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Momentary start power switch or not?

in 912iS Technical Questions 8 years ago

  • Re: Momentary start power switch or not?

    by » 8 years ago

    sounds like a good plan for the switches Bill.
    For your procedure I just want to add that you should wait for the Lane lamps to go OFF before hitting the starter button:
    Procedure:
    Advance Throttle as Needed.
    Start Power ON
    Lane lights ON, then OFF
    Check fuel pressure.
    CLEAR!
    START!
    Retard Throttle as needed.
    Start Power OFF.
    Verify Both Lane Lights OFF.
    Verify Oil Pressure.
    This way the ECU can finish its self-checks and the fuel pressure has stabilized.
      
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  • Re: Momentary start power switch or not?

    by » 8 years ago

    Okay. I will ask them for a toggle switch then. Thanks.

    Bill. Nice to see you back. You might remember the other thread with the plane I got where we got in trouble on its maiden flight. It is still the same. We are just waiting for come and repair it. With the wires showing sign of melted isolation and one pin in the start power being very lose (looks like it is melted inside), I insist they change the switches. So question was to use a toggle like before, or a momentary type like specified by Rotax.

    Kind regards, Claus
      
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  • Re: Momentary start power switch or not?

    by » 8 years ago

    Bill, than you for your comment about using a key switch that locks out the battery backup circuit. I agree with you that a double alternator failure and a key switch failure would leave me out of luck. I'm not even sure how I would know that something had failed except for the ammeter showing a discharging battery if an alternator had failed. The key switch fail mode is as you described a silent aeroplane! Maybe I can make a switch lock for the master and backup battery switches.

    My aircraft is likely to have to be parked on low security airstrips for much of the time and their are weird people who like to "meddle" with aircraft. I need to be sure that it is not possible to start the engine without unlocking something!

    On a different matter, a question for Rob and maybe a possible solution for everyones problem regarding the use of Two switches - start power and start switch.

    There is a three position military grade four pole switch MS 27406 -2 which has a momentary position in the "up" position. I think maybe it is possible to use this switch so that "down" is off, "centre" actuates start power and the momentary "up" position maintains start power as well as actuates the starter circuit.

    That way we only need one switch with three positions off, start power and start. We need to remember to place it back to "off" after a successful start. We only then need one finger to start the engine.

    There may be an issue with the battery backup switch. If that is used, presumably we do not want the start power circuit energised, just the start function. That is I think possible by using switch MS24525 - 23 for battery backup. It is a two position Four pole switch that can do the job and also interrupt the start power switch circuit so that the "start" is still available but the start power circuit is deactivated.

    Switch data sheets : http://www.farnell.com/datasheets/1850689.pdf?_ga=1.245669636.1658704978.1471931453

    I hpoe all this makes sense, my apologies if I'm forgetting something. I'd welcome your thoughts.
      
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  • Re: Momentary start power switch or not?

    by » 8 years ago

    Does MS27406-2 maintain the center contacts when in the momentary position? I was not able to find this configuration.

    I think it is OK to have the start-power and the Back-up switch ON at the same time but I will ask the Dr.
      
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  • Re: Momentary start power switch or not?

    by » 8 years ago

    Does MS27406-2 maintain the center contacts when in the momentary position? I was not able to find this configuration.

    It is kind of an unusual switch.
    It is a 4 pole, Double Throw.
    In the center position, 2 of the Poles transfer. 2 ON, 2 OFF
    In the momentary Position, The other 2 Poles transfer. All 4 ON.

    4 pole is overkill. There is a 2 pole, Double Throw version available.


    [quote]I think it is OK to have the start-power and the Back-up switch ON at the same time but I will ask the Dr.[/quote]
    If it weren't, how would you restart the engine after a dual Gen failure? :(

    Bill Hertzel
    Rotax 912is
    North Ridgeville, OH, USA
    Clicking the "Thank You" is Always Appreciated by Everyone.

      
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