RPM restriction - is brief operation within it on final a problem?

[LeRoy Johnston]

I have a 1996 M20J MSE with the McCauley prop and the rpm restriction.  The restriction area is right where I want my power during short final.  I want to operate there for about 20 - 30  seconds.   Do you think that will damage the engine?   The book says avoid continuous operation there, but that seems a little vague.  You have to pass through that range to operate the engine.   Thanks. --LeRoy Johnston

[Ragsf15e]

There are lots of opinions on that.  My F has a restriction (mcauley 3 blade and A1A engine) that works out right about where you need it set on ILS final with gear and T/O flaps.  Personally, I avoid it when possible but don’t worry about it when in the pattern or landing.  So I won’t cruise in it or do radar vectors for an approach but I will be there on final.  I’m sure someone will chime in with more insight.

[DCarlton]

47 minutes ago, Ragsf15e said:

There are lots of opinions on that.  My F has a restriction (mcauley 3 blade and A1A engine) that works out right about where you need it set on ILS final with gear and T/O flaps.  Personally, I avoid it when possible but don’t worry about it when in the pattern or landing.  So I won’t cruise in it or do radar vectors for an approach but I will be there on final.  I’m sure someone will chime in with more insight.

I have the same prop/engine combo.  If I notice a vibration I don't like, I might make an adjustment on final but don't typically watch the numbers on final or in the pattern.  Perhaps I should?  Looking forward to other opinions and will pay more attention to the numbers next time I fly.  I do have one major issue; my RPM restriction placard is misspelled.  :/   

[Marauder]

I have the same prop/engine combo.  If I notice a vibration I don't like, I might make an adjustment on final but don't typically watch the numbers on final or in the pattern.  Perhaps I should?  Looking forward to other opinions and will pay more attention to the numbers next time I fly.  I do have one major issue; my RPM restriction placard is misspelled.  :/   

If you read several of the ADs and service bulletins related to these limitations, the main concern is not for short term usage but for continuous operation in the limited range. These ADs and bulletins talk about making sure the tachometer is calibrated correctly to avoid cruising in the restricted range.

Like rags and you, there is no way I can fly an approach without being in the limited zone. I have always taken this restriction to mean not to fly a long flight sitting in the restricted zone.


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[Hank]

10 minutes ago, bluehighwayflyer said:

Same here.  I don’t cruise in the restricted range but I totally disregard it when landing.  No ill affects noted.

 

Me too? Me neither? I generally enter the pattern at 2300 and whatever MP gets me down below flap speed, Vfe = 125 mph. After that, I'm generally too busy to watch the tach on the right side, but my red zone is 2000-2250. Ain't had no problems in 800 hours so far . . .

[N201MKTurbo]

I try to avoid operating in the yellow arc. I can land without using that RPM range. I can feel the vibrations. It is torsional so it won’t shake your engine the way most vibration will.  It puts excessive stress on the crankshaft and propeller. If you want to baby your engine, don’t operate in that range.

[Bartman]

We all do our best to avoid the restricted RPM range, but it cannot be eliminated. When VFR I often use 2,000 rpm in that last mile until short final which puts me a little fast, and cut to idle and glide much farther than when I was training in the Cherokee or the 172. That’s the best option I have found. If it is an IFR approach I fly the speed and glideslope don’t worry about the RPM restriction nearly as much. 

[David Lloyd]

9 hours ago, LeRoy Johnston said:

I have a 1996 M20J MSE with the McCauley prop and the rpm restriction.  The restriction area is right where I want my power during short final.  I want to operate there for about 20 - 30  seconds.   Do you think that will damage the engine?   The book says avoid continuous operation there, but that seems a little vague.  You have to pass through that range to operate the engine.   Thanks. --LeRoy Johnston

No, being in that range on an approach will not hurt it.  Continuous operation refers to a cruise setting.

[N201MKTurbo]

14 minutes ago, David Lloyd said:

No, being in that range on an approach will not hurt it.  Continuous operation refers to a cruise setting.

Who would ever cruise in that range?

[David Lloyd]

1 hour ago, N201MKTurbo said:

Who would ever cruise in that range?

The same logic applies to a NOTAM for a 180' unlighted tower 5.3 miles from an airport.  Who would ever do that?

[N201MKTurbo]

We are free (well, we used to be) here in the USA. You guys bought and paid for your engines, you can operate them any way you like.

[cferr59]

I was concerned about this for my C model so I called Lycoming.  They basically said that it is ok for short periods of time like landing or transitioning power settings, but to stay out of it during cruise.  Given that, I try to stay out of it all times except when landing and avoid it on landing if practical.

[steingar]

I used to worry about it, now I don't.  Just don't run the prop in the restricted zone in cruise. 23 squared is a good power setting for lots of cruise flights.

[LeRoy Johnston]

I appreciate all your comments.   Thank you so much.  This is a great forum.  --LeRoy

[OR75]

I changed to the scimitar prop and the yellow arc is gone . 
before that , above the yellow arc on the long approach and idle as I get close to rwy threshold. Acts like speed brakes
what I am saying is that you just need to feel what traction the rpm gives  

[Skates97]

My POH refers specifically to cruise settings in that range.

[PT20J]

The restriction is actually "Avoid continuous operation between 1500 and 1950 rpm with power settings below 15" Hg manifold pressure."

On my airplane I find that instrument approaches flown at 90kts with flaps 15 require about 15 in and keeps the rpm above the yellow arc.

For pattern work I reduce throttle abeam the numbers until the rpm is at the bottom of the yellow arc and slow to about 70-75 and set full flaps. I try to plan my base and final turns without adjusting power and on final I do whatever I need to maintain about 65 kts and glide path.

Skip

[jaylw314]

48 minutes ago, Skates97 said:

My POH refers specifically to cruise settings in that range.

To the C guys chiming in, as @PT20J noted above, the J's have a very different caution range from the C's.  The caution range is obviously not for any kind of cruise setting  

When I had the Macauley prop, I just made a point of mostly ignoring it since it would happen only briefly in the pattern.  The only sustained time might be a long descent, so I would keep RPM's above 2000, which usually worked fine.

Since then, I've replaced it with the Hartzell (Top Prop) which has no restriction.  I have to admit, it's pretty cool making fast descents with the prop at 1800 RPM!  You can get down in a hurry that way without any cooling alarms going off on the engine monitor.

[Skates97]

27 minutes ago, jaylw314 said:

To the C guys chiming in, as @PT20J noted above, the J's have a very different caution range from the C's.  The caution range is obviously not for any kind of cruise setting  

When I had the Macauley prop, I just made a point of mostly ignoring it since it would happen only briefly in the pattern.  The only sustained time might be a long descent, so I would keep RPM's above 2000, which usually worked fine.

Since then, I've replaced it with the Hartzell (Top Prop) which has no restriction.  I have to admit, it's pretty cool making fast descents with the prop at 1800 RPM!  You can get down in a hurry that way without any cooling alarms going off on the engine monitor.

Yes, different range for the J's, same wording about continuous operation. Posting the C POH is just showing the reference to cruise power that you mention above, which doesn't seem to be spelled out in the J POH. However, this topic comes up a few times every year as new people join the board with people essentially asking the same question and not understanding that "continuous" is talking about a cruise setting.

 

[jaylw314]

16 minutes ago, Skates97 said:

Yes, different range for the J's, same wording about continuous operation. Posting the C POH is just showing the reference to cruise power that you mention above, which doesn't seem to be spelled out in the J POH. However, this topic comes up a few times every year as new people join the board with people essentially asking the same question and not understanding that "continuous" is talking about a cruise setting.

Again, the J POH adds more distinction as the recommendation about the caution range is in the DESCENT part of the Normal Procedures, not the CRUISE section, so the confusion is understandable.  In any case, you're not going to get very far in cruise with an MP of 15" and RPM of 1950

[N201MKTurbo]

44 minutes ago, jaylw314 said:

 In any case, you're not going to get very far in cruise with an MP of 15" and RPM of 1950

Oh, you will go quite far, just not very fast!  The cars will be passing you.

[Hank]

52 minutes ago, N201MKTurbo said:

Oh, you will go quite far, just not very fast!  The cars will be passing you.

At 12,500 my C is supposed to do 155 mph at 19.8"/1950 (the only power setting shown for 1950), down to 128 moh at sea level. The next lowest power settings are 16"/2300 for 145 mph, losing about 4 mph per inch reduced. 

But I find the controls mushy there. To fly slow comfortably, like on plane ride day with 172s and Cherokees, I generally keep 2300 and just reduce throttle to ~110 mph.

Are Js really that much slower?

[N201MKTurbo]

21 minutes ago, Hank said:

At 12,500 my C is supposed to do 155 mph at 19.8"/1950 (the only power setting shown for 1950), down to 128 moh at sea level. The next lowest power settings are 16"/2300 for 145 mph, losing about 4 mph per inch reduced. 

But I find the controls mushy there. To fly slow comfortably, like on plane ride day with 172s and Cherokees, I generally keep 2300 and just reduce throttle to ~110 mph.

Are Js really that much slower?

We should find out. You go fly at 1950 and 15" and I'll go fly at 1950 and 15" and we will see who trues out the fastest. A race would be more fun and farer because we would be flying in the same air. Why don't you meet me at KCHD and we will go out and do it.

[Hank]

12 minutes ago, N201MKTurbo said:

We should find out. You go fly at 1950 and 15" and I'll go fly at 1950 and 15" and we will see who trues out the fastest. A race would be more fun and farer because we would be flying in the same air. Why don't you meet me at KCHD and we will go out and do it.

Somewhere in the DFW area would be "meeting in the middle," and about a full-tank range for me unless I flew at 20"/1950, which extends my range from my normal ~800 sm to 1000 sm plus 45 minute reserve, if I make the trip at sea level . . .

[EricJ]

3 hours ago, jaylw314 said:

To the C guys chiming in, as @PT20J noted above, the J's have a very different caution range from the C's.  The caution range is obviously not for any kind of cruise setting  

One difference is whether the crank has the dynamic counterbalances or not.   J models do have them, so they're potentially more sensitive to conditions that disturb the counterweights.    Lycoming SB245D talks about it a bit, including why it is more problematic at low Manifold Pressure, and SI 2012L talks about it as well.   The yellow arc torsional vibrations are not created equal even across Lycoming four-cylinders for this reason.

I have a Hartzell Top Prop that deletes the restriction, presumably because it is a heavier propeller, but I still avoid the yellow arc except on final, where I'm kinda never looking at the tach.