for propellers? Any chance someone could send me a copy of the STC or at least the prop model numbers?

Thanks,
Keith

Hi,
My copy of the IC170A STC SA7441SW , states the following for props;
on Drawing No RM-2 rev2
McCauley 1C172-EM series props
Sensenich M74DC series props.

John

jatkins wrote:Hi,
My copy of the IC170A STC SA7441SW , states the following for props;
on Drawing No RM-2 rev2
McCauley 1C172-EM series props
Sensenich M74DC series props.

John

Thanks John,
That is what I needed. I thought it was the 1C172 but my prop guy said a 25% restocking fee to return it so I wanted to be sure before ordering.

Thanks again,
Keith

http://www.cessna170.org/forums/viewtop ... =buzzlatka

Here is a thread on the difference in a 53 and 51 prop.

To sum it up we went from a 7653 at 109kts cruise to a 7651 at 104 kts cruise. The all around climb and takeoff performance is much better at well as the cruise. It seemed that in cruise if you hit turbulence or got lazy with the old prop you could decelerate below 100 kts and it took awhile to get back up to 109. With the new one it gets right up to 104 and stays there. Also I think I actually go faster on cross country flights because I spend less time in climb and more time at cruise.

As you already know the numbers refer to length and pitch. Its all math. The Pitch is directly related to inches forward. Using the following formula will give you a close estimate of what your propeller will drag you through the air, of course that is relative to the other drag. The longer prop has more drag. New designs have made improvements in reducing weight and improving performance, but for the age, the following will give you an idea what to expect.

(Pitch x RPM) x 60 =(RPM per Hr) / 12 (Inches in a foot) = Feet per hour / 5280 or 6000 = will give you Miles or Knots per Hour.

Using 2250 RPM works out to the following: 55 = 117 MPH, 53 = 113 MPH, 51 = 109 MPH, 43 = 92 MPH.

Of course length effects the climb performance, (as all length is better performance) if you want to go faster with a long prop you have to increase the rpm, which works out to about 2800 RPM with a 43 pitch propeller to get 115 MPH.

Going from a 76-53 to an 80-42 I lost about 12-13 mph and now flight plan my 170B with 26" Bushwheels right at 100 mph at 2475 rpm. As was pointed out the get up and go from short /tight strips is much better and the trade off is more than worth it to me.