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Momentary start power switch or not?

in 912iS Technical Questions 8 years ago
If you could select, would you then chose a momentary start power switch or not?
If using an on/off type, I will not need to hold the power switch when pressing the start button. Right after, you have to change the start power switch back to flight position.

My concern not using the momentary type is if the ECU skips any of the engine check if the power switch is left in start position too long.
My concern with the momentary type is that the engine start with a quite high RPM (55-65%), and I cannot have the hand on the throttle when the engine start.

What would you select?

Kind regards, Claus

  • Re: Momentary start power switch or not?

    by » 8 years ago

    Consider a third alternative.

    Utilize the typical OFF/ON/START Switch.
    The Master Switch is separate and NOT part of the Keyed Switch.
    The ON Position energizes the Start Power Relay.
    The START Position enables the Starter.

    After starting, and before you remove your hand from the Key,
    Wait for the Lane Lights to extinguish then Switch the Key Back to OFF. Easy to remember.
    Start Power is then disabled.
    One Hand on the Key, The other on the Throttle.

    The Lane Switches Enable the ECU. Both Lanes OFF, The Engine stops.

    The Master Switch Powers the panel.
    The Key Switch powers the starting circuits only. No Key, No Start.

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

      
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  • Re: Momentary start power switch or not?

    by » 8 years ago

    I was planning on a key switch to energise the main contactor and two momentary toggle switches for start power and start side by side. Two fingers of one hand should therefore do the start. The key switch locks out everything including the backup battery switch. Open circuit in the key switch should still leave the engine and avionics running, ,just no battery charging. There may be better ideas out there.
      
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  • Re: Momentary start power switch or not?

    by » 8 years ago

    My switch arrangement is: lower left of panel; lane switches with master and start switches below them. Start is momentary push button ( circular guard). Others are single pole single throw toggle type. Throttle; mounted in middle lower portion of panel. Start power switch is single pole momentary toggle mounted to the left and slightly below the throttle. Start sequence is; Right hand on throttle with throttle open to percentage called for in manual for outside temperature. Right thumb pushes start power switch up. Left hand activates lane switches and following lane self tests left index finger pushes start momentary switch. When engine starts, index finger off start switch, right thumb off start power switch and right hand controls engine RPM. It is nearly the same hand functions as starting most general aviation aircraft.
      
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  • Re: Momentary start power switch or not?

    by » 8 years ago

    I was planning on a key switch to energise the main contactor and two momentary toggle switches for start power and start side by side. Two fingers of one hand should therefore do the start. The key switch locks out everything including the backup battery switch. Open circuit in the key switch should still leave the engine and avionics running, just no battery charging. There may be better ideas out there.


    The Key Switch should never disable the Battery Backup Function!
    The Battery Backup is your emergency Power supply for when all else fails.

    If the Key Switch Disables the Battery Backup Switch, Then, if the Key Switch goes open circuit(OFF), and the Generators fail, the engine will stop.
    The Main Contactor will drop out and the panel will go dead.
    With the Battery Backup disabled, a restart will not be possible.
    You will then be in a glider without any power.

    Yes, it is a very unlikely senerio, But you you need to design the system so that it still works with multiple simultanious failures, no matter what!

    I am not saying that Key Switches are junk, but they are the lease relable of all the switches in the plane.
    If any switch is going to go bad in the next twenty years, The Key switch will likely be the first to go.

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

      
    Report

  • Re: Momentary start power switch or not?

    by » 8 years ago

    If you are thinking of a OFF/ON/START switch you must not go from ON to START until the lane lights have cycled. You must give the fuel pumps time to charge the injectors and the ECU to boot and run its checks.
    So the procedure: Master ON, key to ON (start-power), wait for Lane lights to go OFF, key to START. Test the switch to make sure it does not break the start-power contact when going to Start.

    The big thing I don't like about this idea is the reliability of the key switches. They have a bad reputation in aviation. The best option is still a good quality toggle switch.

    Off the topic and it has been said before but needs to be repeated: Please, Please, Please, Please, Please do not consider using a ON/LEFT/RIGHT/BOTH switch for the Lanes.
      
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