Folks, I love being positive and cheerful. I’d much rather write about pleasant things, good memories, good products, good people, and fun things.
I didn’t enjoy doing the Whyalla column, and I’m not going to enjoy this one. But Flying (July 2002, page 73, “Can your engine run too lean?“) missed the boat so badly, and so many people will be led terribly astray, that I must. I don’t know the author, but I’d guess we have many things in common, and I certainly don’t enjoy criticizing his work. I can believe his errors were not deliberate, as he simply accepted the ATSB’s “report” as factual – as we all should have been able to do. On the rare occasions I’ve read Flying, I’ve always enjoyed J. Mac McClellan’s stuff, and mostly agree with what he writes. With apologies in advance to these gentlemen, I am forced to comment.
Part of the problem is that we “older pilots” have “grown up” reading accident reports, and learning from them. We all tend to take them pretty much at face value, especially in the highly technical areas outside our expertise. After all, we are merely airborne bus drivers (airline pilots), chauffeurs (corporate), and sport flyers (others), and cannot be expected to know chemical terms, physical processes, and what the terrible evidence of an accident means. There are special schools for that sort of thing, and the evidence is often confusing (or lacking).
However, accident investigation has changed in recent years, and not for the better.
Accident Investigation: Science vs. Politics
It is now often a political process. Sometimes it’s hard to tell when it is “real science” or something political that is driving the results. When it is conducted in the harsh glare of publicity from “The Media,” who prides itself on knowing nothing at all – then one best be pretty careful about accepting the results at face value .
I’ve had “reporters” claim it is “better” to send out a reporter or investigator who knows nothing of the subject, because the reporter will be writing for mass consumption, and will do a better report than an expert (who might confuse the masses with facts)! That is unspeakably stupid, in my opinion.
(And please, folks, I do not malign all media, or all reporters. You good ones know who you are, and this is not aimed at you. It’s usually the real turkeys who take offense, anyway.)
I often say, “The only stupid question is the unasked one,” but I think I’m going to have to make an exception for the media. One has only to watch a press conference (on anything) and listen to some of the truly stupid questions they ask … often several times. The real issues, and the real meat of the matter get lost in the competition to get a question in, any question at all, relevant or not.
This “Accident Investigation by Press Conference” has not improved accident reporting.
Accident investigators are not improving, either. They are often overworked and underpaid (budget cuts, y’know). That drives away the good ones, and the inevitable result is inferior investigators, and inferior accident reports. These people used to work magic with crumpled, bloody, burned airplanes. The TIA accident in JFK many years ago was one of the finest I’ve ever read. A DC-8 nosed up sharply on takeoff, stalled, fell off on one wing, and crashed, killing three crewmembers, if I recall correctly. The probable cause was a small stone that was probably kicked up from the airport surface, and which lodged in the crack between the horizontal stabilizer and the elevator, jamming it in the airplane nose-up position. The usual flight control check would not reveal that problem, and once the industry knew that, airlines all over the world instituted a much more effective pitch control check. The accident report was fascinating reading, and led me to admire the NTSB for many, many years. I’ve lost a lot of that respect very slowly in recent years, and TWA 800 killed what little remained. The way the FBI trampled the evidence didn’t help, and the obvious turf wars were reprehensible. (No, I don’t think there was a conspiracy, the agencies involved are too stupid to pull one off.)
Another part of the problem in recent years is that hiring in various governmental agencies has been corrupted by the need for political correctness and affirmative action. For years, women and minorities were NOT hired because of their sex or race. In more recent times, they were (or are) hired BECAUSE of their sex or race, or whatever the “discrimination du jour” happens to be. Disgusting, either way. Some of them are very talented, and THAT’S what should have gotten them hired.
What a mess all that “P.C. stuff” has created. Ok, let me off that soap box, for now.
The ATSB – Australia’s equivalent of the U.S. NTSB – botched the Whyalla crash investigation badly. I don’t know, or care, who did the legwork, or who wrote it. Regardless, I think it’s the worst accident report I’ve ever read. Unfortunately, Flying seems to have accepted it at face value, and started from that point.
Unfortunately, many Americans will read only Flying, and take away some really bad information.
The Flying Article
|The ATSB Roars (Whimpers) Back
This is being inserted very close to publication, after the main column was written.
Apparently my last column hit a few raw nerves within the Australian ATSB, as they have taken the unusual (if not unprecedented) step of responding with some heat on their own web site, even naming me specifically. There’s not a lot to respond to, as it’s mostly a re-statement of their position.
Which is untenable, I think.
They do expend space stating that there is indeed such a thing as “lead oxybromide.” Whether there is, or not, or whether it’s just an odd usage for some other compound with a similar name is beside the major point. The point is that NONE of those compounds could have possibly caused either of the engine failures that tragic night. Furthermore, to my knowledge, this is the first time this theory has ever been advanced for an engine failure. All those compounds (which I listed in the sidebar) melt or vaporize at temperatures FAR below those necessary to cause pre-ignition. Since I wrote that, even Lycoming has very firmly stated this was in no way any part of the cause of the engine failures, or the accident.
The ASTB accuse me of “venom.” I wouldn’t have used that word, but I’ll confess to “massive irritation” over the ATSBs starting an original Old Wives’ Tale (OWT), one we’ll probably be fighting forever. If I’m lucky enough to live to 100, I’ll still be arguing with people who cite that dreadful report in support of the theory that “lead oxybromide is known to cause engine failure, the ATSB said so.”
We’ve already got so many OWTs “out there” that will never go away, we really don’t need more, especially from a “respected government body.”
When I first started writing the column, several scientists I know had never heard of “lead oxybromide.” One finally turned up the references I put in the sidebar.
If questioning the existence of this substance was a mistake, then I made a mistake. It won’t be my first, and it sure won’t be my last!
Speaking of which, another reader states that in having errors in my column, I detract from it. That’s probably true, but I don’t think anyone can write very much and not make mistakes. I can’t, I make ’em all the time, and I EXPECT you to take me to task for it. If you’re looking for perfection, try the New Testament, where someone reportedly got crucified for it.
If I helped in some small way to focus some attention on the report that brings about a more competent investigation, then I’ll be very happy, mistakes and all.
I was certainly surprised to hear the ATSB imply their job was not to determine probable cause. You could have fooled me!
– John Deakin
To begin with, the title of the Flying article is misleading:
“Can your engine run too lean?”
Well, no, to pick a minor nit, if it’s “too lean,” it won’t run at all! It won’t run “too rich,” either.
The article’s subtitle is better:
“There is no one answer on how best to set the mixture on your piston engine.”
That’s true, for there are many variables, and it depends on what you want to do. There IS one answer on where NOT to run your engine, and it’s distressingly close to where the marketing departments of many airframe manufacturers try to tell you to run.
The first two paragraphs go on about how everyone fears the mixture control, which may be true, but it seems to leave the impression that such fear is justified. It’s not; the mixture control is simply one more device to give the pilot control of the engine. If you pull the throttle too far out, the airplane will descend, and if you pull the mixture too far out, the airplane will descend. Restoring the control restores power. Simple.
Flying takes a mild swipe at Pilot Operating Handbooks (POHs) when I would have nuked many of them, but never mind.
“So as students there are only two positions we learn for the mixture control; full forward for takeoff, climb and airwork below 5,000 feet, and idle cutoff to shut down the engine at the end of the flight.”
True statement, and very sad. The problem is, it’s very, very rare for pilots to rise above this student training. More often than not, no one ever tells them, “Now that you’re not a student anymore, you need to learn about mixture.” The FAA rightly says, “Pilots learn best that which they learn first,” and they call it “primacy.” Pilots at the Private and even Commercial Level end up with NO knowledge of the red knob, and some, as Flying points out, run short of fuel as a result.
“The reason for full rich for high-power maneuvers like takeoff and climbs is that there is actually a little more fuel than is needed for combustion, and the excess helps to cool the engine when it’s working its hardest.”
At the lowest level of understanding, this is true, but it makes me twitch because it’s horribly incomplete. It would take only a few more words to be accurate, and convey a lot more information. For one thing, it’s not a “little more,” it’s usually a LOT more fuel … often closer to half again the amount of fuel it would take for an ideal mixture, sometimes double.
Flying might better have said something like: “Excess fuel on the rich side slows the speed of combustion, delays the onset of peak pressure, and lowers the combustion temperature. That means less heat to be carried away by the cylinder head, and less chance of detonation.”
They might also have added, “Excess air on the lean side has the same effect, but since there is less fuel to burn, there is less power.” Considering Flying‘s bias against lean-of-peak (LOP) operation, that would have been too much to expect.
“A ratio of about 15 pounds of air to one pound of fuel is about right to support combustion.”
Well, in a word, no. Combustible mixtures range from 20:1 (very lean) to 8:1 (very rich). 15:1 is the theoretical point at which all fuel and all oxygen is burned (“stoichiometric” for the crossword puzzlers). In reality, even that “sacred” number may not be quite correct in an internal combustion engine, but it’s “close enough.”
“The simplest, but the one that makes for a bit of puckering, is to simply lean the mixture until the engine runs rough and then richen it until the engine again runs smoothly.”
I won’t quibble with this much, but only improper training would cause “puckering.” They might have pointed out that a properly balanced engine (same mixture to all cylinders) will not run rough at all, but will gradually lose power as it is leaned, and will finally wheeze and die without ever running rough at all. I can show you this in my Bonanza, and on two big R-2800 engines that I fly all the time.
“The rough-running engine is a result of the leanest cylinder losing power compared to the other cylinders.”
BRAVO, Flying! Thanks for not using the old “lean misfire” junk! The loss of power in one or more cylinders due to leaning is PRECISELY why roughness occurs, and PRECISELY why GAMIjectors where invented!
“Each airplane POH typically has a chart that shows the EGT reading for two conditions; best economy and best power.”
Maybe, but few get it right. There is no need for a chart, and most POHs, like Flying, get this wrong. Flying is quite correct that different POHs have different, often conflicting information. Why didn’t they ask, “Why?” Does installing a given engine in a Piper cause combustion characteristics different from that same engine in a Beech? Of course not! The engine doesn’t know whether it’s powering an airboat, an airplane, or a helicopter!
The fact is that ALL spark-fired, fixed-timing, gasoline-driven, internal-combustion engines are the same when it comes to the combustion event! From your lawn mower to the giant radials of yesteryear, they all act the same. Lean from full rich (usually about 250F ROP), and EGT, CHT, ICP (Internal Combustion Pressure), HP, and HP per gallon ALL rise, at first. HP will peak FIRST, at about 80F ROP and then start falling, then the CHT and ICP peak at about 40F ROP, and start falling, then peak EGT occurs, and starts falling. On the lean side of peak EGT, all those parameters continue falling, then at about 40F LOP, HP per gallon peaks, and begins to fall. From there, it’s downhill all the way for all parameters, until the engine quits from lack of fuel.
(Cut me some slack on the 40F LOP number, which I use here for simplicity. In reality, the max HP/gallon number may reach its maximum value at anywhere from 10F LOP out to 80F LOP, depending on some other issues. The curve is so flat in this area, that it makes little difference as to the actual value of HP/gallon whether you check it at 10F LOP or 80F LOP. The same comment can be applied to max power mixture, for that curve is very flat, too.)
If you run ANY of these engines at about 80F ROP, you will get the most HP that can be had at that MP and RPM. If you run it at 40F ROP, you will see the hottest CHT and the highest ICP, at peak you’ll see the highest EGT (of course), and at 40F LOP, you’ll get the most HP per gallon. The laws of physics don’t change with the label that says “Textron Lycoming” or “Teledyne Continental,” or “Beech,” or “Piper.”
Flying uses examples:
“The Cessna Cardinal POH, for example, calls for leaning the Lycoming IO-360 engine to peak EGT for best economy and 25 rich of peak for “recommended lean.”
Well, peak EGT is NEVER “best economy” in ANY engine! “Best Economy” is 40F LOP! And just what does “recommended lean” mean, anyway? Recommended by whom, and why?
“With the same LYCOMING engine [emphasis mine], the Piper Arrow IV (PA-28RT-201) manual points out that its speed/power-performance cruise graphs are based on the engine being ‘leaned to 100F rich of peak EGT.'”
Flying does point out accurately:
“But it’s important to recognize that the figures in the POH may be based on best power, best economy, or somewhere in between.”
Hell, why don’t we just say, “Anywhere at all”? They might have pointed out that the only consistency is inconsistency, and questioned why. However, perhaps that would affect advertising revenues.
Lean of Peak
“It’s interesting that although historically operating lean of peak was once a standard procedure, it’s no longer recommended for all engines.”
Flying completely misses the real reason why this is so. Operating LOP is a BETTER way to operate ALL these engines. It is EASIER, SAFER, COOLER, CLEANER, and more economical to do so. Why doesn’t LycoContinentBeechPiper want to talk about it?
I’ll tell you why.
It’s because most post-WWII “flat-six” (and “flat-four”) engines have fuel delivery systems that are so poorly designed, with such poor quality control, the engines CANNOT operate LOP at all! One or more cylinders will peak first, and “slide down the backside,” while other cylinders are just coming up on peak power! No one can stand the vibration that causes, so right around peak EGT on the leanest cylinder becomes the limit, the very leanest point at which the whole engine will run smoothly!
If you accept that peak EGT is the leanest a given engine will run, then it becomes easy to call that “too hot” with increasing power. It becomes easy for the FAA to create knowledge tests that claim the only right answer is “leaner is hotter.” Generation after generation of pilots and CFIs learn this as absolute fact. It becomes a matter of “everyone knows that!”
“If all the fools in town are on your side, that’s majority enough.” -Unknown
Sorry, ’tain’t so. Leaner from peak CHT (or peak EGT) is COOLER for any given cylinder, and if you can get equal mixtures to all cylinders, you’re back to the WWII engines that ran “better, cleaner, cooler” on LOP mixtures, for hundreds of millions of hours, with TBOs of up to 3,600 hours.
But all the time we didn’t know it was the flat engine’s fuel delivery system that was at fault (lack of good instrumentation in the field, and lack of intellectual curiosity at the factories), the real engineers at Lycoming and TCM were dying and retiring from the bureaucracy. Corporate memories faded, and now everyone at the factory is convinced that we’re all too stupid to learn there IS an easier, simpler, cleaner, cooler way to operate, even if they do know it.
Poor fellows. They’d have to admit that they’ve been misleading themselves, all these years, and us, too. They’d have to admit giving BAD advice, and their lawyers are probably warning them of dire legal consequences, perhaps lawsuits over every engine failure in flat-engine history.
Flying goes on, with:
“Charles Lindbergh is credited with showing military pilots how to increase their range by operating lean of peak.”
Not so fast, here! I don’t believe that’s quite true. Lindbergh certainly pioneered the use of some long-range flight techniques, but I don’t think he “invented” them, or ever thought of “lean of peak,” as EGT was not well-known (or used) then. He did use several techniques in combination to accomplish his unique purpose, among them very low RPM, high MP, and flight very close to the optimum range airspeed for the gross weight, a high speed at first, and slowing with fuel burn-off.
There are credible reports from at least one pilot who is still alive and who was actually at Roosevelt field in May of 1927 that assert that Lindbergh carefully tweaked the mixture on each of the three carburetors which each fed three cylinders in order to get the engine in the Spirit to operate smoothly at very lean mixtures. The end result may very well have been LOP operation, but I don’t think he thought of it those terms. He did a fair amount of empirical testing, and found mixture settings that gave him the best range. Those were almost certainly LOP, but that’s probably not the way he got there. I wish he were still around so we could ask him!
“The technique of operating lean of peak and power recovery was discontinued due to the resulting increase in service issues. Burned pistons, valves, ruined rod and main bearings, were traced to the inability of pilot to utilize this technique with the instrumentation and distractions found in the typical general aviation aircraft.”
Lycoming and Continental DID NOT discontinue anything, for the engines wouldn’t run there at all! Over the years, they went to strenuous efforts to make engines that WOULD run LOP. They had some modest success with the engines in the Malibu (which they REQUIRED to be run LOP and ONLY LOP to this day). But those engines would not ordinarily run leaner than about 50 LOP, and many pilots didn’t understand that “leaner is cooler,” so they’d enrich just a little, “just to be safe.” Up went the CHTs, and up went the failures and accident rates. The “problems” were because those engines couldn’t run lean enough!
“According to the engineers, ‘Lean of peak EGT will result in low CHT, but exhaust port temperatures will still be relatively high.'”
Rubbish! “Relatively high?” Compared to what, an ice cube? The FACT is, exhaust valve SEAT temperatures, and exhaust valve STEM temperatures DROP precisely with the drop in CHT, which peaks at 40F ROP.
Lycoming itself publishes good data to support this! This DATA agrees with ALL the old literature! The Lycoming and TCM “engineers” really need to review their own data!
“Shortened exhaust valve life can be expected, especially if high power settings, above 65 percent power, are used in a lean of peak mixture setting.”
How on EARTH can Lycoming RECOMMEND 40F ROP, the very hottest point for CHT AND exhaust valve temperatures (by their own correct data), and then turn around and condemn LOP operation (cooler) as worse? It just doesn’t compute.
Flying mentions Lycoming’s recent service bulletin. That document is a very thinly-veiled attack on GAMI, and the “new-old” methods. It is my guess that Lycoming will someday be as embarrassed and humiliated by that document as TCM will be by the failure of the current FADEC system (the subject of a coming column).
The World According to Moffett …
But even in that document, there are signs of cracks in the concrete monolith of Lycoming’s thought processes. Notice that Rick Moffett – Textron Lycoming’s VP of engineering – is quoted by Flying saying:
“If you ask what’s wrong with operating lean of peak, the answer’s very simple. Nothing. You can run the engine there; we do it in the laboratory.”
Coming from Lycoming, that is a profound reversal! Perhaps in the future, they’ll come all the way around to logic and science, and admit it’s “better.”
Moffett goes on:
“On normally aspirated engines, it probably won’t do anything.”
I assume he meant LOP won’t do any harm, because it certainly does save fuel for any given HP, the engine runs cleaner and cooler, with lower internal pressures.
“Where you get into the possibility of difficulties is with high performance turbocharged engines. Even then, you can operate an engine there [lean of peak].
My goodness. Compare that with some of the stuff we’ve heard in the past few years! He is starting to sound positively enlightened!
“The problem is that the potential for engine mismanagement is there.”
Yes, it always is, and mismanagement is MORE LIKELY if you attempt operation ROP!
Flying then quotes Lycoming (implicitly agreeing):
“It’s because of the possibility of mismanagement that the Lycoming Flyer Key Reprints emphatically states that, “leaning past the peak is not recommended.”
Now, let me get this straight? We should lean to 40F ROP (the hottest possible setting) because mismanagement after that would not endanger the engine?
That’s a little like beating my head against a brick wall as hard as I can, on the theory that after that, beating it less vigorously will hurt less. That may be true, but I’ll pass, thanks.
Moffett is quoted as saying:
“I think the single least understood thing in an airplane is leaning.”
I would agree completely, especially by the factory.
“Many people were trained never to touch the red knob. In fact, I never touched it till I came here [to Lycoming] to work.
Frankly, I find that admission absolutely breathtaking. Rick, how much total time DO you have, and how much have you actually flown an airplane since you joined Lycoming? Were ANY of those airplanes properly instrumented, and did you touch the red knob in them?
“Lycoming, Moffett said, tries to give fairly simple instructions that most of the public can adhere to.”
Yes, indeed. Very simple. To operate the engines at close to the worst possible mixture available.
“Everyone agrees that properly managing the fuel requires accurate instrumentation, and Lycoming and Continental strongly recommend that all instrumentation for manifold pressure, engine rpm, oil temperature, cylinder head temperature, exhaust gas temperature and turbine inlet temperature should be calibrated annually.”
They do? Well, in some instances involving some engines and airframes, they do, but it is spotty, inconsistent and not widely disseminated.
There is some common sense there, but I’ve never seen ANY such “requirement.” Can someone help? Just HOW do we meet that “requirement”?
Now me, I check my MP for accuracy before every engine start. At sea level, engine at rest, the MP needle should show the altimeter setting. For elevations above sea level, subtract 1″ MP per thousand feet. Easy.
Tach? I did an end run around that by installing an electronic digital tach (two, in fact, the JPI EDM-800 has one, too), which shows RPM accurate to 1 RPM, or it doesn’t work at all.
The rest of the instruments? Gee, I don’t think I’ve ever had ’em calibrated, they seem to show the same thing in normal flight, every time. If they show abnormal, then it’s time to look harder, maybe swap a gauge, or boil a thermocouple, or something.
“And the EGT system must be in perfect working order to give accurate readings.”
I believe that’s called a “red herring.” This reveals a lack of experience with EGT and TIT gauges. In the first place, “accuracy” isn’t always needed, all we need to do is find peak, wherever that is, and use an offset from that. Second, with the exception of the Malibu/ Mirage crowd, I’ve rarely seen or heard of an EGT degrading in accuracy. I’ve had ’em fail totally, in which case the display for that cylinder blanks (at least on the JPI). I’ve had ’em go intermittent, where they jump around all over the place, and that’s easy to figure out. However, in general, if one shows 1300F today, it’ll show 1300F tomorrow, and next year, under the same conditions. Four of the EGT probes in my airplane are now WELL OVER 10 years old, and two have been replaced after failing. The patterns are uniform and consistent, when the engine is normal.
Now, you CAN get a problem with a millivolt ground loop in an EGT/TIT instrument circuit, and that CAN cause an error. It is almost always an initial installation error, not something that just “happens over time.”
“Remember,” Continental’s engineers emphasize,” the engine fuel system setup must always be maintained properly and it must be inspected and adjusted periodically to compensate for changes that may occur.”
Well, okay. Does that mean if you run ROP, it doesn’t? With modern instrumentation, the PILOT can tell the mechanic EXACTLY what’s wrong, and what needs to be adjusted, if anything.
“Excessive leaning under high power conditions can cause detonation and/or pre-ignition and possible engine damage.”
No. NO. NO! BADLY SAID!
Almost everyone falls for this fundamental flaw in logic!
The correct statement is, “Setting the mixture at the wrong point at high power can cause detonation, pre-ignition, and engine destruction. That point is centered around 40F ROP.”
If you run an engine at 40F ROP, and add power until detonation actually begins, then moving the mixture in EITHER DIRECTION will stop the detonation! The higher the power setting, the FURTHER from 40F ROP (in either direction) you must run to prevent detonation.
Possibly the worst aspect of the Flying article, other than their treatment of the ATSB accident report, is this: Read the quoted material in the article from TCM about where TCM recommends to set the mixture. Then read the quoted material from Lycoming. Those recommendations are in serious and direct conflict. Yet, they both deal with the SAME ENGINE that both operate under the same laws of physics. One is wrong. One is close to right. They are very different. Yet Flying failed to even take issue with this obvious contradictory set of recommendations. Come on, Flying! Where is your journalistic curiosity?
The World According to McClellan …
Now, to J. Mac’s sidebar. Unfortunately, it appears that he also bought the report, in full, with nary a questioning thought. Mac, ya gotta be more critical.
The title is “Lean Mixture Makes More Than Just Heat.”
Untrue. Leaning from very rich to peak makes more heat, but continuing to lean makes less heat.
“After the most exhaustive investigation and analysis of a piston-engine failure that I have ever read, and certainly the most through (sic) examination any safety authority as done since piston engines powered major airliners, the ATSB determined that lean mixture operation probably contributed to the failure of both engines, but in slightly different ways.”
|Advanced Pilot Seminars
I’m pleased to announce that I will be a part of “Advanced Pilot Seminars,” a new company devoted to imparting accurate knowledge of the internal combustion engine attached to our general aviation airplanes. George Braly, Walter Atkinson and I will be teaching these two-day courses at the GAMI facility in Ada, Oklahoma.
Class dates will be as follows:
Please contact me via email for further details.
Well, it was 138 pages in the original hardcopy, 150 in PDF format, and there were some nice color pictures. By now, you will have the distinct impression that I don’t think much of the quality of the conclusions evident and not evident in the report. I’ll bet even Lycoming doesn’t think much good about it either.
In short, the ATSB has produced a fatally flawed accident report, and Flying fell for it, hook, line, lead oxybromide bait, and all. Worse, Flying has now compounded the damage done to the aviation community by the flawed ATSB report, by passing that report off, uncritically, as revealing some new bromide as gospel.
Mac, I have a question for you. Did you ever think to call up Lycoming and see what Lycoming had to say about “lead oxybromide” before you published this entirely new theory of engine self-destruction in the most widely read flying magazine in the world? I have a hot tip for you: Why don’t you follow up and call Lycoming, and if Lycoming’s lawyers will let Lycoming talk to you about it, I will bet you a tank of gas in your airplane that Lycoming will tell you that lead oxybromide had nothing whatsoever to do with that tragic accident.
Does anyone want to make any bets on whether or not ATSB or Flying will ever correct themselves on this one?
Be careful up there!