What Type of Prop?

How to keep the Cessna 170 flying and airworthy.

Moderators: GAHorn, Karl Towle, Bruce Fenstermacher

User avatar
rnealon1
Posts: 219
Joined: Wed Sep 19, 2018 7:28 pm

What Type of Prop?

Post by rnealon1 »

My '54 170B has a IA170/DM7554 prop. I understand the numbers refer to length and pitch, but what type of prop would this be in terms of cruise/climb/in between?

Thanks,

Bob
Bob Nealon

Southbury, CT
User avatar
Bruce Fenstermacher
Posts: 10313
Joined: Tue Apr 23, 2002 11:24 am

Re: What Type of Prop?

Post by Bruce Fenstermacher »

If this prop was 76" long, conventional thought is a 51" pitch is climb, 53" is standard and 55" is cruise on a 170. But what this really means is that 51" and 55" pitch props at a length of 76" will fall at the the bottom and top of the allowed static RPM range of the TCDS and 53" will be in the middle. There are no pitches specified in the TCDS

Your prop is a 75" prop which is allowed on a 170, minumum length being 74.5". So it is not a standard prop for a 170. You should note that performance numbers in the owners manual are based on a standard McCauley IA170 DM prop.

So let's try to make your apple into an orange so we can compare. Being a shorter prop, your engine can probably spin the prop at a slightly higher RPM than if it was 76". As it is a 54" pitch and slightly more course a pitch than 53", the top end RPM and aircraft airspeed ends up about the same as the standard 76"/53"pitch prop. However acceleration vs RPM will not be the same. A 53" prop would likely accelerate the plane at a faster rate than a 54" though eventually your top speed would end up the same.

Now you may have noticed I used the word probably a lot in my explanation. This is because there is lots more to this. No two propellors of the same dimension and pitch act exactly the same. This is due to many things such as the tolerances allowed building the prop and changes as the prop wears.

If you really want to examine this further talk to a prop shop. They have basic formulas that will ball park a RPM change of an engine if the diameter or pitch of a prop is changed.
CAUTION - My forum posts may be worth what you paid for them!

Bruce Fenstermacher, Past President, TIC170A
Email: brucefenster at gmail.com
User avatar
rnealon1
Posts: 219
Joined: Wed Sep 19, 2018 7:28 pm

Re: What Type of Prop?

Post by rnealon1 »

Hi Bruce,

Thank you very much!

Bob
Bob Nealon

Southbury, CT
User avatar
GAHorn
Posts: 20967
Joined: Fri Apr 12, 2002 8:45 pm

Re: What Type of Prop?

Post by GAHorn »

Bruce Fenstermacher wrote:...
Your prop is a 75" prop which is allowed on a 170, minumum length being 74.5". So it is not a standard prop for a 170. You should note that performance numbers in the owners manual are based on a standard McCauley IA170 DM prop.
...
I'm not sure if Bruce meant what I understood his sentence to say. One "standard" prop for this airplane is a McCauley 1A170. There are others which were "standard" in the sense that they did not require additional approval for installation, and the 1A170 could come in variants which would also be considered "standard", depending upon if you were viewing from the position of McCauley, Cessna, Salesman, or FAA.

I suspect what Bruce meant by "standard" is the one most-commonly installed by Cessna which was the DM7653, also considered a "standard performance" variant (and presumably the one the performance numbers in the Airplane Flight Manual were based upon.) A 7651 was referred to as the "standard climb" and the 7655 was the "standard cruise" models. Other pitches are available and are legal as long as that static RPM limitation is met.

That 1A170 can come in a lot of flavors. The DM identifies certain features which can further refine a 1A170. DM identifies certain aspects/measurements of the hub. It also identifies the profile of the tip (squared-off with radius'd corners at the tip as identified in the McCauley overhaul manual. A 1A170/DF prop would have a rounded tip, for example.) There are several other variables that a 1A170 can come with, and the Type Certificate does not mention them so presumably any 1A170 prop can be installed as long as it meets the other specifics identified such as Bruce mentioned (74.5" - 76" diameter) and within the static RPM ranges specified. (Examples besides the DM are the DF, the L, and the LL, all of which are legal per the T.C. and if the T.C. operating limits are met. The actual pitch of the prop is not limited except as to how it affects the allowable static RPM.

There. More than anyone cares about. Bruce said it more succinctly. :mrgreen:
'53 B-model N146YS SN:25713
50th Anniversary of Flight Model. Winner-Best Original 170B, 100th Anniversary of Flight Convention.
An originality nut (mostly) for the right reasons. ;)
User avatar
rnealon1
Posts: 219
Joined: Wed Sep 19, 2018 7:28 pm

Re: What Type of Prop?

Post by rnealon1 »

Thanks guys, this is exactly the kind of description I was looking for. I now have a lot more information but I am no smarter...

If I do understand correctly I have a prop that meets the TCDS requirements in regard to length, the pitch is a little bit "cruisier" in pitch than the "standard performance" prop, is shorter than maximum length so theoretically allows for higher RPM, and assuming static RPM at max permissible throttle is between 2230 and 2330, all within limits.

Bob
Bob Nealon

Southbury, CT
User avatar
Bruce Fenstermacher
Posts: 10313
Joined: Tue Apr 23, 2002 11:24 am

Re: What Type of Prop?

Post by Bruce Fenstermacher »

I think you have it Bob.

You have a legal prop for a 170 but shorter than most by an inch. Shortening the prop allows more RPM but makes the prop less capable pulling forward and so forward speed would be slower and in effect a slight climb prop. Increasing the pitch to 54" slows the prop down and regains some of the ability for the prop to pull forward moving it the combination closer to what we call a standard prop.

But your prop is not equal in my opinion to a 76" x 53" when your aircraft is slow and accelerating such as in takeoff however at cruise you should see little difference in top airspeed between props. I think we are talking only a small difference in acceleration perhaps most pilots wouldn't notice.
CAUTION - My forum posts may be worth what you paid for them!

Bruce Fenstermacher, Past President, TIC170A
Email: brucefenster at gmail.com
User avatar
GAHorn
Posts: 20967
Joined: Fri Apr 12, 2002 8:45 pm

Re: What Type of Prop?

Post by GAHorn »

To add further to the discussion, I'd like to know if your prop was actually STAMPED on the hub (beneath the spinner if any) as a DM7554... or is it OVER-stamped or RE-stamped to those numbers. Or have you MIS-TYPED or misread it?
If it was originally stamped by McCauley as a DM7554, I cannot say it's a mistake, but I haven't found it listed by McCauley as a propeller they produced. Does it have a serial number? (also stamped on the hub)

I recently was shopping for another airplane, a 172 for a trainer for family members. A good family friend had one for sale and I flew over to Huntsville, TX to look at it. The logs indicated a prop that was not legal for a 172.

It had been overhauled two years previously by a prop shop in AZ. The datatag showed the prop-model that was logged onto the airplane. My friend's A&P/IA also logged that prop model (which was incorrect) onto the airplane. So, according to logs, the owner/pilot, the A&P/IA, and the Prop shop ALL HAD LEGAL ISSUES with regard to that prop, which had been flying on that airplane for more than two years!

So we pulled the spinner off and looked at the prop hub and found the aircraft logs had mistakenly entered the incorrect prop onto the airplane. Further investigation proved that the prop shop in AZ had MISTAKEN the identity of the prop and logged the incorrect prop model into the prop records and onto the "yellow tag" (8130-1).

Now the question was: Did they use the incorrect data to overhaul a prop to the wrong specifications? If they'd used data for a different prop/blade design to reshape the prop then everyone has a problem. His A&P/IA who had reinstalled it on the airplane ALSO has a problem for installing an incorrect prop on a 172.

Contacting the prop shop, they agreed to take the prop back into the shop for inspection, and it was determined that the prop actually met the correct design and the error was in the identification. It was actually a 1C172/MDM7653 prop which had been misidentified ONLY on the PAPERWORK!
But consider this: What if there'd been an accident? What if that accident was loss of the propeller when it hit the water?

(I turned down the airplane for my purposes, and two months later my friend had his prop problem resolved at the expense of the prop shop and the labor expense of his A&P/IA...and at the owner's expense of loss of his airplane for two months which cost him two sales opportunities and two more months of hangar rent.)

Back to YOUR propeller: Are you certain of the model prop installed on your airplane? You might wish to inspect the prop hub.
C170McCauleyApps.pdf
Notice who owns the STCs for some of these props
(210.22 KiB) Downloaded 913 times
'53 B-model N146YS SN:25713
50th Anniversary of Flight Model. Winner-Best Original 170B, 100th Anniversary of Flight Convention.
An originality nut (mostly) for the right reasons. ;)
User avatar
ghostflyer
Posts: 1390
Joined: Mon Apr 21, 2008 3:06 am

Re: What Type of Prop?

Post by ghostflyer »

This a major issue on many owners about conformity with the TDCS . When a aircraft comes into the shop the TDCS is printed off for that aircraft and placed with the paper work. . Surprise , surprise , the number of non conforming aircraft will astound you. All having the issues that George was confronted with. We had a near new Cessna 182 come into the shop for a first 100 hly. It was having pitch control issues with the prop. Incorrect part number fitted , wrong prop hub . So it’s a warranty job. Back to the dealer about the issue . Total disbelief by all ,130 photos later including the log book . It had been written up as fitted by Cessna. A complete new propellor and governor turned up and the old one shipped back . Why did this happen ???? Or how did it happen?? Where is quality control?? A report was written out and sent to the appropriate authorities. Still no answer after 14 months . I did note that Cessna raised a SB.on the issue . Plus there was seven signatures in history saying the aircraft was airworthy.
User avatar
ghostflyer
Posts: 1390
Joined: Mon Apr 21, 2008 3:06 am

Re: What Type of Prop?

Post by ghostflyer »

The “worse “ one that we have encountered of non conformity was a Beechcraft sundowner . It had a bad prop strike which had destroyed the engine ,prop. And nose gear . The insurance assessor was looking over the aircraft and called me over . He said the log books do not match what’s fitted with the aircraft . I told him it was the first time it had been in our shop. This was the first time I had looked at it. It had a 200 hp engine fitted [IO-360 Lycoming ] and it had been plugged in the crank shalf and fitted with a fixed pitch prop. Plus the nose gear had came from another Beechcraft sundowner model . A “home made” exhaust was fitted. Some of the rippling on the under side which looked very old suggested that this wasn’t the first time this had a bad landing. The assessor wrote a 14 page report and said we are not covering this . No insurance .
A copy of the report was sent into the authorities and to the owner. The owner had purchased the aircraft a couple of months earlier with the help of a motor mechanic mate . The aircraft now sits down in the grave yard and is slowly disappearing with parts “falling off during the night”.
User avatar
rnealon1
Posts: 219
Joined: Wed Sep 19, 2018 7:28 pm

Re: What Type of Prop?

Post by rnealon1 »

Hi George, I only know what the propeller logbook says; I will have to see what is stamped on the hub. Thanks to all for the information.

Bob
Bob Nealon

Southbury, CT
User avatar
rnealon1
Posts: 219
Joined: Wed Sep 19, 2018 7:28 pm

Re: What Type of Prop?

Post by rnealon1 »

gahorn wrote:To add further to the discussion, I'd like to know if your prop was actually STAMPED on the hub (beneath the spinner if any) as a DM7554... or is it OVER-stamped or RE-stamped to those numbers. Or have you MIS-TYPED or misread it?
If it was originally stamped by McCauley as a DM7554, I cannot say it's a mistake, but I haven't found it listed by McCauley as a propeller they produced. Does it have a serial number? (also stamped on the hub)

Back to YOUR propeller: Are you certain of the model prop installed on your airplane? You might wish to inspect the prop hub.
C170McCauleyApps.pdf
Hi George (and all),

I finally got to look at the hub, it is indeed stamped "DM7554" "1A170" "Serial No. 61529". Not sure what this means, I also cannot find it listed as a McCauley prop.

Thanks,

Bob
Bob Nealon

Southbury, CT
User avatar
rnealon1
Posts: 219
Joined: Wed Sep 19, 2018 7:28 pm

Re: What Type of Prop?

Post by rnealon1 »

Hi George (and all),

As a little more follow up I called McCauley about this prop model. Although there is no explanation for why it is not listed in the Application Guide, it does meet all of the specifications of the TCDS for the aircraft, engine, and for the prop, including the static RPM.

Thanks,

Bob
Bob Nealon

Southbury, CT
User avatar
sgrimsley2717
Posts: 20
Joined: Sat Feb 12, 2005 7:41 pm

Re: What Type of Prop?

Post by sgrimsley2717 »

Fellas,
The Airplane Specification No. A-799 document which we should all be carrying in our airplanes lists both the 1A170 DM series and the 1A172 MDM series propellers. Both of these propellers have the 8-bolt hub to fit on the older C-145 / O-300A crankshafts. The pitch for the full 76 inch diameter propellers are DM7647 seaplane, DM7651 climb, and DM7653 standard pitch. There is no listed cruse pitch for the DM propellers. The later MDM series propellers for the 172's are 3 pounds lighter than the DM propellers and are pitched slightly higher and still can make the static RPM limits. The MDM propellers are MDM7653 climb, MDM 7655 standard, and MDM 7656 cruse pitch. I wasn't able to find a seaplane pitch designated for the MDM propellers. All of these propellers are still available from McCauley new however, it appears that they are made to order only with a 4 to 6 week delivery schedule. Please be aware that the crankshafts that these propellers fit on has been out of manufacture for 40 years. One interesting note. The McCauley propellers use to be made in Dayton, OH back in the 1950's. These early propellers were made with 76 1/8 inch diameters. I have one of these vintage propellers from when our airplanes were made. I got it at the auction in Cody last year and it is full diameter with good squared off tips but it has some nicks on the back side near the hub that may make it just a polished wall hanger even though the leading edge looks very good. Only a prop shop can make the determination. Steve Grimsley #3204
Attachments
Dayton manufacture DM7653 propeller.
Dayton manufacture DM7653 propeller.
User avatar
RealCowboyPilot
Posts: 8
Joined: Sun Mar 13, 2022 2:13 pm

Re: What Type of Prop?

Post by RealCowboyPilot »

My flight to Oshkosh this year was very slow ! I was told by the IA during my annual that I had a climb prop. ( Im still green behind the ears on all this airplane stuff.) Anyway I checked for myself the stamp on my prop this week and it was stamped DM7648. It will get off of the ground very well but is extremely slow. I like that part. Question is what is y’all’s opinion on having 2 props ? Keep my climb prop and buy maybe a DM7653 for cross country trips?
User avatar
Bruce Fenstermacher
Posts: 10313
Joined: Tue Apr 23, 2002 11:24 am

Re: What Type of Prop?

Post by Bruce Fenstermacher »

RealCowboyPilot wrote:My flight to Oshkosh this year was very slow ! I was told by the IA during my annual that I had a climb prop. ( Im still green behind the ears on all this airplane stuff.) Anyway I checked for myself the stamp on my prop this week and it was stamped DM7648. It will get off of the ground very well but is extremely slow. I like that part. Question is what is y’all’s opinion on having 2 props ? Keep my climb prop and buy maybe a DM7653 for cross country trips?
The DM7648 is a seaplane prop, not a climb prop. Likely it is not legal on anything but a seaplane because a 48 pitch would allow a static rpm higher than is allowed for a landplane. The static rpm ranges for the 1A170 are Landplane: Not over 2330, not under 2230, Seaplane (Models 170A and 170B): Not over 2525, not under 2300.

So, I'd be looking for a 7653 or at least one with a pitch in the range of 51 to 55.

Of course, IF your static rpm is within the limits for a landplane, you have another issue, besides the prop when you figure that why your engine can't spin that prop too fast. And I'm assuming you don't actually have a seaplane 8O .

As for having 2 props, I can say about half the time I've owned an airplane I've had two props I could install. I even had a Sensenich 73BR-50 and 2 1A170s of different pitches to choose or 3 different prop performances. Other than once for curiosity I never switched props. I doubt you would ever reinstall the 7648 after flying behind a 7651, 53 or 55.

You might have your 7648 repitched. to 51. But that is a significant change I'm not so sure you can even have made. Your 7648 is probably worth more as it is though I can't say what the market is for a 7648 seaplane prop.
CAUTION - My forum posts may be worth what you paid for them!

Bruce Fenstermacher, Past President, TIC170A
Email: brucefenster at gmail.com
Post Reply