Re: Ground leaning

Re: Ground leaning

Over in the Carb Heat thread there was mention of ground leaning.

We recommend ground leaning AT ALL TIMES as aggressively as possible--even to slight engine roughness.  So lean that if you forgot and pushed the throttle in, it would die.  That way, you can't takeoff with inadequate fuel flow.

Those who ground lean aggressively are having NO problems with fouled plugs and get much better mag checks as a matter of routine.

Walter Atkinson
Advanced Pilot Seminars

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Re: Re: Ground leaning

I use this method along with 1 minute of 1200rpm before shutdown and have had absolutely no fouled plugs or other engine related problems with my O-200.

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Re: Re: Ground leaning

Vin:

If you are agressively ground leaning, you can skip the 1200 rpms for one minute.  It is unnecessary.  That comes from dry-sump days on big radials where we were trying to scavange the oil out of the engine.  I still do that on the DC-3 I fly.  Not on ANY of the TCM or Lycoming engines.  On your engine it is only serving to keep you from getting to the beer sooner.

<g>

Walter Atkinson
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Re: Re: Ground leaning

Walter, what good does it do to lean below 1000 rpm on the ground?

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Re: Re: Ground leaning

Agressive ground leaning does several things. 

1) it keeps plugs from fouling.

2) it keeps the piston head and valve heads from picking up deposits.

3) A ground leaned mag check is MUCH more diagnositc of ignition problems than a Rich mag check.

4) a properly, aggressively leaned engine on the ground will have lower CHTs prior to takeoff power being applied.

There are NO known downsides to agressively leaning on the ground.  Leaning inadequately is not good.  Be very aggressive.  So much so that it won't take power without dying.  Since praticing this, I have not had a fouled plug (in ten years) and I have picked up weak plugs many times which passed the full rich mag check.

Walter Atkinson
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Re: Re: Ground leaning

Allow me to quote from the Marvel-Schebler Carburetor Maintenance Manual for MA-3SPA carburetors (and this note applies to every other carb. they made):
"C. Operation
1) Idle System (4, Fig 32.)
  With the throttle fly slightly open to permit idling, the suction of vacuum aboe the throttle on the manifold side is very high.  Very little air passes through the venturi at the time, and hece with very low suction on the main nozzle, it does not disharge fuel. ....
fuel and air passes upward through the idle emulsion channel where it is finally drawn into the throttle barrel through the primary idle delivery opening, subject to regulation of the idle adjusting needle, where a small amount of air passing the throttle fly mixes with it, forming a combustible mixture for idling the engine.  The idle adjusting needle controls the quantity of rich emulsion supplied to the throttle varrel, and therefore controls the quality of the idle mixture.  Turning the needle counterclockwise away from its seat richens the idle mixture in the engine,...  All fuel delivery on idle, and also at steady propeller speeds up to approximately 1000 R.P.M. is from the idle system. ....."

In other words, the mixture control has no effect at such low R.P.M.s.

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Re: Re: Ground leaning

If the mixture control has no effect at such low rpms, why am I able to get such a egt rise when I pull the knob? 
The subject of proper leaning will never go away until we are all electronic and fuel injected.  Everybody seems to have something that works for them.  I don't worry to much about fouling, but, I keep my rpms up, try to keep ground operations to a minimum, keep additives in my fuel, and aggressively lean while in the air.  Occasionally I will get some roughness on run up from my left mag, and this is due to oil that has settled in the bottom of the jugs.  When I experience this, I'll do a 2200rpm run and lean until the roughness clears.  I run on both 100LL and Mogas, and have had excellent results, with next to no fouling or build up on the plugs or valve stems and guides.  This is with a mid time O-200.

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Re: Re: Ground leaning

The reason for a rise in RPM when going to Idle Mixtrure Cutoff is because you pass through the optimum air/fuel ratio.

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Re: Re: Ground leaning

It’s clear the mixture cutoff shuts off all fuel flow even flow through the idle adjust needle valve.  (or my engine would still be running….grin)

Question:  If that's the case when you pull the Mixture Control, then I would think at some point while it is being pulled, it may partially reduce flow through the idle adjust needle valve thereby leaning the mixture.  What do you think?  (i.e. when the mixture control valve restriction becomes significant compared to the idle adjust needle valve restriction.)

If this is the case, then it has consequences when ground leaning. 

When you increase the throttle, say to taxi, the carburetor will draw fuel normally as enough air is drawn through the venturi to start the fuel flow.  Now the leaning you did in combination with the idle adjust is no longer valid for operation above whenever the idle adjust phase is no longer governing (~1000 RPM).  So to prevent fouling, you would need to lean again whenever going from idle to above idle condition and then back again.  You folks with the 4 CHTs and 4 EGTs can test this presumption if you wish.  Just a thought...

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Re: Re: Ground leaning

Another reason for "Ground Leaning" is density altitude.
If you are in Denver on a hot day, you may not be able to achieve enough power to take off.  Your engine may even die because of an overly rich mixture.
You need to lean for the highest static RPM before take off.
I have always enjoyed flying with pilots and students who have never encountered high altitude or high density altitude airports.  It is fun to watch their face when the engine faulters when the put to coals to the engine.  They abort the take off and are convinced that there is something wrong with the engine.  I ask them if they remember the lessons on engine leaning and the meaning of density altitude.  Once they have had actual experience with this situation, the light bulb comes on in their head.

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Re: Re: Ground leaning

Clay,

Good point, I've been there....well Lake Tahoe anyway. 

I think the ground leaning that is being discussed is restricted to ground leaning when the engine is at low RPM during, such as idle. 

Another question about these carburetors:

George, does the throttle shut off the idle adjust flow as you insert it?  If so, ignore my previous post.   (That's probably why the engine will keep running if you pull the throttle out all the way and then yank on the mixture knob).

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Re: Re: Ground leaning

For those doubting the efficiency of my recommendations, try this.

1) Start the engine.
2) lean slowly while watching the EGT guage. Keep going.
3) The EGT value will rise.
4) Explain how the EGT rises without the mixture being leaned.

Guys, I've done this on R-985s, and R-2800s, and O-470s--all carbureted. Yes, it's easier to do on injected engines.

Confusious say, "Don't tell man something impossible when he is already doing it."

<g>

Walter Atkinson
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Re: Re: Ground leaning

First of all, the idle mixture adjustment (needle valve) is set for standard atmosphere (sea level) PLUS some extra richness in order to compensate for high-pressure days in order to prevent a too-lean condition for starting/idling. 
My previous question was a rhetorical one, regarding leaning below 1000 RPM.  I asked it, not to disparage Walter's excellent advice on ground leaning, ...but to help everyone to recognize a common fallacy regarding leaning operations on the ground.
  "author" asked why he was able to get a "rise" before the engine dies during shut-down.  He didn't say what density altitude he was at, but if one carefully and slowly pulls the mixture towards idle-cut-off one should notice a slight (50 rpm or so) rise before the engine dies.  This confirms that the idle mixture needle is properly set.
Since we know a correct idle setting is deliberately set rich, that aggressive leaning on the ground might reduce spark-plug fouling from too-rich ground operations, primarily encountered at high density alititudes.  (Barry correctly points out that at some point the mixture control will reduce idle fuel to the point of complete fuel starvation as the mixture is pulled toward idle cut-off.)  But this is not "leaning" per se.  And my point in all this is that the suggestion that operating so lean as to further stress the engine (in an effort to more aggresively challenge the ignition systems) during run-up in the pre-takeoff checks is improper procedure.  (Any such stress from this leaned condition is merely proof that the mixture is too lean!  It's not a valid ignition check.)
  When the engine is "run-up" we are no longer operating it on the idle circuit.  At about 1400 rpm it is operating on the main venturi jet(s), (carbureted engines only,...fuel injection is a slightly different matter.)  During run-up and take-off, the mixture should be exactly where you intend it to be during takeoff!  This means if you're operating at Telluride you'd better be leaned for maximum power, best rpm, PLUS a slight amount to ensure cooling.  (That "PLUS" amount should be at the point of maximum rpm, then enriched to the point just prior to any rpm reduction.  THAT is the correct takeoff mixture setting.)  Meanwhile, until you get to the runup pad, you might avoid unecessary spark plug fouling by operating ABOVE 1000 rpm (to by-pass the idle circuit) in a ground-leaned condition,...but remembering to allow the engine to thouroghly warm up and lean it for takeoff prior to performing the run-up.
  If you read your engine's operator's manual, you'll likely find that most pilots have not operated in accordance with mfr's recommendations.  Mfr's of fuel injected engines frequently recommend ground leaning, and most also recommend especially after landing to operate to the parking area with the mixture in a leaned condiditon.  The same is true of carbureted engines.  (Compare that procedure to the common practice of shoving the mixture full-rich on short final.  Talk about spark plug fouling!  Not to mention shock cooling.)
  The warm-up period should be performed at 1200 rpm, not the minimum rpm that the throttle is set at.  This ensures that enough oil is slung off the crankshaft to lubricate upper cylinder walls during the warm-up.  This also helps warm the oil up more quickly as the oil warmed by the upper cylinders drains back into the sump.  (Pilots frequently believe that minimum idle speed is best during warm-up.  Not so.  After oil pressure is up for 30 seconds, the rpm should be increased to 800-1200 as a minumum.  The engine should never be idled below 800 rpm for more than a minute or the upper cylinders and pistons will be starving for lubrication.
  After the engine is sufficiently warmed, then lean for takeoff power, perform the magneto/propellor/alternate air (or carb. heat) checks, and then the engine is ready for flight.

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Re: Re: Ground leaning

George:

Your message has some good advise and some misinformation in it.  Let me try to take it one statement at a time.

<First of all, the idle mixture adjustment (needle valve) is set for standard atmosphere (sea level) PLUS some extra richness in order to compensate for high-pressure days in order to prevent a too-lean condition for starting/idling. >

This is correct.  FOR STARTING.

<Since we know a correct idle setting is deliberately set rich, that aggressive leaning on the ground might reduce spark-plug fouling from too-rich ground operations, primarily encountered at high density alititudes. >

And, at sea level as well. Ground lean at sea level, too.  The idle mixture is set rich to HELP the start procedure only, it is NOT optimal for idling. It is too rich for idling--even at sea level.

<And my point in all this is that the suggestion that operating so lean as to further stress the engine (in an effort to more aggresively challenge the ignition systems) during run-up in the pre-takeoff checks is improper procedure.>

Improper according to what engineering data?  I have been doing this for a loooong time as a standard procedure since the engineering data supports this as better than doing a runup full rich.  I am more than willing to SHOW you this.   Run-ups LOP are much more diagnostic for ignition problems than full rich run-ups which are all but worthless.  I routinely find bad plugs on a leaned run-up (and even more often during an in-flight mag check LOP--you are doing in-flight LOP mag checks, aren't you??) than you will ever find when ROP.  As a matter of fact,I found a bad plug on a 206 last week during this leaned run-up that showed as OK when the runup was done ROP.  Would you rather know or not know that you have a failing plug?  Would you rather know this before or after it completely fails?

<(Any such stress from this leaned condition is merely proof that the mixture is too lean!  It's not a valid ignition check.)>

This appears to be a statement with no basis.  What is too lean?  I call idle cutoff too lean.  If it's running, it's not too lean.  If you call any mixture that shows a problem, too lean, then you do not have a conforming engine and you'll seldom see a problem before you have a complete plug/ignition failure.  Me?  I want to know before it fails so I can fix it before it delays a trip.

<During run-up and take-off, the mixture should be exactly where you intend it to be during takeoff! >>

Not unless you don't care whether or not the run-up is diagnostic for ignition problems.  Have you ever SEEN LOP runups preformed?  Have you experienced these early identifications of problems?  If you are not doing your run-ups AGGRESSIVELY leaned, the answer is no.  I would be happy to demonastrate these for you and we show these in great detail during the Advanced Pilot Seminars.

<This means if you're operating at Telluride you'd better be leaned for maximum power, best rpm, PLUS a slight amount to ensure cooling.  (That "PLUS" amount should be at the point of maximum rpm, then enriched to the point just prior to any rpm reduction.  THAT is the correct takeoff mixture setting.) >

That depends on the engine. Sometimes yes; sometimes no. This topic is too broad for this thread.  IT would take a CHAPTER to properly respond to that statement.

<Meanwhile, until you get to the runup pad, you might avoid unecessary spark plug fouling by operating ABOVE 1000 rpm (to by-pass the idle circuit) in a ground-leaned condition,...but remembering to allow the engine to thouroghly warm up and lean it for takeoff prior to performing the run-up.>

This recommendation is without engineering support, although I'll admit that it does have many years of Old Wive's Tale support.  It also wears out a lot of brake linings.  <g>  A rich condition at 1200 rpms is not much better at avoiding fouling than at 900 rpms.  An engine leaned aggressively CANNOT foul a plug at ANY rpm.  Period.  There is nothing left unburned. This has been proven.  It is not opinion.

The method which is in harmony with the physics of combustion is to lean as aggressively as the engine will run as soon as the engine is started.  It will idle cleaner, without fouling. It will idle cooler which is good.  Do the run-up in this aggressively leaned mixture setting and get the best indication of a healthy ignition system as possible.  This will also keep the CHT's lower so the takeoff power doesn't heat them as much as quickly.  This is good. Then lean to the Target EGT you should have established at sea level.  This assures the best power available for the altitude, while ensuring a rich enough mixture not to have CHTs higher than necessary during the takeoff and climb.

These recommendations are engineeering data supported and are presented in the Advanced Pilot Seminars.  This venue does not allow for the thorough presentation of said data as the graphs are voluminous.  You can download a free PowerPoint presentation off of our website on Target EGT and how to lean for takeoff effectively at any DA, or OAT. <www.advancedpilot.com>

<If you read your engine's operator's manual, you'll likely find that most pilots have not operated in accordance with mfr's recommendations. >

Sometimes that's good.  Sometimes that's bad.

<Mfr's of fuel injected engines frequently recommend ground leaning, and most also recommend especially after landing to operate to the parking area with the mixture in a leaned condiditon.  The same is true of carbureted engines.>

This agrees with my position.  What is the difference in the physics of combustion in carbureted vs injected engines?  The cylinder, air, and spark don't know how the fuel got there.

<(Compare that procedure to the common practice of shoving the mixture full-rich on short final.  Talk about spark plug fouling!  Not to mention shock cooling.)>

I'll agree that it's fouling and a bad idea.  Shock cooling???  Another Old Wive's Tale we'll save for another thread.

<The warm-up period should be performed at 1200 rpm, not the minimum rpm that the throttle is set at.>

Disagree.  The lower the rpm, the lower the wear during warm up.

<This ensures that enough oil is slung off the crankshaft to lubricate upper cylinder walls during the warm-up.>

Have you ever SEEN the oil movement during idle?  SEEN IT??  Not envisioned it.  Actually SEEN it?  It is a fog.  It is not slung up there better during higher rpms.  It's already a FOG.  This is an often misunderstood issue--that higher rpms sling the oil up higher. Tain't so.  I've SEEN it.  Slap a puddle of oil 900 times a minute and see what a mess you have!  <VBG>  You won't have  a bigger mess if you slap it 1200 times a minute !!!  (yeah, that was smartalleck, but it kinda puts things into perspective)

<(Pilots frequently believe that minimum idle speed is best during warm-up.  Not so.  After oil pressure is up for 30 seconds, the rpm should be increased to 800-1200 as a minumum.  The engine should never be idled below 800 rpm for more than a minute or the upper cylinders and pistons will be starving for lubrication.>

Please provide data to support this as it is simply not supported by ANY data I've ever seen.  My Mark-One eyeballs have observed the opposite.  Will running it at 1000 rpm hurt anything after it's intially warmed up?  No.  Is it necessary?  No.  I can't warm my R-985 in the winter without running the rpms up, but in the summer, I can get complete warm-up at 800 rpms and will continue to do so since I know that the wear stress on the engine is lower at lower rpms until the oil warms up.

Respectfully, George, I have heard these things for all of my aviation career, and they are unfounded, unsupported, and will not die as old wive's tales.  That doesn't make them compatible with the laws of physics or the know data or observations.  I once championed them myself.  I now know better.  I'm learning all the time.  Data is a wonderous thing.

Walter Atkinson
Advanced Pilot Seminars

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Re: Re: Ground leaning

Wow.  A lot of cut-and-pasting could make this thread more and more lengthy until we run out of video memory!
  Walter, I realize that your messages are highly promotional for your "advanced" seminars.  I salute your efforts.  But not your "engineering" claims.  Your demands for "engineering data" (which yourself has already noted would be inappropriate for this forum) are a good debate ploy.  They are not informative with regards the truth.
  The only "data" I felt appropriate or necessary I've already quoted: the Engine Manufacturer's Operator's Handbook manual. (I assume you'll agree that the mfr. has "engineering data" available to their engineers?)   Let me quote from the Teledyne Continental Operator's Handbook for C series, 6 Cylinder Aircraft Engines:Item 3. Warm-up and Ground Test, b) "After at least one minute at 800 R.P.M., increase speed to 1200 RPM and continue warm-up until at least 75-degrees oil temperature is indicated.  Part of this period may be spent taxiing."
  From the Engine Operating Details section, Item 6 "Idling engine: ...at engine speeds below 800 RPM satisfactory piston lubrication cannot be maintained.  Therefore it is recommended that the engine not be allowed to operate below 800 rpm for prolonged intervals."  So, Walter, go ahead if you wish and continue to preach "Disagree.  The lower the rpm, the lower the wear during warm up."  (I doubt "slapping a puddle of oil" meets the engineering criteria you seek.  I hope the above quote from the manufacturer's manual was helpful in resolving the discrepancy with "any engineering data" you've "ever seen." )    But perhaps you should tell TCM and their designers and engineers how "This is an often misunderstood issue--that higher rpms sling the oil up higher."
  The idle mixture is NOT set just for starting.  It is not a "starting" mixture, it is an idling mixture, designed to keep the engine running, hot or cold.  The primer system is designed for starting.  (We agree that the idling mixture is more than rich enough to sustain idle in virtually all cases (especially a warm engine) and that the engine will still idle acceptably well at leaner settings, and I have no problem with taxiing around with an aggressively leaned mixture.)  But,...
  Regarding your deviations from the factory recommended procedures, I don't know if "a loooong time" is an engineering term or not, but I hardly think it qualifies as acceptable data.  It is contrary to ALL the checklists issued by the mfrs, approved by the authorities, and taught by all the well established (and approved) schools.  I recommend to all pilots to read and use their mfr. checklists. 
  As for LOP run-ups, you might find TCM's Cautionary note interesting: "Excessively lean fuel-air mixture will cause overheating and may cause detonation."
  Your admonishment to perform " an in-flight mag check LOP--you are doing in-flight LOP mag checks, aren't you??" is irresponsible in my opinion.  The last place I want to find (or cause) detonation is at cruise power settings, in flight no less!!  (Clue: Did you ever notice what happens to your EGT's when you run it on only one mag in flight?  Have you ever had an exhaust system or turbo-charger or induction system blow apart in flight?  With this technique, someday you might.)
  Regarding my opinion that a run-up leaned so far as to create roughness during mag-checks is improper, you stated, "This appears to be a statement with no basis. What is too lean? I call idle cutoff too lean.  If it's running, it's not too lean.  If you call any mixture that shows a problem, too lean, then you do not have a conforming engine..."   Dear Walter, if you've leaned that engine so far that it runs rough on one mag....it's because your RUN-UP PROCEDURE IS NON-CONFORMING!  The purpose of a mag check is not to see how lean you can make it run on one mag, it's to see that all the plugs are firing in a RICH MIXTURE....not a lean one!  If your plugs don't fire in a rich mixture then you've diagnosed a failed IGNITION system.  If you get roughness because of an aggressively leaned mixture you've diagnosed an EXCESSIVELY LEAN FUEL SYSTEM.    That's exactly why the mfr's want you to run it up rich.  (If you've got a fouled plug due to excessive operation in a too-rich mixture, then lean it out to clear the plug, then go back to the rich condition to check the ignition.)
  Your statement "Not unless you don't care whether or not the run-up is diagnostic..." is ignorant of the statement you're criticizing, in which I specifically stated "During run-up and takeoff, the mixture should be exactly where you intend it to be during takeoff!"  That's because the purpose in performing the run-up is to determine whether the engine will be "conforming" sufficiently to actually PERFORM that takeoff.  It hasn't got a thing to do with experimenting with some half-cooked technique for getting it to cough and sputter through a too lean run-up mixture that we can erroneously blame on ignition failure.  I'll guarantee you can find every engine in the fleet that will cough and sputter at some leaned mixture setting that's too lean to support combustion in every cylinder.  That's because carbureted engines do not have evenly distributed fuel to all cylinders.  (Neither do most fuel injected engines.  That's why GAMI makes and successfully markets their fine product line of calibrated fuel injectors.) 
  Walter, if you lean to the pont of backfire it's because you've got at least one cylinder with insufficient fuel to properly ignite, even with a healthy ignition system.  No engine has all it's cylinders running the same exact mixture, and therein lies the folly of your teaching.
  My Telluride example doesn't take a "chapter" to discuss.  It's pretty simple to understand.  At high altitudes, prior to takeoff, the pilot sets takeoff power, leans to maximum available power, and then runs the mixture back towards rich very slightly before he releases the brakes.  It's all any manufacturer asks the pilot to do.  It gives you a workable mixture setting to obtain maximum available power at that altitude without unduly cooking, overheating, or otherwise overstressing your engine.  Pooh-pooh it if you wish, but you'll be contradicting thousands of years of combined experience (and engineers) at the engine maker's. 
  Your declaration of proper operating procedures, manufacturer's checklists, and years of experience as "old wives tales" is misleading and irreconcileable with good operating practices.  (John Deakin can get away with that phrase because he did his homework.)   You can't legitimately just use it and expect it to knock down long-established techniques endorsed by the designers and engineers at the mfr's, and successfully used by so many before you, that differ from those you might wish to use to promote "advanced" seminars.  My 2 cents.

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Re: Re: Ground leaning

Heavy duty discussion here!
I have a 1962 182E with its original 1962 0-470-R engine with 1350 hours. After many sputtering mag checks after starting, I have made some changes in my procedures. Some may like them and some may not, but it works for me. After engine start, I lean my mixture, immediately. Then I move the throttle up to 1200rpm. and lean aggressively. This does a couple of things, one of which is that my generator has come on line by then, and I am not depositing lead on my plugs, because the engine is now running hotter. I suppose if Alcor TCP were available that that would be a help.
As soon as I have landed, I lean aggressively. Also, I do not move the mixture to rich while in the pattern. If I have to do a go-around, the mixture is the first control reset to rich. When I get back to my parking place, I throttle up to 1700 and run the engine for about 15 seconds, idle back to 1200, then pull the mixture to idle cutoff.
Glenn

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Re: Re: Ground leaning

George:

If being in business and offering my qualifications offends you, I'm sorry. For your information only:

I hold an ATP, SEL&S, MEL&S; CFII, MEI; and A&P.  My education includes a BS, and doctorate.  I fly and maintain multiple types of airplanes which include GA aircraft (Cessnas, Beeches, Pipers, Cirruses, Lancirs, etc) and big, radial-engined warbirds (C-46, C-47, B-24, etc.) I am not a casual aviation enthusiest.

I'm going to try to answer each of your comments with explanations which are compatible with the laws of physics.

Anyone who thinks that the text recommendations in the POH are
a good source of engineering data, prepare yourself.  It was not written by engineers.  It, in some cases, wasn't even written by a pilot.  In some cases the POH recommendations in the text are not even in harmony with their own engineering graphs in the SAME POH. Quoting the POH text can get you into engineering trouble. Take the time to LOOK at and study the graphs, not just read the text.

The POH recommendation to increase rpm to 1200 is to aid in the raising of temps.  Engine speeds *below* 800 rpm can result in poor bearing lubrication under certain circumstances (like HIGH oil temp).  It has nothing to do with splashing oil up under the cylinders. The quickest way to raise engine temps is to lean away from the idle rich mixture!

It is not necessary for me to tell TCM's enginers (if they had any left) that oil splashing up is not an issue where rpm is concerned.  It has to do with bearing oil pressure with a slow turning oil pump and high oil temp.  BTW, there is only ONE powerplant engineer at TCM. He's in the LEGAL department.  Don't believe me?  It's true. I agree, it's hard to believe. It's also depressing.  But, since the last thing "new" to come out of TCM was in the 60's, what do they need to be paying a powerplant engineer for?
 
<<As for LOP run-ups, you might find TCM's Cautionary note interesting: "Excessively lean fuel-air mixture will cause overheating and may cause detonation.">>

You know, this is so WRONG it's hard to respond to.  It's very misleading.  The above statement relates to takeoff power, not idle, low-power mixtures and the statement is really misleading.  It is WRONG.  There is NO lean mixture which can cause detonation and the engineers have known this to be true since the twenties or thirties.  What they should have said was, "not rich enough mixtures can cause overheating and may cause detonation."  That would be an absolutely TRUE statement.  "Too lean" and "not rich enough" are NOT the same thing.  The statement you quoted from the POH is absolutely FALSE and is proven false by their own engineering data--probably in the same POH. That's not my opinon, it's according to ALL of the engineering data from EVERYBODY.

I can't help it. I've gotta cut and paste this one.
<<Your admonishment to perform " an in-flight mag check LOP--you are doing in-flight LOP mag checks, aren't you??" is irresponsible in my opinion.  The last place I want to find (or cause) detonation is at cruise power settings, in flight no less!!  (Clue: Did you ever notice what happens to your EGT's when you run it on only one mag in flight?  Have you ever had an exhaust system or turbo-charger or induction system blow apart in flight?  With this technique, someday you might.)>>

This is a strong indication that there are some serious holes in your understanding of the physics of combustion.  If one were to experience detonation, one of the quickest ways to STOP it is to turn one mag OFF.  That causes the ThetaPP to be retarded, which retards the "effective" timing, which lowers the peak internal cylinder pressures and STOPS the detonation event.  John Deakin, George Braly, and I have done it many times on the engine test stand to PROVE it.  I've seen it done in flight to stop a detonation event.

The reason the EGT goes UP is this retarded timing issue.  More of the unburned charge is still burning as the valve opens.  This makes the EGT reading go UP.  You have no-doubt noticed what happens to the CHT.  It goes DOWN on one mag. That makes detonation less likely.  Detonation  requires high CHTs and higher pressures, not lower ones.  George, I can only surmise that you have not SEEN these things.  I invite you to come SEE them for yourself (shameless promotion for Advanced Pilot Seminars, which would educate anyone wishing to observe these phenomenon for themselves). 

Now, as for the admonishment that I'm gonna blow the exhaust off the airplane with an in-flight mag check. I do an in-flight mag check on every flight.  I do them in my radial-powered Twin Beech.  I do them in my IO-550 Bonanza and I do them in the IO-520 C-206 I fly regularly.  EVERY FLIGHT.  I've found many bad plugs that passed a rich run-up check and we were able to change them before they completely failed. I've never had an engine quit while doing this (it would require a completely dead mag), but if I did, I would not switch back to BOTH, I'd let it die, pull the mixture, go to BOTH mags, then push the mixture in slowly to restart without worrying about an exhaust after-fire.  You called it a backfire, which is technically incorrect.  A backfire goes BACKWARDS into the intake system. An afterfire occurs in the exhaust.  A piccdillo, but since we're trying to be accurate...

The purpose of the run-up is to determine that things are working prior to flight. PERIOD.  Wouldn't you like to know how healthy things are?  The mag check has NOTHING to do with mixture.  It has to do with checking the health of the ignition system.  This is poorly done ROP since the stress on the ignition system is low.  The stress on the system is higher when very lean mixtures are used.  If you care about the health of the system, do this as lean as you can.  A healthy ignition system will run smoothly during the mag check at ANY mixture which was smooth on both mags.  Would you like to SEE this done?  I will be happy to SHOW you this on any one of the aforementioned airplanes (so you don't have to worry about hurting yours!).  You are correct about one thing, if your mags don't fire on a rich mixture run-up, you have a failed system.  I like to know I have a problem BEFORE it fails completely.  There is no such thing as an excessively lean system as long as it's running.  An excessively lean system won't run at all.  If you do your lean mag checks instead of rich ones, you will not have a fouled plug.
 
You knock my statements and declare that John Deakin can get away with saying what he does because he's done his homework.  I've got bad news for you.  John Deakin is my PARTNER in the Advanced Pilot Seminars.  Where do you think he gets some of his carefully researched material?  Go back and read his articles.  You will notice that in one article about six months ago, he credited ME with figuring out how to run carbureted engines LOP--in a C-182.

George, with all due respect, we've had a number of guys who took your position come learn for themselves. Some have had to kill an awful lot of old wive's tales.  The latest include people from the FAA engine directorate as well as the Queen's Coroner from Australia, OEM engineers, and the owners of five of the best engine overhaul shops in the world.  Not one of them has stated that the inofrmation and the time and money spent to come SEE for themselves wasn't worth twice what they paid for it.

I used to think what you are saying was correct.  I was wrong for thirty years.  I was dead wrong.  Come see for yourself. (shameless business promotion in an effort to allay any confusion you might still have).

I would be most interested in talking with you by phone about these and other issues.  I HATE trying to communicate these difficult issues by keyboard.  It's inefficient and has a tendancy to sound curt and impolite.  I do not intend any of my remarks to be such. Please feel free to call. (225) 925-2066.

If the object of this board is to inpart knowledge and make flying safer, then I'm in.  If the object is to sit around and glad-hand, grin, and spread Old Wive's Tales, take hangar-flying loudmouths at their words without challange, maybe I'm in the wrong place.

Walter Atkinson
Advanced Pilot Seminars










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Re: Re: Ground leaning

Glenn:

If I were going to fly your airplane and be as kind to it as I could, I would handle the mixture exactly as you have described for the flight regimes you have listed.

Since you handle your airplane like that, I'd be comfortable letting you handle mine like that.  Your practices are compatible with the know engineering data compiled by all of the engine manufacturers and verified in the most advanced engine test facility in the world.

Walter Atkinson
Advanced Pilot Seminars

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Re: Re: Ground leaning

As an aside: There has been only 1 cylinder replaced on my 0-470-R in its life since new. My compressions have stayed above 68.
Glenn

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Re: Re: Ground leaning

I have found this thread very informative on both sides.  This just goes to show how a group of people can have such different views on the same thing.  This reminds me of the discussions of years past about weather or not Auto gas is good for the plane or not.  I have my opinion based on my personal experience but it is different that many others.

I have enjoyed reading the different views on the subject.

       Dave

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Re: Re: Ground leaning

<There has been only 1 cylinder replaced on my 0-470-R in its life since new. My compressions have stayed above 68.>

That's great.  When and by whom was your engine last rebuilt?

Walter Atkinson
Advanced Pilot Seminars

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Re: Re: Ground leaning

Dave:

I'm glad you have enjoyed the exchange and found it educational.  As it turns out, the auto fuel debate is finally getting some research data collected.

A) It seems that the old wives tale about engines needing lead to lubricate the valves is total nonsense.

B) The valves on engines using auto fuel DID experience valve problems and we now think we know why.  Auto fuel burns faster than 100LL and as a result, the engine labors under higher internal cylinder pressures.  THIS is what created the problem.  We now appreciate that engines run at the same ThetaPP on ANY fuel will have the same stresses on them.

C) The new PRISM elctronic ignition will address this very problem by adjusting the spark timing to keep the ThetaPP at the proper point so all current GA engines can be run on unleaded fuel without detriment.  This is an answer for any future fuel crisis which does not require any caustic additives.

Walter Atkinson
Advanced Pilot Seminars

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Re: Re: Ground leaning

Walter, could you explain ThetaPP.  I must say, that is a new one on me! (computer search says check my spelling?)

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Re: Re: Ground leaning

Jon

     ThetaPP = theta prime
I think it's going to take a course in trig or calculus to understand it.
That's all I know about it...
(careful what you ask for...the server could run out of "ink")  :p

Michael

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Re: Re: Ground leaning

Walter,
My engine has not been rebuilt. The log books show a couple of periods of several years where the engine has not been run, or run very little. I have owned the plane for 3 years and have experienced no problems. My annual flying is between 50 & 60 hrs. per year.
Yesterday, we started the annual and the engine compressions were between 68-73. The dye check of the nose fork revealed cracks so that has to be replaced. Oh well!!
Glenn

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