Propeller Repitch

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Propeller Repitch

Postby oliverbarth » Wed Jun 13, 2018 8:10 am

I posted it in another forum but I thought it might be worth sharing here too?
My idea was to run the engine just a little bit faster and get the same cruise speed. It seems to work.

I did the repitch from 7653 to 7651. Static rpm went from 2195 rpm (53 pitch) to 2270 rpm (51 pitch).
Speed at 2000ft: 115 - 118 mph indicated but with 2450 rpm (53 pitch) and 2500 rpm (51 pitch).
Speed at 7500ft: 110 - 112 mph indicated but with 2450 rpm (53 pitch) and 2580 (51 pitch).
I am very happy, the airplane (engine) feels no longer like "driving in the high gear". Full fuel, solo gives a solid 800fpm climb (at 25°C), gross weight and 30°C still gives 400fpm climb. RPM was messured with an optical tachometer.

Another plus: At 10.000ft the airplane would slow down when I hit a downdraft. Even with full throttle it took an eternity to accelerate again, because the engine was not running fast enough. This is much better now, at 10.000ft I run the engine at 2600 rpm, which is not full throttle and when I hit a downdraft I just advance the throttle to keep the 2600 rpm and does hardly loose any speed.
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Re: Propeller Repitch

Postby Bruce Fenstermacher » Wed Jun 13, 2018 12:23 pm

Yep, works every time.

But here is the thing. Many can't stand running their engine, hours on end, at the higher RPM. Like they are in 1st gear rather than high gear. And so they don't and they go slower.

And it seems you have one of those slippery 170s that does 115-118 with a 53 pitch prop at 2450. I'm thrilled to see over 110 consistently with mine with same setup. This is why I'm running the 53 pitch even though I operate out of at 1800 ft grass, one way strip. For a few seconds at the start of every flight I wish I had my spare 51 pitch prop installed but that is quickly forgotten as I'm trying to get to the breakfast place in the same half day as by buddies. :lol:

What's all this nutty talk of 7500ft. And 10000ft, that is just crazy talk to a helicopter pilot. 8O
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Re: Propeller Repitch

Postby gfeher » Wed Jun 13, 2018 12:47 pm

I also repitched my prop recently to clumb. It's a 1C172/MDM7655 (standard) repitched to 7653 (climb). I'm very happy with the change. I'm now seeing a solid 900 fpm climbout at SL on standard day, solo with fuel fuel. It takes off about 200-300' shorter on my grass field, again standard day, SL, solo, full fuel. I lost about 5-7 mph on cruise using the same settings I used prior to the repitch (cruise at about 2350 RPM at 2000', standard day), but I don't really care. I don't need to go anywhere quickly. I prefer the shorter TO distance and better climb rate. Now I don't think about the climb rate every time I take off. Repitch was done by Sensenich Propeller Services in Lititz, PA. Nice folks and quick turn around when I did it in April. Not a 180 hp upgrade, but good enough for me.
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Re: Propeller Repitch

Postby ghostflyer » Wed Jun 13, 2018 11:10 pm

You can never have too much altitude . I have found the most economical cruising altitude is 7500 to 8500 ft . Plus it keeps you away from the 2 legged cockroaches that fly from 1500ft to 4500ft and have no ideas of the rules . I often cruise at 10,000ft above looking for the best winds around but have a o2 meter on my finger if I need the o2 hit.
Plus it is sometimes away from the thermals and makes flying a little smoother and so much easier to navigate .
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Re: Propeller Repitch

Postby gahorn » Fri Jun 15, 2018 10:16 pm

gfeher wrote:I also repitched my prop recently to clumb. It's a 1C172/MDM7655 (standard) repitched to 7653 (climb). ...


Just a little nudge... are you certain about that prop model number??.... that it's not a 1C172/EM7655 repitched?

The "original" 8-bolt McCauley DM prop (1A170) was subsequently changed in blade profile to a slightly more efficient/thinner MDM blade, which was copied when the (lighter hub) six-bolt EM series was developed. Essentially, except for hub-weight/crank-flange(bolt#), the MDM and the EM are the same blade profile.
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Re: Propeller Repitch

Postby gfeher » Sat Jun 16, 2018 8:00 pm

Just a little nudge... are you certain about that prop model number??.... that it's not a 1C172/EM7655 repitched?

Yep I'm certain. It's an MDM - item 1(f) on the TCDS.
(Wow, I think George might have been stumped a little bit on this one. :D :wink: )
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Re: Propeller Repitch

Postby gahorn » Sun Jun 17, 2018 1:18 pm

gfeher wrote:
Just a little nudge... are you certain about that prop model number??.... that it's not a 1C172/EM7655 repitched?

Yep I'm certain. It's an MDM - item 1(f) on the TCDS.
(Wow, I think George might have been stumped a little bit on this one. :D :wink: )


Yeah... I'm suff'ring from bran phartts, even more than usual this week. :oops:

Just for clarification... here's the dimensional differences in the two props designs:

1A170 McCauley Blade Dimensions.pdf
(651.7 KiB) Downloaded 665 times


1C172 McCauley Blade Dimensions.pdf
(1.03 MiB) Downloaded 636 times
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Re: Propeller Repitch

Postby gobrien » Tue Mar 24, 2020 4:20 pm

gahorn wrote:
Just for clarification... here's the dimensional differences in the two props designs:

1A170 McCauley Blade Dimensions.pdf


1C172 McCauley Blade Dimensions.pdf


Hey George,

I have an O-300-B from an early 172 going into my 170 rag-wing. It's getting a full overhaul (rebuild) despite being 700 hours SMOH because it took a prop strike. The crank is out of spec and the replacement crank is a yellow tag from an O-300-D.

Follow all that? Yeah, well I had to explain it all to an engineer at the IAA this morning and the next question was confusion about having a 1C172/EM7653 propeller to go on the front, which is not what the type cert for a 170 says and is not matched to a C145 or O-300-A (per the TCDS)!

Using the STC/337 library and especially posts from you and other (like this one with the prop overhaul spec) I was able to pull together all the relevant information and joint the dots and they approved the installation.

This is just one example of how TIC170A is making my project so much smoother and increasing my confidence to keep going!

Thank you!

Gareth.
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Re: Propeller Repitch

Postby Bruce Fenstermacher » Tue Mar 24, 2020 8:15 pm

Gareth,

Let start at the beginning so others in your situation might follow along. The only engines approved by the TCDS for the 170 (not the 170A or B) is the C-145-2 and the 0-300A. Your 0-300B is not approved unless you bought the Associations STC SA01837SE that specifically allows a C-145-2H or 0-300B on a 170 (as well as the other models) The props approved for the C-145-2H or 0-300B are only those props originally approved for the C-145-2 or 0-300A.

You are installing a 0-300D crank in your 0-300B. What you are doing, assuming your are not changing the accessory case and going with the angle starter, by using your B model accessory case and starer, is converting your 0-300B to a 0-300C. Approval to do this comes from Continental M75-6R1 viewtopic.php?f=29&t=2303.

Now one would need the Associations other STC, SA7441SW, which allows the 0-300C (D or E) to be installed on any model 170 (and some 172) and that STC indicates what 6 bolt props and spinners are approved as well at the original skull cap spinner.

Now if in your case Gareth, your aviation authority approved what our STC does in the states (and most other countries) without buying the STC from the Association, you are really ahead of the game and most lucky. Most aviation authorities will not do that including ours in the states today.
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Re: Propeller Repitch

Postby gahorn » Wed Mar 25, 2020 3:01 am

Well, Gareth... I certainly hope I made THAT clear! :lol:

(Thx to Bruce)
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Re: Propeller Repitch

Postby gobrien » Wed Mar 25, 2020 10:22 am

Thanks to both of you! (Bruce, I will update my documentation with those references!)

In Ireland (and I'm pretty sure the UK is similar) we can take a Type Certified aircraft off the register and make it a Permit-to-Fly aircraft if (and only if):
  1. It is a non complex aircraft
  2. whose initial design was established before 1st Jan 1955
  3. and production has been stopped before 1st Jan 1975

ILAS (https://ilas.ie/permit-aviation) explains it well.

This makes it similar to FAA Experimental. However, while STCs and 337 help for reference, they are not required to be assigned to the aircraft; simply that they exist is enough to keep the IAA happy. The IAA deligates ILAS (somewhat similar to the EAA) to do the day-to-day management of the permit system with final authority for registration resting with an IAA inspector. Work has to be approved by an ILAS inspector (typically an A&P - mine is EASA and FAA certified) and its documentation approved by the technical committee. This is all local (national) legislation and outside EASA. The limitations are then the aircraft can fly only in Ireland, the UK and France which have reciprocal recognition of each others permits-to-fly.

I've been really impressed by the system and the people that operate it have been really helpful.

G.
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Re: Propeller Repitch

Postby Kyle Wolfe » Wed Apr 01, 2020 1:21 am

Just curious for anyone who has repitched a prop... I understand that 1” change makes about 25 RPM difference but does a change of 2” really make a noticeable difference or does it take 4” to become recognizable?
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Re: Propeller Repitch

Postby ghostflyer » Wed Apr 01, 2020 6:58 am

I have removed this item at the request of 2 stake holders in the story. I wasn’t passing judgement and my intention wasn’t to offend anybody only educate.
Last edited by ghostflyer on Wed Apr 01, 2020 12:07 pm, edited 1 time in total.
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Re: Propeller Repitch

Postby Bruce Fenstermacher » Wed Apr 01, 2020 9:45 am

Kyle Wolfe wrote:Just curious for anyone who has repitched a prop... I understand that 1” change makes about 25 RPM difference but does a change of 2” really make a noticeable difference or does it take 4” to become recognizable?


I have repitched 2 props. Both McCauleys, one for my Cub and one for my first 170.

The Cub prop was to flat allowing the engine to overspeed in the air. We added pitch. Of course before hand I did lots of research and examined lots of RPM vs pitch vs airspeed scenerios on a spread sheet. Went to sensenich Propeller Service with the prop and talked to them about what I wanted to do. They said that all the rules of thumb are just that. The rules are not perfect. The recommended repitching in small increments with actual flight trials in between. They were right. I wanted 2" of change, we did 1". That prop was so perfect that quite honestly I hated to sell it with the plane.

On my 170, I noted that though the prop was a 7653 standard pitch, it performed rpm and speed wise as if it was flatter or maybe a 7652. Again I did lots of calculations and tracked performance for several years. I then had Sensenich repitch the prop 1" more. I did not tell them to pitch it to 54", just add 1" to what ever they found. RPM and airspeed acted pretty much as I expected and I was happy.

So yes the rules of thumb work. And yes you will note the difference between 1" of change if you track your performance of many flights, not just one.
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Re: Propeller Repitch

Postby gfeher » Wed Apr 01, 2020 1:01 pm

Hi Kyle. When I re-pitched my 1C172 prop 2" (mentioned above in this thread) on my 170B to climb pitch, I saw about a 50-75 rpm increase, as predicted by others I consulted before the re-pitch. While I don't have the exact numbers handy, my recollection is that the static rpm went from near the lower limit in the TCDS for the prop to near the upper limit. As I said, it made a difference to me.

Edit: When I was at my hangar today I remembered to check my records. My actual static RPM ncrease from the re-pitch was 63 rpm. It went from 2267 rpm before the re-pitch to 2330 rpm after, measured with a Tru-tach digital tachometer.
Last edited by gfeher on Mon Apr 06, 2020 12:30 am, edited 2 times in total.
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