ROP vs LOP

[Cyril Gibb]

I know this topic has been discussed ad nauseum, but my curiosity is about WHY people have decided to operate their engines one way or the other. 

Sources of information can be: common sense; personal experience; fellow pilots; the POH; engine manufacturers; AMEs; blogs; historical documents and finally what I call test results. When I mean test results, it's the findings of instrumented test cells.  The best example I've found of that is the test facilities for Advanced Pilot Seminars / GAMI. 

I'm aware of the pros and cons of engine management based on the above knowledge bases, and have decided that LOP is my preference.  Being a retired geek, I find current objective test results to be more compelling than older or more subjective data points. 

*when I use the term "test results" in the questions, I mean the stuff that Mike Busch preaches or what you can read in Pelicans Perch etc. based on instrumented test facilities

[gsengle]

I run LOP in cruise. I do so because the difference between lop and rop can be 4 gph, which is at $5/gallon saves even with slightly reduced cruise speed $20/flight hour or $40,000 over the life of the engine. Aka enough to pay for the overhaul.

I'm at 1978 hours so I think I'll exceed TBO.

My cylinders run cool but not too cool, the engine is smooth. I've yet to hear a credible explanation as to how I'm harming it.

I have a good engine monitor.

This photo is a good illustration of how good the Ovation can be lop. This is lower than I normally cruise, my typical fuel flow is 13gph.

Greg




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[Browncbr1]

Following the advice from others on MS, I have found that my engine is smoother and happier overall if I alternate ROP and LOP. I'll usually run ROP half way, then go LOP for the other half all the way to the ground.


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[carusoam]

LOP @TOC to TPA....  

2gph, roughly speaking, in less FF.

Cleaner oil.

Better CHT.

10KIAS lost flying around at 10k'

Go LOP for the 100% conversion of dinosaurs to noise.

Helps to have FI, and FF with a JPI... (my experience)

I am educated in terms of GAMI spread knowledge.

Best regards,

-a-

Edited April 30, 2017 by carusoam

[Hank]

My carb now runs smoothly up to 25° LOP, but I'm not cruising there until I get a full engine monitor. Hoping for good Oshkosh specials, but unsure what I will remove to make space . . . . SOMEthing has to come out . . . . .

[bonal]

When I lean to rough on my carburetor 180 and returning to smooth according to my not to be to trusted single EGT gauge I'm about 25 degrees lean of peak when the engine smoothes out. What are the thoughts about right at peak. Seems like it's always a discussion of lean or rich of peak. These days not traveling far and have been going pretty easy at around 45 mp + rpm so I know I'm not pushing it.

[pkellercfii]

For most general cross country cruise flight, my preference is LOP largely because I'm a CB. Well, sort of. It'd probably be more accurate to say I'm selective about how I spend money. Spending money enriching the oil companies for avgas isn't exactly my favorite way to spend money. Since I bought a Mooney, and the specific Mooney model I did buy, for altitude performance and economy, in that order, the minor speed loss associated with LOP operation isn't much of an issue. I lose about 15 KTAS out of 155-200 KTAS running LOP, in exchange for about a 3-4 gph reduction in FF, from 13+ down to around 10. That the engine runs cooler and cleaner are added bennies.

That said, I sometimes do run ROP when I'm in a hurry, most often because I'm trying to get ahead of weather, and frequently run at peak TIT. I use peak TIT for what I think of as arrival terminal maneuvering, and for instrument practice, since, for my instrument flying, I'm Mr. Militant about staying instrument current & proficient. As a result, I spend a lot of flying time doing instrument practice with a safety pilot, since I'm located in a desert where there are few opportunities to get actual IMC practice. For that sort of flying, I'm typically running 20"/2300 RPM, which is about 50% power, at peak TIT. Peak TIT at that power level is harmless to the engine, and I've found it to be the most economic way of keeping the engine warm, which is a challenge at that low power setting. Contrary to what I've read in numerous places, my operational experience is that it possible to run an engine too cool, which I would define as CHTs below 300 F. Three years ago I was working hard on my CFII in my own Mooney, which meant lots instrument practice, and so lots of flying time at low altitude, and low power settings, during the winter, which resulted in CHTs always below 300 F. At the annual that spring, my bottom spark plugs came out badly lead fouled, which was something my Mooney expert A&P/IA and I got a bit of a giggle out of, coming out of a normally fire-breathing turbo Mooney. Although my understanding is that fouled plugs by themselves are just a nuisance, frequently fouled plugs can lead to valve guide problems. As a result, I don't run LOP down to touchdown, and, instead, once I'm down to 20" & cruise RPM on descent, I'm also up to peak TIT on the mixture to keep the engine warm. Under those conditions, at best I'll see CHTs in the low 300 F range. YMMV.

 

--Paul Keller

CFI-IA

'89K@RLD

 

[KLRDMD]

27 minutes ago, pkellercfii said:

I lose about 15 KTAS out of 155-200 KTAS running LOP, in exchange for about a 3-4 gph reduction in FF, from 13+ down to around 10. That the engine runs cooler and cleaner are added bennies.

With a turbo, you shouldn't lose any speed LOP 

65% power is the same airspeed whether LOP or ROP.

75% power is the same airspeed whether LOP or ROP.

If you're losing airspeed in a turbo running LOP, you're also running a reduced power setting.

13+ GPH in a TSIO-360 is 75% power ROP. 10 GPH is 65% power, LOP. That's why you're seeing a speed loss going LOP.  It isn't the LOP doing it, it is the reduced power.

[KLRDMD]

25 minutes ago, pkellercfii said:

Contrary to what I've read in numerous places, my operational experience is that it possible to run an engine too cool, which I would define as CHTs below 300 F. Three years ago I was working hard on my CFII in my own Mooney, which meant lots instrument practice, and so lots of flying time at low altitude, and low power settings, during the winter, which resulted in CHTs always below 300 F. At the annual that spring, my bottom spark plugs came out badly lead fouled.

That's a result of running to rich, not too cool. Many people equate cool with rich and there are many instances in which that is true, but they are two separate entities that can be controlled separately.

[pkellercfii]

Ken Reed wrote:

>With a turbo, you shouldn't lose any speed LOP 

I will because I can't run the power settings as high LOP as ROP due to TIT limitations. I limit my cruise TIT to 1600 F, which limits my power settings to 60-70% power, depending on altitude.

>That's a result of running to rich, not too cool.

 

28 minutes ago, pkellercfii said:

Contrary to what I've read in numerous places, my operational experience is that it possible to run an engine too cool, which I would define as CHTs below 300 F. Three years ago I was working hard on my CFII in my own Mooney, which meant lots instrument practice, and so lots of flying time at low altitude, and low power settings, during the winter, which resulted in CHTs always below 300 F. At the annual that spring, my bottom spark plugs came out badly lead fouled.

>That's a result of running to rich, not too cool.

Please provide your evidence and data to back up this claim. My evidence to support my claim that it's the result of running too cool is that I only see plug fouling in spring, after a winter's worth of low CHT flying. I typically pull & clean the plugs once or twice a year outside of the spring annual, and rarely see much of any lead fouling then. Same engine, set same way, run the same way. Only difference is flying in warmer weather, with resulting warmer CHTs.

 

--Paul Keller

 

[gsengle]

Plugs foul because you're too rich...


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[KLRDMD]

6 hours ago, KLRDMD said:

With a turbo, you shouldn't lose any speed LOP 

 

6 hours ago, pkellercfii said:

I will because I can't run the power settings as high LOP as ROP due to TIT limitations. I limit my cruise TIT to 1600 F, which limits my power settings to 60-70% power, depending on altitude.

You aren't going slower because you're flying LOP, you're going slower because you're flying at a lower power setting. You specifically blamed slower airspeed on LOP operations which simply is not true in a turbo.

[KLRDMD]

6 hours ago, KLRDMD said:

That's a result of running to rich, not too cool. Many people equate cool with rich and there are many instances in which that is true, but they are two separate entities that can be controlled separately.

 

6 hours ago, pkellercfii said:

Please provide your evidence and data to back up this claim. My evidence to support my claim that it's the result of running too cool is that I only see plug fouling in spring, after a winter's worth of low CHT flying. I typically pull & clean the plugs once or twice a year outside of the spring annual, and rarely see much of any lead fouling then. Same engine, set same way, run the same way. Only difference is flying in warmer weather, with resulting warmer CHTs.

Google is your friend.

[gsxrpilot]

No one's said it yet so I will. Attend the Advanced Pilot Seminar (APS) class in Ada, OK. I consider myself a "middle class" airplane owner. That means I can afford to own and fly an airplane, but I have to be careful and take care of that airplane and specifically take care of the engine. I can't afford to just throw an engine at it anytime it needs one. I need to make TBO if at all possible. With that in mind, the $1 AMU to attend the weekend long APS class is the best investment I've made in aviation. 

It's not just reading a book, an article, or listening to someone's opinion. It's looking at actual data recorded from many years of testing, AND going out to the test facility and watching tests run live and reading the data that results.

And it's not only getting to TBO... it's also learning how to read my engine monitor. Just this bit has already saved me in maintenance, nearly the cost of the class. It's learning how to listen to my engine and know what it's saying. 

There are plenty of skeptics, but I'm an engineer and therefore understand and believe in Math, Science and the scientific method. 

Science is a thing whether you believe in it or not 

[201er]

1 hour ago, gsxrpilot said:

 I need to make TBO if at all possible. With that in mind, the $1 AMU to attend the weekend long APS class is the best investment I've made in aviation. 

Not going, letting someone like you go and come back to tell us about it, and then flying LOP the way guys like you learned, the $0 AMU to read it on Mooneyspace is the best investment I've made in aviation.

[gsxrpilot]

8 hours ago, 201er said:

Not going, letting someone like you go and come back to tell us about it, and then flying LOP the way guys like you learned, the $0 AMU to read it on Mooneyspace is the best investment I've made in aviation.

Well played Sir 

[Bob - S50]

I run LOP for several reasons:

1.  Saves money on gas.  Same speed on lower fuel flow or a couple knots slower on even lower fuel flow.

2.  Saves money on maintenance.  Less likely to foul a plug.  Less likely to develop morning sickness.

3.  Less crap in the oil from the blowby.

4.  Safer.  Much lower CO in the exhaust.

5.  Better for the environment.  Dumping an extra 1.5 GPH of fuel into the air cannot be good for it.

6.  Improved range or payload.  I can go the same distance on less fuel so I can carry more payload.  Or, for a given payload, I can go further which gives me more refueling options (which saves me more money).

[pinerunner]

I run 100 ROP for higher power settings, which can get me close to the red line in my old E model so I only do that on very smooth days and if I'm in a hurry on a shorter trip. For medium cruise power setting I go LOP both to save fuel and because it's actually cooler on the CHT's for the same power/airspeed (once LOP MP and RPM do not tell you what power you have). I made a point of getting fuel flow added to my UBG-16 and use that to judge power when LOP. I use MP and RPM to judge power when ROP.  At very low power settings I set mixture to get peak EGTs because I want to keep the temperatures up. I'll also use lower RPM's like 1900 (especially in the winter) to try to help keep the temperatures up at very low power settings.

I'm getting ready for my instrument check ride so I've gone back to full rich on downwind to keep it simple and be ready for a go-around. When I'm not being judged by someone (like my new instrument instructor) I pull power until prop goes out of governance then lean until the RPMs drop a little and then add back to get the RPMs back. So at about 2550 RPM I'm at peak with a low power setting, less than 20" MP. From there on I just treat RPMs as the power reading making it simpler just like back in the Piper Cub. That's enough power to arrest descent. I tried going back to full rich on short final but that's a busy time and it's easy to forget and land with it still leaned so you would not have full power for a possible go around. I'm active enough on the mixture that I would think to add the mixture back if I needed to abort my landing at the last moment but it might take a second or two when I want power right now. That's part of why I went back to full rich in the pattern.

I basically buy into everything John Deakins is saying in Pelican's Perch but come up against the question.. How complicated do I want to make it for myself?

[N6758N]

22 hours ago, bonal said:

When I lean to rough on my carburetor 180 and returning to smooth according to my not to be to trusted single EGT gauge I'm about 25 degrees lean of peak when the engine smoothes out. What are the thoughts about right at peak. Seems like it's always a discussion of lean or rich of peak. These days not traveling far and have been going pretty easy at around 45 mp + rpm so I know I'm not pushing it.

You never want to run the engine at peak because that means your cylinders are at their hottest, which is no good for longevity of engine parts. Hence why you should be either lean of peak or rich of peak. In a carbureted C model like you and I have, LOP is NOT an option. Because of the design of the air intake/fuel system on the O-360 the fuel can not be evenly distributed enough to run LOP. I run mine right around 50 ROP.

[KSMooniac]

You never want to run the engine at peak because that means your cylinders are at their hottest, which is no good for longevity of engine parts.

That is quite incorrect. 40 ROP is the absolute hottest setting you can run, which is why 50 ROP is pretty bad too. Peak is far easier on the engine.

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[Browncbr1]

You never want to run the engine at peak because that means your cylinders are at their hottest, which is no good for longevity of engine parts. Hence why you should be either lean of peak or rich of peak. In a carbureted C model like you and I have, LOP is NOT an option. Because of the design of the air intake/fuel system on the O-360 the fuel can not be evenly distributed enough to run LOP. I run mine right around 50 ROP.

Peak is a very good and safe mixture setting as long as your not over 75% or so power setting. It is 50 degree ROP that is the hottest (highest internal cylinder pressure) and most damaging at higher power settings. Below about 60% power, it doesn't really matter what mixture is used, but if you are running 50ROP at a higher power setting, then you'll probably be replacing jugs eventually. My CHTs are cooler at peak compared to 100ROP at the same power setting.

[N6758N]

9 minutes ago, Browncbr1 said:

 

Peak is a very good and safe mixture setting as long as your not over 75% or so power setting. It is 50 degree ROP that is the hottest (highest internal cylinder pressure) and most damaging at higher power settings. Below about 60% power, it doesn't really matter what mixture is used, but if you are running 50ROP at a higher power setting, then you'll probably be replacing jugs eventually. My CHTs are cooler at peak compared to 100ROP at the same power setting.

 

You may be referring to a fuel injected engine, to the OP who posted about a carbureted engine however, LOP is not a good idea. 

[Hank]

47 minutes ago, N6758N said:

You never want to run the engine at peak because that means your cylinders are at their hottest, which is no good for longevity of engine parts. Hence why you should be either lean of peak or rich of peak. In a carbureted C model like you and I have, LOP is NOT an option. Because of the design of the air intake/fuel system on the O-360 the fuel can not be evenly distributed enough to run LOP. I run mine right around 50 ROP.

That was my experience, too--cocked throttle body, partial carb heat and all.

Then I spent two annuals resurrecting my dog house and rebuilding the carb heat flapper up front, and viola! My C now runs smoothly down to about 25ºLOP.

Check around under your cowl, how well does your doghouse seal when you screw it together?

[N6758N]

3 minutes ago, Hank said:

That was my experience, too--cocked throttle body, partial carb heat and all.

Then I spent two annuals resurrecting my dog house and rebuilding the carb heat flapper up front, and viola! My C now runs smoothly down to about 25ºLOP.

Check around under your cowl, how well does your doghouse seal when you screw it together?

Interesting Hank, I never really tried to run LOP in my C because of my A&P schooling as I was taught never to run LOP in a carbureted engine for reasons I mentioned above. I just wanted Bonal to know that it can be risky to run LOP in a carbureted engine without a good engine monitor and healthy baffling. Fuel injected engines vs. carbureted engines are two different animals when it comes to fuel distribution and LOP vs ROP. I do run LOP in the fuel injected continentals that I fly. I spent a lot of time rebuilding my doghouse when I overhauled my engine 2 years ago. I may give it a try though based on your experience. Here is an excerpt from the M20C POH. 

To quote Anthony, "Not an expert, just a commercial, instrument rated pilot and IA with 500hrs in my C."

 

 

[gsxrpilot]

37 minutes ago, N6758N said:

I never really tried to run LOP in my C because of my A&P schooling as I was taught never to run LOP in a carbureted engine for reasons I mentioned above.

 

1 hour ago, N6758N said:

In a carbureted C model like you and I have, LOP is NOT an option. Because of the design of the air intake/fuel system on the O-360 the fuel can not be evenly distributed enough to run LOP.

Many of us who have actually run our carbureted C LOP for many hours will know the above statement is completely incorrect.  Any gasoline piston engine will run LOP as long as all cylinders can be burning fuel at close to the same rate. This is of course often easier with a fuel injected engine. But that doesn't mean it's impossible in a carbureted engine. Any engine needs to be well tuned to run deep LOP. For a fuel injected engine that often means a matched set of injectors from GAMI. In a carbureted engine it often means overhauling the carb, ensuring the doghouse is right, possibly using a little carb heat, and disabling the enrichment circuit with throttle position.

My experience consists of 400 hours in a carbureted C running 25 - 30 degrees LOP, nice and smooth.