Mixture during maneuvers?

Discussion in 'Pilot Training' started by Pedals2Paddles, Dec 18, 2014.

  1. Pedals2Paddles

    Pedals2Paddles Cleared for Takeoff

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    The traditional thing I learned a long time ago was to go full rich during maneuvers. But that was also from people who think full rich during taxi is a best practice. I've also had some say leave it leaned. So what are others finding as a best practice?

    Mixture full rich?
    Mixture at peak?
    Mixture at LOP?

    Are you leaving it at the mixture you set in cruise? Or are you resetting the mixture after slowing to the maneuver entry speed? By maneuvers, I'm talking about things like steep turns, turns around a point, stalls, etc.
     
  2. poadeleted20

    poadeleted20 Deleted

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    Put the mixture at the right place for the power setting and altitude you'll be using during the maneuver. That might be any of the three you mentioned or something else, too.
     
  3. Geico266

    Geico266 Touchdown! Greaser!

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    The engine really doesn't care what the airframe is doing unless the maneuver cuts off fuel.
     
  4. midlifeflyer

    midlifeflyer Touchdown! Greaser!

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    There you go. Although I think it might be kind of fun to watch someone go full rich when doing power-on stalls in the Denver area. See how they do with the conversion to a power-off emergency landing.
     
  5. Stewartb

    Stewartb Final Approach

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    I live at 63' above sea level. If you increase throttle during the maneuver you're expected to enriched before applying throttle. For most maneuvers it's easier to anticipate the enrichment than deal with it mid-maneuver. You can expand the concept to mixture management on short final. Do you land with your mixture leaned? I don't. My carb heat and mixture go full in about half way down final. If I have to go around I'm prepared to do so. It's the carbureted version of staying ahead of the airplane.
     
  6. bullwinkle

    bullwinkle Pattern Altitude

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    Unless the maneuver is going to cause a rapid change in altitude, why would the engine care? Leave it where it was set for the altitude you are at.
     
  7. midlifeflyer

    midlifeflyer Touchdown! Greaser!

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    It's also called, using the appropriate mixture "for the power setting and altitude you'll be using" (quoting Ron).

    Do I land with my mixture leaned? Not recently but definitely did the 20 years I flew in Colorado. I liked the idea of having power available for a go-around, something I would not have had if I went to full rich.
     
  8. MAKG1

    MAKG1 Touchdown! Greaser!

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    Above 3000 DA (in a Cessna), you're not going to damage the engine no matter where the mixture is. So, leave it leaned, not where you need it during the maneuver (unless it's at full power), but where you need it on recovery from the maneuver.

    So, set your stalls, slow flight, steep turns, chandelles, etc., leaned for cruise or maximum performance climbs. Ground reference maneuvers should be full rich over sea level terrain, 'cause you will recover from them with a full power climb. Note that it may be advisable to stay leaned at any altitude in the summer. 2000 AGL DA is doable on a hot as hell day.

    Landing full rich at high DA is not recommended. Enrich just enough to keep the engine smooth, no more. Don't try to go looking for peak EGT at low throttle; it doesn't work.

    Of course, this is all different with turbocharging. For those "sea level" persists up to the reference altitude.
     
  9. Stewartb

    Stewartb Final Approach

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    Clearly a pilot needs to have some knowledge of his surroundings and his aircraft. At 3000' and -5*, not an unusual day for me, the DA may be -400'. Should I lean like there's no consequence? No.

    To put temp into perspective, my cabin winter LZ requires high performance. Sometimes the temps drop more than we anticipate. I'm at about 10' ASL and temps may be near -40F. That's a DA of around -7500'. Leaning is not something we worry about. Getting enough fuel is. But dang, the wings sure work good in those conditions. :)
     
    Last edited: Dec 18, 2014
  10. Pedals2Paddles

    Pedals2Paddles Cleared for Takeoff

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    I do understand that full rich not something you would ever do at high DA locations. I guess I should elaborate. I'll be at 1000 to 3000 MSL.

    So it sounds like I should leave where I had it leaned for cruise RPM. That way it is where it needs to be coming out of the maneuver. But.... Cruising at 2600rpm, leaned 50rpm LOP may not be appropriate for a full power stall recovery?
     
    Last edited: Dec 18, 2014
  11. nddons

    nddons Touchdown! Greaser!

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    -40F? I'm staying by the fire!
     
  12. MAKG1

    MAKG1 Touchdown! Greaser!

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    Not MSL. DA. Your airplane doesn't care how high you really are. It only cares what the air density is.

    I've seen over 3000 DA at KTCY before. Real sucky day to be doing landings in a Warrior (and it gave me some problems with the heat, so that stunt is on my list of "things to never do again"). And you have to lean your 172 on the ground when it's that hot if you don't want to inspect the cement plant real close.
     
  13. Pedals2Paddles

    Pedals2Paddles Cleared for Takeoff

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    Good point. This time of year, a high DA ain't a problem, which is nice. For both power, climb, and comfort!
     
  14. Stewartb

    Stewartb Final Approach

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    Stan,

    At those temps it's hard to keep the cabin warm so getting back to town becomes a priority. I don't like flying below about -10*. Metal makes funny noises and does funny things when it's that cold. You guys worry about shock cooling. We worry about shock heating.
     
  15. poadeleted20

    poadeleted20 Deleted

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    Because the maneuver requires a significant change in throttle setting? Many such maneuvers (e.g., chandelle) require a large increase in throttle setting from where it was, and you might well need to enrich as you advance the throttle. OTOH, for slow flight, you might be at a much lower throttle setting, and thus need to lean a bit more as you begin the maneuver. So, I'll stick with what I said above: "Put the mixture at the right place for the power setting and altitude you'll be using during the maneuver."
     
  16. poadeleted20

    poadeleted20 Deleted

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    If cruise power is what you'll be using during the maneuver, that's great. If not, adjust the mixture as appropriate to the power setting you're actually using.
     
  17. Pedals2Paddles

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    I'll reword. If I'm leaned for 50rpm LOP in a 2600 RPM cruise, and want to slow to a 2300rpm maneuver such a steep turns, should I readjust the mixture once I've slowed the the maneuver entry speed, or just leave it where it was at cruise speed? Does the mixture need to be adjusted when reducing RPM, or just when increasing? No change in altitude.
     
  18. poadeleted20

    poadeleted20 Deleted

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    Normally you lean to EGT values when trying to lean to LOP, not RPM. I'm wondering where you got the idea that leaning to 50 RPM LOP was an appropriate technique.

    Again, I've never heard of a "2300 RPM maneuver", just target speeds for maneuvers. But if 2300 RPM gives you the target entry speed at a particular weight/altitude, so be it.

    With a carbureted engine, you would normally need to lean the mixture some when reducing power that much in order to stay at the same point on the mixture curve. With an injected engine, the difference is probably smaller.
     
  19. CharlieTango

    CharlieTango Line Up and Wait

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    2 differences at altitude, 1 has already been discussed and that is I need to be leaned for best power and 2 I don't have to anticipate adjusting the mixture for WOT because I am at WOT already in cruise.

    At least that was true until I bought a Rotax powered light sport which is perfectly happy to be full rich all the time except in descents.
     
  20. Pedals2Paddles

    Pedals2Paddles Cleared for Takeoff

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    Verbatim from the POH :D. Cessna 172 with an O320-E2D. Absent a 4cyl EGT, it's the best you can do for best econ.

    I made up the number to illustrate reducing power to the maneuver speed. So it is as you said.

    OK. So I guess the only thing I'm not sure of is when the maneuver requires a power change. Stalls require full power application. But then again, those are setup to be mimicking takeoff or landing. So mixture would already be full rich (or otherwise as appropriate for high DA locations). Which answers my question completely.
     
  21. kgruber

    kgruber En-Route

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    If you are maneuvering below 3000'DA and changing the throttle, just go to full rich. It won't harm anything and you can take your mind off one variable.

    And yes, I know all about Deakin/LOP/etc infinitum. I was GAMI serial number 0019.

    Keep it simple.
     
  22. poadeleted20

    poadeleted20 Deleted

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    I'd like to that POH. For one thing, I doubt it's really operating lean of peak EGT at that setting, and when we talk about LOP/ROP operation, we're talking about peak EGT, not peak RPM. Due to the relatively uneven distribution in the various cylinders, carbureted engines are generally not tolerant of true LOP operation since one cylinder generally goes too lean before the richest cylinder gets lean enough. True LOP operation works well only in fuel injected engines with well-balanced injectors (especially the GAMIjectors mentioned above, which were designed to lend themselves to such fine tuning).

    Then I'd suggest getting back with your instructor to learn when power changes are required/appropriate for each maneuver.

    Some do, some don't, although most stall recoveries required application of full throttle (which does not result in full power at higher DA's). Of course, it would be more appropriate on an approach to landing stall to start with the mixture where it would be in the pattern (i.e., at low power setting), and then advance the mixture as you add throttle during the recovery.

    Right. So for a takeoff/departure stall, you'd set the mixture to wherever it would be for takeoff at the power setting/DA at which the maneuver is being performed, or in some higher performance aircraft, at the power setting for 65% power at that DA.

    That's not entirely true for all planes, but in a 172 with an O-320-E engine, yes, that would be true for a takeoff/departure stall.
     
    Last edited: Dec 18, 2014
  23. MAKG1

    MAKG1 Touchdown! Greaser!

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    I have yet to see a Cessna 172 that discusses lean-of-peak at all.

    I've seen 50 deg ROP for best power, and at peak for best economy, for carbureted 172s.

    Which year was that?
     
  24. James_Dean

    James_Dean Pattern Altitude PoA Supporter

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    Cooling airflow?
     
  25. MAKG1

    MAKG1 Touchdown! Greaser!

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    Yeah, I've seen CHT's get a bit warm after repeated departure stall exercises.
     
  26. nddons

    nddons Touchdown! Greaser!

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    Stewart, you guys are tough dudes up there. I can't wait to visit AK, but I don't think I will do it in the winter. My hands got cold watching Flying Wild Alaska!

    We had some negative teen temps here last year with the polar vortex, and those days were miserable. I couldn't imagine anything sub -20F.

    I presume young Captain White's blood has thinned in his time up in Alaska.
     
  27. Silvaire

    Silvaire En-Route

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    I suppose this has already been answered but you set your power in cruise and then adjust your mixture. So that mixture setting is for that power and altitude. If you are going to move the throttle or change altitude then that mixture setting is no longer relevant. I think the "go full rich" (or whatever would be appropriate short of that if you are in Denver or such) just covers your bases so you can manipulate the throttle and change altitude at will. Of course if all you are going to do are some turns then it wouldn't be necessary.
     
  28. TazzyTazzy

    TazzyTazzy Pre-takeoff checklist

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    I learned and still fly a 172 (newbie). I was taught anything out of the green arc on engine RPM, carb heat on. No exceptions. An carb heat when suspected carb icing.

    The POH states in the Before Landing checklist, Carb Heat On.

    Don't want to have to need power for faster than expect sink rate or go-around and find the engine starving for air. :) At least that's what I'm told, i'm a new PPL. Feel free to correct me.
     
  29. N801BH

    N801BH Touchdown! Greaser! Gone West

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    Go around = carb heat OFF...
     
  30. Stewartb

    Stewartb Final Approach

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    Mitch,

    The first time you have an oh **** go-around moment you'll likely forget two things. Mixture and carb heat. Carb heat will rob you of power. Whether the crosswind is pushing you through the runway lights or your lack of climb has the gear dragging through the trees? You learn that you might be better off pushing the mixture and carb heat in BEFORE the next big event. If you pull carb heat on downwind there's no ice potential left when you're on short final. I always tell new pilots or pilots fixing to land in a new spot, a landing is just an aborted go-around.
     
  31. Pedals2Paddles

    Pedals2Paddles Cleared for Takeoff

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    I think he means to prevent the build up of carb ice on final. Cause if you have carb ice and need to go around, you're probably still going to land....

    Yes, absolutely, once you have to go around, it's carb heat off to facilitate maximum power.

    I like that.

    So lets ask this one... lets say your turn off the carb heat on downwind or base, so you don't need to worry about it if you have to go around. How fast after turning the carb heat off can ice build up again? Is base and final enough time for ice to form? Or are you generally in the clear? Or "it depends"?
     
    Last edited: Dec 18, 2014
  32. TazzyTazzy

    TazzyTazzy Pre-takeoff checklist

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    Yes, I know carb heat off on go around.. Maybe to mitigate carb ice and have some power if u forget, half carb heat on final???

    I enriched the mixture on descent, as I was taught...but as with all things, still willing to learn better methods. :)
     
  33. poadeleted20

    poadeleted20 Deleted

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    Depends on the 172. If you're flying one of the older models with the Continental O-300 engine, absolutely yes, do it that way. With the middle range 172's with the carbureted Lycoming O-320 engine, it's not nearly as critical, and using carb heat only when symptoms of carb icing are detected is OK. And for the later 172's with the injected Lycoming IO-360 engine, you don't even have a carburetor to heat.

    As for go-arounds in the carbureted models, just make sure your thumb is catching the carb heat knob and pushing it forward as you advance the throttle and you'll do fine.
     
  34. poadeleted20

    poadeleted20 Deleted

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    Just make sure you don't push off the carb heat before you advance the throttle. You need that engine powering up and developing heat to melt out any carb ice which may have developed while you were at idle power on short final before you turn off the carb heat.
     
  35. poadeleted20

    poadeleted20 Deleted

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    Unless you have a carb air temp gauge so you can modulate carb heat to stay in the green zone, never use partial carb heat -- it might make things worse rather than better.

    With carbureted engines, there is no need to enrich during descent unless/until you advance the throttle above where it was in cruise. The reduction in throttle results in a slightly richer mixture all by itself, and enriching it further by advancing the mixture only creates greater potential for plug fouling during the descent.
     
  36. nddons

    nddons Touchdown! Greaser!

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    Interesting. I never looked at it that way. I'll actually think more about the "M" in GUMPS.
     
  37. Stewartb

    Stewartb Final Approach

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    No need to enrich on descent is the inverse of no need to lean with altitude.
     
  38. MAKG1

    MAKG1 Touchdown! Greaser!

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    No, it isn't, unless you descend at climb power.

    Enriching on descent at high DA can easily flood the engine and cause it to quit, as it is rather difficult to lean precisely at low throttle.
     
  39. mrkbbd

    mrkbbd Pre-takeoff checklist

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    If you're based in Denver and only fly in the high altitudes, do people set the basic mixture to be more lean? i.e. the full rich setting is different there than at a sea level operation?
     
  40. MAKG1

    MAKG1 Touchdown! Greaser!

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    That would preclude you from ever taking off from a low altitude airport. Seems rather limiting for a transportation device.

    High altitude procedure is to lean for best power at run-up.