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Thread: Leaning for peak power during high altitude takeoff

  1. #1

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    Leaning for peak power during high altitude takeoff

    I’m interested to hear what others do to lean for max performance when operating out of high altitude (or high density altitude) strips.
    carbureted O-320,
    8000’ plus agl.

  2. #2

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    Lean for best power while flying, leave it when you land and shut down with mags, or use finger to measure distance and pull that on start, or hold brakes and lean for best RPM (hard on prop). At sea level I can get an extra 25 RPM by leaning on takeoff, use it when needed.
    DENNY
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    JimParker256's Avatar
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    Next time you're at (or near) sea level, take note of your EGT reading during full-rich takeoff. That reading becomes your "target EGT" when leaning for takeoff and during climb at pretty much ANY altitude. Makes it very simple.

    PS - source for this is the Advanced Pilot Seminar. Here's a link to the PowerPoint presentation on this topic: Target EGT Presentation. Note that the presentation file is 'zipped' (compressed) to save space and reduce download times.
    Jim Parker
    2007 Rans S-6ES
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  4. #4
    Cub Builder's Avatar
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    Quote Originally Posted by Oliver View Post
    I’m interested to hear what others do to lean for max performance when operating out of high altitude (or high density altitude) strips.
    carbureted O-320,
    8000’ plus agl.
    Yes. Lean as soon as the engine starts, then set the mixture lean for best power during your run up. At that altitude, you are making less than 75% power to begin with, so you can't make enough power or lean it enough to hurt the engine. If you don't lean, you'll tend to foul plugs and will be down on HP on take off and climb out. I was based at an airport >7000' for 32 years.

    -Cub Builder

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    BC12D-4-85's Avatar
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    I like those mixture cables that "click" in small steps as the knob is moved in and out. Count the clicks for previous best mixture before takeoff or in flight, then adjust as required.

    Gary
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  6. #6
    DJ's Avatar
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    Great responses already. I'll add a bit of detail because I remember the stress of my first high altitude takeoff, wondering if I was doing okay.

    It helps to find a clean spot and do a full power run up the first time or two to note mixture for max rpm and egt. Then richen it up a bit (100 degrees ROP at least). I note the mixture knob position related to a finger joint for quick reference. Then on climbout I'm looking for 1250 EGT. That is about the leanest mixture to stay below 400 CHT on a long climb with my setup. Figure out what works for your engine/instrumentation.

    I can get a little more power momentarily by leaning closer to that 100 ROP number (~1350+ egt) but have to richen up after takeoff.
    With a little practice it becomes very second nature.
    For landing I estimate, (using my reference) what will be needed based on altitude of the LZ and then pump the throttle a couple of times to ensure quick smooth response. Too rich and it will hesitate and burp. Too lean and it will quit on rollout after the throttle is closed. If in doubt I do a brief full power climb to verify my target egt.

    My 2 cents...there may be better ways.

    Sent from my SM-G965U1 using SuperCub.Org mobile app
    The heavens declare the glory of God; the skies proclaim the work of His hands. Psalms 19:1
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  7. #7

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    Above 8000' da, I always start at full rich and 2000 rpm (stick full back!!). Then lean for max rpm. Then, enrichen about 50 rpm, less than that if really high (above 10K).

    This, just to have a little margin above peak EGT mixture. Our engines are air and fuel cooled.

  8. #8
    WindOnHisNose's Avatar
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    Thanks, folks, a very useful thread!

    I remember flying into the JC area for the first time, landing for fuel at Salmon ID. I did my usual runup (full mixture), things checked out OK, took off and felt a distinct lack of power. It took me a very short time to figure this out, I leaned the engine and full power was restored.

    These tips are good. Thank you for sharing your knowledge!

    Randy
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    cubflier's Avatar
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    In the winter, I lean for landing more than take off. This is because most of my high altitude flying involves landing in snow that can vary in it's resistance to forward motion. The technique I use is to lean with carb heat on when I'm on approach then push carb heat back in for the landing/track packing. Taking any stumble out of the engine in this configuration seems to address all variables that make up the density altitude effect. This way when I hit the snow and have go to full power I don't have an engine cough that can cause me to get hung off the front side of a ridge. Also when I'm on top and pull the power back the engine doesn't quit (from too lean) and leave me skiing down the other side dead stick. As far as the take off part in the snow up high the initial lean on landing is noted and gives me enough of an idea of where to put the mixture on take off. I doubt that it's going to give a perfect max performance power setting but seems to keep me out of trouble.

    On tires in the summer if I'm on some little place up high where I need to count my pennies on take off I will lean on one mag. This allows me to lean and a much lower RPM this saving all the potential vacuuming of particles through the propeller.

    I don't have a lot of monitoring gadgets so this is what I do.

    Jerry
    If it looks smooth...it might be

    If it looks rough...it is!!
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