Engine Analyzer
 

(Note from webmaster: This thread has been split. Please answer the rich of peak/lean of peak questions here, and engine analyzer questions in this thread:

http://www.337skymaster.com/messages...&threadid=1209

Thank you.)


I am the new owner of a NA 75 337 with GAMI jectors and JPI 760 analyzer which I am trying to sort out. Anyone with this setup or similar who might be able to give me feedback on their experiences, settings etc., would be appreciated. I have been reading a little about the raging debate on LOP and ROP and will be attending an Advanced Pilot Seminar at GAMI facility. Anyone have any comment on this topic? With fuel at $3.60/gal, in the US Virgin Islands where I live, I sure am inclined to go LOP. Any 337 owner visiting St. Thomas in the USVI is welcome to give me a call for a sightseeing tour in return for pearls of wisdom. More questions to come.
Regards,
Nick Bailey
nickbailey23@hotmail.com

I have been running my NA engines LOP for years.
Bob

Nick:

Arguably, this website was created partly as a result of a vociferous argument on ROP vs LOP on another website. I'm a mechanical/aerospace engineer (MS Caltech) who attempted -- unsuccesfully -- to mediate the discord. You can read the for-LOP arguments in GAMI's website (I attended a mini-version of their seminar and had an opportunity to discuss it with their people).

Here's my take, for what it's worth, and I should alert readers that my views have changed a bit since my GAMI visit and given the escalating price of fuel (I fly the Bahamas a lot, where fuel is the same as in the Virgin Islands).

For the average pilot (read: not technically savvy) with standard instruments and unwilling to give added attention to engine management in flight, stick with the POH directions to operate at ROP (typically 50-100 degrees ROP).

Those who are technically astute (you don't have to be an engineer or a mechanic, just someone who is technically inclined and understands the subject), who have installed GAMI injectors for smooth operation across all cylinders at LOP, who have cylinder-by-cylinder engine management/monitoring equipment, who are willing to to give a bit more attention to engine management in flight, and whose engine is no longer under warranty (notice this new point) can run LOP at cruise, and I think they will benefit from it.

BTW, 6 years ago I cruised the Virgin Islands for a week on a rented boat (something between a yacht and a trawler) with 3 other couples and loved it. My favorite: the Baths at Virgin Gorda. Would love some day to see the islands from the air, so I might take you up on your offer.

Ernie

The website page below has a Lycoming technical paper on operating lean of peak (LOP). It's "must read" for anyone planning such operation. The website was listed in the other Skymaster message board.

http://www.lycoming.textron.com/supp...ps/SSP700A.pdf

Ernie

For completeness, it's worth reading Deakin's rebuttal to the Lycoming paper.

http://www.avweb.com/news/columns/182131-1.html

By the way, Peter Garrison mentions this subject in his November 2004 Flying column.

Nick Bailey has started a more recent thread entitled "Advanced Pilot Seminar" which deals in part with LOP operation. If they haven't done so already, readers of that thread are encouraged to also read this thread, especially the two references cited immediately above this message.

Ernie

I've been running my engines LOP for a year now. Panel includes the JPI as well. Run the front 50 LOP and rear 75-100 ROP. Fuel flows

8.5 front
10.3 rear

Pretty amazing. Head temps on my bird has never been above 410 yet. JPI with the EGView program is just like having a black box. I have every second of data from every flight from the last 250 hours. Neat program.

Richard:

Just curious. Why do you run one engine LOP and the other ROP?

Mark

Peak, ROP, LOP.....
 

Richard,
Do you have have GAMMI injectors? If you do, how close in degrees are the EGT's during lean find mode? I have a JPI and run at peak when at 65% or less which is usually #5 or #6 cylinder on either engine. Not sure exactly but I think there is about 100 degrees difference in EGT's between hotest and coolest cylinder. guy....

I do have Gami injectors. Looking at my last flight.

Front engine:
Lowest EGT = #1 @ 1398
Highest EGT = #4 @ 1424

Rear Engine
Lowest EGT = #1 @ 1373
Next to Hightest = #4 @ 1433
Highest EGT = #5 @ 1475

I'm having some tuning issues with the rear engine #5. Too lean.

Guy,

The absolute temps for EGT's are actually not very important. Among other things, a difference in probe placement introduces some variations.

What matters is where they are relative to peak. In an ideal world (or with the aid of GAMIs), all EGTs would peak at nearly the same fuel flow. If the spread is too wide, it means some cylinders are much richer than others. Let's say you want to run 125 dROP, then your leanest cylinder (the one that peaks first) should be set to that temp. This means that your richest cylinder might be 225 dROP - which is clearly just wasting gas - perhaps to the tune of 1 to 3 gallons per hour.

If you wanted to run LOP, a wide EGT peak spread would imply that's not possible. A cylinder's not going to run much leaner than 100 dLOP. So if your target was 50 dLOP (for the richest cylinder), that means the leanest would be at 150 dLOP - and would not be producing power. LOP operation requires all cylinders to peak at nearly the same fuel flow. So if you set you’re your power such that the richest cylinder was 50 dLOP, then the leanest might be 80 dLOP. All othes would be between those numbers.

Kevin is right on about EGTs. important thing is CHTs in terms of engine life. EGTs are for reference only, absolute temps do not matter much except as giving info about the timing of the combustion event. Cool CHTs are supposed to translate to longer engne life, and more importantly if they are cool LOP. ROP operation is typically not as clean a combustion event, not to mention the much higher fuel flows. Empirical Data supporting this was shown at at the AP Seminar. But as Kevin mentioned in the APS thread, the worst place to operate an engine is typically in between ROP and LOP. Most of the engine manuals actually call for operation in this "red box" which actually makes for higher CHTs, and much higher internal combustion pressure (IPC), which shortens engine life. This is because as Kevin mentioned, factory injectors are so poor that the cylinders vary wildly in fuel flow. Hence a typical factory engine, without signifigant tinkering, swithcing of injectors etc, cannot be run LOP. Do the GAMIS make a difference? The AC I bought had them installed already so I can't say. One thing you notice with Gamis is as you lean, engine does not ever start missing cylinders. It just loses power and then all cylinders stop working at the same time. Best test i've had so far regarding fuel flow, is a 450 mile round trip at 7000-8000 ft. and engines averaged about 8.3 gals each at cruise, 2300 RPM, wide open throttle (21 In rear, 22 In front), 149-152 TAS. CHTs were 310-340, oil about 180 front, 195 rear. I was hoping to hear from other owners about their numbers. If you fly 200 hours a year and the GAMIs can save you 4 gals an hour, plus clean plugs, clean engine, potentially longer engine life due to cooler cleaner running, they may start to look more attractive. another thing i have never had a problem with is hot starts, and i wonder if the GAMIs have something to do with that too... Would like to hear more from other owners with monitors and Gamis...

Really Interesting Info
 

Kevin M. mentioned John Deakin's rebuttal of the Lycoming paper earlier in this thread.

I recently went over to the avweb.com site and read most of Deakin's articles on engine management (he writes "Pelican's Perch" under the columns section - look for the Pelican's Perch index).

All of this was incredibly interesting. Deakin is unabashedly a LOP advocate. He backs up his arguments with a lot of very good data (much of which comes from GAMI). If you want to get a "full dose" of the rationale behind LOP operation without having to go to a seminar, these articles are the best source that I have found. I highly recommend them.

On the subject of LOP operation, I am going to summarize my current understanding of the subject, as it would apply to operating a P337 in the real-world. I would like to hear from any of you that are knowlegable on the subject if you detect in errors in my thinking.

1. The main argument for running LOP is that you can save around 10% on fuel at the same effective power setting (same BMEP). Secondary arguments are that LOP operations are cleaner, and therefore better for the engine and the environment, and that peak cylinder pressures and temperatures are also lower.

In a P-skymaster flown 100 hours per year, this would translate into approximately 250 gallons saved per year, or around $750 on fuel costs (about $7.50 per hour). There is the potential for further savings resulting from cleaner running and having good engine monitoring (eg: spotting problems early). These savings could be substantial, but are difficult to quantify.

2. The main impediments to running LOP are that (1) the air/fuel distribution to individual cylinders varies too much and, therefore, they peak at different times. So, if you lean enough to get the richest cylinder running LOP, the leanest cylinder will probably be too lean to run properly, resulting in rough operation. This is the problem that GAMI injectors are designed to solve.

3. The secondary impediment to running LOP is that you need good instrumentation to make sure that each individual cylinder is running within appropriate temperature limits even if you have GAMI injectors, because there is still some variability between cylinders. This problem is solved by getting an engine monitor (eg: JPI).

4. While some people do climb LOP, most people restrict LOP operations to the cruise mode of flight. To implement LOP in cruise, the power is set at some known level (eg: 65%) according to the POH settings. The engine is then leaned so that the richest cylinder is operating at around 50 degrees LOP. This leaning should be done fairly quickly (especially at higher power settings) because you don't want to spend much time at settings in the neighborhood of 50 degrees rich of peak (this is where temperatures and pressures are greatest). The manifold pressure is then advanced to restore the lost airspeed (used as a proxy for power). If done correctly, this should result in the engine operating at the same power, but with CHT's approximately 30 degrees cooler than the same power given by the POH at "best power" settings. It will also result in the roughly 10% fuel savings.

5. In any event, one is not likely to cause detonation, or otherwize damage the engine, if indivual CHT's are kept below 400 degrees or so, no matter what you do with the mixture control (or the manifold pressure for that matter).

Comments?

You're essentially right. The only other points to add, and some may consider them minor, are these: a) I would expect the pilot to be somewhat knowledgeable in what he's doing (like you are); b) he/she must be willing to devote somewhat more time to engine management during flight than ROP, taking away from sightseeing and other chores; c) engine is not under warranty (LOP voids it); and d) make sure payback period works for you.

Ernie

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.

"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?

Step right up!
 

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

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

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

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

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.)

PURPOSE?
 

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!

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.

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

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.

>>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

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.

Go Fast or Go Far
 

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.

.

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,

TGresham makes excellent points supporting LOP operation. My own analysis came up with similar results (I think I figures 7.50 per gallon). However, at my rate of usage, it would take 10 to 15 years to reach TBO, and my payback period would have been well over 5 years. This is a longer payback period than I was comfortable with. But, that is a personal choice.

On the other hand, if I can reach a comfort level that the purchase of an expensive engine analyzer is going to pay for itself within that time frame due to extended engine life or maintenance savings, the purchase decision becomes easier.

I appreciate Walter's comments.

On the subject of whether the manufacturers established a "design point" to help "idiot-proof" engine operations, or whether they were unduly influenced by the marketing department is certainly a fun topic for debate. I too am skeptical of the marketing guys, and nothing they did would surprise me.

On the other hand, their reasons have nothing to do with the science of this issue, and speculating on their reasons does tend to make the issue more emotionally charged.

I freely admit that I am pretty new to this issue, and am here to learn from those of you that know a lot more about it than I do. I am just trying to make sure I understand the facts and don't tear up my airplane.

Let's examine the premise that is it OK to operate the engines according to the manufacturers recommendations. I am already convinced that this is not optimal from an effeciency standpoint. Alas, right now, I really can't afford to properly instrument my engine and get GAMI injectors, so for some period of time, I am going to have to continue operating the plane with nothing more than the factory supplied instrumentation and the optional single-probe factory EGT. Under those circumstances, I want to answer the following questions:

1. Is it OK to follow the POH recommendations. My POH says:
a. operate at 75 percent power or less in cruise flight.
b. operate 50 degrees rich of peak egt when at 65-75% power.
c. operate at peak cht at 65% power or less.

As far as I can tell, no one is disputing that (c) is OK, so let's focus on (b) at 75% power (If anybody is disputing this, please say so).

Walter indicates that this 50 ROP EGT setting is between peak CHT (40 ROP EGT) and best power (80 ROP EGT) based on the tests that they have done. Based on the GAMI charts that I have seen in George's Braley's articles, the CHT's are within 10 degrees of those found at best power. With the instrumentation that I have, my margin of imprecision is high enough that, for all practical purposes, this setting is equivilant to both best power and peak cht (probably some cylinders will be at one, and other cylinders at another).

In order to REALLY know if this setting is OK, I would need to know if the CHT's for each cylinder are running below 400 degrees. If they are, I'm OK, and if they are not, I am running too hot (again, if there is any disputing this point, please say so).

Unfortunately, this is a catch 22. I can't know this with certainty without an engine monitor. So, we are reduced to asking, is this OK IF the engine is functioning properly.

If the engine is functioning properly, then the cylinder with the CHT probe should be the hottest running cylinder, by design. THIS IS A MAJOR ASSUMPTION. Perhaps those of you with engine monitors on the skymaster can answer this question. If it is not the hottest cylinder, then the temperature limit would have to be adjusted down to some extent. By analyzing the data of those of you have engine monitors, we could answer the question "how much."

2. Irregardless of the answer to question 1, is there a better way to operate these engines IF you don't have an engine analyzer.

3. I think a large percentage of us use no more than 65% power in cruise (perhaps because of economy, or concerns about engine wear, or both). Is there any reason to not do this? Does it add enough of a "margin of error" that it becomes extremely unlikely that we will damage the engine no matter what we do with the mixture control?

Kyle:

Yep. My position is that GAMI's can save you money....... but, an engine monitor can save your life. The engine monitor is much more important and GAMI will tell you the same thing. If you can only afford one or the other, the people at GAMI will strongly suggest that you get the engine monitor. That speaks well of their integrity in my view.

Here's the problem.

As soon as an owner installs an engine monitor and find out how crummy his F:A ratios are--even ROP--many folks get the GAMIjectors so their engine will run like it should have been running in the first place.

Oh, well, such is life. <g>

The really confusing part
 

WOOPS! In my previous post, item (c) should have said "operate at peak EGT" not "operate at peak CHT".

Now, on to my real question.

I don't actually think that the LOP guys and the manufacturers are as far apart as they appear. They certainly aren't that far apart on their data.

Taking the manufacturers "side" for a moment, I believe that we all agree that:

(1) at the time most of these airplanes were built, multi-probe engine monitors were either not available or were prohibitively expensive (they are still pretty expensive); and

(2) without these engine monitors, there is no better alternative than following the manufacturers recommended power and mixture settings, provided we keep an eye on the CHT's (by running them at 400 degrees or less).

Now, here is the part that I "don't get." Cessna has the charts, GAMI has the (even better) charts. If I am reading them correctly, then operating by the manufacturers settings at 75% power leads to the highest possible CHT's for that power setting. They just aren't going to get any higher, no matter what you do (o, if you want to split hairs, they can't get more than a few degrees higher, since true peak CHT is more like 40 DROP EGT).

If this is true, and if "everybody" knows that operating at peak EGT is actually going to be cooler than operating at 50 DROP, then why does the POH say you shouldn't lean to peak EGT above 65% power?

Correct me if I am wrong, but I can's see anything wrong with setting MP and RPM for 75% power, then leaning to peak egt and leaving it there (instead of enrichening to 50 DROP).

Extending this argument further, I don't see any reason that I couldn't continue to lean the engine until I was running at 50 DLOP (assuming that the engine would run smoothly at this point, which it probably wouldn't without gami's).

But for argument's sake, lets say I have GAMI's but my engine monitor died or whatever, so I'm having to rely on the factory gauges.

I absolutely don't see how this would hurt anything.

Of course, the "catch" is, that if I leaned to peak EGT, or leaner, then I would not still be making 75% power. I would be making some lesser amount. But if I am OK with making this lesser amount of power, I really don't see how this could possibly hurt anything.

And this is where I guess the "kicker" is. In order to perform LOP operations AT HIGHER POWER SETTINGS (I am guessing settings where the real power exceeds around 65 to 70 percent), it is necessary to move the manifold pressure and/or RPM controls to a position HIGHER than the factory recommended settings for 75% power operation (the "power recovery" step).

If I do this (eg: by advancing MP until the airspeed is what it was before I started leaning) and I DON'T have an engine monitor, then it is possible that an individual cylinder could be running at some power setting greater than "book 75%" because of unbalanced fuel flows.

So, I can see why this would be a no-no.

However, I can't see why I shouldn't lean as much as I want to from the factory 75% setting, provided that I don't do the "power recovery" step.

Am I thinking right, or not?

Kyle:

It seems to me that you're gaining a pretty good hold on the concepts. Some points to further your understanding:

**I don't actually think that the LOP guys and the manufacturers are as far apart as they appear. They certainly aren't that far apart on their data.**

Actually, there is no argument at all on the data. None. Period. It all agrees 100% because, as Sir Isaac Newton said, "The physics are everywhere the same."

**(2) without these engine monitors, there is no better alternative than following the manufacturers recommended power and mixture settings, provided we keep an eye on the CHT's (by running them at 400 degrees or less).**

That's close, but not altogether precise. Keeping CHT's below 400 is a good guide but it does not address ICPs completely, but it's difficult to be too argumentative with that statement. It's pretty close.

You comments about the charts are correct. The Cessna and GAMI charts are in agreement because the physics are, indeed, everywhere the same.

**If this is true, and if "everybody" knows that operating at peak EGT is actually going to be cooler than operating at 50 DROP, then why does the POH say you shouldn't lean to peak EGT above 65% power?**

Because an engineer didn't write the POH! I, too, would like to see a scientific explanation for that statement. I know of none. OTOH, be aware that the common recommendation not to lean above 75% power is an attempt to keep the pilot from operating inside what we later termed the Red Box. It was an admonition by the OEM that assumed that the pilot was not knowledgeable and had little instrumentation--which in many cases isn't all that bad of an assumption!

**Correct me if I am wrong, but I can's see anything wrong with setting MP and RPM for 75% power, then leaning to peak egt and leaving it there (instead of enrichening to 50 DROP).**

Our research indicates that peak EGT is not quite lean enough at 75% power to keep the ICPs low enough to be in harmony with longevity concerns. You are absolutely correct that it is a better choice than 50dF ROP. I'd say peak is "less bad" at 75% power. <g>

**Extending this argument further, I don't see any reason that I couldn't continue to lean the engine until I was running at 50 DLOP (assuming that the engine would run smoothly at this point, which it probably wouldn't without gami's).**

That is 100% in harmony with all of the known physics.

**I absolutely don't see how this would hurt anything.**

It won't. It's actually better.

**And this is where I guess the "kicker" is. In order to perform LOP operations AT HIGHER POWER SETTINGS (I am guessing settings where the real power exceeds around 65 to 70 percent), it is necessary to move the manifold pressure and/or RPM controls to a position HIGHER than the factory recommended settings for 75% power operation (the "power recovery" step).**

Correct. You have to get the mass airflow up so you can put the fuel to it. I currently, routinely operate at about 60dF LOP, 85-90% power in cruise. The engine loves it..... and I go faster on lower FF than if I were making 75% power ROP.

**If I do this (eg: by advancing MP until the airspeed is what it was before I started leaning) and I DON'T have an engine monitor, then it is possible that an individual cylinder could be running at some power setting greater than "book 75%" because of unbalanced fuel flows.**

Right... but... if it's running smooth LOP, it MUST have balanced FFs. <g> In that case, you don't need an engine monitor to run LOP.

Duzzat make sense? <g>

Walter:

Yes. This clears up a lot of the questions that I had.

The one thing that I hadn't realized is that your research indicates that operating 50 degrees rich of peak egt at 75% power, per the manufacturers recommendations, actually causes the engines to run in the "red box" because the ICP's are at some level that is objectively "bad"?

Am I understanding you correctly on this one?

Kyle:

You understand that correctly. To keep ICPs under control at 75% power you need to be richer than about 125dF ROP or leaner than about 20dF LOP. Doing so is beneficial to longevity. The Red box grows as power increases and it shrinks as power decreases until it no longer exists somewhere between 60 and 65% power. To follow the science, you must either allow range to suffer or be able to run LOP at power settings above 60-65%. That's why the manufacturer's recommended cruise power settings are as low as they are.

The Manufacturer's MARKETING Department's recommendations of 50dF ROP at 75% power are not, in our view, a good idea based on the observations we have made over many hunderds of hours of test cell work and the field observations. If longevity is not an issue, then 25-50dF ROP is the mixture setting that will result in the best trade-off between airspeed and range--just like the Marketing Department suggests.

Those who have been operating at high powers LOP have been getting excellent results because range and speed are both better while keeping ICPs controlled for increased longevity. I routinely run between 85 and 90% power in cruise with a cool engine and good range. My engine is pristine clean with no buildup of anything on the pistons, or valves. The oil stays clear for 20-25 hours. You can acheive the same longevity with very rich mixtures, but the engine will run a lot dirtier. ROP is OK if you are rich enough. It will result in higher maintenance since it will have much more deposits in the combustion chamber and the oil will get dirtier quicker. I donlt have any hard data, but it makes sense that clean oil is better than dirty oil.

According to Carl Goulet, former VP of Engineering at TCM, "Cooler is better. Cleaner is better. LOP is cooler and cleaner." His position is certainly in harmony with the science as we have observed it. <g>

Regards,

Kyle:

In answer to your questions, this was posted on the Cessna board this morning. It speaks directly to the points we are discussing. He's flying a CARBURETED 182. Notice that he's flying faster, cooler and on less fuel! This is a common response.

Walter

*****

Flew Santa Barbara (SBA) to John Wayne (SNA) at 5500'. Started with 7 degrees C carb temp, WOT, 2425 RPM, 10.3 GPH. Got 25-30 LOP. 76% HP. Hottest CHT was 329 with cowl flaps closed. I'm usually up around 16 GPH 200 ROP to get 75% power. Normally I fly 65% power at 25 ROP. I gained a few knots IAS today and burned a bit less gas. Very cool .
I strongly encourage everyone to attend the APS course. It's fun, informative and worth every cent. It is so nice to have the entire power/mixture spectrum available.

Thanks Walter and George.

Randy

Walter,

Thanks for taking the time to answer my questions.

As you know from following the thread, I am "sold" on the LOP concept provided that one has an engine monitor, particularly in terms of effeciency. I've looked at the data, and it says what it says.

Also, Continental's new FADEC system runs LOP I understand, and I guess they wouldn't do that if it was going to tear up the engine. This gives me some additional comfort.

On the subject of ICP's, I still don't have a firm understanding of how much is too much. I understand that it varies with crank angle, and in any event, I'm not going to be able to measure this directly.

Right now, I don't have an engine monitor, and I've already blown this year's "goody budget" on a new GNS480 (hopefully installed in 2 weeks).

So, for at least the next year, I'm going to have to run with what I've got. My main concern is not doing any damage to the engines in the mean time.

Heretofore, it has been my practice to take off at full power, reduce to 75% power at about 500-1000 AGL (with everything at the top of the green including fuel flow), and cruise at "65% power" and peak EGT (which would actually be somewhat less than 65% power, really). I generally use the cruise power (and mixture) setting in my initial descent, and gradually reduce power so that I am at approach speed when I level out (assuming I am going to be at the IAF at that time). This gradually cools the CHT's.

I suppose the main thing that I need to verify at this point is whether the "top of the green" fuel flow used in climb is at least 125 degrees rich of peak EGT.

If so, then my operating practices should be OK (provided of course that I keep the CHT under 400).

If there is not a 125 ROP margin in my climb power setting, then I need to enrichen enough in the climb to get 125 degree temperature margin.

Is this correct?

Is this a reasonable and conservative way to operate until I get all the goodies?

Thanks,

Kyle

PS: I recently read an article by Mike Busch over at CPA. He endorsed LOP operations in his article.

Kyle,

Walter and others will certainly express their opinion, but in my view, and in the view of the very knowledgeable turbocharged piston engine mechanic that used to work on my P, there is no reason to pull the mixture lever back at all during climb. Reduce to the climb power setting that Cessna specifies, but then leave the mixture in. You will burn a bit more fuel, but will reduce the risk of hurting your engine. Depending on the fuel flow gauge is not a good idea. They can go out of calibration very quickly, and you could fry your engine fast.

I will be interested in Walter's reply to the concept of running at peak EGT and 65% in cruise. I have previously been told that this is not a good idea, because (with GAMIs) fuel distribution to the cylinders is uneven, and you could end up with one or more cylinders inside that red box he talks about, even though you have leaned to peak based on your Cessna (I guess that is what you are using) EGT guage. I've also been told that at 65%, you can run it anywhere up to and including peak, and it won't hurt it, so it would seem that what you suggest would be OK.

But anyway, my only point was that pulling back the mixture to the top of the green is not the best practice, in my view. I ran my P337 the way I describe for several years. It simplified operation, used a little fuel for cooling, and gave me a bit more peace of mind. I did this even when I had an analyzer, because leaning for climb with an analyzer (in an IFR step climb for example) seemed like a pain.

Kevin