How much to lean the mixture?

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MultiMediaWill

Pre-takeoff checklist
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Will
I was wondering imagine if I was to takeoff from Boulder, CO in a C172. The airport elevation is 5,300 MSL. How much would you lean the mixture for takeoff? I train in the very flat midwest and the highest airport elevation around here is 1000ft MSL so I never have to lean the mixture on takeoff.
 
Lean for best power at high elevation airports as you are rolling. Add just a tad rich to be safe if you don't have EGT monitors.

At Laramie, WY. elevation 7,400' MSL, I just lean for best power as the elevation is high enough not to cause excessive EGT temps in a non turboed engine.
 
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MultiMediaWill said:
I was wondering imagine if I was to takeoff from Boulder, CO in a C172. The airport elevation is 5,300 MSL. How much would you lean the mixture for takeoff? I train in the very flat midwest and the highest airport elevation around here is 1000ft MSL so I never have to lean the mixture on takeoff.
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It's pretty straightforward. During a full throttle runup find peak EGT (or find RPM drop) then about 5 each 1/2 twists on the mixture (toward rich). It works pretty good even at BDU - I trained at BJC.

Of course the best thing to do is fly a turbo'd aircraft and then it's mixture and prop fulll. See Frankekota, nee Turbo Dakota. :D
 
MultiMediaWill said:
I was wondering imagine if I was to takeoff from Boulder, CO in a C172. The airport elevation is 5,300 MSL. How much would you lean the mixture for takeoff? I train in the very flat midwest and the highest airport elevation around here is 1000ft MSL so I never have to lean the mixture on takeoff.
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I would pull it back until it made the most RPM at WOT during the runnup, or 75* ROP if I had the instrumentation. Leave that mixture setting for take off.
 
Clark1961 said:
It's pretty straightforward. During a full throttle runup find peak EGT (or find RPM drop) then about 5 each 1/2 twists on the mixture (toward rich). It works pretty good even at BDU - I trained at BJC.

Of course the best thing to do is fly a turbo'd aircraft and then it's mixture and prop fulll. See Frankekota, nee Turbo Dakota. :D
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Yep, it did very well even up in Steamboat. I loved the manual turbos on my Travelair.
 
Henning said:
I would pull it back until it made the most RPM at WOT during the runnup,
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Concur.
or 75* ROP if I had the instrumentation. Leave that mixture setting for take off.
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Forget the instrumentation -- peak RPM at full throttle on static run-up. This is also Lycoming's recommendation (assuming he's got a 1968 or later 172), but it will still do the best job with a pre-68 Continental powered 172.
 
Ron Levy said:
Concur.
Forget the instrumentation -- peak RPM at full throttle on static run-up. This is also Lycoming's recommendation (assuming he's got a 1968 or later 172), but it will still do the best job with a pre-68 Continental powered 172.
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It works just as well with the 0-300, both engines take the same carbs.

Yes the part numbers are different, that simply reflects the jetting for the different cubic inch difference of the engines.

Continental sez lean for best power at all power settings.
 
And remember that unless you have additional instrumentation and know how to use it for this (a longer treatise), don't lean for takeoff below 5000 density altitude (not MSL), which can happen at lower elevations in the summer time.
 
Ron Levy said:
And remember that unless you have additional instrumentation and know how to use it for this (a longer treatise), don't lean for takeoff below 5000 density altitude (not MSL), which can happen at lower elevations in the summer time.
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Remember, the Venturi in the carb acts upon the same theory as the wing. So, when the wing is having troubles so is the carb.

DA is DA, it effects all aspects of the aircraft.
 
Ron Levy said:
Concur.
Forget the instrumentation -- peak RPM at full throttle on static run-up. This is also Lycoming's recommendation (assuming he's got a 1968 or later 172), but it will still do the best job with a pre-68 Continental powered 172.
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Forget the instrumentation nothing, if you have the instrumentation available you fine tune to the best of one's ability.
 
another thought on this subject, You may lean to best RPM on run up, but remember you can also lean or richen to best climb rate in the departure climb.

your VSI is your horse power meter.
 
Ron Levy said:
And remember that unless you have additional instrumentation and know how to use it for this (a longer treatise), don't lean for takeoff below 5000 density altitude (not MSL), which can happen at lower elevations in the summer time.
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Why shouldn't I lean below 5000 density altitude?
 
What about landing, rather than taking off, at high altitude airports?

Going full rich would yield less power if you have to do a go-around. I haven't flown that much to higher airports, but in a C-152 and a C-172 during my GUMPS check I've set the mixture near full rich and did a quick lean till loss of RPM; then in enough to max RPM at that throttle setting. The problem is that it isn't full throttle, so I'm not sure if the procedure is doing me any good should I need to do a go-around.
 
Everyone with these questions are invited to attend the Colorado Pilots Association High Elevation ground school June 2013 or August 2013 (exact dates TBD) to learn exactly why and how to lean up here. 'Specially in the summer.
 
Jim Logajan said:
What about landing, rather than taking off, at high altitude airports?
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Leave it lean when landing, no need to go full rich. In fact the engine may sputter or die. Try it at your location. Go to 10,000' and pull the thottle back for slow flight and give it full rich setting and see what happens.
 
Jim Logajan said:
What about landing, rather than taking off, at high altitude airports?

Going full rich would yield less power if you have to do a go-around. I haven't flown that much to higher airports, but in a C-152 and a C-172 during my GUMPS check I've set the mixture near full rich and did a quick lean till loss of RPM; then in enough to max RPM at that throttle setting. The problem is that it isn't full throttle, so I'm not sure if the procedure is doing me any good should I need to do a go-around.
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Prior to landing lean for max RPM at WOT. You don't have to stay at full power long so do it on the downwind or prior to entering the pattern.
 
Clark1961 said:
Sure, SOP training is wrong. Gotcha, I'll change my practices immediately.
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Tom-D said:
Another thought on this subject, you may lean to best RPM on run up, but remember you can also lean or richen to best climb rate in the departure climb.

your VSI is your horse power meter.
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Maybe your SOP needs revising. ;)
 
I use the technique that's taught by the boys in Ada...

If you have an engine monitor, or even a simple single cylinder EGT gage, you can use the same leaning technique for take-off and climb-out regardless of the altitude.

One simply determines what the full rich EGT temp is during take-off on a standard day at sea level. (if you have a monitor then pick one cylinder and use only that one temp).

Then, regardless of the altitude, always lean to that EGT during take-off and climb out, gradually leaning during the climb.
 
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Read some mountain flying manuals. You'll see that they discuss leaning at 3000' density altitude. With airports around here, above 4000', leaning has always been part of flying. It's always surpising how many times sea level pilots get caught offguard.......and are surprised by a total lack of takeoff power. Same goes for landings and go-arounds.
 
timwinters said:
I use the technique that's taught by the boys in Ada...

If you have an engine monitor, or even a simple single cylinder EGT gage, you can use the same leaning technique for take-off and climb-out regardless of the altitude.

One simply determines what the full rich EGT temp is during take-off on a standard day at sea level. (if you have a monitor then pick one cylinder and use only that one temp).

Then, regardless of the altitude, always lean to that EGT during take-off and climb out, gradually leaning dring the climb.
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Thanks Tim, good advice ... as always. :D
 
Turbos, although generally easier to manage, require some special care at high DA airports. Although somewhat dependent on the wastegate setup (in my case a fixed gate TSIO 360) one leans on the ground for idle and taxi, then goes full rich on takeoff regardless of the altitude. Landings are whatever you are leaned out for at altitude (I don't go richer.) Go arounds require a subsequent full rich mixture, and careful leaning in the pattern for the next landing attempt. You have to be careful to richen the mixture slowly as you advance the throttle to allow the turbocharger to spool up, and conversely lean slowly at the same time you retract the throttle in the pattern, or you can end up over rich and sputter out.
 
Henning said:
Forget the instrumentation nothing, if you have the instrumentation available you fine tune to the best of one's ability.
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With a fixed pitch prop, peak RPM is the only thing that tells you for sure you're leaned for best power, and the only instrumentation you need for that is a tach. EGT is only an approximation, and the amount rich of peak EGT for best power is not a fixed value. What is more useful when leaning at low altitudes is CHT, as that will tell you if you're going to cook the engine, but above 5000 DA that can't happen when leaned for peak RPM unless you have some other problem.
 
MultiMediaWill said:
Why shouldn't I lean below 5000 density altitude?
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Because without full engine instrumentation (all cylinder EGT and CHT) it is possible to overtemp the cylinders if you lean at full throttle. Lycoming specifically warns of this. OTOH, if you are below 75% power (which is pretty much guaranteed even at full throttle with a fixed pitch prop at climb speeds above 5000 DA), it's not an issue. So, below 5000 DA, you can lean at cruise power of 75% or less, but don't lean at full throttle.
 
Jim Logajan said:
What about landing, rather than taking off, at high altitude airports?

Going full rich would yield less power if you have to do a go-around.
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Jim's right. When landing at a high DA airport, you should set the mixture for peak power, not full rich. If you took off from that airport, note the mixture position when you leaned for takeoff, and just set it there again for landing. If you're arriving from a low DA airport and don't know where to set it, you can leave it at the cruise mixture setting during descent and pattern entry, and go full rich only when you add power for the go-around, but be ready to lean it to peak RPM in the climb.

For more on leaning Lycoming engines, see the Lycoming Key Reprints and SL 185B.
http://www.lycoming.com/support/tips-advice/key-reprints/index.html
http://www.lycoming.com/support/publications/service-letters/pdfs/SL185B.pdf
 
Sac Arrow said:
Turbos, although generally easier to manage, require some special care at high DA airports. Although somewhat dependent on the wastegate setup (in my case a fixed gate TSIO 360) one leans on the ground for idle and taxi, then goes full rich on takeoff regardless of the altitude. Landings are whatever you are leaned out for at altitude (I don't go richer.) Go arounds require a subsequent full rich mixture, and careful leaning in the pattern for the next landing attempt. You have to be careful to richen the mixture slowly as you advance the throttle to allow the turbocharger to spool up, and conversely lean slowly at the same time you retract the throttle in the pattern, or you can end up over rich and sputter out.
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All true, but the OP was asking about flying a 172, which has a fixed pitch prop and no turbo. My advice has been crafted accordingly. Anyone with a turbocharger or c/s prop will need to do things differently, although those recommendations (at least for Lycomings) are in the Lycoming Key Reprints linked above.
 
Ron Levy said:
With a fixed pitch prop, peak RPM is the only thing that tells you for sure you're leaned for best power, and the only instrumentation you need for that is a tach. EGT is only an approximation, and the amount rich of peak EGT for best power is not a fixed value. What is more useful when leaning at low altitudes is CHT, as that will tell you if you're going to cook the engine, but above 5000 DA that can't happen when leaned for peak RPM unless you have some other problem.
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You can maintain peak RPM through a pretty broad range of mixture settings. Above 5000' you have no worries on cooking a Naturally Aspirated engine so the best burn for power is safe from detonation and that is going to be right around 75ROP. You'll see if you do a static test you'll see what will be indistinguishable RPM between 75 and 200 ROP, but it will be pulling harder and running cleaner.
 
No need to move the mixture for landing at low elevations either. Leave it leaned out and keep the spark plugs cleaner.
 
Henning said:
You can maintain peak RPM through a pretty broad range of mixture settings. Above 5000' you have no worries on cooking a Naturally Aspirated engine so the best burn for power is safe from detonation and that is going to be right around 75ROP. You'll see if you do a static test you'll see what will be indistinguishable RPM between 75 and 200 ROP, but it will be pulling harder and running cleaner.
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Since RPM is a direct measure of power with a fixed pitch prop, how can it be "pulling harder" at the same RPM with varying mixture settings? :confused: Also, with a carbureted engine, the EGT spread will be so great that peak power may occur with one cylinder near peak EGT and another 150 or more ROP. So which cylinder do you set 75 ROP? It's less dramatic with injected engines, but still true unless you have really well-tuned Gamijectors.

At the end of the day, for this specific purpose (obtaining peak power at full throttle with a fixed pitch prop), you get no additional useful information about power output with an engine analyzer -- the only thing more useful would be a digital tach so you can read RPM more accurately.
 
Sac Arrow said:
Turbos, although generally easier to manage, require some special care at high DA airports. Although somewhat dependent on the wastegate setup (in my case a fixed gate TSIO 360) one leans on the ground for idle and taxi, then goes full rich on takeoff regardless of the altitude. Landings are whatever you are leaned out for at altitude (I don't go richer.) Go arounds require a subsequent full rich mixture, and careful leaning in the pattern for the next landing attempt. You have to be careful to richen the mixture slowly as you advance the throttle to allow the turbocharger to spool up, and conversely lean slowly at the same time you retract the throttle in the pattern, or you can end up over rich and sputter out.
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I'll suggest have to look at the fuel setup if you're having problems. A TSIO-360 should not have any problems such as you describe. I've run both the -F & -K fuel systems and the only times I've had problems were: 1) bad mag 2) inadvertently left the electric fuel pump on at high DA.

I always go full rich on final (usually short final) and max rpm on the prop once power is below the control range. This operation is IAW the POH. I do lean again on the roll-out. If I'm doing t-n-goes then I leave it full rich.
 
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Tom-D said:
There is no reason not to.

but there are reasons to.
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The question is a misquote. It says not to lean for best power at takeoff below 5000 ft DA. The reason is detonation.

You can lean partially below that, or to best RPM if you can keep the throttle below 75% power. You should also lean partially for engine start, as full rich may flood the engine even with no priming for sufficiently high DA.

Above 5000 ft DA, you will not detonate even at full throttle.

As for the idea of leaning in the climb, this is a bad idea because you may not get that far at high DA. Full rich is not appropriate at any time at high altitude.
 
JHW said:
No need to move the mixture for landing at low elevations either. Leave it leaned out and keep the spark plugs cleaner.
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True for landings. Not for go-arounds. You must enrich the mixture before cramming the throttle (or removing the carb heat) or you risk an engine stall at the worst possible time.
 
MAKG1 said:
True for landings. Not for go-arounds. You must enrich the mixture before cramming the throttle (or removing the carb heat) or you risk an engine stall at the worst possible time.
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If you advance them all together (throttle, mixture, and carb heat), the engine will be fine. You can also leave advancing the carb heat control for last. Just don't advance the throttle first. Finally, there is rarely a need to "cram" the throttle, which can choke the engine even if the other controls are properly set. A smooth advance of the throttle is quite sufficient.
 
I'm surprised at the number of full power run-up advocates in the thread. We don't see folks typically doing full power run-ups here in the city area much, only up in the hills. Unless they're loaded to max gross or something. Kinda hard on props, sucking crap into them.

Most schools here will lean for peak RPM at normal run up RPM which leaves you a tad rich at full throttle once you go there and then they'll have you twist two-three 1/2 turns in from there... for a normal run-up anyway. They'll recommend the full power run-up for short runways, heavy loads, or any other reason you think you'll need max performance.

Season to taste. ;)

And of course, Tom and others are right too... you can adjust after takeoff. Just don't be in a huge hurry unless the engine is not happy. :)

Another pro tip from the mechanic long ago that stuck... Carbureted airplane, if you know about where that red knob usually ends up at, after doing that leaning procedure, pull the darn knob out to roughly that point (a couple of inches back usually) for engine START. Makes starting go a hell of a lot easier on you and your engine. ;-)

On the ground, I lean aggressively enough that the engine will be just about to stumble and will stumble if throttle is added. "Learned" that habit from a Cessna 172RG that LOVED to foul plugs up here. Heck, it loved to foul plugs at any altitude.
 
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