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Hello all.

Does anyone know if there is a manual or bulletin from Rotax that states the normal range for EGT temperature at cruise rpm, as well as a maximum EGT temperature difference between cylinders? I can only find information about max EGT temperature.

Thanks 

Petter

  • Re: EGT normal range and max difference

    by » 3 months ago


    Following various recommendations it is suggested to not focus too much on absolute figures on the instruments. Various factors will make your setup a bit unique and different from others. You will know what's normal to your setup soon after you get used to noticing the values. When things start to change significantly you need to check. 
    Regards

    Peter


  • Re: EGT normal range and max difference

    by » 3 months ago


    From what I've seen over the years normal EGT temp in cruise run around 1250F (a little low) to 1450F. Average in the 1300's. Several things can affect this so don't get hung up on any one temp. You usually don't want to see a spread over 125F between cylinders. Normal spread, depending on other factors and throttle position, is 15F - 80F. On a Dynon instrument you may even get a "spread" alarm letting you know about the larger difference. Throttle setting affects the EGT temps as you fly and they can vary between engines so don't strictly compare to another engine. Carb sync when you're supposed too and don't neglect that.


    Roger Lee
    LSRM-A & Rotax Instructor & Rotax IRC
    Tucson, AZ Ryan Airfield (KRYN)
    520-349-7056 Cell


    Thank you said by: David HEAL

  • Re: EGT normal range and max difference

    by » 3 months ago


    Thank you both for your answers. 

    The reason I am asking this question is that our club has an Aeroprakt A-32, and in cruise (around 4650 rpm) the spread in EGT is high between the front and rear cylinders. EGT in cylinder 1 is around 1100 degrees F, and in cylinder 3 around 1310 degrees F. The difference seems high in my mind, but I have little experience with these engines. 

    In climb however, at around 5200 rpm (WOT) the EGT´s are more equal at around 1380 degrees F. Temperatures are also close to equal during descend at around 3500 rpm. 

    The prop pitch is adjusted so that that when climbing WOT at speed Vy, engine rpm is approximately 5070, but I don´t know if this has anything to do with the "problem".

    I am adding some pictures from cruise and climb. Speed is in km/h and temps in degrees celcius. 

    Regards

    Petter

    28859_2_EGT difference.png (You do not have access to download this file.)
    28859_2_EGT climb.png (You do not have access to download this file.)

  • Re: EGT normal range and max difference

    by » 3 months ago


    This is just an opinion from a non-expert, but if you're climbing with a wide open throttle, and seeing only 5070 rpm, your prop is WAY over-pitched.  (But your attached picture shows almost 5200 rpm in climb...)  At around 5000 rpm, you're putting a lot of strain on the engine – demanding a lot of torque well below the RPM where the engine is capable of producing its best power.  It's like trying to climb a steep hill on a bicycle in the highest gear.  You'd be standing on the pedals, and straining really hard, and still climbing very slowly!  Decreasing the prop pitch is like changing to a lower gear, and the expense of pedalling a bit faster. 

    The trick is to find a balance between too high of a pitch (straining the engine at low rpm in climb) and too low of a pitch (easily over-revving the engine in cruise flight).  Roger Lee has responded to this question multiple times in this forum.  You can search for those threads, but to get you started, here's one of them, and here's another one.  

    As you can read in those threads, Roger generally recommends setting the prop pitch so that in level cruise flight, with wide open throttle at your normal cruising altitude, your engine is turning 5600-5650 RPM.  That results in a prop pitch that is an excellent compromise between good climb performance and good cruise performance.

    I'm sure Roger will chime in eventually, but pre-reading his earlier posts will get you a head start...


  • Re: EGT normal range and max difference

    by » 3 months ago


    Thanks James.

    Although I haven´t much practical experience with these engines, I try to read what I can. I am known to what you are writing in your post, and I have read Roger Lees earlier posts in this regard. And I agree. The climb showing 5200 rpm was at a speed a little faster than Vy (120 km/h), so that is the reason. I also know that Rotax has a bulletin that states that rpm at WOT not should be below 5250 rpm. It is however not my airplane, so I can´t just do what I feel is right. 

    Let us say that we reduced the propeller pitch. This would lead to a higher rpm in cruise, and maybe we would avoid the rpm range where the EGT difference is so big? 

    Regards

    Petter


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