Leaning Off
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Yes, simple answer!!
We owe it to our students to teach them the correct method of managing all of the systems in the aircraft they fly. This includes the use of the mixture setting AND the theory behind it.
We owe it to our students to teach them the correct method of managing all of the systems in the aircraft they fly. This includes the use of the mixture setting AND the theory behind it.
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Yes, always. But unfortunately our club doesn't have a leaning policy so many instructors (including the CFI) don't bother. Methinks the membership should be asking why hourly rental charges are rather volatile. 
Then again, we are still in denial mode believing that the only aircraft suitable for training must have Cessna written on the aircraft.
Then again, we are still in denial mode believing that the only aircraft suitable for training must have Cessna written on the aircraft.
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Of the 4 schools I have flown with, only one seems to teach the use of mixture correctly as a standard practice.
One school says the reason they don't (and in fact ask me not to) is that incorrect use of the mixture can do more harm than good, particularly if flying too lean. So they think it's better in the long run for the engine to run fully rich all the time.
Another reason I've had is that during a training flight, you rarely get high enough to warrent leaning the aircraft. Some POH do state not to lean below 5000'. How often do you take students higher than that, now that spinning isn't a requirement.
I myself was not taught to lean correctly until i did my FI rating. I had some idea, and had read the book, but an instructor had never mentioned it.
One school says the reason they don't (and in fact ask me not to) is that incorrect use of the mixture can do more harm than good, particularly if flying too lean. So they think it's better in the long run for the engine to run fully rich all the time.
Another reason I've had is that during a training flight, you rarely get high enough to warrent leaning the aircraft. Some POH do state not to lean below 5000'. How often do you take students higher than that, now that spinning isn't a requirement.
I myself was not taught to lean correctly until i did my FI rating. I had some idea, and had read the book, but an instructor had never mentioned it.
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Some POH do state not to lean below 5000'
Some of us lean and save avgas succesfully and without engine damage at 2500' despite POH statements.
The POH is something every pilot should respect, BUT it's not a bible.
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Perhaps "leaning off" is a way of saying "leaning." Got it.
Actually, so far as the aircraft goes, it is. It's part of the legal certification of the airplane, and the airplane is unairworthy without it. The airplane is also unairworthy unless it is operated in accordance with the Aircraft Handbook, Pilot Operating Handbook, Aircraft Flight Manual, or whatever particular document is assigned that aircraft.
One must be careful, however, to differentiate between guidelines and limitations.
Some manufacturers recommend leaning above a particular altitude, not because the aircraft should not be leaned below that altitude, but as a way of "idiot proofing" the airplane.
Yes, improper leaning can result in damage to the engine (and ultimately the airplane and occupants). No, leaning below 3,000', 4,000', or 5,000' will not hurt the engine, airplane, or occupants. A recommendation to lean at higher altitudes is a gentle way of saying that one shouldn't lean above 75% power...or more specifically, that one can't hurt the engine when leaning below 75% power. By the time your mighty steed reaches several thousand feet, a normally aspirated (non-turbocharged, non-supercharged, non-turbocompound engine) isn't producing enough power and can't be run at a high enough power setting, to do harm.
Leaning for takeoff is necessary at higher elevation airports to protect the engine from fouling, to allow it to run cleanly, and to allow the engine to produce the most power possible for takeoff. This is safe, because one is unable to harm the engine...it won't produce enough power to cause damage.
Leaning should be accomplished per density altitude; One may very well be sitting at sea level and be able to lean with abandon, even for takeoff, due to density altitude. A hot summer day at 100 degrees F (37 deg C), one is already at a 3,400' density altitude on a standard-altimeter day with high humidity...one is very close to being able to lean as though one were flying at 3,000 MSL on an ISA standard day.
This may or may not be true for aircraft based at a sea level airport, but as we've just ,seen, one may easily be at an altitude where leaning is important, before we take off...at sea level...based on density altitude.
I learned to fly light airplanes at field density altitudes of 7,000' to 10,000, where leaning for takeoff was always necessary. Even if one is based at sea level, leaning for takeoff may be advisable, or necessary.
Does your operating handbook specifically state that one should NOT lean below 5,000'?
What does that mean, and how does it relate in any way to leaning an airplane engine?
Leaning a piston aircraft engine is basic to operating the engine. There is absolutely no excuse for failure to teach a student to properly lean the engine.
This is nonsensical. The same logic would dictate that one never take off, because one might crash. It's better for all concerned to stay in the ground, then.
Ridiculous.
A student should be taught proper ground operation of the mixture, and proper use in flight, every bit as much as proper operation of carburetor heat, fuel management, and emergency procedures.
The POH is something every pilot should respect, BUT it's not a bible.
One must be careful, however, to differentiate between guidelines and limitations.
Some manufacturers recommend leaning above a particular altitude, not because the aircraft should not be leaned below that altitude, but as a way of "idiot proofing" the airplane.
Yes, improper leaning can result in damage to the engine (and ultimately the airplane and occupants). No, leaning below 3,000', 4,000', or 5,000' will not hurt the engine, airplane, or occupants. A recommendation to lean at higher altitudes is a gentle way of saying that one shouldn't lean above 75% power...or more specifically, that one can't hurt the engine when leaning below 75% power. By the time your mighty steed reaches several thousand feet, a normally aspirated (non-turbocharged, non-supercharged, non-turbocompound engine) isn't producing enough power and can't be run at a high enough power setting, to do harm.
Leaning for takeoff is necessary at higher elevation airports to protect the engine from fouling, to allow it to run cleanly, and to allow the engine to produce the most power possible for takeoff. This is safe, because one is unable to harm the engine...it won't produce enough power to cause damage.
Leaning should be accomplished per density altitude; One may very well be sitting at sea level and be able to lean with abandon, even for takeoff, due to density altitude. A hot summer day at 100 degrees F (37 deg C), one is already at a 3,400' density altitude on a standard-altimeter day with high humidity...one is very close to being able to lean as though one were flying at 3,000 MSL on an ISA standard day.
Another reason I've had is that during a training flight, you rarely get high enough to warrent leaning the aircraft. Some POH do state not to lean below 5000'. How often do you take students higher than that, now that spinning isn't a requirement.
I learned to fly light airplanes at field density altitudes of 7,000' to 10,000, where leaning for takeoff was always necessary. Even if one is based at sea level, leaning for takeoff may be advisable, or necessary.
Does your operating handbook specifically state that one should NOT lean below 5,000'?
Then again, we are still in denial mode believing that the only aircraft suitable for training must have Cessna written on the aircraft.
Leaning a piston aircraft engine is basic to operating the engine. There is absolutely no excuse for failure to teach a student to properly lean the engine.
One school says the reason they don't (and in fact ask me not to) is that incorrect use of the mixture can do more harm than good, particularly if flying too lean. So they think it's better in the long run for the engine to run fully rich all the time.
Ridiculous.
A student should be taught proper ground operation of the mixture, and proper use in flight, every bit as much as proper operation of carburetor heat, fuel management, and emergency procedures.
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A number of years ago a pilot flying a C172 with 3 pax got his fuel sums a little wrong and realised that he was getting somewhat low on his return leg. He therefore slowed down to what he thought was the speed for maximum range and leaned out his engine as much as he could (2000'). He made it home - just and the following day the aircraft was found to be unable to develop its normal static full power R.P.M. The licensed engineer arrived and discovered that five out of six cylinders were cracked due to being overheated. An expensive bill for the owners!
P.P.
P.P.
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A number of years ago a pilot flying a C172 with 3 pax got his fuel sums a little wrong and realised that he was getting somewhat low on his return leg. He therefore slowed down to what he thought was the speed for maximum range and leaned out his engine as much as he could (2000'). He made it home - just and the following day the aircraft was found to be unable to develop its normal static full power R.P.M. The licensed engineer arrived and discovered that five out of six cylinders were cracked due to being overheated. An expensive bill for the owners!
P.Pilcher, thats an interesting story. So if we taught pilots to lean correctly on a regular basis, would this damage to cylinders be avoided?
Btw, on Ex 4 we teach (don't we?) the effect of the mixture control rather than how to lean off correctly?
Unless the exemplar pilot thought best range is at a high power (>65 to 75% and unlikely considering he reduced speed from cruise so must have reduced power from normal cruise setting) then he could lean all he wanted and do no damage to the engine. Indeed, if he reduced enough the engine would be lean of peak and run *cooler*.
More likely is that the engine had developed cracked cylinders over time but the cracks were only just found and/or the pilot in this example leaned at some power setting greater than 75% eg during climb at lower altitudes.
As for the original question: I always taught my students to lean at any altitude with 'leanable' power settings, starting from effects of controls. Usually not emphasized (although encouraged) during ab-initio stages but definitely required once navexes started.
More likely is that the engine had developed cracked cylinders over time but the cracks were only just found and/or the pilot in this example leaned at some power setting greater than 75% eg during climb at lower altitudes.
As for the original question: I always taught my students to lean at any altitude with 'leanable' power settings, starting from effects of controls. Usually not emphasized (although encouraged) during ab-initio stages but definitely required once navexes started.
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I teach the method for leaning as specified in the engine manufacturer's operator's manual which is often partially copied into the AFM / POH.
If you fly with a Lycoming then this is essential reading;
http://www.lycoming.textron.com/supp...Operations.pdf
I am in agreement with Cows getting bigger regarding agressiveleaning on the ground. This must be agressive to prevent full power being set with a lean setting. In this regard it is a good exercise to taxi the aircraft using the mixture to adjust the RPM (fixed prop)while also maintaining a smooth operation.
Very few pilots will have ever read the Engine Operating Manual for their aircraft. This is the first big mistake.
The second one is that few if any schools ask that the aircraft is operated at a particular power setting in the cruise. They frequently ask that the aircraft is cruised at 2400 RPM (fixed pitch prop) or 23" / 2300 RPM (VP prop) and ignore the fact that the power output at those figures will vary from both day to day and from one altitude to the next.
Lycoming recomends that the engines are operated at 65% or less and give excellent instructions on how to lean for both Best Power and Best Economy. The AFM/POH will specify fuel flow for various cruise (pressure) altitudes at 65% power with either best economy or best power leaning.
Unfortunately, if you ask an instructor what RPM they are going to use to get 65% power at 3000ft QNH 993 and ISA -10 they will give you a very blank look. They simply use 2400RPM but don't know what that gives and therefore have no idea of what the fuel consumption should be.
Can't comment on the Continental powered 172 - would have to look at the continental engine manual. However, if it was the bog standard Lycoming 4 cylinder version that was in use as above, Lycoming would clearly refer you to their publication above which dismisses the posibility of leaning being a cause of such damage at low power settings.
Such damage is more likely to be caused by shock cooling and was probably already there prior to the flight and the extra fuel consumption being a good possible indication.
I can tell you from experience that pilots do damage club engines by excessive leaning. They hire the aircraft at £x per hour (take-off to landing + 10 minutes) including whatever fuel they happen to burn. What they do is fly at very high power settings to reduce the flight time (on which they are billed) as much as possible and then lean the mixture to prevent the excessive fuel burn being noticed. Since most clubs don't have that accurate a fuel burn figure they get away with it. The engines don't meet their full life and the report from the overhaul shop cites over leaning and the school bans leaning. But people still do it anyway!!
Operate the engine in the cruise at 65% or less and Lean as per the engine manufacturer's instruction (best economy or best power) and you will a) have a long engine life and b) get very close to the published fuel burn figures if you keep accurate records.
---------------
PS
Most of the "don't lean" / "leaning will damage the engine" instructions come from training organisations. They often have stories about how they had engines damaged by excessive leaning.
They seem to ignore that on a regular basis the aircraft cruises for 10 minutes after departure and sudenly the throttle is closed, the engine idles (with a few brief demands of high power) for 5 minutes then operates at max power for 5 minutes which is followed by a brief cruise and again the throttle is suddenly closed. This is repeated several times per hour and the exercise happens daily sometimes and often more than once a week. But they blame leaning for the engine not reaching it's recommended number of hours before overhaul.
Lycoming don't design an engine for training in PFL's or Stalls or EFATO and are adamant that shock cooling is to be avoided. They even specify a maximum rate of cooling. Ignoring this is what breaks engines.
If you fly with a Lycoming then this is essential reading;
http://www.lycoming.textron.com/supp...Operations.pdf
I am in agreement with Cows getting bigger regarding agressiveleaning on the ground. This must be agressive to prevent full power being set with a lean setting. In this regard it is a good exercise to taxi the aircraft using the mixture to adjust the RPM (fixed prop)while also maintaining a smooth operation.
Very few pilots will have ever read the Engine Operating Manual for their aircraft. This is the first big mistake.
The second one is that few if any schools ask that the aircraft is operated at a particular power setting in the cruise. They frequently ask that the aircraft is cruised at 2400 RPM (fixed pitch prop) or 23" / 2300 RPM (VP prop) and ignore the fact that the power output at those figures will vary from both day to day and from one altitude to the next.
Lycoming recomends that the engines are operated at 65% or less and give excellent instructions on how to lean for both Best Power and Best Economy. The AFM/POH will specify fuel flow for various cruise (pressure) altitudes at 65% power with either best economy or best power leaning.
Unfortunately, if you ask an instructor what RPM they are going to use to get 65% power at 3000ft QNH 993 and ISA -10 they will give you a very blank look. They simply use 2400RPM but don't know what that gives and therefore have no idea of what the fuel consumption should be.
A number of years ago a pilot flying a C172 with 3 pax got his fuel sums a little wrong and realised that he was getting somewhat low on his return leg. He therefore slowed down to what he thought was the speed for maximum range and leaned out his engine as much as he could (2000'). He made it home - just and the following day the aircraft was found to be unable to develop its normal static full power R.P.M. The licensed engineer arrived and discovered that five out of six cylinders were cracked due to being overheated. An expensive bill for the owners!
Such damage is more likely to be caused by shock cooling and was probably already there prior to the flight and the extra fuel consumption being a good possible indication.
I can tell you from experience that pilots do damage club engines by excessive leaning. They hire the aircraft at £x per hour (take-off to landing + 10 minutes) including whatever fuel they happen to burn. What they do is fly at very high power settings to reduce the flight time (on which they are billed) as much as possible and then lean the mixture to prevent the excessive fuel burn being noticed. Since most clubs don't have that accurate a fuel burn figure they get away with it. The engines don't meet their full life and the report from the overhaul shop cites over leaning and the school bans leaning. But people still do it anyway!!
Operate the engine in the cruise at 65% or less and Lean as per the engine manufacturer's instruction (best economy or best power) and you will a) have a long engine life and b) get very close to the published fuel burn figures if you keep accurate records.
---------------
PS
Most of the "don't lean" / "leaning will damage the engine" instructions come from training organisations. They often have stories about how they had engines damaged by excessive leaning.
They seem to ignore that on a regular basis the aircraft cruises for 10 minutes after departure and sudenly the throttle is closed, the engine idles (with a few brief demands of high power) for 5 minutes then operates at max power for 5 minutes which is followed by a brief cruise and again the throttle is suddenly closed. This is repeated several times per hour and the exercise happens daily sometimes and often more than once a week. But they blame leaning for the engine not reaching it's recommended number of hours before overhaul.
Lycoming don't design an engine for training in PFL's or Stalls or EFATO and are adamant that shock cooling is to be avoided. They even specify a maximum rate of cooling. Ignoring this is what breaks engines.
Last edited by DFC; 30th Apr 2010 at 22:15.
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I've always taught students how to lean ON the the aircraft whilst wearing shades and to spout lines from Top Gun in order to help them pull women.
Or is that not what you are asking?
If you mean do you teach them how to manage the engine properly, which includes leaning, then of course. What do you think FI's are? Incompetent morons?
Or is that not what you are asking?
If you mean do you teach them how to manage the engine properly, which includes leaning, then of course. What do you think FI's are? Incompetent morons?
Unless the exemplar pilot thought best range is at a high power (>65 to 75% and unlikely considering he reduced speed from cruise so must have reduced power from normal cruise setting) then he could lean all he wanted and do no damage to the engine. Indeed, if he reduced enough the engine would be lean of peak and run *cooler*.
More likely is that the engine had developed cracked cylinders over time but the cracks were only just found and/or the pilot in this example leaned at some power setting greater than 75% eg during climb at lower altitudes.
As for the original question: I always taught my students to lean at any altitude with 'leanable' power settings, starting from effects of controls. Usually not emphasized (although encouraged) during ab-initio stages but definitely required once navexes started.
More likely is that the engine had developed cracked cylinders over time but the cracks were only just found and/or the pilot in this example leaned at some power setting greater than 75% eg during climb at lower altitudes.
As for the original question: I always taught my students to lean at any altitude with 'leanable' power settings, starting from effects of controls. Usually not emphasized (although encouraged) during ab-initio stages but definitely required once navexes started.
Engine damage in training aircraft due to miss handling comes in two varieties.
1) Cracked cylinders due to shock cooling. This occurs when the pilot rapidly reduces power from high power settings to idle or very low power settings, particularly on cold days. It is exacerbated if a prolonged descent is subsequently made at higher airspeeds and, especially bad if followed by suddenly going to a high power setting. Unfortunately a bit of this kind of abuse is necessary to carry out some training exercises, particularly the practice forced approach manoevre.
2) Burnt cylinders due to overheating is usually cause by long climbs at full power at low airspeeds and on hot days. Since most training aircraft do not have cylinder temperature guages there will be no immediate indication of this condition allthough the oil temp will provided a lagging indicator.
However there is no reason training aircraft have to suffer these problems if some basic good operating practices are taught. These include
1) Let the engine warm up. Runup (and especially takeoff) power should only be applied when the oil temp is in the green arc.
2) Make all (non emergency) throttle movements slow and deleberate.
3) After solo, drill into the students that the throttle and mixture control are connected. Except for the part of the flight immediately after takeoff, and after the prelanding (or HASEL)check has been carried out, all power changes start with verifying the position of the mixture control.
4) When carrying out PFL's, if possible start with a lower than normal cruise power setting and avoid back to back approaches. Allow a few minutes for the engine temps to stabilize before going into the second PFL. After the first PFL I take control, establish a low power setting, and use this time to debrief the student.
5) Point out to the student what is "normal" oil temp and oil pressure for the conditions. Make sure the student is actually paying attention by periodically covering the engine guages with your fingers and ask "what were they iondicating"
6) Have a formal brief for precautions required for engien operations on hot days (ground and air)
7) Teach the student how to properly lean and at the later stages of training have them lean in the cruise segment every no matter how short it is.
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A number of years ago a pilot flying a C172 with 3 pax got his fuel sums a little wrong and realised that he was getting somewhat low on his return leg. He therefore slowed down to what he thought was the speed for maximum range and leaned out his engine as much as he could (2000').
If he was flying at best range than the power setting would have been in the range of 45 %.
Speaking generally;
In zero wind conditions the speed for maximum range is the best lift/drag ratio speed - best glide speed.
In a tailwind it pays to reduce towards minimum drag (minimum sink speed).
In a headwind it pays to increase speed.
The best example being having a GS of 0 when at 75% power setting in level flight. In that case increasing power will increase range.
So someone stating that they got the best [B]range[/BB] from the aircraft may in some cases indicate that they were operating at a lot more than 75% power if they were at a level that is lower than that at which the engine is unable to produce more than 75% power (normally aspirated).
He therefore slowed down to what he thought was the speed for maximum range and leaned out his engine as much as he could (2000'). He made it home - just and the following day the aircraft was found to be unable to develop its normal static full power R.P.M. The licensed engineer arrived and discovered that five out of six cylinders were cracked due to being overheated. An expensive bill for the owners!
Over time, with cylinders that have already been re-conditioned several times cracking is to be expected. If aircraft owners are so tight with their money to the extent they cut corners to avoid installing new cylinders at overhaul time, then cracking of several times over reconditioned cylinders is inevitable, and you can't blame the pilot for that - no matter how convenient for the owner.
In my experience, very few private pilots even know what minimum static RPM means - or where to find the figure in the flight manual; let alone its significance as far as engine performance is concerned. Some pilots assume (wrongly) if the take off RPM is in the green band on the RPM gauge, the engine is delivering full power.
It is quite possible that in the Cessna 172 mentioned, the aircraft had failed to attain minimum static RPM for months, and no one had noticed.
Last edited by Centaurus; 3rd May 2010 at 11:58.
However there is no reason training aircraft have to suffer these problems if some basic good operating practices are taught. These include
1) Let the engine warm up. Runup (and especially takeoff) power should only be applied when the oil temp is in the green arc.
1) Let the engine warm up. Runup (and especially takeoff) power should only be applied when the oil temp is in the green arc.
Note there is no mention about oil temperature being in the green before run-up or take-off.
Similarly, the Cessna 152 Information Manual under WARM-UP, has this to say:
"Most of the warm-up time will have been conducted during taxi and additional warm-up before take-off should be restricted to the checklist procedures. Since the engine is closely cowled for efficient in-flight cooling, precautions should be taken to avoid overheating on the ground".
Those precautions would possibly include conducting any run-up into wind and avoidance of prolonged idling while conducting checks. That includes waiting for oil temperatures to rise when this is not required by the manufacturer.
Since neither the Cessna 172 or Cessna 152 are equipped with cylinder head temperature gauges it is difficult for the pilot to judge whether or not the engine is over-heating on the ground.
The Limitations Section of both the C172 and C152 make no mention of a requirement to have the oil temperature "in the green" before run-up or take off.
Turning now to the Normal Procedures (Cold weather operation) in both the C172 and C152 Information Manuals - where both state the following:
"During cold weather operations, no indication will be apparent on the oil temperature gauge prior to take-off if OAT are very cold. After a suitable warm-up period (2-5 minutes at 1000RPM). accelerate the engine several times to a higher engine RPM. If the engine accelerates smoothly and oil pressure remains normal, and steady, the airplane is ready for take-off".
Well surely that proves the point beyond doubt that waiting for the oil temperature to rise into the green sector before engine run-up or take off on these aircraft types, is unnecessary; and may even be counter-productive with regards to engine overheating possibility.
In the venerable DH 82A Tiger Moth there is no oil temperature gauge and the only engine limitation before run-up is to check the oil pressure normal at 35 PSI at 1000RPM.
Of course, the above comments apply to Cessna 152, 172 and the Tiger Moth and I do not have copies of the Information manuals of other light training types. Some aircraft with large radial engines certainly do have an engine oil temperature limitation before run-up is started. The Sea Fury has an oil temperature lower limit of 15 C as well as 120C CHT. The Convair 440 with its R2800 radials required a min oil temp of 40 C before run-up while the DC3 has an oil temp limit of 40C.
With light training types such as the C172, not only is there no operational requirement to have the engine oil temperature in the green sector before run-up but this waiting time for the oil temperature to reach the green sector often means sitting on the ground at the holding point for a long time. As Cessna warns - this can lead to overheating of the engine due to the close fitting cowls that are designed for efficient cooling while airborne.
Another factor not often realised by private pilots, is that as cylinder temperatures rise caused by lack of cooling airflow through the cowls on the ground, there is a steady loss of power due to hotter and less dense fuel entering each cylinder. This shows up in the minimum static RPM test if one is carried out.
It is important for instructors to be aware of the engine operating procedures published in specific aircraft types they may instruct on. Instructors must be careful not to rely too much on their personal opinions when it comes to engine handling and where possible stick to the facts as published in the relevant flight operational documents of the aircraft manufacturer.
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I like the way the crew leaned the engines on night charters on the Derby Airways/British Midalnd, Canadair Argonaughts with 4 Merlin engines.
The first officer was sent back to observe the colour of the exhaust flame!
Bob-- the most important effect is that if you get it mixed up with the throttle it can get very quiet!
The first officer was sent back to observe the colour of the exhaust flame!
Btw, on Ex 4 we teach (don't we?) the effect of the mixture control rather than how to lean off correctly?