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Hand Starting?

in 912iS Technical Questions 6 years ago
Not that I plan to, but is it possible to hand start a 912 iS in battery backup or normal mode? It is alsoa safety issue if the prop was moved with the ECU powered up and fuel pump running.

  • Re: Hand Starting?

    by » 6 years ago

    It would be very hard for a human to do this; the ECU will not engage the ignition until it detects a steady 100 rpm for min 2 full revolutions of crankshaft.
    912iS has a 2.43:1 ratio. I am sure Bill can do the math for us :)
      
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  • Re: Hand Starting?

    by » 6 years ago

    As Rob surmised...
    Getting the plugs on a 912is engine to fire by moving the prop by hand will require a super-human effort.

    There are no physical points that open at a specific point in the rotation.
    The crankshaft position sensors sense a set of toothlike tabs on the generator stator.
    There is a missing tooth at the point indicating Top Dead Center of cylinder #1 and #2
    The ECU will need to detect this point twice to determine where the crankshaft is in its rotation.
    Depending on where the engine stopped and how long it takes to get up to an acceptable cranking speed,
    It could take from just over 1 crankshaft revolution to just under 2 revolutions to acquire sync.
    Assuming it takes about a half revolution to get up to cranking speed and closer to 2 revs to get synced,
    followed by at least another half turn for the engine to reach the intake stroke where the fuel is injected,
    Plus the first compression stroke to get to the ignition point,
    It could take about three and a half full turns of the crankshaft or about one and a half full turns of the prop before the first injector and plug fired.
    That would mean you would need to hand prop the propeller about a full revolution and a half in a continuous fluid motion before the first plug fired.
    Good Luck with that!

    When using the electric starter on a fuel injected engine, the fuel pressure is already established before the cranking starts.
    So once the ECU can determine the crankshaft position, you get plugs firing immediately.
    The result is what looks like a dead engine that makes one to two prop revolutions and then immediately comes to life.
    There are seldom any long cranking events. It just goes Pucka-Pucka-Vroom!

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

      
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  • Re: Hand Starting?

    by » 6 years ago

    Thank you for the explanation. I will still treat the prop as always “live” for safety’s sake. I will also investigate the idea of a backup. battery if flying to the boondocks.
      
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