Yet Another Prop Question(s)

[edbooth]

Don't trust your tach when doing the static test. Get an optical tester to make sure are spot on. I was really worried about not making static until I tested it with the optical tach and found my mechanical tach was 150 rpm off.

A quick old timer check is to taxi up to a florescent light at night, run up the RPM until the prop appears to stand still. Your tach should read 1800 RPM. Cool However this is not a good tach check as your only checking at one point.

[cessna170bdriver]

I never tried it, but you should also be able to check the tach at 450 (if it will run stably that slow), 514(+), 600, 720, 900 1200, and 1800 RPM. A fluorescent light is essentially a 7200 flash/minute strobe light, so any RPM where the quotient of the number blade passes per minute (RPM x 2 for most 170's) is equal to 7200 divided by a whole number should "stop" the prop.

[GAHorn]

This discussion is degrading into lots of opinion and less fact than what Pdogace requests.
Not to start an argument but, when making RPM comparisons... internal friction has nothing to do with prop performance. 2450 RPM is 2450 RPM regardless of internal friction.... it just takes more throttle to achieve that RPM with a high-friction engine... which brings me to the point of reminding everyone that lots and lots of folks believe that engine performance is affected by which way the tailpipes are facing. Bullshrimp!
(They should fact forward but that has nothing to do with "backpressure" or any other performance issue. It has to do with keeping the cowling clean.)

I only make that comment as an example of how personally-held opinions about prop performance is like opinions about motor oil. It's great argument material and very little fact involved.

Pdog.... the comparison between the two props pitched differently is a relative matter...not a hard, scientifically derived performance guarantee. Even if you wanted to document that difference (which is a project I once planned myself, as I have a cruise and a climb McCauley with which to experiment)... it's such a troublesome project that I have procrastinated until I lost interest in it.
I'd have to find a nice, relatively unoccupied runway, on a standard day (during which the temperature did not change) and spend the better part of several hours, needing a couple of assistants and observers to stand by the runway to determine the exact point of lift-off, using stop-watches and other instruments... not likely any of them being calibrated more than casually.... only to end up with a perception of performance.

Generally speaking, the climb prop will reduce sea level takeoff distances on dry, level pavement by a couple hundred feet. (I base that on observations made when I was a young pipeline pilot....hardly a scientific project.) Unfortunately, one was an all-metal C-140-A and the other a straight, fabric-wing 140. One had an O200 engines of 100 HP and the other a C-90 engine. The 90 HP ragwing lept off the ground with a climb prop....and the boss promptly changed that prop to a cruise prop for economic reasons. The takeoff performance was not as lively but the airplane spent all day on the pipeline cruising along about 5-10 mph faster... and that's about all the science you're likely to get out of an anecdotal conversation like this thread.

(And the comparison of a 76 to an 80 inch prop is not helpful, IMO, because that is such a radical departure from the standard that it's like comparing the airplane to one with an entirely different engine. 80 inch props are rarely in the same category for this installation, and it only adds more uncertainty to the picture.)

So... if you want shorter takeoffs and higher climb rates...go to the climb prop. It's really that simple. For the standard 170 this would be the McCauley DM or MDM 7651...or EM7653, if you have the 6-bolt crank. (The EM series prop is thinner and more efficient and is therefore pitched 2" greater/coarser than the DM or MDM series.)

[Pdogace]

Thanks for the post gahorn. I agree with with you that all the talk about props might be on par with an engine oil discussion. Which from some of the posts I have read on that topic get very spirited. My big picture question has been is there significant performance differences between a climb prop and a cruise prop on the 170 with an o300 engine and a certified prop. From what I can tell its roughly a 5 to 8% increase in cruise speed so I will use some basic logic and translate that to takeoff performance to get a rough guess. So a couple hundred feet shorter takeoff and 100 fpm increase in climb. I thought that with all the advanced aerodynamics and theory in the discussion I was missing something. Like a climb prop would change my world of flying and allow me to do some amazing adventures that I would not have other wise been able to do with a standard prop or a cruise prop. I am in GA, and I do get if I was in high country it could help a little but at the end of the day we have Cessna 170s and in order to change MY flying world it requires more power and lots of $$$$$$$. I will say that I would prefer the cruise prop for the type of flying that I do. On a side note we can't wait to meet all of you next month at the convention. I am bringing the whole family which includes my 5 month old so we are planning a lot of pool time.

[juredd1]

Ok George,

Can you help me out a little bit more? Looking on the net for propellers I am trying to search for things like "McCauley DM" or "McCauley MDM". The TCDS lists "McCauley 1A170", Sensenich M74DR (With an * beside of it), and "McCauley 1C172/MDM" with min and max lengths. So a quick search got me a "McCauley 1A170DM" but the length was 71.5 so since that is below the min length listed in the TCDS then I know that is not for my plane.....right? I guess my point is I could search for hours and not find what I'm looking for if I don't know what to look for. It's not your job to educate me how to search the internet for propellers. Just trying to get an understanding of what I need to look for. Will it usually be listed as a McCauley 1A170 or McCauley DM7653?

Also, I don't see the 80inch props listed in the TCDS. Although it appears some 170's are running them. Is that allowed per field approval? Since you didn't discuss that much in your opinion is that not a good direction to go?

Just trying to learn here, thank you for your patience.

Justin

[pdb]

The STC for the 1A175DM 80/40 prop is available from Kenmore Air Harbor in Seattle.

http://www.kenmoreairharbor.com/stcs.html

The prop is a McCauley available through their dealers and probably from the usual suspects like Aircraft Spruce.

[pdb]

This thread may help you understand the pros and cons of climb props.

http://www.cessna170.org/forums/viewtop ... rop#p50752

[juredd1]

Thanks Pete for the info, much appreciated.

Justin

[GAHorn]

OK Justin, let me give this a short-course attempt.

The McCauley 1A170 prop is a particular blade design/model which can have several versions. The version approved for the C170 aircraft standard engine (C145/O300) is an 8-bolt hub and is a particular variant called the DM. It is a 76" diameter and was usually pitched at 53". This means it would be referred to as a 1A170/7653DM propeller...but colloquially known as the "DM" prop.

McCauley produced a later blade design/model (1C172) which was slightly lighter weight (lighter hub, a good thing) and slightly thinner blade which made it slightly more efficient. This was called their "Modified DM" or "MDM" prop... it's full name being 1C172/7653MDM.

They also produced it to fit the prop-flange of the later version of the O300 engines...the C and D models... with a 6-bolt hub. This was referred to as the "EM" series.... more particularly as 1C172/7653EM.

You will notice that for convenience I've kept all three props at 76" diameter and 53" pitch, as this was considered the "standard pitch", however as refinements came along it was recognized by Cessna that the airplanes of the day (by then, the 172) performed slightly better off the more commonly used pavement runways with a higher pitch and the standard prop went from 53" to 55"... so the props most often encountered were EM7655 (using the common shorthand we all use when we talk about props because we rarely care about the actual type certificate/model designations of 1A170 or 1C172.... we become accustomed to recognizing that a DM prop is a 1A170 design and a MDM is a 1C172 design, and a EM is a 1C172 with a 6 bolt hub.

(Originally a DM 7653 was standard, with a DM7651 a climb prop and a DM7655 cruise prop. The MDM followed the same pitch schedule. The EM series experienced a slight increase performance and was generally given 2" more pitch, so a climb EM would be 7651 thru 7653, a standard would be 7655 and a cruise was 7656. Those increases were intended for the 172 aircraft but that is what is often found when they are imported to the 170 also.)

Soooo... the original prop on 170s were 1A170 DM props. Later props were 1C172 MDM and still later 6-bolt props (usually installed on 172s but still later adapted along with their C/D engines to 170s) are referred to as EM props.

The 170 type certificate specifies the min/max diameter of the DM or MDM props. The same applies to the EM props due to their assignations to the 172 which fathered them.

The 80" props mentioned elsewhere were never factory installed...they were custom modifications which required an STC (Supplemental Type Certificate) before they could be installed on the airplane. I seriously doubt you are interested in an 80" prop and would not recommend it for standard 170 landplanes, but to elaborate, there were some experiments conducted by some enterprising people who thinned the blades still further so that they would "flex" in operation and mimic a prop which changed pitch depending upon RPM and forward speed. Some folks who have them really love them. But if you think the comparison between climb and cruise props are a bit fuzzy and undefined... then consider how further variables added into the mix can get.

In my own opinion, for most operators, it is probably best to stick with the standard blades that have wide acceptance, are easily serviced, require no special paperwork approvals and have wide acceptance. This would be the DM/MDM and EM 7651 thru 7655 props, as appropriate to your crankshaft/engine.

[canav8]

Call Propellerman down in Kissimmee, FL. He usually has one or two props.
1733 Bridgets Ct, Kissimmee, FL 34744
(407) 932-2222

[lowNslow]

Here are the available McCauley props and STC holders. I did not know the 170Assoc. owned an STC for a 80" prop?

[GAHorn]

Here are the available McCauley props and STC holders. I did not know the 170Assoc. owned an STC for a 80" prop?

What is the source for that document?

[lowNslow]

What is the source for that document?

http://www.mccauley.textron.com/pga_propellers.html
Look under "Products" --> "Application Guide"

[Bruce Fenstermacher]

Hmmm. The 1A175DM 80/40 is a prop listed as approved on our STC.

I'm sure it was included to make it clear if you had an additional approval for this prop, it would be ok. But our STC does not specify another approval is necessary and our STC might be construed as being approval enough.

[Kyle Wolfe]

George, did you ever do the prop switch?

If so, results?