Leaning the C172 aircraft?
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Leaning the C172 aircraft?
I am a quite new pilot but I've really never understood how exactly I should lean my C172 aircraft properly.
I do understand that I should be on the rich side of peak. I have EGT and RPM instruments.
But how fast should I lean? Should you drag the mixture control out first or should you from the beginning only start to turn the knob for it to go out slowly? Or a combination dragging and then turning the knob?
I tried once to get the EGT to peak. First it went higher and higher. But it never turned to go any lower. It just kept going higher and higher until the RPM dropped more and more.
What did I do wrong?
I do understand that I should be on the rich side of peak. I have EGT and RPM instruments.
But how fast should I lean? Should you drag the mixture control out first or should you from the beginning only start to turn the knob for it to go out slowly? Or a combination dragging and then turning the knob?
I tried once to get the EGT to peak. First it went higher and higher. But it never turned to go any lower. It just kept going higher and higher until the RPM dropped more and more.
What did I do wrong?
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From what you describe I deduct that you have an aircraft with EGT monitoring on 1 cylinder. It sounds like the other cylinders have reached peak and gone well on the lean side before the cylinder your instrument monitors reach peak.
This is not an instruction, just telling you what I would have told a student of mine in the same situation: Your only choice is to use the old ways... lean until it runs rough and then push it in until its smooth again plus whatever margin you want... and as always, stay below 75% effect and make sure to follow whatever instructions the manufacturer/manual, owner or operator tells you.
This is not an instruction, just telling you what I would have told a student of mine in the same situation: Your only choice is to use the old ways... lean until it runs rough and then push it in until its smooth again plus whatever margin you want... and as always, stay below 75% effect and make sure to follow whatever instructions the manufacturer/manual, owner or operator tells you.
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Ok thanks
But how fast can I lean?
Should I always start with only turning the mixture control 1/2 around and wait 3-5 seconds. Or can I drag it out a bit first and then start the turning?
Thanks!
But how fast can I lean?
Should I always start with only turning the mixture control 1/2 around and wait 3-5 seconds. Or can I drag it out a bit first and then start the turning?
Thanks!
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ctrl's correct, read your POH on leaning and the lycoming O-320 series operating manual, its free to download.
Last edited by Ralis; 12th Sep 2013 at 09:59.
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Search for John Deakin's articles on engine management. You can pull the mixture control at a fair pace, until you feel a slight deceleration. If the engine remains smooth, then you are already LOP and all is well. If it is not smooth, enrich until smooth.
if you do this at 65% or less, you cannot hurt the engine with the mixture control. Carbureted engines are more difficult to run LOP because the fuel/air distribution is less uniform. Some cylinders may be running ROP while others may be LOP. LOP will provide less horsepower than ROP and thus loss of smoothness.
EGT is just a way to navigate the power/mixture curve. Hottest CHT (the temperature that matters most) is found at about 40°F ROP.
if you do this at 65% or less, you cannot hurt the engine with the mixture control. Carbureted engines are more difficult to run LOP because the fuel/air distribution is less uniform. Some cylinders may be running ROP while others may be LOP. LOP will provide less horsepower than ROP and thus loss of smoothness.
EGT is just a way to navigate the power/mixture curve. Hottest CHT (the temperature that matters most) is found at about 40°F ROP.
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I love Deakins articles but most of what you read in them can only be applied in an AC with good engine instrumentation and with a fuel injected engine...
To the question of time... turning the knob is just pointless accuracy for this way of leaning, pull slowly, I do not really know how slowly I do it but it definitely takes less than 10 seconds, maybe under 5 from full rich until I get at rough engine and in the Cessna I fly its just a 1cm push from that to have a great running engine that uses several liters less per hour than running full rich.
To the question of time... turning the knob is just pointless accuracy for this way of leaning, pull slowly, I do not really know how slowly I do it but it definitely takes less than 10 seconds, maybe under 5 from full rich until I get at rough engine and in the Cessna I fly its just a 1cm push from that to have a great running engine that uses several liters less per hour than running full rich.
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Ok, great.
So the quickest way to find the EGT peak is to pull smoothly on the mixture until the engine goes rough and then back. Then start turning the knob slowly to get the peak value and set the yellow indicator to that.
Then turn back 50 degrees F on rich side to get recommended lean.
So the quickest way to find the EGT peak is to pull smoothly on the mixture until the engine goes rough and then back. Then start turning the knob slowly to get the peak value and set the yellow indicator to that.
Then turn back 50 degrees F on rich side to get recommended lean.
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As mentioned above, use a basic technique.
Level off at cruise altitude. Set engine to say 2250 RPM. Pull out mixture a nominal amount say 2 cm. Then slowly rotate outwards until engine runs rough and enrich to smooth running.
Obviously check the Flight Manual.
Flyme.
Level off at cruise altitude. Set engine to say 2250 RPM. Pull out mixture a nominal amount say 2 cm. Then slowly rotate outwards until engine runs rough and enrich to smooth running.
Obviously check the Flight Manual.
Flyme.
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Another question in this context:
During training, we generally leaned only above 3,000ft.
At my current location, when I go flying, I rarely climb above 3,000 ft. due to airspace and frequent cloud.
Would it be a good idea to lean when cruising at, say, 2300 ft.?
From my understanding, the "fully rich below 3,000 ft" applies to the climb only and anything else is just a sort of safety precaution in the training environment?
During training, we generally leaned only above 3,000ft.
At my current location, when I go flying, I rarely climb above 3,000 ft. due to airspace and frequent cloud.
Would it be a good idea to lean when cruising at, say, 2300 ft.?
From my understanding, the "fully rich below 3,000 ft" applies to the climb only and anything else is just a sort of safety precaution in the training environment?
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Julifly,
You are oversimplifying a bit. Peak EGT cannot be found by feel, only by instrument. Leaning till roughness and then enriching, you could be LOP but anywhere else too. Running AT peak EGT (smooth engine) is better and cooler than 50°F ROP.
You can lean at any altitude. The full rich position is there to protect the engine at full power. A very rich mixture slows down combustion and lowers CHTs. A LOP mixture also lowers CHTs and is less stressful on the engine. In my airplane, running LOP (all the time except take-off and climb) saves enough fuel to pay for the engine overhaul at TBO. My engine is in perfectly good health according to the oil analysis.
You are oversimplifying a bit. Peak EGT cannot be found by feel, only by instrument. Leaning till roughness and then enriching, you could be LOP but anywhere else too. Running AT peak EGT (smooth engine) is better and cooler than 50°F ROP.
You can lean at any altitude. The full rich position is there to protect the engine at full power. A very rich mixture slows down combustion and lowers CHTs. A LOP mixture also lowers CHTs and is less stressful on the engine. In my airplane, running LOP (all the time except take-off and climb) saves enough fuel to pay for the engine overhaul at TBO. My engine is in perfectly good health according to the oil analysis.
I tell all my students to go to the Lycoming web home page. They have a great section called Lycoming tips. I also encourage pilots to get a copy of the Lycoming engine operating manual for the engine type in their aircraft.
To answer your question. Lycoming is unequivocal about leaning. You can lean your engine at any altitude as long as the power it is developing is less than 75%. For climbs to higher ( eg above 5000 feet ASL) altitudes at full throttle leaning is mandatory to achieve POH book performance.
I lean in cruise at all altitudes all the time. It is actually better for the engine and it saves gas.
As for technique on your average trainer/tourer that has a carburated 4 cylinder engine pull the mixture until the engine starts to run rough then slowly enrich until the engine is smooth again, job done.
When leaning it should take about 10 seconds of slowly moving the knob from the full rich position to when the engine starts to run rough. Leaning faster than that will usually cause you to overshoot the actual moment when the engine starts to run rough indicating a too lean state.
Last edited by Big Pistons Forever; 12th Sep 2013 at 17:38.
I was taught like others to lean only above 2500, until I tried it on a solo cross country one day and was amazed at how much fuel I saved (I dipped the tanks at the end of each leg). In the 180HP 172R I was flying it amounted to about 5 liters per hour I was literally throwing away by not leaning.
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why does everyone find simple stuff so damned hard?
ok first thing. make sure the engine is warmed up and the oil is at normal cruising temperature. it is pointless leaning a cold engine.
establish in straight and level cruise.
look at your rpm dial.
slowly pull out the mixture knob watching the revs. they should increase about 50rpm until optimum mixture is achieved then the rpm will fall off.
push the mixture back in until the peak rpm returns. then screw in (richen) the mixture two turns and leave it at that.
if you change altitude or you need to use carby heat just push in the mixture knob and then do it again.
in a properly sorted engine you dont need EGT gauges. you can do it quite adequately watching the RPM.
ok first thing. make sure the engine is warmed up and the oil is at normal cruising temperature. it is pointless leaning a cold engine.
establish in straight and level cruise.
look at your rpm dial.
slowly pull out the mixture knob watching the revs. they should increase about 50rpm until optimum mixture is achieved then the rpm will fall off.
push the mixture back in until the peak rpm returns. then screw in (richen) the mixture two turns and leave it at that.
if you change altitude or you need to use carby heat just push in the mixture knob and then do it again.
in a properly sorted engine you dont need EGT gauges. you can do it quite adequately watching the RPM.
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Originally Posted by dubbleyew eight
look at your rpm dial.
slowly pull out the mixture knob watching the revs. they should increase about 50rpm until optimum mixture is achieved then the rpm will fall off.
push the mixture back in until the peak rpm returns. then screw in (richen) the mixture two turns and leave it at that.
slowly pull out the mixture knob watching the revs. they should increase about 50rpm until optimum mixture is achieved then the rpm will fall off.
push the mixture back in until the peak rpm returns. then screw in (richen) the mixture two turns and leave it at that.
For best economy on aircraft without proper engine instrumentation, one of the proper ways is to lean until the engine starts running rough and then increase mixture just a little bit so to have a smooth running engine, which should put you around peak EGT. And since you have cooler temperatures (CHT) than at best power and the engine is running smooth, there's absolutely no harm to the engine (again, below 75%).
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some friends of mine bought a cherokee that was reputed to be incredibly fuel efficient and leaned out well in flight.
the engine was sent in for a check as part of the refurbishment.
eighth inch wide cracks in the inside of the cylinder heads. it proved cheaper to scrap the engine than to fix all the damage.
fuel is cheap, engines are expensive.
the engine was sent in for a check as part of the refurbishment.
eighth inch wide cracks in the inside of the cylinder heads. it proved cheaper to scrap the engine than to fix all the damage.
fuel is cheap, engines are expensive.
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ok first thing. make sure the engine is warmed up and the oil is at normal cruising temperature. it is pointless leaning a cold engine.
Even with carburettor engines I was taught to lean on the ground in high temperatures.
Edited to add: My local commercial training school taught their students flying Warriors on cross countries to set full throttle above 5000ft and lean to reqired power setting. The engines nearly always made recommended TBO.
D.O.
Last edited by dont overfil; 13th Sep 2013 at 12:25.
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W8,
Detonation, auto-ignition, bad maintenance. Every pilot should inform himself about the proper leaning procedures for his engine. Even the POH is no always to be trusted since it was first written by engineers (mostly correct) then proofread by the lawyers (....) and then 'adjusted' by the marketing dept.
No proper engineer would recommend operating at 50°ROP at high power, but it suits the marketing dept just fine, giving a few more knots (with no regard to engine life).
Detonation, auto-ignition, bad maintenance. Every pilot should inform himself about the proper leaning procedures for his engine. Even the POH is no always to be trusted since it was first written by engineers (mostly correct) then proofread by the lawyers (....) and then 'adjusted' by the marketing dept.
No proper engineer would recommend operating at 50°ROP at high power, but it suits the marketing dept just fine, giving a few more knots (with no regard to engine life).
