Mixture Leaning

Discussion in 'Maintenance Bay' started by Ronnie Godfrey, Nov 29, 2017.

  1. Ronnie Godfrey

    Ronnie Godfrey Pre-Flight

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    As a new owner, I’ve been doing a lot of research on leaning. I’ve watched the Savvy Avation video about it and he basically says the only times for full rich are start up and takeoff, which I pretty well adhere to with one big exception. I’ve always been taught to go full rich on approach just in case there’s a go-around, which makes sense to me. The Savvy video doesn’t address it.

    So, what are your thoughts on leaning (or not) when on approach? FWIW, I have an 0-320 behind a fixed pitch prop.
     
  2. Skates97

    Skates97 Pre-takeoff checklist

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    Follow what you have been taught.

    GUMPS

    Gas (Fullest Tank)
    Undercarriage (Gear Down)
    Mixture (Full rich in preparation for a go around)
    Prop (No worries with Fixed Pitch)
    Seatbelts (Fastened and tight)
     
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  3. Tom-D

    Tom-D Taxi to Parking

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    Are you in an area that leaning is required for take off?
     
  4. Pilawt

    Pilawt Final Approach

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    Well ... yes and no. I'd prefer to state it as "Mixture (set as appropriate in preparation for go-around)"

    At sea level on a standard day, full rich would be appropriate. But on a warm day at a high-altitude airport, full rich would (a) rob a lot of much-needed power in event of a go-around; and (b) be conducive to plug fouling at idle. Be aware of your arrival airport's density altitude, and set the mixture for what would be appropriate for a full-power climb in those conditions.

    Some folks prefer to leave the mixture at cruise setting through the approach, asserting that in event of a go-around they will remember to enrichen the mixture as they advance the throttle. That may be true, but for lower-time pilots it's probably safer to pre-set the mixture for go-around as part of the "GUMPS" check.
     
  5. SkyHog

    SkyHog Touchdown! Greaser!

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    IMHO, one of the most dangerous rules is the idea that mixture goes full rich for takeoff or landing. That may be correct, but for half of the country it is not.

    You should set the mixture for best power for takeoff and landing. No other setting is appropriate.
     
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  6. James331

    James331 Touchdown! Greaser!

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    NO.

    MIXTURE to DA

    Go full rich for G/A in Vegas in summer, or big bear for takeoff, you're going to have a bad time.
     
  7. midlifeflyer

    midlifeflyer Final Approach

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    As others commented, let's change all those "mixture -- rich" to "mixture -- set as appropriate" or whatever alternative phrase you like (I adopted "PRN" as a shortcut from medical/pharm).

    With that out of the way, your question is pretty much, on arrival, when should I set the mixture to its "final setting."

    Let's start with this as a concept: The POH recommends a target density altitude above which you should lean for takeoff. Whether you are one of those who, who lean for takeoff below that target, that typical 3,000 to 5,000 ft target tells you something about how much leeway you have. It's a range, not requiring rocket science accuracy. So, what I do is, as I descend from cruise, I periodically enrichen the mixture so I am at my "as appropriate" target for landing/go/around/takeoff by the time I am at pattern altitude VFR or on those final vectors for an approach IFR.
     
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  8. AKBill

    AKBill Pattern Altitude

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    Typically I start leaning at 3000ft. No EGT so by rpm
     
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  9. Timbeck2

    Timbeck2 Final Approach

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    So do I and field elevation is around that so after start up I lean for taxi. At run up I lean for take off. At 5000' I lean again.

    I tried to do a touch and go in the rain one time with full rich selected. Nothing happened when I pushed the throttle up except for black smoke out of the exhaust pipe. Lesson learned.
     
  10. Tantalum

    Tantalum En-Route

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    PFGUMPS is what I was taught, do this on downwind after crossing threshold, base, and final again. Or if on instrument approach then 2-3 miles before FAF and again crossing the FAF

    P=power set
    F=flaps set
    G=gas, check fuel selector, fuel pressure
    U=undercarriage, down and welded
    M=mixture SET. I was not taught full rich. So at Big Bear we leave it alone... at MYF we go full rich
    P=pumps, fuel pump on
    S=switches (lights)

    **The plane I fly is tuned in pretty well... in other words, once you start leaning (if at sea level) you see a definite rise in CHTs... (I have flown planes where there is not much CHT rise just a a big change in FF, basically at sea level they're just pouring gas into the engine) so generally under about 5K MSL we leave full rich unless we're cruising at a reduce power setting. Otherwise on taxi we lean very aggressively and same in flight. The plane does have a JPI and fuel flow so it makes dialing in the mixture to the POH figures while keeping the CHTs happy a pretty easy exercise

    Otherwise, the old school method I was taught was lean slowly until rough, then bring the mixture up slightly to peak RPM

    [Grumpy Cat Mode On]: Incidentally, those of you that know me better know that I hate the whole "I'm a chemist" thing with the mixture. It's no big mystery that the stoichiometric air fuel mixture is about 15:1, generally. If we don't trust electronics to adjust the mixture for us (Lycoming has an engine that does it electronically) then this isn't hard to dial in mechanically either with an altitude compensating pump, like Cirrus has. Or if we're super paranoid about robot overlords and complex mechances then you could put a back up mixture over-ride somewhere in the cockpit (just like we have alt static, etc.). How many people have had engine failures or damage due to inappropriate leaning technique.. personally I think taking the human out of it would be A.) bring us out of the 1940s and B.) be safer. [Grumpy Cat Mode Off]
     
  11. flyingron

    flyingron Touchdown! Greaser!

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    Lycoming says full rich for max power climbs up to 5000'.
    Continental says full rich until you are only making max cruise or less. However, digging through a performance chart shows that to be roughly at 5000' DA as well.
     
  12. CC268

    CC268 Final Approach

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    Yea idk I lean for takeoff everytime. Doesn't matter what the elevation is. I suppose if I was on the coast of California at sea level then I would leave it full rich. I lean for taxi and for takeoff and again at cruise. I enrichen just a little bit as necessary when landing.
     
  13. bobmrg

    bobmrg En-Route

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    I am leery of any recommendation to always do something or never do something. The world is not that black-and-white. My own take on it is that a pilot would have to be lacking in situational awareness if the need for a go-around suddenly appeared. Is there a plane at the hold line waiting to taxi onto the runway? You can bet that as soon as I detect any motion toward the runway I am going around, with plenty of time to set the power controls correctly. Kid on a bicycle riding along a road near a rural runway? S/he gets a lot of attention until I am sure that there will be no incursion...if there were one it would not be a surprise calling for a rapid reaction. One rule i drummed into my students heads was "Don't just do something, sit there!" because there are a very limited number of situations that require instantaneous response. Bottom line: I do not go to full rich on final unless an actual (not a potential) reason for doing so exists.

    Bob
     
  14. flyingron

    flyingron Touchdown! Greaser!

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    I follow the manufacturer's recommendation. Neither Lycoming or Continental (nor the FAA for that matter) says to do that.
     
  15. CC268

    CC268 Final Approach

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    I should amend what I said. I use the 3000ft rule as well. So if it is indeed below 3000ft DA then I will leave at full rich till at cruise altitude (around here that doesn't happen a ton) . But yea your right I don't follow the 5000 ft rule as presented by the manufacturer. I guess I could change my practices.
     
  16. midlifeflyer

    midlifeflyer Final Approach

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    The typical POH has, for decades, been deficient with information regarding high density altitude operations. Even the Cessna 172S POH calls for "Mixture -- RICH" for landing. Looking at other procedures or the expanded procedures doesn't help much. The takeoff checklist and the enroute climb checklist both talk about leaning for best power above 3,000'. But nothing more than "RICH" for descent and before landing.

    No, 20 years in Colorado, never did, never will follow the POH on that. Of course, I have seen it done, with Tower pretty peeved at the airplane whose engine quit during rollout.
     
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  17. flyingron

    flyingron Touchdown! Greaser!

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    I am not talking about the "typical" POH. I'm talking about the ENGINE manufacturer's specific instructions for the operation of their engines.

    Yes, in Colorado, you're going to be at the point where it makes sense to lean for best power prior to takeoff. You're not making anywhere near rated power. Continental pretty much says you can do what you want with the mixture at that point, you're not going to damage the engine. Lycoming wants the additional cooling from richer mixtures at lower altitutde.

    However. not everybody is in Colorado, and many here have proposed aggressive leaning for full power (meaning lower DA)) takeoffs and that's not good for your engine and is not going to give you much performance boost anyhow.
     
  18. SkyHog

    SkyHog Touchdown! Greaser!

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    It’s not a Colorado thing. This applies to California, Nevada, Utah, Arizona, New Mexico, Wyoming, Montana, Idaho, Alaska and possibly a few other states. These are huge states with lots of airports. The advice is sage - set mixture as appropriate. That means don’t go full rich at higher elevations. Set for best power.
     
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  19. edo2000

    edo2000 Pre-takeoff checklist

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    But, then, many of us do operate at higher altitude airports. I learned to fly in Alaska (Soldotna - PASX - altitude ~110 ft). Summers were cool, full rich worked well for T/O and pre-landing checklist. Recently, I moved to New Mexico, western slope of Rockies. My hangar is at ~6000 msl and it is often hot. Definitely had to adjust my engine operations procedures. Many airports I fly to now are MUCH higher than my home field. Here, you best know that shoving the mixture all the way in is pretty much never a good idea. Instead, you have to know how to set it for your target field for T/O or landing. Otherwise, as someone already said, you could be having a very bad day.

    My opinion for the OP - if you fly in an out of airports above 4000 ft msl - get some pointers from a knowledgeable instructor on leaning in different situations. It isn't rocket science but it definitely can be done wrong with serious consequences.
     
  20. unsafervguy

    unsafervguy Cleared for Takeoff

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    we see DA over 1000 here in florida on a hot day sometimes..........
     
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  21. denverpilot

    denverpilot Taxi to Parking

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    I don’t know. How many? I haven’t met any in two decades of flying, but perhaps you have?

    Gettin cra-cray down there! ;) 1000’. Man you guys might get a nosebleed. ;)
     
  22. Pilawt

    Pilawt Final Approach

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    My home drome is only at 971' MSL, but on a toasty summer Arizona day the density altitude can get up to 5,000'. Take off (or go around) with full rich mixture in those conditions, and it's a sick bird, even below 1,000' MSL. Unwind the mixture knob to where it would normally be at a 5,000' MSL full power climb in standard conditions, and -- voilà -- there's that missing 150 rpm and now the engine runs smoothly. And all four CHTs are still well in the normal range.
     
  23. SixPapaCharlie

    SixPapaCharlie May the force be with you

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    Does your 320 ever get grumpy in the pattern when you are full rich on on hot Longview TX summer days?
    Mine does. So I just lean as necessary on my descent. Rarely do I land full rich anymore and no more grumbles from my engine.

    If I have to go around, I can push 2 knobs at once.

    Both my planes POH's say Lean "as needed" or "As required" for landing.
     
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  24. Brad Smith

    Brad Smith Pre-takeoff checklist

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    My PA-28-181 manual is a little better than the C152/172 manual where is states:

    MIXTURE /BEFORE TAKE OFF - "set"
    MIXTURE/DESCENT - "RICH"
    MIXTURE/DESCENT POWER OFF - "as required"
    MIXTURE/APPROACH AND LANDING - "set"

    Seems that Piper is a little more on the ball than Cessna when it comes to checklists.
    BTW- Brush up on your water ditching skills before you take off from Big Bear, CA with a full-rich mixture.
     
  25. midlifeflyer

    midlifeflyer Final Approach

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    Even the eastern mountains have airports with elevations that will have good leaning techniques applicable.
     
  26. denverpilot

    denverpilot Taxi to Parking

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    Or Piper just worried their pilots were dumber back in the seventies when everyone knew how to set a carb and what altitude does to mixture. ;)

    I’m kidding of course. But most aircraft have little detail on this in just the checklists, but it’s all laid out for the pilot in the rest of that POH. Usually. Unless it’s too old for even that, and that’s back when people rebuilt their own engines at home regularly. LOL.

    “Mechanic” was just a guy who did it for a living. Everyone was a mechanic.
     
  27. Brad Smith

    Brad Smith Pre-takeoff checklist

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    Nowadays mechanics are called Technicians. An upgrade for sure!
     
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  28. flyingron

    flyingron Touchdown! Greaser!

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    Did you bother to read my post? I didn't say you should lean at higher altitudes, I said that the statement that you should always lean no matter what the altitude is INCORRECT and DANGEROUS and contrary to information provided by the engine manufactures. Why is it so hard that "one procedure doesn't fit every situation?"

    Do you also fly with the throttle firewalled when you're flying at low altitudes (2000 MSL)? That doesn't work well either.

    Yes I learned in Colorado as well. I've flown there recently. I know the importance of leaning, but I also know the importance of not running high engine loads without adequate cooling. You don't lean at 2000' MSL fields. The question is where do you start. We can argue that as a gray area, but I told you what Lycoming and Continental said. Lycoming says not below 5000. Continental says not below an altitude that gives you the continuous cruise power setting at your takeoff power (which is nebulous but is probably a DA of 4000-5000'.).
     
  29. wrbix

    wrbix Pattern Altitude

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    .....yeah, but it's HUMID heat.
     
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  30. Pilawt

    Pilawt Final Approach

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    There is some citrus mixed in with the apples here.

    How is field elevation even relevant? I lean according to density altitude; that's what determines power output and aircraft performance. As mentioned above, I can and do lean for takeoff, even below 1,000' MSL field elevation, if the density altitude warrants it. And in these parts, it warrants it more often than not, because the DA may be several thousand feet above field elevation.

    Imprecise language in my C-172N's POH doesn't help. It says, "Prior to takeoff from fields above 3000 feet elevation, the mixture should be leaned to give maximum RPM in a full-throttle, static runup" [emphasis added]. I submit that more precisely it should read 3,000' Density Altitude, but the manual was likely written for the lowest common denominator of consumers. The air density at sea level and 104˚F is no different from 3,000' MSL in ISA conditions.

    I know (after flying my airplane for years in a cool, sea level climate in the Pacific Northwest) that after takeoff in ISA conditions at sea level with full rich mixture, the EGT of my hottest cylinder stabilizes at 1290 degrees. As I climb to altitude I just periodically lean to keep it at that same 1290˚ all the way up. No reason for it to be richer than it would be with the red knob all the way in at sea level on a cool day, and there is plenty of reason not to sacrifice the performance by flying over-rich. If the density altitude is higher at takeoff, I'll just lean to that same 1290˚ happy place. In normal cruise-climb oil temp stays well in the green, and CHTs are all less than 370˚. The engine is past mid-time; compressions are high, oil consumption is low, and plugs don't foul.
     
  31. James331

    James331 Touchdown! Greaser!

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    Y'all talking 3,000', 5,000'

    We talking AGL or DA here?




    [​IMG]
     
  32. edo2000

    edo2000 Pre-takeoff checklist

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    Yes, I read your post. In it, you said a lot of things and you even mentioned that in Colorado it makes sense to lean to best power for takeoff. All I said was, that for large sections of the country where high DA is common, including states other than Colorado, you better know how to set the mixture(and not full rich) correctly for takeoff and landing configuration. I'm not sure that would have been obvious to the OP from your post.
     
  33. CC268

    CC268 Final Approach

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    You know I've just learned that Mr. Flyingron is a little rough around the edges.
     
    Last edited: Nov 30, 2017
  34. frfly172

    frfly172 Touchdown! Greaser!

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    Fadec,takes the worry out. Push the throttle open to WOT,release the brakes and go.
     
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  35. James331

    James331 Touchdown! Greaser!

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    What happens when it fails?

    Or when you're in the bush with a dead battery?
     
  36. AKBill

    AKBill Pattern Altitude

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    I'm at sea level and DA is normally below sea level. Today it's -1123ft...:)

    Unless I'm flying over the ice fields I don't normally get over 3000ft. Over the ice fields takes me to 8000 to 10000ft

    100%
     
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  37. edo2000

    edo2000 Pre-takeoff checklist

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    Yeah, that's the way I remember it on the Kenai Peninsula. It was a definite reeducation to go from a 300hp/C185 based at sea level in Alaska to 180 and 160hp fixed pitch prop aircraft based at 6000 msl in New Mexico. You use the mixture control a lot more and you use a lot more runway, too. I do see a lot more blue skies though... :)
     
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  38. Tantalum

    Tantalum En-Route

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    Not sure you would have the engine catastrophically come from together, but fowled plugs and damaged heads and valves from improper temps resulting from poor leaning technique can definitely reduce the lifespan of an engine and effect its performance..

    Side note, I was curious so I did a quick NTSB search.. seems it does happen from time to time
    https://ntsb.gov/_layouts/ntsb.aviation/brief.aspx?ev_id=20001214X36430&key=1
    upload_2017-12-1_11-52-32.png

    https://www.ntsb.gov/_layouts/NTSB.Aviation/brief.aspx?ev_id=20001206X01397&key=1
    upload_2017-12-1_11-53-5.png
     
  39. cgrab

    cgrab Cleared for Takeoff

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    I heard (either from Busch or Machado) the reason you go full rich on landing is because of a lawsuit. I leave mine where it does the most good. Usually where I was on decent. I think if I have to go richer, I can reach the knob when pushing in the throttle.
     
  40. jimhorner

    jimhorner Pre-takeoff checklist

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    For some reason, some of the posts here remind me of Richard Bach’s excellent story, “Found at Pharisee”. It was published in his collection of stories, “A Gift of Wings”.

    If you are familar with the story, you’ll know what I mean.


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