Leaning a C-172

[LoadMasterC141]

From the FAA

How to Lean

• Tachometer Method (for use with fixed or variable pitch propellers): Set the controls for the desired cruise power setting as shown in the POH. Then gradually lean the mixture from full rich until the tachometer reading peaks. In smooth air, you should also notice a slight increase in aircraft speed. At peak RPM, the engine is operating within the maximum power range. For best economy operation, the mixture is first leaned from full rich to maximum power, then the leaning process is slowly continued until the engine starts to run rough. Then, enrich the mixture sufficiently to obtain a smooth firing engine. Obviously, some engine power and airspeed is sacrificed when operating at best economy. What you gain, however, is increased endurance.

• Engine "Rough" Method (for use with fixed or variable pitch propellers and engines equipped with float-type carburetors only): With this method, first set the throttle to the appropriate power setting, (75 percent power or less). Lean the engine gradually until the engine starts to run rough; then enrichen the mixture slightly until the engine is again running smoothly. You will then be operating near the "best economy" mixture setting.

• Fuel Flow Indicator Method (for use with any type propeller): The POH for aircraft equipped with fuel flow gauges contains appropriate fuel flow settings or, alternatively, the fuel flow gauge may be marked for correct flow at each power setting. You need only lean the mixture to the published or marked fuel flow values to achieve the correct mixture.

• Exhaust Gas Temperature (EGT) Method (for use with any type propeller): Peak EGT occurs essentially at the rich edge of the best economy mixture range. Operation at peak EGT not only provides essentially minimum specific fuel consumption but also 95 to 96 percent of the engine's maximum power capabilities for a given engine speed and manifold pressure. In addition, engine operation is very smooth at peak EGT. In comparison, a very noticeable power loss or roughness will occur when the engine is operated at the lean side of the best economy range.

High Altitude Operations:




At high altitude airports (5000 feet density altitude and above), lean for taxi, takeoff, descent and landing. Use the following procedures:

• Startup and Taxi: Lean at 1000 RPM (all propeller combinations) until RPM peaks, then enrichen slightly.
• Before Takeoff: Go to full throttle and lean mixture. With a fixed pitch prop,lean to maximum RPM and then enrichen slightly. With a variable pitch prop on carbureted engines, lean to engine smoothness. If you have an EGT gauge, lean to +100 degrees F. on the rich side of peak. With fuel-injected engine, lean to the correct fuel flow setting according to the POH for your specific airplane.
• Traffic Pattern Ops: Always lean at traffic pattern altitude for landing at high altitude airports, but only after you have established maximum power. This practice will ensure maximum available power in the event that you need to make a go-around.

[FONT=Arial, Helvetica, Tahoma, Verdana, Sans-serif]Review of Leaning Procedures[/FONT]

The chart below summarizes leaning procedures for various propeller/EGT/fuel flow indicator (FFI) combinations.

Leaning Procedures Summary

Type of Prop EGT FFI Leaning Method

Variable No No "Engine Rough"

Fixed/Variable No No Tachometer or "Engine Rough"

Fixed/Variable No Yes POH settings or as marked on FFI

Fixed/Variable Yes No Use POH to set EGT (usually to peak); enrichen until engine runs smooth

Fixed/Variable Yes Yes Use POH to adjust FF; lean by setting EGT per POH

Always follow the engine operating procedures provided by the aircraft manufacturer for your aircraft in the Pilot's Operating Handbook.

 

[cfii2007]

Good info. It drives me crazy every time someone starts an engine with the throttle TOO far forward. Nothing like getting 2000 RPM's with little or no oil circulating.

 

[faceof5]

So if we have to lean above 3000. Then why increase mixture to full rich in pre-descent if we are at say 9,500? Is it because we reduce power?

 

[Cessnaflyer]

So if we have to lean above 3000. Then why increase mixture to full rich in pre-descent if we are at say 9,500? Is it because we reduce power?

Because that is probably how they teach you at your school.

I usually enrich the mixture slowly as I am going down. Once I make it down to about 3,000' MSL it is full rich.

 

[faceof5]

So since the TPA at my landing airport is around 6000, do I slowly enrich from my descent down to TPA and then re-lean to max RPM? I read this is a good technique incase of a go around for a high-density altitude airport.

 

[Cessnaflyer]

So since the TPA at my landing airport is around 6000, do I slowly enrich from my descent down to TPA and then re-lean to max RPM? I read this is a good technique incase of a go around for a high-density altitude airport.

Taken from loadmasters post:

"Traffic Pattern Ops: Always lean at traffic pattern altitude for landing at high altitude airports, but only after you have established maximum power. This practice will ensure maximum available power in the event that you need to make a go-around."

 

[sdfcvoh]

Because that is probably how they teach you at your school.

I usually enrich the mixture slowly as I am going down. Once I make it down to about 3,000' MSL it is full rich.

I've read through a dozen of these threads recently, and all I have to say is that we need to have an actual engine designer talk about this. Everyone has good points, everyone has some background on what they are representing, but seriously - can anyone get with a real designer, and that way we can hear from a real pro on this?

I think our responsibility is to present an actual, factual, and realistic representation of leaning. To talk about the cooling effect, the fouling effect, and all the other byproducts. Anyone - ?

I've heard and read a lot about the why and how, but is it safe to pass on "advice" when it is just what you were taught? Aren't we here to provide safety to those reading, and not just "this is what I was taught, so this is what is right."

 

[Cessnaflyer]

I've read through a dozen of these threads recently, and all I have to say is that we need to have an actual engine designer talk about this. Everyone has good points, everyone has some background on what they are representing, but seriously - can anyone get with a real designer, and that way we can hear from a real pro on this?

I think our responsibility is to present an actual, factual, and realistic representation of leaning. To talk about the cooling effect, the fouling effect, and all the other byproducts. Anyone - ?

I've heard and read a lot about the why and how, but is it safe to pass on "advice" when it is just what you were taught? Aren't we here to provide safety to those reading, and not just "this is what I was taught, so this is what is right."

The problem is that there is not that much information around on proper descent techniques. The reason that I suggest this for a descent from 9,500' is that the added fuel from a full rich mixture can shock cool the engine when used with a lower power setting in the descent.

 

[aloft]

I fouled the crap out of the plugs on my first trip to Tahoe in a 172 several years ago. Engine shook like crazy on runup for my departure, forcing me to stay several extra days as the shop there in TRK was convinced it was a broken rocker boss and pulled the covers before they'd checked the plugs. Had to wait for new gaskets to be shipped in before I could go home.

Live and learn...

 

[faceof5]

Should I lean before starting the engine on the ground with a field elevation at 5000?

 

[bdhill1979]

Should I lean before starting the engine on the ground with a field elevation at 5000?

Most of the time no, it really depends on the DA if you need to do any leaning. During the summertime we will have 9000+ foot DA pretty often and the engines wont start at full rich.

 

[LoadMasterC141]

So tonight I am taking one of my co-workers for a Hard-8 run for the first time....Confident with my new leaning techniques learned from todays' reading, I start playing with the mixture on a long taxi. Before, I just leaned it out but never to the point the engine felt a little rough. A word of warning, leaning at idle is just a bit more "touchy" than leaning in the Green Arc. At the 2000 range, you get quite a bit of obvious warning that roughness is occurring. At idle taxi, there is little to no warning. I am carefully leaning, then the motor shuts off. How embarassing. Thank god I greased both landings to make up for it. Just another learning moment from a 150 hour wonder <Sarcasm>

 

[aloft]

Should I lean before starting the engine on the ground with a field elevation at 5000?

No, but lean it out an inch or so for taxi after it fires up, even at sea level. Then lean for best power during your runup.

 

[Stomp16]

Because that is probably how they teach you at your school.

I usually enrich the mixture slowly as I am going down. Once I make it down to about 3,000' MSL it is full rich.

This is a great thread with great info. I thought I would put down my most recent experience with leaning.

I have been flying for awhile now and currently am at 395 hrs. I have always leaned the mixture after leveling off and getting to cruise speed. Never had any problems, never really thought about it. Last week, I was flying from RVS to MHK in an older 172(M I believe). RVS field elev. is 638. I have just recently started to lean in my climb out after about 3000ft due to the gain in performance. I use the lean until rough method and then 2-3 turns in and your good. Well, on this climb out, the plane was close to max TO weight and it was a hot day. I leaned after 3K and left it. Leveled off at 6500 and let the aircraft gain speed. Once trimmed with the power set, I thought I would "re-lean" for this altitude. Well, this is where the learning starts. Instead of just leaning it out even more, or going just a little rich and starting the lean out from there, I decided to lean it out again from full rich. Not a good idea. I went full rich and the engine sputtered and spat, ran really rough and I immediately thought, great, it's gonna quit. Well after what seemed an eternity(probably 7-9 secs.), it stopped running as bad and I re-leaned. It never did quit. I sat there for the next hour and thought how much of an idiot I would of looked like to my passenger if the engine quit and I had to restart it in the air.

I feel like an idiot after I look back and think about it, but I hope by posting my experience it might help somebody else. But, this is why I love flying. It keeps you in check and I truly learn something new almost every time I go out and fly. Just remember, don't go full rich at altitude after it's been leaned.

 

[Ralgha]

I lean by pulling the mixture all the way out, and then slowly pushing it back up until the engine starts up again. Works like a charm.

No seriously, do what Midlife said and you'll do fine.

 

[MidlifeFlyer]

I feel like an idiot after I look back and think about it,

Don't. Out here where we always lean for takeoff (normally-aspirated), here's what a lot of people do:

Lean for taxi.
At runup, go to full rich and then lean (like you did in the air).

It makes some sense, as it did to you. After all, if you were really leaned out for taxi, it mat be too lean for run-up, so you do want to enrichen it. But, as you learned in the air, it's not necessary to go all the way to full rich to accomplish the purpose.

aloft, to answer about leaning before start - I haven't seen it usually necessary to keep the mixture in a lean position in order to start the engine, although I do do that (and I have seen some sputtering with fuel-injected Cessnas where you go to full rich instead of a lean position on start-up).

My WAG is that since normal start-up in a carbureted engine is often accompanies by increasing the initial fuel with primer anyway, the initial setting of the mixture at full rich is hardly going to make a difference. (Does that WAG make any sense to the folks who really know engines?)

 

[nosehair]

My WAG is that since normal start-up in a carbureted engine is often accompanies by increasing the initial fuel with primer anyway, the initial setting of the mixture at full rich is hardly going to make a difference. (Does that WAG make any sense to the folks who really know engines?)

Purdy darn good for a suit!

 

[aloft]

aloft, to answer about leaning before start - I haven't seen it usually necessary to keep the mixture in a lean position in order to start the engine, although I do do that (and I have seen some sputtering with fuel-injected Cessnas where you go to full rich instead of a lean position on start-up).

I think you might've misread my post, I didn't suggest he lean the mixture for engine start. I don't.

 

[MidlifeFlyer]

I think you might've misread my post, I didn't suggest he lean the mixture for engine start. I don't.

No. I misread the handle. It was faceof5's question.

 

[MidlifeFlyer]

Purdy darn good for a suit!

Thank you kind sir.