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Hi people,

I am new here, but I wonder if any members can tell me the actual fuel consumption figures they are getting from a Rotax 912iS.

I have heard all sorts of claims of 20-30% improvements over the 912ULS and can work out that this is probably between 12 & 15.5 litres an hour, but I can't find anything on the net to confirm this.

I am having an aircraft built (with a 912iS) to do a trip for which long range will be critical, so any info will be greatly appreciated. While the iS is obviously the most efficient engine out there, I am trying to ensure that I can do the longest leg of this trip without ferry fuel tanks, which seems entirely possible with the iS, if it really can hit those figures.

I also note that the engine runs in eco mode at throttle settings below 97%. Can anyone tell me whether this is strictly throttle position or partly manifold pressure related. For instance, if I am cruising at 9500 feet with the throttle wide open to gain manifold pressure, which will, of course, be well down on sea level, does the engine run in eco mode then.

Thanks for any advice
  • Re: Rotax 912is Fuel Consumption

    by » 10 years ago


    Hi Eric,

    The Eco mode is below 92% throttle position. In real numbers I fly a Flight Design (912ULS) along side a Flight Design (912is) and he gets about 1.1 gph better than I do. So when I'm showing 4.8 gph he shows around 3.7 gph usage. This all depends on prop settings and throttle position. If all you can get is 5300 rpm @ WOT and I can get 5600rpm @ WOT I will get better fuel burn than he can because he will have to advance the throttle more to try and keep up. So the point is don't over prop the pitch and you'll do well. He does get better fuel metering at higher altitudes than I do because his system can adapt better. The 912is engine was meant to run at higher rpms so when it comes time to pitch the prop keep that in mind.
    All this said if I'm cruising at 5200 rpm he has to cruise at 5300 rpm to keep up so his fuel savings are gone. The solution is he should unload the prop by another 1/2 degree. If I drop to 5050 rpm and he's at 5150 rpm or there about he gets his fuel economy back. 5200 rpm is the approximate magic number.

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


  • Re: Rotax 912is Fuel Consumption

    by » 10 years ago


    Is it a draggy aircraft Eric?

  • Re: Rotax 912is Fuel Consumption

    by » 10 years ago


    No, it is extremely clean, a WT9 Dynamic with retractable gear, taped hinge lines and as few external aerials as I can manage.

    It will have a 3 blade Airmaster prop with Sensenich "scimtar" blades. These props have preset "constant speed" steps which are electrically selected, they are set during the installation of the propellor.

    The T/O setting is usually 5800, the climb 5500 and the cruise 5200, you simply flick the switch to whatever mode is appropriate and the prop controller looks after it. You can also control the RPM with an "increase/decrease" switch. Great props!

    Roger, do I take it that he is getting 3.7 US an hour at around 5200, and can I also take it that Eco mode is throttle position dependent only?

  • Re: Rotax 912is Fuel Consumption

    by » 10 years ago


    Econ mode is throttle position which should be close to 5200 rpm. (depending partly on how you set your prop pitch).
    5200 rpm is the break point for his Flight Design. Over that he is out of econ mode and below that he's in the econo mode. Up high the engine shines even more over the carbs. If I remember his Skyview Dynon unit shows around 3.8 gph US at 5200 and I'm around 4.8+/-.

    Remember these numbers are predicated on that the Dynon and fuel transducer are giving you accurate numbers, but they should be really close. With the new Rotax modification coming out the fuel economy should be even better.

    You should do very well on fuel economy.

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


    Thank you said by: Eric West

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