Rich of Peak (ROP) vs Lean of Peak (LOP)/Engine operation

[WebMaster]

Also, the guy from TCM who talked to us at Nashville said that if you are running LOP, you actually get less HP. He had a graph on it. He also said because of the runners for the intake, it was difficult to get even air flow to each cylinder. He said the IO-550 has a much better intake manifold, and is therefore more suited for LOP operations.

Oh, and yes, the warranty is void. Important stuff to folks who have recently installed ReMan engines.

[TGresham]

"Oh, and yes, the warranty is void."

Really?

Did he say this?

I have been unable to find any warranty claims which have been refused due to running LOP.

Does anyone know of a specific warranty claim that was rejected due to running LOP?

[SkyKing]

If you've got money to burn, go ahead and burn up a few pistons on a factory new or reman engine by abusing it with snake oil procedures that are not approved and step right up to the plate. My bucks are on TCM... the warranty will be VOID. It's all in the fine print.

SkyKing

[Walter Atkinson]

There have been some really good comments made in this thread, but there are a few statements that I'd like to address:

1) The main reason to operate LOP is not fuel savings, although that is a really nice thing as 100LL prices go up. The real reason to run LOP is that it is where the BSFC(min) is located, the CHTs are cooler and the ICPs are lower and the enigne is likely to last longer. Any internal combustion engine is happier if these issues are addressed.

2) Quite to the contrary of popular statements, it is MUCH MORE important to have an engine monitor if you operate ROP. This can be easily proven as there is no LOP setting which is harder on the engine than 25-50dF ROP. There is a really neat little presentation we give which demonstrates the reality of this where a clogged injector is concerned. engine monitors are a very valuable tool and I won't fly serious IFR without one any more. I've seen too many engine saves and a couple of lives saved through their use. They tend to pay for themselves all at once! The least value they have is for leaning.

3) I find that LOP operation requires far less engine management concentrationand attention than ROP operation. At the top of the climb I set the mixture LOP in less than 3 seconds and I do not again touch the red knob until I'm back on the ground ready to shut down. How much easier can it be? (Well, I do understand this stuff fairly well, too.) Actually, it's a lot harder to manage an engine ROP. All of the bad things are experienced when ROP. Detonation, high CHTs, high pressures, hottest exhaust valves, highest fouling and dirty combustion chambers... all found ROP.

4) If TCM were to void the warranty on engines run LOP, how would you suugest they handle the TSIO-520BE which is LIMITED to ONLY be run LOP in cruise. NO ROP operation is allowed in cruise on that TCM engine. TCM has never refused warranty claims for LOP operation. Anyone who told someone that is either woefully mis-informed or just plain misleading them on purpose. Recently one of the VPs of TCM gave a presentation at an OEM factory and the thrust of his presentation was that what we teach at Advanced Pilot Seminars is correct and in harmony with the science. He even used some of the terms WE invented. That's cool.

5) I have yet to see anyone make negative statements about LOP operation who knows anything about it. Those statements eminate from the poorly educated or ill-informed. ONce upon a time, I said any of those silly things. I educated myself and I don't say them anymore.

6) I run LOP at 85-90% power. How is that less power than 75% power ROP, the max power settign recommended? Granted, if you are NA, there are some issues which must be understood to make things optimal. In a NA Skymaster I would give up about 3 knots to gain about 5 gph in fuel efficiency while running the engines about 20dF cooler. I call that a good trade. 3 knots will be difficult to measure over the normal flight. what's that worth? 30 seconds? A minute?

6) One day, in the not-to-distant future, Lycoming is going to become very embarrassed by their "Experts are Everywhere" document(which was written about my partner, George Braly). It's not even in harmony with their own data. If you read it carefully, what it really says is that LOP is fine and works, but that pilots are too stupid to do it right. No kidding, that's what it says.

We recommend ROP and LOP operation. Just do either correctly. Most pilots (like me) were trained poorly and operate under terrible misinformation. We are trying to correct that pilot education deficiency.

Just for fun, about seven years ago, we offered a $1000 reward to anyone who could provide any data which suggests that running ROP is better for an engine than the SAME HP LOP. So far, we've still got our money.

That oughta be enough stuff to heat up a thread for a while! <gg>

Walter Atkinson
Advanced Pilot Seminars

[TGresham]

Sky King . . .

Thanks for the invitation to "step up."

I already did. I've run my last five airplanes (seven engines) LOP all the time except for climbs. I'll run ROP when warranted, or LOP when I want. I like to use ALL the options, exercising my PIC decision-making abilities. New engines, custom blueprinted engines, reman engines, and high-time engines. I'm flying only about 300 hours a year, but so far, for a number of years, it's working quite well.

I hear what you are saying, and you say it loudly, but I'm not seeing anything to back it up.

Do you have a specific case where TCM has denied a warranty claim because the engine has been run LOP?

Just one.

I'm not asking for hundreds, or dozens.

One will do.

Would you care to step up?

Tom Gresham

[kevin]

Gentlemen,

I am leaving the recent posts up, because on the whole there is a lot of reasoned discussion in them.

But this macho, tit for tat, "will you step up" crap has got to stop. The purpose of this site is to convey information, not to "win" an arguement, and not engage in what I can't think of a better word than to call a "pissing match". These comments apply to some of the people, but not all, on both sides of the discussion.

Please keep the emotional crap out of this, and discuss the subject as politely as possible. When in doubt, be *more* polite that you think necesary, not less.

If you don't like these requests, please hold the discussion elsewhere. We run this site on a volunteer basis, and I *hate* dealing with this crap and having to write messages like this.

Thank you for your help.

Kevin Mackenzie
webmaster

[TGresham]

Kevin:

Wilco.

I do hope you allow us to ask someone to back up a statement hurled out as a challenge.

Without that, the forum bullies dominate and keep knowledge from bubbling up

A civil conversation is much more likely to result in active participation from those who have been beaten back.

I appreciate your efforts.

Tom Gresham
(who thinks that posting under real names goes a long way toward civility.)

[SkyKing]

Maybe the "SOAP" site should be confined to its original intent, to wit: SKYMASTER OWNERS AND OPERATORS. I don't see anything in the description of what we're about as including Bonanzas, Twin Beech, etc... especially when it's an obvious ruse to sell something.

SkyKing

(And I like my privacy from all the nutcases in cyberspace!

[Walter Atkinson]

Some time back I particpated in this forum after being invited to come offer scientific information about piston engine management. There was a very rude Forum Bully here who went by the moniker of {edited by webmaster, personal attacks not allowed} He was a jerk. I have discovered that the only reason people behave like jerks is that they get away with it and I had better things to do with my time so I quit participating.

Recently I was asked by two Skymaster owners and forum participants to please try again since there was a lot of misinformation being offered with no data to back up the misstatements.

I have always liked Skymasters. They have excellent engines and can be properly operated with excellent results. If you decide that you only wish to talk with other Skymaster owners, then you have just limited your sources of knowledge and expertise.

The members at large can decide whether or not they are interested in science and knowledge or would rather allow an annonymous forum bully (who offers no data) to run people off. It's your call.

I plan to do as I promised your members who asked me to return and try to offer factual information that is in harmony with the laws of physics and is fully measureable and confirmable by any observer.

Please let me know if the members are not interested in that kind of information and if this is a waste of my time.

BTW, I do not recall asking anyone here to pay for any information I have offered. Data-backed information for free. That seems like a pretty good deal for the membership.

Then again, if you are not intersted in that kind of information, I could be wrong.

[Ernie Martin]

Walter:

On yourt last message, the one which is just above this reply, I for one welcome your participation.

I want, however, to address your first message on this thread. And, sorry, Walter, but I'm not buying any of it. Don't get me wrong, I'm a believer. I believe that LOP operation, when done right, reduces fuel consumption with no adverse effects on the engine. But that's all -- I'm not buying the rest of your points in that message.

I won't dwell on all of your points, since the meeting in Key West is a better forum for that, but here is a brief outline.

On the claim of longer-lasting engines, readers understand that we're talking cruise operation, when the component stresses (e.g., temperatures) are so much lower than design limits that the differences are immaterial. To say it differently, the exhaust valve at ROP runs much cooler at cruise than design limits, so running it even cooler at LOP doesn't add life.

Saying that engine monitors are more important to have for ROP than LOP defies logic. To your credit, you and other advocates of LOP admit that proper operation at LOP requires a monitor (or analyzer). While the experience of millions of hours of ROP operation show that the basic guages installed originally is all that is needed for reliable ROP operation of these engines (more on the "robustness" of the engines below).

On LOP being less taxing on pilots, please. The Lycoming experience speaks for itself. And, no, Lycoming is not saying that all pilots are stupid, only that some pilots are lazy, not technically savvy, whatever, and these pilots did screw it up when LOP was the norm. So, since their procedures must account for all pilots, they changed to ROP, the easier, more tolerant procedure.

Your warranty response, citing the TCM TSIO-520BE is misleading, since TCM designed this engine for LOP operation. I see no conflict here. They'll honor a 520 warranty which ran LOP (the recommended mode), but will deny a claim for a 360 which ran LOP (the not recommended mode).

And in the related thread George took issue with my statement to stick with what the manufacturer tells you -- ROP -- by citing other manufacturers like Lancair and Cirrus which approve LOP operation. But this is a Skymaster forum and the readers understand that I was discussing Skymasters.

The other point raised in the other thread deals with the robustness of the engines when operated ROP. As that thread developed, today's second message from Kyle Townsend suggests correctly that these engines can deliver extraordinary reliability at the recommended ROP operation ("robustness" as I put it in an earlier message), provided that they are built with adequate quality control, properly maintained, used frequently, and managed in flight as recommended.

Look, you and George may not see it that way, but I'm not an opponent of LOP. If you happen to own an aircraft eqipped with GAMIs and an analyzer, and you are a technically savvy pilot willing to do LOP engine management in flight, and your engine warranty has expired, then I think you should run LOP. For the fuel savings, not to extend life. If you aircraft is not so equipped, I don't think the fuel savings at today's fuel prices justify buying GAMIs and an analyzer. But maybe soon, when prices are closer to $8-$10 per gallon.

Ernie

[Walter Atkinson]

Ernie:

**On yourt last message, the one which is just above this reply, I for one welcome your participation.**

Thank you. That is very kind.

**I'm not buying the rest of your points in that message.**

That's fine. Shall we take them one at a time for the purpose of furthering our understanding?

**I won't dwell on all of your points, since the meeting in Key West is a better forum for that, but here is a brief outline.**

Unfortunately, I am not going to be able to be in Key West.

**On the claim of longer-lasting engines, readers understand that we're talking cruise operation, when the component stresses (e.g., temperatures) are so much lower than design limits that the differences are immaterial.**

You may wish to look at the data on this. If this were true, jump planes which go to altitude at very high powers and do the slam dunk, never spending any time in cruise would not go to TBO. Most do. A cursery look at the ICP data on a live-running engine is convincing that that assumption, while on the surface being logical, is in error. Cruise powers at 25dF ROP is not necessarily good unless the power setting is quite low.

**To say it differently, the exhaust valve at ROP runs much cooler at cruise than design limits, so running it even cooler at LOP doesn't add life.**

Again, you might want to look at the data on this. According to Lycoming's data and others which supports it identically, the temperature of the exhaust valve is frequently hotter in cruise at 25dF ROP than at full takeoff power. This is particularly true in a Skymaster's rear engine. (notice how skillfully I threw in the Skymaster reference! <gg>) A cursory look at the data on exhaust valve temperature as a function of mixture will confirm this. (ref: 1943 NACA study and 1966 Lycoming data.) There is no need to argue this reality as it has been measured. I have the studied charts if you would like to see them. An exhaust valve at 65% power with a CHT of 375 will be running a lot hotter than the same valve at takeoff power with a CHT in the low 300s. It's in the data.

**Saying that engine monitors are more important to have for ROP than LOP defies logic.**

It does seem to defy the common logic, but it's true. I can prove this to you very easily. Consider an engine which has very good F:A ratios and can be run ROP or LOP and still be smooth. Let's assume we are LOP and an injector becomes partially clogged. The engine will instantly run rough and you will know it--without an engine monitor. Now, assume the same engine is being run ROP--say at 100dF ROP. The same event occurs. The partially plugged injector will place that cylinder less rich; it will run a much hotter exhaust valve temperature. It will continue to run smoothly and unless you have an engine monitor, you will not know that you have a clogged injector. On the next takeoff, that cylinder will not be rich enough and may end up detonating. If you do not have an engine monitor and are a ROP guy, you will not know you have a problem until the engine has a failure of the cylinder. This has been a common problem for years and no one has known it until engine monitors came along. We have a rather large file of these very events. It's not uncommon.

**To your credit, you and other advocates of LOP admit that proper operation at LOP requires a monitor (or analyzer).**

Not those who UNDERSTAND the issue above. The need for an engine monitor has little to do with the mixture being LOP. As a matter of fact, if you do not have an engine monitor it is VERY wise and highly recommended that at least every few flights you set a LOP mixture to be sure everything is OK. (see above example)

**While the experience of millions of hours of ROP operation show that the basic guages installed originally is all that is needed for reliable ROP operation of these engines (more on the "robustness" of the engines below).**

We have a gowing number of cases in our files which show this to have been an erroneous concept on our parts in the past. I used to believe that, but no longer do--since I've SEEN the data coming in. In addition there are about 400 MILLION flight hours of data which contradict that notion.

Your reference to Lycoming is not germain. LOP has not been the norm as Lycoming claims since radial engines went out of service. None of these flat engines have ever been routinely run LOP until GAMIjectors came along (exception being the TSIO-520BE). That statement from Lycoming is disengenous. For other really silly statements from Lycoming I recommend reading the recent lawsuit transcripts. Look for the article in Aviation Consumer soon on this topic. At this time I cannot comment further.

**So, since their procedures must account for all pilots, they changed to ROP, the easier, more tolerant procedure.**

No, they want you to think they changed to ROP. That's not factual. They suggested ROP because their engines would not run smoothly LOP because they have poor F:A ratios. They simply didn't want the complaint department phones ringing off the hook. Lycoming's verbal position is not even in harmony with their own data. Their engineering data is correct and does not support Rick Moffett's current position.

We are unaware of ANY TCM warranty denial based on the LOP issue. If there has been one, we would love to have it cited. We cannot find one. Anyone know of one? We have POHs from almost every engine they have built and have numerous references to LOP being OK... including in Cessnas.

**And in the related thread George took issue with my statement to stick with what the manufacturer tells you -- ROP -- by citing other manufacturers like Lancair and Cirrus which approve LOP operation. But this is a Skymaster forum and the readers understand that I was discussing Skymasters.**

He included Cessna. There is absolutely nothing about the engine in a C-337 that makes it any different than the same engine in any other model aircraft. If you know of a germain difference, I would appreciate you letting me know. How does the engine know it's in a Skymaster?

The other points in your post are personal preference items and not factually debatable. I will repeat, the reason to have an engine monitor has little to do with leaning or saving gas. It has to do with saving your engine and your life. The files are growing weekly with examples of this.

Thanks again for your thoughtful comments. As an engineer (I think you are an engineer, right?) you would be quite amazed to SEE this data for yourself. It is compelling. I can assure you that six or seven years ago, I would have agreed with everything you've said. Looking at the data on real, running engines and operating them based on that experience has introduced me to the taste of crow.

Please understand, we teach that ROP and LOP mixtures both have their place. We recommend methods by which either can be accomplished with performance, safety, and longevity concerns addressed.

[gwbraly]

>>Your warranty response, citing the TCM TSIO-520BE is misleading, since TCM designed this engine for LOP operation. I see no conflict here. They'll honor a 520 warranty which ran LOP (the recommended mode), but will deny a claim for a 360 which ran LOP (the not recommended mode).

And in the related thread George took issue with my statement to stick with what the manufacturer tells you -- ROP -- by citing other manufacturers like Lancair and Cirrus which approve LOP operation. But this is a Skymaster forum and the readers understand that I was discussing Skymasters.<<

Ernie,

I was discussing Skymasters, too. So let me try, again.

It is NOT just the TSIO-520BE that TCM approves to be operated LOP. It includes the TSIO-550, the TSIO-360 (yes, the engine in the Cessna Skymaster!!) and Piper approves LOP for their very most difficult engines (Piper Navajo, 350Hp, non-intercooled, 49" of MP on a hot day, slow turning 2575RPM - - mother of them all). Every Bonanza and Baron POH for the last 20 years includes specific instructions telling the pilot how to operate those IO-550 engines LOP at high power settings.

I understand that you THINK the TCM manual for the TSIO-360 Skymaster engine does not approve LOP operation, but, respectfully, if you come join us sometime at an APS seminar, and be patient with us through the weekend, then about 10 or 11 am on Sunday morning, we have a scheduled course segment during which I will walk you through the relevant portions of that TCM TSIO-360 manual (and several others) and let you see with your own eyes, that your understanding has been in error.

Regards, George

[KyleTownsend]

There is a lot of good information being exchanged on this board, and I welcome everyone and am glad to benefit from your views.

I think that the best arguments for LOP operation are (1) fuel economy and (2) the capability of running continuously at higher power settings.

I think everybody gets the "fuel economy" bit.

Assuming that the engine manufacturers knew what they were doing (and I believe the engineers did, since their charts are accurate), they determined that these engines could run continuously at 75% power using "best power" settings. If I understand correctly, best power is somewhere in the range of 50 to 100 degrees rich of peak egt, and is very close to peak CHT (CHT is pretty flat to the rich side of peak cht anyway, dropping only slightly at full rich). So, by definition, any change in mixture from this setting will result in (1) somewhat less power, and (2) somewhat lower (or the same) cht's. In this sense, using these settings is "idiot proof" (assuming you set the MP and RPM according to the book). In other words, it would be impossible to exceed 75% power, or to make the engine run hotter, by playing with the mixture control.

Of course, what the manufacturers were really doing is establishing a "design point" for continuous cylinder temperatures. I don't think that there is any argument regarding the fact that cylinder pressures are much higher at max power than they are at 75% power, no matter how you achieve 75% power? So at cruise power settings, we are mainly interested in limiting temperatures.

What LOP operations permit you to do is to maintain comparable CHT's and pressures relative to this "design point," while operating at higher power settings (perhaps 85% or so). Or, alternately, you can operate at the same 75% power LOP (at higher manifold pressure), and have cooler CHT's.

This second scenario is where some LOP advocates try to make the case that cooler CHT's translate into longer engine life. This is the part of the argument that I am having a hard time buying. I think we could all agree that 380 degrees is much better than 480 degrees. But that's not what is at question. If you are already running at 380, is 370, or 360 really any better? I kind of doubt that it makes any meaningful difference.

[TGresham]

In making the decision to run ROP ("go fast") or LOP ("go far"), the discussion of fuel savings when running LOP tends to focus on saving money.

Two thoughts on that.

1. Some tend to minimize the savings as been inconsequencial. Well, each of us can decide whether a given dollar amount is important, but to do that, we need to know the dollar amount.

Assume (just grabbing numbers) a 1500-hour run on your engines. Assume, also, a 3 gph saving (using 1.5 gph per engine). That's pretty conservative, and I think it would be more than that. To make the math easy, let's use three bucks a gallon.

Saving $9 an hour for 1500 hours is $13,500. Now we have a number which each pilot/owner can use to decide whether it's important.

2. Much more important to me than the dollar savings is the safety,additional utility, and added speed which comes with extended range.

I seems that no matter what the aircraft is, running LOP in a general aviation plane adds at least an hour of range/time.

For planning, adding an hour of range opens more legal IFR alternates.

In the real world, I like getting to my destination knowing I have a lot of fuel, should the weather go down. I love having two or three hours of fuel I can use to get to better weather.

Speed. Extended range is the best speed mod. Eliminating a fuel stop is like picking up 25 knots. Sure, the true airspeed is lower (5 to 7 knots, usually) but if you can fly over the fuel stop, you avoid a delay of 30 minutes to an hour.

.

[Walter Atkinson]

Kyle:

All of you points a very well taken and IF the original assumption were valid concerning the design issues, I would agree 100%. Let's first get one issue attended to , then we can discuss the design issue.

Best Power is as you correctly describe (about 80dF ROP), but max CHT is not at that point; it is a little less rich than best power. CHT's will actually be a tad cooler at Best Power than at 40dF ROP. A minor nit, to be sure, but we do want to be as acurate as possible in a scientific discussion because what follows is important in that discussion.

As for the concept that the manufacturer was setting design limits on their recommendations, the reality will show that that concept might be giving them more credit than they deserve! <g>

Think back to the heyday of GA... the 1960s. Beech, Mooney, Piper, and Cessna were in a serious battle for sales. The competition was intense. Speed and range were the issues that sold airplanes. The engineers made recommendations on where to run the engines. They resulted in either LOP for range (too slow to sell airplanes in a competitive environment) and ROP for speed (but where the engineers wanted the engines run was so rich that range was poor and that didn't sell airplanes). So what happened?

The MARKETING DEPARTMENT wasn't interested in listening to the complaints about the rough running of LOP on their poorly F:A ratio imbalanced engines. Recommneding that was not an option. The MARKETING Department decided that at 75% power and leaned to best power, or even better to 25-50dF ROP, the range and speed numbers would be the most optimal to sell airplanes. The engineers objected. They said that longevity would suffer. The engine makers objected for the same reason. Then the OEM told the engine mamufcaturer they would buy the engines from the competition if they didn't support this notion. It was a competivie market place. They knew that longevity didn't sell airplanes. Speed and range sells airplanes. So the recommendations are what they are. At 25-50dF ROP, the speed is within a knot of Best Power and the range is much better--longevity take the hindmost. The very worst things on metal are heat and pressure and that is the mixture setting where those are the worst.... but they'll make it through the warranty period OK.

Some realy bad things begin to happpen to Aluminum as it reaches about 400 degrees and we know that staying away from that can be quite beneficial where longevity is concerned. These things tended to happen AFTER the warranty period was up on the longevity scale.

That's the long and the short of why Cessna, Beech, Piper, and Mooney recommend what they do. It was NOT based on engineering. It was based on sales concerns. It's the only answer that makes any sense and until someone comes up with an engineering reason, it's the only thing that explains the recommendations.

Best regards,