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  • Re: When exactly do the spark plugs fire in the 912ULS?

    by » 4 years ago


    Before we just blow this off ... and keeping in mind that I have waaay too much time on my hands ... and that I am a self proclaimed Geek Extraordinaire ... Plus, Enquiring minds want to know!  smile

    - - -

    This is just another back of the envelope calculation, but it should put the issue to rest.

    A typical ignition system draws about 1 amp from the power bus.

    1 amp at 12 volts is 12 watts.  1 hp is 745 watts, so a typical ignition steals about 12/745 = 0.016 hp (1/60th). 

    But we have Two, so 1/30th of a hp for the pair.

    - - -

    Looking at it from the other direction...

    A typical spark is about 100mJ (mili-Joules) (0.100 J)

    At 5000 rpm 10,000 sparks are produced per minute. 167 per second.  Time 0.1J  per spark = 16.7J per ignition.

    16.7J / 745 J per Hp = .022hp (1/45 hp).

    And again we have two, so lets be generous and call it 1/25th hp.

    - - -

    1/25th or 1/30th of a hp ??? . . . pretty good agreement for a first approximation. !!!

    So what could we do with another 1/30th hp???

    That would be enough power to increase the rate of climb of a 1000lb aircraft by just over a 1/4 inch per minute.  That is Inch NOT Foot per minute.

    And as P.J. said, " ... It's ... so little that it doesn't matter ..."

    - - -

    I think this should settle the big worry over the cost of Wasted Sparks and everyone should sleep well tonight.  wink

     

     


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


    Thank you said by: , Garrett Wysocki, RotaxOwner Admin

  • Re: When exactly do the spark plugs fire in the 912ULS?

    by » 4 years ago


    Bill Hertzel wrote:

    Both plugs in the same cylinder do not fire "Simultaneously" either.

    The "A" Module fires at 26° BTDC and the "B" Module fires 4° later at 22° BTDC.

    Both A and B fire simultaneously at 26° BTDC on the 912. Only on the 914 is the B module firing 4° later (74-00-00 page 6 and 7 in the heavy maintenance manual).


  • Re: When exactly do the spark plugs fire in the 912ULS?

    by » 4 years ago


    Simple answer. It fires every stroke. 


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


  • Re: When exactly do the spark plugs fire in the 912ULS?

    by » 4 years ago


    Roger Lee wrote:

    Simple answer. It fires every stroke. 

    And it is way more common than you might imagine.
    It happens in any engine that does Not have a distributor.
    This would include most lawn mowers.
    You can see the wasted spark happen in This Video.
    Skip to 6:10 in the video if you have ADHD.


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


  • Re: When exactly do the spark plugs fire in the 912ULS?

    by » 4 years ago


    Roger Lee wrote:

    Simple answer. It fires every stroke. 

    I know. Bill explained it very well. I just needed to nitpick that module A and B fire simultaneously.


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