Mixture Setting for Full Power

Discussion in 'Aerobatics Talk' started by Eric_Anderson, Dec 15, 2017.

  1. Dec 15, 2017 #1

    Eric_Anderson

    Eric_Anderson

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    I am putting this thread under Aerobatics because I know that we tend to be more willing to push our engines. A sane biplane pilot would be much more likely answer whatever is most conservative just as they would a question about redline. I am looking for responses from the less sane.

    What mixture setting are you using for full power? Here is why I ask: My Pitts is the only piston/non-constant speed engine I have flown since the '90s. The first day with it I noticed that I was getting lackluster takeoff performance with full mixture. So I leaned it back about 3/4 inch and enjoyed an additional 100 RPM at 100 MPH and much stronger performance. I thought that this was just a unique thing with my aging motor. But now I have a new motor with a newly overhauled fuel servo. Since the engine is new and I wanted to keep the CHT down I only briefly leaned it before returning to full rich for the initial climb. But the result was the same (100 additional RPM) with full rich a disappointment.

    Thanks!
     
    Last edited: Dec 15, 2017
  2. Dec 15, 2017 #2

    Bond007

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    Normal,they are usually set up rich.
    Danny 007
     
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  3. Dec 15, 2017 #3

    EAABipe40FF

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    My IO320 is exactly the same. I can get an extra 100 rpm/still rich side of peak.
     
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  4. Dec 15, 2017 #4

    Eric_Anderson

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    So what do you guys do? Lean it for performance or keep it rich for cooling (talking takeoff or acro)?
     
  5. Dec 15, 2017 #5

    PittsDriver68

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    What are the CHT and EGT temps? That is the important info.

    I will suggest that if you have invested in a new engine, you want to have an engine monitor that shows you the CHT's and EGT's on every cylinder. I have an EI with a data recorder. JPI also makes a good unit.

    Knowing every temp allows you to know that no one temp is too high while you lean the mixture. The theory is that at full power, at sea level, you want some extra fuel flow so that the cylinders, especially the exhaust valve and piston tops, do not get too hot. This is especially important for a high compression engine.

    When breaking in a new engine you want relatively high temps, but not out of limit temps. Without an engine analyzer you are guessing.

    My experience with breaking in Lyco's has been that initially #2 and #3 are the hotter cylinders at first. As the engine breaks in, #2 runs cooler and #3 will consistently be the hotter cylinder. So if you just have one set of CHT and EGT probes, put them on #3 (right rear).

    And performance is relative. Compared to a Cessna, even running full rich your Pitts is a rocket ship. So that extra 100RPM might not be worth shortening the engine life if the temps run higher than they should.

    Best of luck,

    Wes
     
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  6. Dec 15, 2017 #6

    Bond007

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    Most egt/cht gauges are not very reliable.Do it by feel and RPM,just like u were taught in basic pilot training.
    Keep your eye on oil temp
    Danny 007
     
  7. Dec 15, 2017 #7

    cwilliamrose

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    I never ran it leaned for akro. I was running a pressure carb and I don't remember it being super rich. Maybe FI is different?
     
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  8. Dec 15, 2017 #8

    Neil

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    You should check your fuel flow against the fuel flow chart in the engine operators guide. There should be a chart showing GPH at full throttle/full rich. It is not that uncommon to have to send the fuel servo back for additional tweaking.
    My opinion, and it is only worth the cost, is that a little rich at full throttle/full rich is good to have available.
     
  9. Dec 15, 2017 #9

    TFF1

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    You have to know the temps and lean to the safe. A piston helicopter will
    barely leave the ground if full rich; we don't have cooling problems though. Full horsepower is not rich; it is safe horsepower. Less fuel drooling in the cylinders help the oil too. You have to know numbers though.
     
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  10. Dec 15, 2017 #10

    PittsDriver68

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    Modern engine analyzers are actually pretty accurate. EI and JPI spend do a lot of engineering to make them accurate. And checking is simple. Boil some water and put the temp probe in. The analyzer should report 212F/100C.

    And Lycoming would be happy to sell every one of us an operators manual for the engines. My copy has lots of power vs fuel flow vs altitude graphs. Much better than what the airframe manufacturers put in their AFM's.

    Fuel and oil are cheap...engines are expensive.

    Best of luck,

    Wes
     
  11. Dec 15, 2017 #11

    grassroots

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    Eric, in case you're looking for clear guidance on leaning..... it does not exist. :)
     
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  12. Dec 15, 2017 #12

    Bond007

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    Here we go.U all were thaught this stuff in basic pilot training to get your license.
    Lean it till it starts to slow rpms down,then rich in it up a little past peak rpm.
    I do agree with leaving full rich for acro unless u are in the mountains.
    Your engine needs the fuel to help it keep cool doing acro
    Danny 007
     
  13. Dec 15, 2017 #13

    Bond007

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    And yes Eric S is correct u have opened a big can of worms
    Danny 007
     
  14. Dec 15, 2017 #14

    Cameron

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    I run mine full rich for acro, for what its worth.

    If I were you, I'd call my engine builder and ask him what he recommends, especially during break in.
     
  15. Dec 15, 2017 #15

    Morphewb

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    Go to the GAMI website then read some of the other articles about mixtrue control operation. Most Continental powered airplanes are running lean of peak and have been doing so successfully for over 10 years. These guys will tell you a lot more than you will ever want to know about mixture control.

    When you finish reading you'll still want to run your Lycoming rich of peak since you're in a Pitts instead of a Bonanza and you're doing akro instead of bladder busting, prostate crushing, long range cruising that would make Lindbergh jealous.

    Some of the best education I've read on how combustion works. One of the techniques they teach is the ''big mixture pull''. That's just about what Bond, Danny Bond is talking about. They also recommend you get as many temp probes you can for accurate CHT and EGT. Playing it by ear with one CHT and EGT might get you into the ball park but there are three or five other cylinders pounding away and you have no way of knowing wtf is going on with them internally or externally.

    Well worth the read. One thing they preach is paying really close attention to keeping the CHT below 400 degrees. Supposed to go a long way for cylinder and valve health especially in big bore Continentals. Lycomings have sodium filled exhaust valves were Continental uses some type of metal in the valve production that works with another type of metal in the exhaust valve guide. The common goal is reducing valve stem wear and heat rejection. They just use different manufacturing procedures to get to the same place.

    You won't be trying to fly the Atlantic after you read this stuff but I'm pretty sure you'll be impressed with the overall education you'll get on what the mixture control does besides shutting the engine off.
     
    Last edited: Dec 15, 2017
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  16. Dec 16, 2017 #16

    acropilotbret

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    Maybe I’m a crazy but this is what I do. At sea level I run up my engine at 1800 rpm lean to peak then enriched the vernier half way back and and leave it there for my Akro between 4000 and 2000 ft MSL. If I cruise from sea level start same thing half way back in then at my cruise alt I lean to rpm drop/sound change then 1 full turn from peak RPM. I cruise at 2700 RPM and my CHT run at 325-350 all the time. If in then mountains I lean further. I flew alll the way across the US from MD to CA this way and my compressions that year actually improved during conditional time.
     
  17. Dec 16, 2017 #17

    PittsDriver68

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    One important component of your procedure is that you have a vernier mixture control that allows finer and repeatable adjustments. 99% of Pitts have a simple push-pull control, maybe with a locking button. And the description sounds like you have an instrument that allows the identification of peak temps.

    As Ben notes, there is a lot of good info out there that explains what is going on inside your cylinders. I will note that Lyco's and Continentals are built with different expectations as to how the owners will run them.. What we do to Lyco's will run the maintenance bill on a Continental way up in short order. But even with what acro pilots do to them, the Lyco's will last a very long time with appropriate care.

    Best of luck,

    Wes
     
  18. Dec 16, 2017 #18

    jrs14855

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    PS5, properly set up, will run leaner than the Bendix injection. At low level the PS5 puts out maximum or near maximum power full rich.
    I flew a S2B that after I stopped flying it went to 1500 hours on a new engine. 25 square after takeoff and lean to a fuel flow reading. Barrett got the engine and it was in near perfect condition. Run hard and put away wet its entire life. No CHT. Don't need no steenking CHT.
    I ran my 0 360A4A hard for 1000 hours. Never a problem 3300-3500 r/m depending on prop, no CHT. If the baffles are done properly the engine will cool properly, CHT not an issue.
    The Twin Cessna's that I flew would run red line all summer long in the desert. Oil and CHT. They almost always made TBO.
     
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  19. Dec 16, 2017 #19

    Bond007

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    I agree Jim ,that crap weighs to much.
    Danny 007
     
  20. Dec 16, 2017 #20

    Bond007

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    I personally think that the PS 5 makes more power.It atomizis the fuel better.
    When I NASCAR engines it was all about fuel atomization and fuel curve up high .
    The fuel injection on lycomings does nothing to atomize the fuel.
    The fuel is dumped in behind the intake valve where it sits waiting for that valve to open,that's as crappy as it gets
    Danny 007
     

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