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I’m helping a friend who just got a Sirius TL-3000 with a Rotax 912IS. The POH we have is written for the carb 912 ULS.  So, should we have the aux pump on for start?  It seems to help.

We are also using the aux for takeoff & pattern work. I don’t get the same answer twice on this.

  • Re: Aux Pump

    by » 11 months ago


    I think the best thing to do is to follow the Rotax use manuals for things engine related, not the planes POH. I always use both pumps for pattern work and for take off and landing, and turn aux. for cruise. Pressure should always be between 2.9 and 3.2 bars, if I am not mistaken, regardless if both or only one fuel pumps is active, but having both on critical phases of flight brings welcome redundancy.


  • Re: Aux Pump

    by » 11 months ago


    Albert,
    Read the Rotax 912iS operating manual, section 3.4.  They are very clear to only use one pump when starting, even stating that using both pumps during starting may cause a bad starting behavior.  Just as important is to set the throttle to between 55% and 65%.  This should be done using the throttle position readout on your EFIS, since the physical throttle position is not a good indicator.  It’s typically only about 2cm forward.  

    With a fuel injected engine a higher throttle position delivers a longer fuel pulse, so it’s similar to using a choke on a carbureted engine - it gives you a richer mixture while starting. Using these settings, you will need to reduce the throttle immediately on starting to get the RPM down to 2100.  


  • Re: Aux Pump

    by » 11 months ago


    55 to 65% throttle may be a bit high for most ops. See the more detailed discussion on page 3-9 and the diagram that shows how it is related to temperature.

     

     

    36146_2_912is start diagram.pdf (You do not have access to download this file.)
    36146_2_Untitled.jpg (You do not have access to download this file.)

  • Re: Aux Pump

    by » 11 months ago


    I saw the “bad starting behavior” comment in the manual. I think that was for a carb engine. However, when we hit the start button several flights ago with aux pump off, the engine didn’t start. Now that’s ‘bad behavior’. So the last 4 flights, we started with aux pump on….& each time the engine started right away. Note:  this machine (N191TL) only has one aux pump switch. 


  • Re: Aux Pump

    by » 11 months ago


    Thanks.  I’ve seen this chart, but didn’t connect dots. We’ve been starting with the throttle at idle. So we will set the throttle higher & pull back right away to see if that yields consistent starts.


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