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912 Is performance table is wrong ?

in 912iS Technical Questions 11 years ago
Hello,

It seems to me that the Performance table page 5.3 of the operators manual is wrong.
The Manifold Pressure column indicate very low values. Impossible to be at 65% power with 13,7 in.HG

Is somebody can confirm to me this mistake ??

Thanks
Sylvain

  • Re: 912 Is performance table is wrong ?

    by » 11 years ago

    It is not a mistake. It is calculated from a dyno at WOT. I will get a better description/explanation tomorrow.
      
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  • Re: 912 Is performance table is wrong ?

    by » 11 years ago

    Hi Sylvain,

    Most compressor and engine specs come from either a bench dyno test with optimum circumstances and not always hooked up to the end user uses or they are theoretical from engineering if everything were to be perfect which we know in actual use it is not.
    For example I used to Mfg dive compressors. The Mfg stated that the CFM numbers I was seeing out of the compressor during my test were normal because now I added fittings, hose, OAT's, different engine rpms, ect... So real time use in most cases will always be different than a Mfg's test stand or when outside factors are introduced past the theoretical.

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

      
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  • Re: 912 Is performance table is wrong ?

    by » 11 years ago

    Thanks for your replies, I understand what you mean, but if you compare the two performance tables between 912 ULS and iS, there is very big differences. See the tables below :









    At 75% Power 5000 RPM : 912 ULS = 27,2
    At 75% Power 5000 RPM : 912 iS = 16,5 !!!

    At 65% Power 4800 RPM : 912 ULS = 26,5
    At 65% Power 4800 RPM 912 iS = 13,7...with this set up, my plane fall on the ground !

    At 55% Power 4300 RPM 912 ULS= 26,3
    At 50% Power 4300 RPM 912 iS = 11,1

    It seems to me that the in.Hg column seems like the fuel consumption values :)
    Rotax912iS.png (You do not have access to download this file.)
    Rotax912ULS.png (You do not have access to download this file.)
      
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  • Re: 912 Is performance table is wrong ?

    by » 11 years ago

    HI
    I fully understand what you are explaining about engine data comming from dyno test or calculation, but in flight we don't care such data. In flight we need what we should see on board. That's what Sylvain would know, in order to adjust RPM and MAP to have engin running at 65% or 75% or whatever.
    As we have when it's come to 912 ULS.
    Do you have any advices?
    Bernard
      
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  • Re: 912 Is performance table is wrong ?

    by » 11 years ago

    It is not a mistake. It is calculated from a dyno at WOT. I will get a better description/explanation tomorrow.


    Hi Rob,
    I'm curious to read your explanation, I think the Rotax has confused the consumption value with the MAP value, .... as also saith Sylvain

    Pieri
      
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