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How To Lean The Mixture

by Jason Schappert

I’ve been asked this question a lot. Most recently by James who’s an active Online Ground School member. “How and why do we lean the mixture?”

leaning the mixtureAsk that question around an airport and you might find a lot of answers. Someone once taught me… “Lean it out until the engine quits then screw it back in 3 times!” … I think they were serious is the scary part :)

In the video below I’m going to share with you why we lean and some different scenarios when you should be full rich or lean. I’ll also present to you two performance areas of leaning “lean of peak” and “rich of peak”

Check out the video below and let me know what you think… Enjoy! – Jason



REMEMBER: Every performance chart you read is based on you properly leaning the aircraft. Everything from gallons per hour to RPM and true airspeed. I encourage you to get more comfortable with the leaning procedures for your airplane as it will help you to fly more efficiently just as the engineers designed it.

Still have a question on how to lean your airplane? Or maybe you have a comment about something I said?

Leave me a comment below. I’d love to hear from you.

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  • Roger

    Great video, Thanks Jason. Flying here in Colorado I’ve really learned the importance of leaning the mixture. My home airport is 4700 MSL so we lean before we taxi and then again at run up. My question for you is should I lean the mixture again after reaching altitude? I’m flying a carbureted 172 without an EGT gauge. And will this be an expectation on my check ride? Thanks again! Roger

  • GreenSky

    I lean on taxi and leave it there even for takeoff for max performance. When I fly a fuel injected plane I set the mixture for max static power while on the ground.
    Why do we enrichen it for takeoff?
    Rick

  • bobdaszy

    Jason, I was always told to reduce mixture to the point where the engine gets rough and raise enough to stop the roughness,(c172G continental 0300D) I have never noticed a rise in RPM, maybe never looking for it! Bob

  • mzeroa

    Roger,

    ABSOLUTELY! In your situation it’s going to be important to lean. Density altitude is so high where you are at. If you give that engine more fuel than it needs you’re decreasing your performance and that unused fuel needs to go somewhere :) usually we find it gunked up on the plugs.

    Jason

  • mzeroa

    In your situation Rick (near sea level) Rich is the way to go when either 1: Applying Full Power and 2: Performing flight maneuvers (stalls/slow flight etc…) It’s more of a safety thing… I’ve personally had students lean for taxi, forget about it and try to takeoff without being full rich…. “put… put …. BACKFIRE” as we try to go down the runway… They realize “DOH” I didn’t give it the gas it needed.

    Jason

  • mzeroa

    Well glad you learned something new Bob! Give it a try next time and let me know!

    Jason

  • David Wyatt

    Thanks for sharing your video and experience on this, Jason. My question is let’s say you’re in a carbeurated C172 at 4000′, and you have leaned to peak performance, and now you want to climb to 8000′. Do you keep the mixture at what you already set it to, enrichen and climb, or do you climb and reduce the mixture during the climb if it improves RPM performance?

  • http://twitter.com/Matrioux Matrioux

    How would this method work with a fixed speed prop? Does it affect MP?

  • Ken

    Jason… You’re thoughts on one thermal cycle per flight? (Assuming no flight training) I’ve been taught that we should only have one heating and one cooling event for best engine life, per flight and also not to go full rich until cleared to land. The latter I’m told is to prevent shock cooling from decent and full rich at the same time. Would you offer your thoughts please?

    Thanks
    Ken

  • Mountain Pilot

    Another Colorado Pilot and Instructor here, but I am at 7,610 ft Field Elevation. (KMVI) Not knowing how to lean properly at these altitudes will put you back on the ground before you know it. With proper leaning one can make most any plane work well at these altitudes.

    I have to get up to 11,000 to go anywhere away from the local area and I have operated successfully, 65 hp Luscombes, 85 hp C-140′s, currently I instruct in both Piper Cherokee 140 ( 150 hp ) and a Cessna 150 ( 100 hp )

    Density altitudes during the summer get up to over 11,000 ft. at takeoff. Therefore most summer time instruction here is before 10am..

    Desire to fly the Rocky Mtn’s it is best to get a few hours with an instructor up here first to learn what to do and mainly when not to fly.

  • mzeroa

    As an aircraft owner I can appreciate this…

    Shock cooling is a no no. An easy way to shock cool the engine is to descend more rapidly than needed. (increased airflow)

    However also as a flight school owner I also understand that that’s not always possible (practicing emergency descents for example)

    So here are my thoughts…. Adjust the mixture with the descent. As I descend I give it a quarter turn. A little further down a little more. I WANT to be full rich before the traffic pattern. In fact in this hot Florida weather I WANT to be full rich under 3,000 ft to be honest.

    Do what it takes to keep that engine toasty: Use cowl flaps, descend earlier for a shallower angle etc… Mixture is just one way to do that.

    Jason

  • mzeroa

    GREAT QUESTION David!

    You’re right.. Enrichen then climb. Then adjust for the climb. Keep an eye on engine temps (low airflow + full power = high temps) baby that engine.

    Jason

  • robert

    Great video clip. Do you lean if cross country and 2000-2500 feet?
    thanks again
    robert

  • mzeroa

    Great comment my friend! Thanks for sharing

    Jason

  • mzeroa

    Robert,

    Keep in mind density altitude will play into this as well. You very well maybe 2,500 feet yet the engine doesn’t know that… It may feel more like 4,500 feet based on density altitude.

    My usual rule of thumb is 3,000ft +

    Jason

  • mzeroa

    You shouldn’t notice much of a change in the manifold pressure department. Unless of course you kill the engine leaning too aggressively then you might get a rise because of an increase in atmospheric pressure :)

  • Mike King

    I have a Cirrus SR22 so I use the Lean Assist funtion that permits me to either lean to best performance or best economy. It works great. :)

  • mzeroa

    LOVE IT!!! (and slightly jealous) :)

    Jason

  • Riley

    Hi Jason! I am curious, what program did you use to simulate the guages?

  • mzeroa

    The “Record” Feature inside X-Plane.

    Hope you enjoyed it

    Jason

  • Mike

    Just need a quick clarification. You talk about leaning to RICH of peak, but it seems you are actually leaning to peak. Can you clarify for my please?

  • mzeroa

    Hey Mike!

    Early in the video I shared the differences between Lean of Peak and Rich of Peak and which situations they would apply. Keep in mind lean of peak requires an EGT to know where that true peak is. I’m encouraging students to operate rich of peak 25, 50, even 75 degrees to the rich side of peak.

    Again without an EGT this is hard to tell however the RPM method takes the guess work out of it for pilot’s without an EGT gauge.

    Even then an EGT only operates off a single cylinder. Who’s to say it’s really the hottest one? What if it’s at lean of peak but you’re starving the others?

    And still Peak EGT changes every 5 minutes as atmospheric conditions change

    Make sense?

    Jason

  • Kary Van Allen

    Jason,
    I love your videos and find them to be very helpful. I have one suggestion. Oftentimes your audio is difficult to hear. I would suggest that you use a lapel mic. I think it would greatly improve your audio quality.

    Thanks and keep up the good work

  • Diggerdavid

    Jason,
    I fly a 69 Cherokee 235. Do you suggest leaning in the climb as you move above 3000 and then properly adjust once you’re at cruise? Also, do I set the RPM and MP at crusie and then lean?

  • Mike

    Jason, what you’re saying makes sense. I was focused exclusively on the rpm changes and rich of peak since I fly an aircraft with a carbureted engine. After the rpms maxed out in the video and started to drop it seemed you were saying to adjust rpms back to peak. But to get the 25-75 degrees rich of peak we would have to enrich the three turns, or something like that, with a corresponding slight drop from peak rpm. It would be a guess without an egt.

    One other question for you regarding the leaning procedure sequence. Say you want to cruise at 2400 rpm with the engine leaned. Do you set rpm to 2400 first, then lean, then adjust power back down to 2400?

    Thanks

    Mike

  • VONBOYD2

    You are simply awesome Jason! Thanks for your dedication to “always learning”.

  • Peter King

    Hi Jason:

    Brave of you to take on this topic. I agree that Lean-of-Peak operations should only be performed in fuel injected engines, with balanced injectors and EGT indicators on every cylinder. I was a little confused by your explanation of rich-of-peak operations, so I thought I’d throw in my 10 cents.

    The very first thing I would recommend is READ YOUR POH for leaning instructions. Different aircraft have different engines installed and instrumented in different ways. Leaning a vintage C172 is quite different from leaning a Cirrus SR22T.

    The second thing I would point out is that cruise leaning procedures only apply when the engine power is in the Normal Operating Range (i.e., the green arc). The Cessna 172s (and other fixed pitch aircraft) have a stair-stepped RPM indicator, where the top of the green arc changes with altitude. If your power is set above the green arc for your altitude, then you should lean using takeoff/climb leaning procedures. If your power is set in the green arc, you can lean using cruise leaning procedures.

    In the video, it was not clear when you were talking about Peak EGT or Peak RPM. These do not occur at the same mixture, so I think it’s important to be clear which you are talking about.

    Typically, when pilots are talking about Lean-of-Peak vs. Rich-of-Peak, they are referring to Peak EGT. Best Power is typically 75 dF Rich of Peak EGT. This is where you will see Peak RPM. Again, Peak RPM ~= 75dF Rich of Peak EGT.

    On climb, you generally want to be as rich as possible for cooling. As you climb the mixture becomes more rich (because the air gets thinner). If the mixture ends up too rich, then the engine will start to run rough; lean until smooth. Above 3,000, you can stay ahead of this by leaning a small twist every thousand feet or so. If your RPM drops when you lean in the climb, you’ve leaned too much–richen the mixture until you are back on the rich side of Peak RPM.

    If you need a high-performance takeoff or climb (high altitude/short runway), the POH recommends leaning to Peak RPM, but watch engine temperatures if you do this. In this circumstance, I’d recommend not leaning in the climb until you are at least 3,000 *AGL* to allow the increase in altitude to make the mixture more rich and help with engine cooling. Or if you find the engine getting hot and you don’t need a maximum performance climb any more, richen the mixture yourself to help with cooling.

    Let’s look at what the C172 POH says for cruise leaning. If no EGT, lean to Peak RPM and then lean further until the RPM drops 25-50 RPM (C172N) or 15-40 RPM (C172S). If Peak RPM is on average around 75 dF Rich-of-Peak EGT, leaning a little bit further to get an RPM drop will put you roughly around 50dF Rich-of-Peak EGT.

    If using an EGT indicator, you can be much more precise. Lean until you find Peak EGT (the hottest EGT temperature) and then richen until you are 50 dF rich of that peak EGT.

    I think Jason was recommending simply to lean to Peak RPM during cruise. That is actually a very good setting for engine longevity–better than the manufacturer’s recommended 50dF ROP EGT. Think about it. Peak RPM is a mixture that is acceptable during the more stressful high-power takeoff and climb configurations, so it has to be easier on the engine than the cruise lean power setting.

    However, if you follow Jason’s procedure, you should make sure to increase your fuel consumption calculations during your flight planning. The performance numbers in the POH are based on the Recommended Lean setting, so I would bump those numbers by 0.5 gph or more just to be safe.

    On descent, the mixture becomes more lean because the air gets thicker. If you do nothing, the mixture may end up Lean-of-Peak EGT. We’ve already agreed we don’t want to be there, so you should be richening the mixture in the descent–a twist or two every thousand feet or so.

    Peter King, ATP/MCFI

  • Peter King

    Be careful not to assume that the X-Plane simulated engine behaves like a real engine. From all I’ve read, in a real engine you should expect to see Peak RPM (Best Power) at around 75dF Rich of Peak EGT (depending on the cylinder your EGT gauge is connected to).

  • Peter King

    What does your POH say?

  • Peter King

    I lean any time I’m cruising, regardless of altitude. If you don’t your fuel calculations will be wrong. The cruise performance tables assume you lean per the procedure in the POH.
    You don’t need to overthink density altitude when calculating cruise performance. It is addressed by the temperature adjustments in the performance tables.

  • Peter King

    At full power and certain mixtures (Peak EGT), there is a risk of detonation (especially on a hot day), which can destroy an engine quickly. We run extra rich at high power to prevent detonation and to help keep the engine cool.

    The reason we go full rich during maneuvers is that we are likely going to use full power (for example, in a stall recovery). This is the same reason we go full rich before landing–to set ourselves up for the full-power go-around.

  • Troy Church

    Great video topic. When I was learning to fly I did not lean regularly. It was a component of workload, not really concern for engine performance. I continue to watch your videos as a sort of continuing education. I run a skydiving center, and we lean a bit differently. Against the POH we lean during the climb (although we have an EDM 700 with all 6 EGT, 6 CHT, and oil temp. We take off full rich with prop full forward and full throttle. We don’t touch the prop or throttle until we are at altitude. Cooling is an issue in the normally aspirated 182 or 206 (because we are climbing at between Vx and Vy the entire time), so often times we cannot get to the suggested EGT temp before our head temps exceed 420 (and we don’t like to go past that). As we climb on a standard temp day, we begin leaning to max EGTs while keeping the hottest head at or below 420. The leaning usually begins around 5000′ MSL, a little lower as DA increases. We continue to lean in the climb until we are at jump altitude. On jumprun (the heading at altitude for exit) we initiate carb heat and pull prop back to the bottom of the green arc (by now the MP is below 20″) and close the cowl flaps (now we want to keep heat in to prevent shock cooling). We use the throttle to maintain airspeed during exit. After exit we close the door then begin a rapid descent (up to 2500 ft/min), slipping the aircraft to keep air off the door side and to maintain safe airspeed for the hull. We do not begin enriching the mixture until around 6000′ MSL, and slowly enrich until we are full rich toward the end of our descending downwind leg. On final we open cowl flaps and push prop full forward for a normal landing.
    Our aircraft run very balanced EGTs and CHTs in cruise, but in climb do not.
    Just some information so your followers can see there are other ways to lean an aircraft (for specific operations). Using this method we can get 600+ hours out of plugs, and our cylinders last through TBO and beyond with good compressions (although from time to time we have exhaust valve guide problems…unrelated to leaning).

    Keep it up, I enjoy the emails and truly agree that a good pilot is always learning!

  • Peter King

    I should mention that 50dF Rich-of-Peak (ROP) EGT as a recommended lean is pretty aggressive on the part of Cessna and I think they can get away with it because those engines are relatively low power and bullet-proof.

    I did a quick survey of POHs, and I found that the Arrow II recommends 100dF ROP, the Cessna 182 recommends 125dF ROP. Your POH may vary.

    Just make sure you are at or below 75% power before leaning this way.

  • mzeroa

    Thanks Kary!

    I can work on that :)

    Jason

  • mzeroa

    I would follow what your POH says… Honestly I don’t lean during a climb unless density altitude becomes an issue. The poor engine is working hard and in order to keep temps low it needs the fuel. Now keep in mind I’m a sea level based pilot. So I come from the camp of “Climb, cruise, lean”

    Jason

  • mzeroa

    Thanks dude!

  • mzeroa

    Thanks for your kind words Peter! I appreciate the reply!

    I second your words “Follow the POH”

    Every aircraft, engine, and environment is different. It’s imposible to have a “suit all” approach.

    Jason

  • mzeroa

    Awesome Troy! Thanks for the great comment!

    It’s neat to hear about how everyone gets the job done!. It sounds like you’ve got a neat little business going :)

    Jason

  • Kevin

    Great video. But you sounded like you were in a deep dark cave. Maybe adapt a headset to use for these videos…a little humor is good.

  • James G. Gray

    Is there a certain RPM that’s better to use while leaning? My PA28 151 seems to idle less smoothly under 800 RPM’s?

  • Terence Verma

    ok..u’ve reached a max rpm after which it begins to drop, if u continue leaning. So now where is rich of peak position and how achieved?

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