My 912 ULS 3 does not not have any temperature issues on hot days under full throttle in a climb, but both CHT (coolant) and EGT increase rapidly when the throttle is reduced for descent and entry into the circuit. Temperatures just as quickly decrease if the power is either reduced to idle or increased to a normal cruise setting. This makes it difficult when there are other aircraft in the circuit and you need to reduce to a moderate power setting for separation and landing. I am running a 3 bladed MT propeller with a constant speed unit. I am wondering if the combination of engine and prop is causing some form of back-pressure that is inhibiting the flow of air through the radiator. Has anyone encountered this problem or have any suggestions?
  • Re: High Temps Under Reduced Power Settings

    by » 4 weeks ago


    How are you reducing the rpm?
    Do not confuse rpm with power when using a constant speed propeller.
    A constant speed propeller does not change rpm when reducing power.
    If you command a lower RPM(Coarse Prop) before reducing power(Throttle), you will Lug/Overload the engine and the temperatures will spike. Very Bad!

    Running a High MAP pressure at low RPMs is an engine killer.
    Running High RPMs at a low MAP setting is just fine.

    Is the installation Electric or Hydraulic?
    Automatic or Manual Prop Pitch controll?
    What is your MAP Pressure and RPM when the temperatures increase?

    Bill Hertzel
    Rotax 912is
    North Ridgeville, OH, USA
    whertzel1@yahoo.com
    Clicking the "Thank You" is appreciated by all.

  • Re: High Temps Under Reduced Power Settings

    by » 4 weeks ago


    Hi Bill,
    Power is reduced with throttle, I.e. by reducing manifold pressure. I usually set RPM at 5100 or 5150 for cruise power, and leave this RPM setting when reducing the throttle for entry and landing, until on final, when pitch is set to full fine.

    The CSU is hydraulic and manually controlled by pitch control. The manifold pressure does not have to be reduced that much to start the temperatures rising, usually 23.5” will start temperatures rising. The RPM reduces below 5100 as the MAP is reduced. I don’t believe the engine is being over-propped.

  • Re: High Temps Under Reduced Power Settings

    by » 4 weeks ago


    Well, if it getting too hot, you are either making more heat than you can get rid of or you can't get rid of the heat that you are making.
    Yeah, I know that sounds like double talk.
    But you need to determine if the high temps are a cause or an effect.
    Are you producing more heat, or is something reducing the cooling???

    ---
    Any chance a baffle on the engine is flopping around?
    Any chance a baffle in the muffler is flopping around?

    Bill Hertzel
    Rotax 912is
    North Ridgeville, OH, USA
    whertzel1@yahoo.com
    Clicking the "Thank You" is appreciated by all.

  • Re: High Temps Under Reduced Power Settings

    by » 4 weeks ago


    Hi
    It is interesting that when you reduce the workload the temperature rise.
    What is the configuration of your plane? pusher or tractor

  • Re: High Temps Under Reduced Power Settings

    by » 4 weeks ago


    Nothing appears to be loose or missing. One possibility suggested to me is that the carburettor needle position is incorrect (clip set too high), with the result that the mixture is too lean when under partial load.

    Failing that, I can only assume that there is some form of back pressure in the cowl under reduced power, restricting the flow of air into the radiator and cowl. I may place a lip at the leading edge of the opening at the bottom of the cowl to try and create an area of reduced pressure to help draw the air through.

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