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Just curious, why is 915iS max RPM not electronically limited to 5800? It seems it would be easy to implement on FADEC engine.

Thanks.

  • Re: Why is 915iS max RPM not electronically limited to 5800?

    by » 4 months ago


    I believe it is because in order to be certified by FAA an engine cannot have anything on it that limits power output.


  • Re: Why is 915iS max RPM not electronically limited to 5800?

    by » 4 months ago


     

    Does not Rotax prohibit in the Manual running engine above 5800 RPM? How is it different from electronically limiting engine RPM at redline?


  • Re: Why is 915iS max RPM not electronically limited to 5800?

    by » 4 months ago


    It would just add un-needed complexity.

    Would you also limit it to 5 minutes at 5800 RPM?

    If you needed just another 30 seconds at 5800 to clear the trees at the top of a ridge are you going to be happy with the engine automatically throttling back???  

    And then how long at 5500 rpm before allowing another 5 minutes at 5800 RPM?

    Do we really need to open this can of worms?

     

    An Un-Advertized RPM Limit is that you can run at 6200 RPM for up to 1 minute.  See LMM Section 05-50-00, Page 17.

     

    Most aircraft have ground adjustable props that only reach 5800 rpm in a dive where the pilots normally throttle back anyway.

    Adding an adjustable prop removes the LSA status of the aircraft then requiring a Private License with a 3rd class medical.

     

    The pilot needs to take responsibility for the operation of the aircraft and not rely on automation.

    - - -

    Having said all that; Maybe flashing the Lane lights alternating A and B would be a reasonable Overspeed Warning.


    Bill Hertzel
    Rotax 912is
    North Ridgeville, OH, USA
    Bill.Hertzel@Yahoo.com
    Clicking the "Thank You" is Always Appreciated.


  • Re: Why is 915iS max RPM not electronically limited to 5800?

    by » 4 months ago


    In theory it could limit it to a much higher RPM setting like 7000 RPM that would never be seen in flight even in the worst conditions which could protect the engine from over-revving if it's started without the prop or a spinner. The ULPower UL350iS (it's another pretty light engine with fuel injection, except it's direct drive and wet sump unlike Rotax and its heavier) has a limiter for those purposes and I'm sure it would be easy for Rotax 915iS to do that as well. It might even have that already for all I know (I didn't check). From a software point of view it would not add any undue complexity.

     

    But limiting it to 5800 RPM would be a bad idea like Bill said. Software limits that keep an engine healthy might not keep a person healthy. That's a reason I still enjoy simpler carbureted engines is that they don't have FADEC so I can push them a bit harder. If my engine is overheating but I need to clear some trees then I want to be able to push it to the breaking point. In my perfect world there would be a switch to turn off the FADEC and go fully manual even if it means harming the engine, just for emergencies or if a sensor fails at an inopportune time. But I know that in the real world those kinds of failures are so rare that they don't really matter.


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