CPT BROWN'S ARTICLES
This Section is updated regularly with a selection informative flying articles provided by Cpt Brown.
Starts and Runups
by John Deakin
Let's take a few pot shots at some of the more common errors in the seemingly simple procedures of starting an engine and doing the runup, and also cover some new techniques with engine monitors.
For Starters ...
There seem to be very, very few pilots who take any interest in where their prop blast goes or what it does at startup or during the runup. For example, if your airplane is parked in the common, tightly interlocked double line, starting up in that position and taxiing out is going to blow some serious air in the wrong direction at the flight controls of whatever is behind. Many very light aircraft cannot handle this, and many do not have effective control locks. Do your preflight, get all ready to go, pull your flying flivver out into the alley, and point the tail down the alley. Don't do this first, or dilly-dally around -- someone else may need the alley.
The absolute worst I've ever seen is at Oshkosh, where airplanes have been sitting in very soft grass for a week or more. It takes a lot of power to break away, and I've seen tents blown down two rows away from this. People compound this error by starting with too much RPM (see below) and then they will sit there and warm up, merrily blasting all behind them, or they'll taxi after a short interval, pulling tons of power –- on a still-cold engine!
There are always people around, and it's much better to call out, "Hey, can you guys help me pull this airplane out of the ruts?" Starting with the tail pointing "down the alley" makes you look good, and we all like to look good.
On starting, please don't let that engine roar into life, and go straight to some high RPM. This may be the single most damaging thing you can do to an engine, not to mention whatever is behind you. Most of the oil will have oozed out from in between the surfaces inside the engine, and metal-to-metal contact is always bad. Many experts feel that virtually all the wear in an engine comes from starting, and I certainly agree it's likely. One trick I use is to shut down at about 800 to 1,000 RPM, then never change the throttle setting until the next start. The cold engine should start gently and then come up to that same RPM slowly. As the oil pressure builds and starts lubricating the bearing surfaces, and the pistons and cylinders come up to operating temperature the RPM will build up to that same RPM range. That's plenty of RPM for the crankshaft to splash enough oil on all the moving parts inside the engine case.
Most general aviation (GA) airplanes are set up to idle much too rich. I can guess at a few reasons, easier starting among them. How can we pilots tell?
It's very simple, if you understand the combustion event, and the effect of mixture on it. I've written extensively about this, and the basic chart is produced here again (below). This is a "mixture sweep," a very rich mixture on the left, leaning to a very lean mixture on the right. This chart is the very heart of our engine seminar and is the key to understanding the combustion event. It comes from the back of many of the older TCM engine manuals; although we're starting to see it dropped in the latest versions. That's a pity, because it's excellent data, fully repeatable on the test stand and in any engine with a good monitor.
"Mixture sweep" -- effect of mixture on EGT, CHT, etc.
When these engines are first started, the idle mixture is usually way over on the left side. If this is so, then leaning will produce more and more power, and this will be evident from a slight rise in RPM. Leaning to "peak power" (the black HP curve) on the ground will produce the highest RPM. With further leaning, the RPM will fall again. On some badly-set-up engines, this RPM rise can be several hundred RPM, and this needs to be fixed by a mechanic. The maintenance manuals usually call for a much more modest rise, perhaps 25 to 50. The old manuals usually say, "a barely perceptible rise."
What they don't mention is that this adjustment should be made at sea level, or at the lowest "usual" airport elevation the airplane will see. Once the idle mixture is set at some elevation, any idle operation at higher airports will cause a richer mixture. This is normal, and should be corrected by the pilot with ground leaning. But setting up the idle mixture at Leadville, Colo., (elev. 10,000 feet) will probably make the engine impossible to start at sea level -- it will be too lean.
The idle mixture test (usually done by maintenance) calls for a nice, warm engine, so this is best done after landing. It's a good idea to check it once in awhile. When ready to shut down, slowly pull the mixture knob out (starting at full rich), watching the RPM very carefully. The books usually call for idle RPM, but I prefer to set mine at the usual "taxi RPM," about 900 to 1,000, for that's the RPM range the engine will almost always be at on the ground. As the mixture is leaned, the RPM should rise very slightly as the mixture passes "peak power," then it will fall again.
If you see no rise at all during this "sweep," just the fall, you have no way of knowing how the idle mixture is set. It could be anywhere on the lean side of peak power. This is the reason the manuals call for a slight rise, as that demonstrates the mixture is just rich of peak power, and that's a good enough setting for the factory. It's easier to start the engine, and that's good. That's the idle mixture test, and there's no need to get anal about it. Lean, see a little rise before the engine quits, that's it.
Unfortunately, that's not the best mixture for "clean" operation, and you may see some plug fouling from the "dirty mixture." Where is the "clean" mixture? It's where there are enough fuel and oxygen molecules to "mate and burn" (kinda like some marriages), leaving no residue, and that's at or near peak EGT, which is well on the lean side of "peak power," where the power is starting to fall off.
This is the basis for my recommendation to lean to peak RPM, then look for the fall (or roughness), and leave it there for ground operations. A tiny bit of roughness here is not harmful, unless it causes your significant other to beat on the side of your head. Occasional fouled plugs may be an acceptable alternative in this case.
At the usual power settings on the ground, it is impossible to do any harm to the engine with the mixture control, so don't be nervous about being very aggressive.
Running that lean (lean of peak power) on the ground also absolutely prevents you from taking off with the mixture leaned. This is not true if you take half-measures: Either do it this way, or leave it full rich. I don't care how faithfully you use checklists, you will someday attempt a takeoff with the mixture leaned. If you have properly leaned for taxi, the engine will simply wheeze and lose power, making it very obvious you're not going anywhere. If you take half-measures, the engine will seem perfectly normal, but may well get hot enough to get into detonation, then pre-ignition. With the big, high-performance engines (like the TIO-540 J2DB), this has caused engine failures off the far end of the runway, so it's serious business.
Lean it aggressively on the ground, or not at all!
If significant power (more than 1,000 or 1,200 RPM) is required to start moving (see Oshkosh, above), then sit there patiently and let the engine warm up a bit. If the airplane will move with less than 1,000, then move out when you want. The engine has no way of telling if the airplane is moving or not. Some of the old manuals on the big radials got this confused, saying, "Do not taxi until the oil temperature is above 40 ºC (104 ºF)." It wasn't the taxiing they were worried about, it was the possible power required to move out and then maneuver. Many of the old manuals got it right with some variation of "Do not exceed 1,000 RPM until the oil temperature needle is moving, and do not exceed 1,200 RPM until the oil temperature is 40 ºC or more." The metallurgy and the bearing clearances have remained much the same. Modern oils are much better at their job, so it's probably not as critical as it used to be with 60-weight, single-viscosity oil. But it's not really bad advice today, if a little conservative. Lycoming has for decades said something like, "OK for runup or takeoff when the engine can be accelerated without faltering." I scratch my head over that -- it's not very definitive -- and how do you know unless you try to accelerate it, possibly hurting the engine? On my airplane, the JPI engine monitor has the oil temperature option, and the probe is at the far end of the oil passages, so I have the "low" alarm set at 90 ºF, and will do the runup when that minimum is reached. By the time I've done even a short runup that temperature will be up over 100 ºF, and that's good enough for me.
If you have the mixture properly ground leaned, and it takes more than 1,200 RPM to start moving, you may be so lean you can't get above 1,200. That's great. Just give the mixture a turn or a tweak, start moving, and reset it. Heck, if you want, you can even modulate the taxi speed with the mixture alone, lean for less power, enrich for more. Try it, for practice, and see how nicely that red knob works. You know, the one your CFI told you, "Don't touch that red knob, you'll burn up the engine!"
Please try to avoid the ham-footed practice of setting too much power during taxi, and controlling the taxi speed with the brakes. I've seen some very high-time pilots do this, and it's very hard on brakes and tires. One even said he was afraid of fouling the plugs with very low power. With aggressive ground leaning, this problem goes away. I have never had a fouled plug in my engines.
Picking A Spot
Where do we do a runup? Well, if there are homes or quiet areas on this end of the airport, and nothing down yonder on the other end, go make your unwanted noise down yonder. Even those aviation nuts who work in the hangar or at the airport office will appreciate you putting some distance between them and your noise-maker, if it's practical to do so. Pay some attention to your runup spot. The "traditional" spot may have changed, there may be an airplane parked behind, or a new building, or perhaps just a dust pile. I've seen big airplanes kick up a dust cloud that slowly drifts downwind for many, many minutes, and many miles. How do you think those folks will vote, next time the airport is under fire?
For the larger airplanes, I prefer to park back in the corner of the runup pad, with my tail swung into the corner where no little airplane can taxi. If someone is dumb enough to taxi behind, you might not feel particularly guilty at blowing him over, but I'd feel terrible, even if the fault was not mine. We need to look out for the unaware.
Consider the wind direction. Tradition teaches us to runup into the wind, but like so many old wives tales (OWTs), this is not especially helpful. There is probably no more cooling into the wind than downwind, and in fact downwind may provide more cooling. We have the data to prove it. What is harmful is doing a high-power runup in a strong crosswind. This unbalances the forces on the prop, and may cause undesirable stress. The usual 1,700 RPM is not likely to do any damage, anyway.
Set the Brakes?
A very strong "No!" answers this question, for those airplanes with anything but power brakes. For example, my Bonanza has the conventional "master/slave" cylinder type, where the foot pedal squeezes the hydraulic fluid, making pressure in the line down to the brake. There the fluid presses against "something" that creates friction. It may be an expander tube, a set of brake pucks, or disc brakes. The key is that line between the cockpit and the brake. There is no provision for expansion, no hydraulic accumulator in that line, and pulling the parking brake handle simply closes a valve and traps whatever fluid is in there, sealing it off. It takes only a tiny, unnoticeable leak to drop that pressure to nothing, and the parking brake will no longer hold the airplane. At the other extreme, set that parking brake on a cool evening, then have the temperature heat up a lot the next day. If that line is perfect, and holds pressure, you may see enough pressure rise to blow the plumbing.
For runup, hold the brakes, and above all, maintain "outside awareness," both for "creeping," and for whatever else might be taking place. I have seen people set the inadequate parking brake, then do a runup, and creep clear across the runup pad, not recognizing the crisis until the aircraft moves into the rough. They look silly, and wonder how they got there. If at all possible, I'll remain silent and let them do that. It's an excellent lesson, as long as no damage is done.
On the larger airplanes, there are "power brakes." These usually have a simple mechanical latch that holds the brake pedals depressed, just as the pilot would in the absence of a parking brake. The lines will be under system pressure all the time (probably through reducers), and the brake system will almost always have a hydraulic accumulator that keeps a constant head of pressure on the hydraulic fluid by means of compressed nitrogen on the other side of a bladder. These are very reliable parking brakes, although I have seen airplanes creep with high power, especially right after brake maintenance.
With either system keep a wary eye out for movement.
For starters, many overdo this simple procedure. I constantly hear engines being run up at what sounds like full power, sometimes for very long periods. I know of no good reason to ever do this, even after maintenance. It's very hard on the engine because there is almost no cooling airflow at all. The prop may be moving a lot of air, but little or none of it is going into the cowling, because the prop blades are round at the base, and for the first foot or so. They don't have an airfoil section until well outside the cowl inlets, and thus cannot move air. I shudder to think of the hot spots being developed during those high-power runups, and I don't like to run the traditional 1,700 for any longer than necessary.
Props also take a beating on the ground -- more beating during runup -- and high-power runups are really abusive. Any dirt and grit on the surface will get sucked up, sandblasting the leading edges of the prop, and sometimes worse. Keep high-power operation to an absolute minimum.
Cowl flaps should always be fully open on the ground, even in arctic conditions. Their purpose is to act as an airfoil, and create a low-pressure area outside the engine cowl, helping to suck air out of the engine compartment. Whatever air is sucked out must be replaced, and that will suck in a little bit of cool air from the inlets.
Since you should have the mixture leaned so much that runup RPM is not possible, enrich just enough to get that RPM. Yes, you can go full rich, but the leaner the mixture, the more definitive the mag check.
Basically, all we're checking at the usual 1700 RPM is gross function. Bad timing can be detected here, but the engine monitor is a far better way to show that (by abnormal EGT/CHT).
As you bring the RPM up, this is a good time to check that the generator/ alternator(s) kick in. On most twins, the generator at the higher RPM will take most or all the load, so you can alter that relationship to make sure both are working.
Does the carb heat work (if installed)? Do this first, in case there is any automatic mixture control, so there's more time before takeoff for this device to stabilize at ambient temperatures again. This is true of most of the big radials. If this device is still warmer than ambient on the takeoff, it will automatically (and abnormally) lean the mixture, which is not good. The usual drop in runup RPM from carb heat is enough to check function. If there is a carburetor air temperature (CAT) gauge, carb heat function can be checked during the taxi to the runup pad, and observing the instrument.
Are the mags working? The leaner the mixture, the more mag drop you'll see on one mag, and that's normal. What you should really be looking at is the engine monitor while you check the mags. Some like to put it in "Normalize" mode, but that's too much fiddling for me; the "Percentage" mode works just fine. What you really want to see is that all EGTs rise during single mag operation. You can even go from BOTH, to LEFT, to RIGHT, and back to both. The EGTs should rise on the first single-mag operation, stay there for the second, then drop again on the return to BOTH. That rise is proof-positive the entire ignition system is working, and working well, and the leaner the mixture, the more diagnostic it is. On my engine, I'll often see a 300-RPM drop on one mag, but if all those EGTs rise, I know it's fine. If any of them fail to rise or even drop during single-mag operation, there is a problem with that plug, the wire, or the mag. On most engines, one or more EGTs may rise off-scale, and others may rise only a couple bars.
If you do this check well-leaned, the engine may even run a bit rough during single-mag operation, but as long as that EGT rises, you're in good shape, and can ignore the roughness. If the roughness really bothers you, enrich a little and repeat.
Don't wear the poor thing out, especially on the single-engine aircraft. Many do three or more cycles, often to very low RPM. Not necessary, and probably not desirable, it just prolongs the whole event, making the engine hotter, and going to full low RPM may be hard on the prop and engine mounts as the blades flail the air. Repeated cycles are probably a carry-over from the old radials.
The big old radials do often need several cycles to flush all the really cold oil out of the prop system. This can be clearly seen on cold starts after the engine has been at rest for a time. During the first cycle, the RPM will drop much more slowly than usual, and it will probably even drop erratically, from "slugs" of oil sludge going through. I've had to exercise them as much as a dozen times to get a nice smooth drop. It's also required to cycle them to the low RPM stop at least once to make sure the system has been adjusted properly; the minimum governor setting is generally 1,200 RPM. These prop systems are somewhat different from those on most GA aircraft.
GA props on single-engine GA aircraft do not keep a lot of oil in the prop hub when at rest: There's a big, strong spring that pushes the blades "flat," and it takes engine and governor oil pressure to get any oil in there at all. A single cycle is sufficient to check function, and frankly, this check is unlikely to find any problems. I frequently skip it entirely. If the RPM comes up to nominal takeoff RPM (on the takeoff run), and stays there, that's function check enough.
(You know, I think there are probably people out there who want to put the airplane up on jacks before every flight so they can roll the wheels to make sure they rotate before they taxi. We tend to do a lot of "checking" in aviation that is really doing nothing more than wearing things out prematurely.)
On the other hand, light twins usually have the spring pushing the prop into feather, and the dome will be full of oil at rest, so they may benefit from a few cycles on a cold day. But modern oils don't sludge up as much as the old straight 60-weight in the radials and the GA props should be well-oiled with one or two short RPM drops on the check. If I owned a twin, I'd probably do a feather check once a month in the air, for real. Certainly before and after the annual, and let it go at that.
In summary, start the engine gently when cold. Lean past "peak power" right after the start, enrich only as much as needed for the runup. After the runup, either go full rich or lean back again. Perform a short runup as a function check, and get on with the show. Skip the prop check on the singles, once or twice on the twins, and as needed on the big radials. Do the mag check leaned out, watching the engine monitor for an EGT rise, ignoring the large RPM drop.
Experts Are Everywhere – The Rebuttal
By John Deakin ©June, 2013
This article may be copied, printed and posted anywhere,
PROVIDED it is quoted in full.
A Little History
In the year 2000, Lycoming wrote a paper titled:
"EXPERTS" ARE EVERYWHERE TO HELP YOU
THE "NEW" OLD LEANING TECHNIQUE
Rick Moffett, the VP of Engineering at the time, probably wrote it.
I did a rebuttal column on it, and it was posted on AvWeb as “Pelican’s Perch #42.” shortly thereafter, in May of 2001. George Braly, of GAMIjectorTM fame begged me to withdraw it, as he felt Lycoming was having a change of heart, and the column might make the situation more difficult. I did so.
Now, more than 10 years later, that dreadful document is still on Lycoming’s website, in spite of several promises by the top executives to take it down. Ignorant people skim it, and say “I follow the POH and use this document to fly my aircraft, not the advice of some fellow on the Internet.”
In my opinion, Lycoming should be writing this rebuttal, and apologizing to the GA community and George Braly for publishing it the first place.
So, here is that long-suppressed column, updated to reflect my thoughts today.
I find Lycoming's treatise ignorant of the facts, condescending to the reader, insulting to the intelligence, and full of "fuzzy logic." I'd like to tell you why. I'm going to extract snippets here and there, place them in italics, and then comment in normal typeface, much as we commonly do in email.
In order that you may judge for yourself whether I have taken anything out of context, the entire document is available at:
(The link is broken, apparently removed by Lycoming. Please stand by.)
Dumb and dumber
Make no mistake, I like both companies! Both build fine engines that last a long time, and operate with fuel specifics that are better than the most modern automobile engines. But both companies have problems with quality control, and their warranties are questionable.
Neither company has the expertise to properly operate their engines. Let me illustrate with a quote from our APS course:
“A concert pianist does not take lessons from the fellow who tunes the piano.” Stu Spindel
CMI (nee TCM) and Lycoming ARE experts when building an engine, and telling us what the limitations are! But they are NOT expert at anything to do with FLYING those engines, because they do not fly them. They are limited to very primitive test stands with none of the sophisticated Engine Monitor Systems (EMS) owners install today. In fact, neither company has even mentioned them in official publications of which I am aware. It’s been 30 years and more!
The official attitude seems to be (figuratively and condescendingly patting us pilots on the head), “Just operate the way we tell you and you’ll be ok.”
I am often asked in reference to LOP (Lean of Peak EGT) operations: "But what will this do to my warranty?" Both companies have stated, in writing, that operating their engines LOP will NOT invalidate the warranties. They waffle a bit by going on to say, “improper operation will.” This word has apparently not trickled down to the “Tech Reps.”
While I'm at it, let me take a swipe at "field tech reps."
Lycoming and TCM field tech reps seem to me to serve but two purposes. First, if the engine is running at all, no matter how badly, they must be able to look you right in the eye and keep a straight face and say, "Oh, that's normal." Second, if the engine has failed catastrophically, it is their job to find any scrap of evidence that will allow them to say: "Pilot abuse, not covered by warranty."
I’ll never forget the Lycoming “Tech Rep” at the Arlington WA airshow somewhere around 20 years ago whose sole contribution to the discussion was literally screaming, “I wouldn’t recommend lean of peak to my worst enemy!” He said this over and over as if bombast and volume made his point.
As with any rule, there are exceptions -- and I suspect the good field tech reps will mostly agree with the above.
But I digress...
Okay, enough of that, let me walk you through Lycoming's white paper on LOP operations.
There are many "experts" today with new products and techniques to help customers in the operation of their engines.
Thank goodness for that! The factories sure aren't doing anything! Notice the condescending quotation marks around "experts." It is astonishing to me that TCM and Lycoming don't JUMP on some of the latest research, with an attitude of "Tell us more!" We can all learn something from almost anyone -- and believe me, those two factories could learn a lot!
One that is receiving public attention by way of aggressive advertising is a company manufacturing fuel injection nozzles and espousing an operating technique that is "better" than that recommended by the engine manufacturer.
Gosh, whom DO you suppose they mean? Could it possibly be George Braly and the GAMI/TAT gang down there in three-letter town (Ada, Oklahoma)? Could they be referring to the aeronautical engineer who built and refined the most sophisticated piston engine test stand in the world? The folks who found a wonderful niche market making precision fuel injectors that the factories (TCM and Lycoming) can only dream of? The GAMIjector folks who will quietly read an Internet message from one pilot to another about a slight imbalance in a customer's engine, and will overnight a new injector or two for a try, without even being asked directly? Or the Tornado Alley Turbo folks who thought there might be a problem with a turbo mount, published a bulletin, and sent out parts to all customers, without even being asked? (One customer complained loudly about parts sent that he didn't order. Takes all kinds, I guess.) The folks who spend prodigious amounts of time online and at (free) seminars, patiently answering the same questions, over and over again, responding with REAL DATA and REAL SCIENCE instead of regurgitated old wives' tales?
George Braly having a little fun at Sun N' Fun
"Aggressive advertising"? I see modest ads in a few publications, and a LOT of word-of-mouth advertising by happy customers, who now own about 22,000 engines equipped with GAMIjectors. The TAT shop is booked for months in advance for turbo installations, too.
The newly discovered method of operating on the lean side of peak exhaust gas temperature has been known since Charles Lindbergh employed it to navigate the Atlantic Ocean and Max Conrad established distance records in his Comanche.
Well, we might quibble over Lindbergh, although he certainly did long-distance flying pretty well! The CONCEPT of "lean of peak" wasn't around then (no EGT gauges), but leaning by the color of the exhaust was very common, and the end result was the same. Lindbergh did indeed tweak his three carburetors for a balanced fuel flow for smooth LOP operation. Widespread understanding and use of LOP didn't come until later, towards the end of the era of the great piston airliners, and even then, it wasn't called that, because there were still no EGT gauges. I first saw an EGT gauge in about 1960, and they did not become common for many years after that.
Whether you use the exhaust color (at night), the old BMEP/Torque drop method, or lean of peak EGT, the final mixture setting is about the same, with only minor variations. There are literally hundreds of millions of hours of LOP operation, even if it wasn't called that.
Why not LOP?
In fact, those old manuals were part of the inspiration for the current trend towards better operation, much of it in spite of the Lycoming and TCM factories. During development of GAMIjectors and the techniques to use them, the question was, "Why can't we run these flat engines the same way?
There are two reasons. Primarily because TCM and Lycoming themselves forgot the old methods, AND they did not know how to make engines that would run properly LOP! This was compounded by sloppy specifications, and exacerbated by poor quality control. (For example, TCM injectors, for which the engineering specs are far too loose to begin with, are manufactured so sloppily that they often don't even meet TCM's own specs right out of the box.) To cap it all off, TCM and Lycoming just didn't care, because "fuel is cheap," "that's the way we've always done it," and "pilots are too stupid to do it right."
This procedure was employed on large supercharged and turbocharged radial engines effectively during the era of large transport aircraft such as the Lockheed Constellation and Douglas D-6 (sic).
[Deakin note, Lycoming probably meant the Douglas DC-7.]
Yes. In fact, in developing these techniques, the airlines discovered that these techniques DIRECTLY allowed previously impossible flights (trans-Atlantic operations, for one example), helped to nearly double TBO (to as much as 3,600 hours in some engines), and DIRECTLY saved prodigious amounts of fuel. This was the historical precedent that seemed to hold so much promise for LOP operations in GA aircraft, and I find it nearly criminal that Lycoming and TCM didn't incorporate this knowledge into their engines and manuals decades ago.
Of course those of you who are knowledgeable about that part of aviation history know that there was a full time member of the flight crew, the Flight Engineer, responsible for engine management.
Not so fast! Engine management was indeed a part of the old-time flight engineer's job, with four often-temperamental engines. But the airplanes also had monstrous systems that needed constant attention, and some of the tools were pretty primitive and time-consuming to use. I would also point out that some later airplanes like the Martin 404 I fly today had all those systems, and were quite successfully operated with two pilots.
He did not have to worry about flying the airplane or dealing with complicated ATC clearance instructions. There was a full panel of engine instruments and controls directly in front of him ...
There was indeed a panel full of engine instruments, mostly because there was a wing full of engines! Some had four manifold pressure instruments, and none, to my knowledge, had more than two needles per instrument. Of course there was a panel full! The PRIMARY function of a professional flight engineer is to run the systems and assist the pilots in the overall operation of the aircraft, to spot and correct the mistakes made by the pilots (and we do make them!), and to help watch for traffic at low levels. Sadly, the industry has gotten away from Flight Engineers in favor of automation, and some of the recent accidents may give mute testimony to the wisdom of that. But that is another subject.
My Bonanza has far more INFORMATION available, in a much more usable form, with automatic alarms, most of which is made possible by modern electronics. Many of the functions that used to be performed manually by a human are now fully automated, and transparent to the crew (oil temperature control, for example), and many will now show an alarm if pilot-preset limits are exceeded.
... including a detonation monitoring system ...
If this is referring to the "vibration detector" that came with some of the old "ignition analyzers," (Oscilloscopes) they were a joke, and all but useless. In fact, the ignition analyzers themselves were more trouble than they were worth. Properly used, they were a big help, but far too many flight engineers (and pilots) buried their heads in the hoods, and looked for a problem until they thought they found one, then fiddled with things to "make it better." I have personally witnessed many occasions where an FE would see a perfectly normal power check and runup, then fiddle with the ignition analyzer for long agonizing minutes, in the belief that he could see something wrong. Meanwhile, plugs were fouling, engines were getting hot, and time was a-wasting. In each case, the order was finally given, some variation of "Get your face out of that ^%$#$# thing, and let's go!"
(To be fair, the old "Chinese TV" was useful when there was indeed something wrong with the engine. The FE could sometimes tell the ground crew exactly what was wrong, and with which cylinder.)
... and, in some installations, a torquemeter to avoid critical operational areas.
No. The major purpose of the torquemeter (or BMEP gauge) was to set cruise power by leaning to peak power, then on to the lean side of peak power to some value of power loss. Some said "12 BMEP drop" (R-2800 on the M-404), while others said "10% drop in power." The power sensor was in the nose case of the engine, picked off the outer "floating" ring gear of the prop reduction gearing. We generally don't have that in flat engines, and where we do the gearing system is different, so we cannot easily measure pure power or torque.
Once everything stabilized with the power drop, manifold pressure was added back to regain the lost power, at the leaner mixture. CHT was monitored closely, to make sure the mixture was correct and remained that way.
However, by knowing the relationship of EGT, CHT, BHP and fuel flow, we can now accomplish the same results even more easily with modern instrumentation, monitor it with electronics, and even flash a warning to the pilot if limits are reached, all without the need to set it for lower power first. No more “add back.”
How to run hard and hot while wasting fuel
For optimum service life, Lycoming suggests operating 50 degrees rich of peak EGT or TIT.
It always boggles my mind to see that recommendation from the factory, while they criticize LOP. It's true, if you're at 65% of power or so, 50°F ROP probably won't get you in trouble, and will give you pretty close to maximum power for that manifold pressure and RPM. But the fact is 50°F ROP (give or take a few degrees) will produce the absolute hottest possible temperatures for all parts of the engine.
On an engine like the TIO-540-AE2A, this translates into a difference in cruise fuel economy of approximately 2-3 gallons per hour compared with peak or lean of peak operation.
This is (roughly) a 10-15% savings in fuel, for a small airspeed loss! Airline executives would murder their mothers for a 1% fuel saving! If 15% doesn't seem like much to you, think of nearly a $1.00 discount on all fuel purchases. A permanent discount. Does that sound better?
With a normally aspirated engine, if leaning is initiated at 75% power and leaning past peak EGT is accomplished, it is unlikely (but not impossible) to induce detonation by opening the throttle to regain power.
Where is the DATA for this ridiculous statement? In fact, I have a pretty strong suspicion that the person who wrote this document has consistently ignored DIRECT evidence to the contrary!
In the first place, it is very difficult when running conforming fuel to deliberately induce detonation in the normally aspirated engines, even for a test. You have to work really, really hard at it. Go full-bore with an IO-540 at sea level, and reduce the RPM to 2400 or 2300 while 50°F ROP, cowl flaps closed, and CHTs well over 460°F, and you'll see the beginning signs of detonation. That's about the only way I know to demonstrate it. On the other hand, set the same power and 50°F LOP, and there is no chance of detonation.
Second, by leaning past peak EGT, the detonation margin is greatly expanded. Lean of peak, detonation becomes impossible in any normal flight regime, assuming good fuel. I'd like to experiment with gear down, full flaps, and a prolonged slow-airspeed climb, cowl flaps closed, and 50°F rich of peak EGT, I suppose that might eventually get things hot enough to get some detonation. Maybe.
Thirdly, in all cases, detonation will not occur without a dramatic rise in CHT, which will be obvious with an Engine Monitor if the pilot has set it to alarm at 400°F.
In our initial examples, both Lindbergh and Conrad were operating engines that had little potential for detonation based on the fuel they were using.
You know, I'd love to go back in time and put an Engine Monitor in Conrad's record-setting Comanche. He usually took off at more than double the max gross weight of the airplane, and had to use pretty high power settings at first. He knew all the tricks, but low airspeed, super heavy weights, and high power (at first) are more likely to induce detonation. If he didn't get it, no one would!
What about turbos?
A highly turbocharged engine is another matter.
Spark-fired, gasoline-powered engines have identical combustion characteristics, whether in a lawn mower, a garden tractor, or the old B-36, with six giant R-4360s (4,360 cubic inches of displacement). The RELATIONSHIPS between BHP, EGT, TIT, CHT, and BSFC are identical.
Employing this same technique will put the engine into a narrow operating envelope where detonation is possible if the mixture is richened slightly.
Wait. There is a terrible fallacy, here. Start with a 75% "book" power setting, at the factory- recommended 50°F ROP. I shudder at this near-criminal recommendation, but never mind, that is what the factory says, right? (Actually, it's what MARKETING says, because they want nice big cruise speed numbers and reasonable range.)
Remember, 50°F ROP is the worst possible mixture setting from a detonation standpoint, from an overall heat standpoint, and from a stress standpoint, because the peak pressures are occurring very soon after TDC, beating on that poor piston like the hammer of Thor.
At that 75% power setting, NOTE THE CHT. Remember, this is the HOTTEST it can possibly be for 75% power!
Leaner is cooler and cleaner
Simply leaning from that setting to 50°F LOP will reduce fuel flow and cost you power. It will save substantially more fuel (in percent) than it will cost you in reduced power output and lost airspeed (in percent) and is therefore more economical (makes more horsepower per pound of fuel and more miles per gallon), but ignore that for the moment. The CHTs will be MUCH cooler and the EGT will remain the same (50°F ROP and 50°F LOP are the same EGT). The internal stresses will be FAR less, because the peak pressure has shifted away from TDC, giving longer but gentler "pushes" on the piston and power train.
Now, continuing with our example, assume we're 50°F LOP, less power, further from detonation, and much cooler. Now add back the MP (about 3”) to come back up to 75% power (just recover the lost airspeed on a smooth day). In all the engines we've seen, the actual mixture ratio will remain unchanged, or will get very slightly leaner. The person who probably wrote the Lycoming document has seen specific data on the IO-540 engine that demonstrates this, and continues to ignore all the evidence. But you can prove it to yourself with a little thought experiment, or by actual testing!
(George Braly says: "There is no data I have ever seen that supports that idea that adding back 2 -3" of MP during cruise flight, with the CHTs limited to the same value as when the engine is ROP, is going to induce detonation. So long as we add back only a few inches of MP, and limit the CHT to the same value we had when ROP, we cannot possibly cause detonation!")
In fact, testing proves that if you set exactly 75% power at 50°F ROP, and note the CHT, then set up (by whatever means) 75% power anywhere LOP, the CHT will be LESS, by at least 30°F!
In our example here, if we add a few inches of MP to recover the lost IAS, the CHT will be about 30°F cooler than we were when ROP.
Same power, cooler CHT. Same power, cleaner exhaust. Cooler and cleaner is better. MUCH further away from detonation than the 50°F ROP suggested by Lycoming.
Note that it is NOT necessary to go through all this foolishness to set LOP on your engine! On yours, merely set the MP where it will ultimately be, and do the “Big Mixture Pull” to the LOP side in three or four seconds, and be done with it. That brief transit through “The Red Box” won’t raise the CHT by even 1 degree, and again, without a hot CHT, detonation is impossible with conforming fuel.
Richer is cooler and dirtier
Remember, there are an infinite number of MP, RPM, and mixture settings to produce a given HP. Most people have seen just one power chart for their airplane for a given power, and this gives them the idea there is one and only one combination of settings to get that power. Most also believe that MP and RPM are the major players. The truth is there are MANY reasonable ways to get any power setting, and ALL of them absolutely require a proper mixture setting.
For example, you can be ROP, and set 75% power with a "best power" mixture (as Lycoming recommends). That's one setting. It will produce the hottest possible combustion temperature and pressure, and CHT.
Now, think about this: You can go RICHER, and that will cause a slight power loss. You can, of course, add a bit more MP, and regain the power. Richer still, and add even more MP, and still have 75%. The power to the crank/prop is the same, but the pressure peak is further from TDC (richer mixture burns more slowly), and the STRESSES are less at the same power. I wouldn't recommend running this rich, since it's very "dirty" combustion, very likely to develop valve guide problems in the future. It makes the oil dirtier sooner, it produces lots of carbon monoxide, it fouls plugs, it costs more money in both fuel and maintenance bills, and it probably reduces TBO.
Continuing our example and starting from 50°F ROP and 75%, you can also lean it a little, lose a little power, regain the power with a little extra MP. Lean it more, add more MP, and still pull 75% power with all settings (if you have enough MP available). In fact, even with a highly supercharged engine, if it will run lean enough, you could run WOT (Wide Open Throttle), with extraordinarily high MP settings, and still be at 75% power, cooler than ever, much further from detonation, with a more efficient engine! But few engines will run this lean and remain smooth, or run at all.
The only reason the engine does not experience detonation is that the mixture is too lean to support it.
No. To be more accurate, a too-lean OR a too-rich mixture slows the combustion event down, putting it further after TDC, where the chamber volume is higher, and growing larger faster, with a greater mechanical advantage. It is at 50°F ROP where detonation is most likely, for that is the mixture setting (roughly) that produces the fastest possible burn, placing the pressure peak the closest to TDC.
At this point, there are a number of factors that can assume control over your engine and cause problems. If the initial leaning is not accomplished carefully it is possible that the engine is not really set at 50 degrees lean of peak where intended.
Yessir, boys and girls, that old evil ole LOP genie is just a-settin' there, waitin' to assume control of your engine. Let me get this straight, Lycoming. Pilots can "carefully" lean to 50°F ROP in accordance with the factory recommendation, but they are not capable of "carefully" setting 50°F LOP? What am I missing, here?
Properly leaning an engine is undoubtedly the least understood area of power management.
Yes, that's true, especially at the factory. I don't see either TCM or Lycoming making any efforts at education of pilots on this subject. In fact, they have been known to denigrate and ridicule those who ARE trying to educate.
During the attempt at power recovery, it is a major assumption that opening the throttle to regain power will not cause a richening of the mixture.
No, it is NOT a major assumption -- it is an empirically determined fact, backed up by readily available data obtained from the very engine we are discussing. On a fuel-injected Lycoming engine, opening the throttle to regain power DOES NOT in fact cause a richening of the mixture. Lycoming has the data that proves this (George sent it to Rick Moffett), but apparently either they don't know how to interpret it, or they don't care. (Even if Lycoming's suggestion that opening the throttle does cause detonation did turn out to be true on certain engines, it would be easily caught and corrected by reference to the CHT on the engine monitor.)
Unfortunately, some fuel metering units tend to provide richer fuel schedules as the throttle is opened and manifold pressure is increased.
This is another incorrect statement, at least in regard to the cruise power range. On all the engines I've seen so far, fuel flow increases with throttle movement, maintaining about the same fuel to air RATIO (mixture) until the climb power area is reached. There may be minor deviations, but again, all the data I've seen suggests the mixture goes LEANER, not richer.
Operating an engine “on the edge” is possible provided the pilot is extremely precise, has good instrumentation, and monitors the engine condition full time.
Lycoming considers LOP to be “on the edge.” In fact, the opposite is true, and here’s why.
Assume the 350 HP TIO-540-J2BD in the Piper Chieftain, with NO ENGINE MONITOR at all, just the way Lycoming likes it, as we don’t want to confuse the poor pilot with all that messy data now, do we? The pilot carefully establishes climb power and leans the engine to 1500°F on the TIT gauge by the POH. Remember, there’s only one TIT probe, and one factory CHT probe that may or may not be on the hottest cylinder.
This is a ROP setting, but in my opinion, it is much too hot! The engine is operating on the edge of light detonation, perhaps even in and out of detonation. Now a little detonation can be a good thing, but I don’t recommend it, as it can lead to medium and heavy detonation, and even preignition, which is definitely not good!
Now suppose one injector becomes clogged? The same fuel flow exists, but now one cylinder gets even less fuel, while five others get a little more. This puts that one cylinder right in the middle of what we call “The Red Box,” which leads to more and more detonation, rising CHT in that cylinder, preignition, and a catastrophic engine failure. Unless that one cylinder happens to be the one with the single CHT probe, the pilot will remain blissfully unaware of the event until preignition eats a hole in the piston, and the engine begins to run rough. This was one of the causes of the Wyalla (Australia) crash in 2001.
Now let’s reset. Cruising along, same airplane, still no Monitor System installed, but now LOP and one injector becomes fouled. That cylinder will suddenly begin running leaner! That will be harmless to the engine, and also it will instantly run rough, due to the leaner mixture. The pilot will instantly know there is something wrong, and can take steps to correct it, with no harm done.
The real experts say, “The ROP pilot needs an engine monitor far more than the LOP pilot does!”
It bears repeating here. If you are at the 50°F ROP mixture setting recommended by Lycoming for ANY power, you are just about as close to detonation as you can possibly get with ANY mixture setting at that MP and RPM. Enriching OR leaning from 50°F ROP will REDUCE the likelihood of detonation and increase the detonation margin.
The instrumentation issue
Unfortunately, many of these variables are out of the control of the operator who is relying on the premise that this is just a simple leaning technique.
Oh, rubbish! The above notwithstanding, NO ONE is recommending these techniques without FIRST having a good engine monitor. NO ONE is suggesting that an ignorant pilot lean without KNOWING what he is doing, and UNDERSTANDING the process. Besides, the 50°F ROP setting is the most critical setting for the ignorant pilot!
If a pilot is NOT prepared to invest in a good monitoring system AND to understand what he is doing, then my best advice is to use full rich for climb, never exceed 65% MP and RPM settings, and lean to any setting that seems about right. For the really abysmally ignorant and unequipped, just leave it full rich all the time! (Sadly, many "modern" CFIs teach exactly that: "See that red knob? Red means danger, don't touch it." And we wonder why people run out of fuel!)
As the last strike, once the engine has been established in the lean of peak condition, and the throttle has been advanced for power recovery, there is no means to confirm that the mixture is properly leaned.
Wrong. The temperatures on the engine monitor will tell the tale. It is TRIVIAL to do this.
The only way would be to richen the mixture to confirm peak TIT. This could move the engine into detonation.
No. It takes TIME to develop conditions for detonation. From a stable cruise condition with the CHTs in a proper range (around 380F or less, for example) it is trivial, and harmless to enrich momentarily to see where peak EGT lies. EGT response is nearly instantaneous, and the readings can be taken before the CHTs move more than a few degrees higher. This has been confirmed time and time again in the test cell at GAMI in Ada. In fact, it is possible to go from full power full rich mixture, straight to LOP in one stroke, without a trace of detonation, provided one does not linger near the 50°F ROP area for any significant period of time. By “significant” I mean one or two MINUTES.
It is also not possible to confirm what margin remains between the setting and the onset of detonation.
Lycoming is being seriously disingenuous here. Think about this. It is equally impossible to confirm what the detonation margin is at 50°F ROP! What's their point?
At least when operating LOP the CHTs will be at least 30°F F cooler, and that alone creates a better detonation margin. An intellectually honest analysis would seem to indicate that trying to set 50°F ROP is far more hazardous to the engine's health than trying to set 50°F LOP.
But it certainly is possible to check the detonation margin in the test cell! From that, some rough guidelines emerge that maintain a HUGE margin LOP, FAR more margin than 50°F ROP will!
The lean of peak methodology places strong emphasis on proper pilot techniques, accurate calibrated engine instrumentation...
What's wrong with that? Flying itself depends on that. No one ever said otherwise. Besides, if you are setting LOP, the actual accuracy of the instrumentation is not nearly as critical as when setting ROP.
...does not allow for confirmation of the proper mixture setting.
Wrong. I'll bet the folks who wrote that document have literally never been in an airplane with these techniques in use. The techniques are easier and much safer than the factory recommended techniques. In fact, I've had passengers comment, "Gosh, you sure don't seem to fiddle with the engine much!"
Any lapse in either can be financially costly or worse.
Especially operation at 50°F ROP!
The punch line
Lycoming is in complete agreement that it is possible to operate an engine on the lean side of peak TIT. It is done on engines in our well-instrumented Experimental Test laboratory every day. There is nothing detrimental in operating an engine in this manner.
Thanks for that, Lycoming! Some honesty at last, although this doesn't go the distance. LOP is cleaner and cooler, and cleaner and cooler is better for the engine.
Let me repeat what Lycoming states:
There is nothing detrimental in operating an engine in this manner.
How then, can the author of that Lycoming document threaten loss of warranty for LOP operation?
In the sales literature provided for this "new" technique, it is stated that Lycoming recommended this operational procedure in an owner's manual that dates back to the late '60's. No mention is made why it is no longer recommended on our present engines.
There seems to be a logical explanation for that. That's because Lycoming (and TCM) won't bother to do the quality control and set the specs high enough to ensure that the engines will operate smoothly when LOP. It's that simple. The stock engines usually CANNOT be operated LOP because of uneven mixture distribution among the cylinders, except a few, like those on the Malibu, and even those often require adjustment (with GAMIjectors) to run properly lean of peak.
The fact is that 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 pilots to utilize this technique with the instrumentation and distractions found in the typical general aviation aircraft.
Wrong, again. The reason was that Lycoming (and TCM) did not EDUCATE pilots as to the real processes at work. LOP was a scary idea then, and far too many pilots would set the book power settings, discover temperatures that were hotter than they liked, and would ENRICH (rather than further lean) just a little (to be "safe") over book settings, without regard for the actual results if they could read them at all on the factory-supplied instrumentation. By enriching a bit from the lean side at the very high power settings (recommended by the factory), owners and pilots INCREASED the heat produced, increased the power produced, and increased the stresses on the engine. Had the factories emphasized, "Try a little leaner," there might be a lot more Malibu’s today.
The end customer might be assured that if there is a problem resulting from engine mismanagement, the "experts" with their fuel nozzles and leaning recommendations will not be offering to pay the warranty to repair or replace the engine.
Neither does Lycoming or TCM, no matter what the cause! Well, that's a bit strong. Both DO pay warranty claims, if grudgingly, and sometimes even in cases of mismanagement, because they often cannot prove it.
When asked about this warranty policy in the event of a problem, the answer came back that this is regarded as a "improper operation on the part of the operator".
What? "... the answer came back..." From whom? Who asked? WHO gave that answer? Where has Lycoming or TCM made that statement, in writing, as official policy? Exactly what was covered by this purported statement? "Improper management," or LOP operations? I hear a lot of ignorant claptrap from tech reps that continue to parrot the OWTs (old wives' tales) they learned from who-knows-where, but if this is official policy, it's the first I've heard of it.
Operating an engine "on the edge" is possible provided the pilot is extremely precise, has good instrumentation, and monitors the engine condition full time.
Yes, especially if you're going to operate at the factory-recommended "edge" at 50°F ROP!
In the year 2013, AOPA published the results of a poll asking whether respondents thought LOP or ROP was “better for the engine.” Fifteen years ago, the answer would have been overwhelmingly in favor of ROP, perhaps approaching 100%. Today with better education, better instrumentation (and higher fuel prices) it’s about an even tie. As more and more people become more knowledgeable, that will continue to shift in favor of LOP operation. In fact, there is research going on that will make ROP operation an artifact of history, like the dinosaurs.