The question was posed to me recently if Air-Starting a 912 was possible.
A little research finds that the sailplane crowd performs the maneuver on occasion.
So we can assume it is at least possible under some circumstances.
Most reports indicate that they were using the lower compression 912UL engine with Featherable Props.
A Featherable Prop traverses a zone of Extremely Coarse Pitch as it comes out of feather, so this may be a unique situation and not practical with a fixed pitch prop or the higher compression engines.

Please: If you Have Never attempted an Air-Start with a 912UL, 912ULS, 912is, 914, or 915 Engine or any of its variations, please do not respond.  I am not asking if it is or is not a recommended procedure. I am asking if it can be successfully performed.

And for completeness, an AIR-START is the procedure of using Airflow to windmill the propeller to obtain an engine restart in flight WITHOUT the use of the Electrical Starter.

The Survey:

If you HAVE attempted an Air-Start with any of the 900 series engines, and either Were or Were-Not Successful in getting an Air Start, please describe your experience including the following details.

Which Engine Model?
Tractor or Pusher Configuration?
Fixed or Adjustable Propeller?
Number of Blades?
Did it successfully Start?
Airspeed Needed, or Max Speed Attempted?
Altitude lost?

Thanks, Bill

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

  • Re: Engine Air-Start Survey

    by » 7 months ago

    Here is a video of a Remos GX performing a in air restart after engine stopped.

    The Remos GX aircraft has a 912 ULS and a 3 bade Neuform propellor installed.



    Thank you said by: Bill Hertzel, Rotax Wizard

  • Re: Engine Air-Start Survey

    by » 6 months ago

    I’ve successfully restarted a 912ULS hundreds of times in a Diamond Xtreme motorglider while setting altitude records in the flight levels and demonstrating the procedure as a Diamond check pilot for new Diamond Xtreme motorglider owners. Successfully demonstrated with both electric and hydraulic constant speed 2-blade props. Must put prop in takeoff pitch, dive to 120 kts and will loose between 1500-2500’. While soaring wave above 20,000’ for an hour or longer, the battery and engine would be too cold soaked for a restart and would glide to airport, land, and let things warm up 30-60 min to restart the engine. This a little more dicey with an airplane with a lower L/D and retractable gear. I’ll be doing air start flight tests in the new high performance Rotax powered Pelegrin Tarragon.  It is a turbocharged EFI engine but the Rotax engine has two stators which should provide sufficient electrical power to the ignitions for a restart in addition to the ECU backup battery. As long as the engine remains warm, should be able to airstart a Rotax in most applications. Flight testing the Tarragon 1st quarter of 2022. - ATP, Rotax Tech, LSRI, “Gold Seal” CFI, USAF (Ret)


    Thank you said by: RotaxOwner Admin, Bill Hertzel

  • Re: Engine Air-Start Survey

    by » 5 months ago

    An interesting question!

    My ship is a Super Ximango AMT-200S motorglider with a tractor-mount 100 hp 912S4 (ULS) engine and Hoffman 2-blade, mechanically selectable 3-position prop. The official factory manual specifies an airstart speed greater than 110 knots. My experience doing this is far less extensive than that of Mr. Elves, only a half-dozen times, but I find the following so far.

    When airstarting, I'm not quite following the procedure in the manual. Beginning at 60 kt with engine off and feathered, I first un-feather, which puts the prop into climb (fine) pitch. Throttle closed, fuel on, electric fuel pump on, mags on. Stone cold, I hold the choke open. If warm (oil temperature gauge reading something above the bottom point), choke remains closed. Then dive *quite abruptly*. So far, the prop starts spinning around 85-90 kt and the engine will start well under 100 kt. This will clearly depend a lot on how cold the engine gets. The swoop down probably takes only a few hundred feet with some of that recovered by converting airspeed to altitude. What really takes time/altitude is warming up the engine afterwards. Cold starting on the ground, it takes me on average about 6-7 minutes to get 50C oil temperature. Airborne, one has a 60 kt wind blowing on the nose and lower OAT which really slows things down. Simply waiting with closed throttle may have one running out of fuel before reaching 50C. Instead, I use the oil pressure gauge, nudging the throttle up until just touching the bypass opening pressure ~80 psi, waiting until it comes down to ~70 psi, the opening a little again. All the while, I'm drifting downward until about 3,500 rpm at which it maintains altitude. After about a 1,500-2,000 ft altitude loss, and as much as 15 minutes I feel able to climb again at a reasonable rate. If in gliding range of an airport, I'll wait to as low as 2,500' agl before restarting, if not I get nervous below 3,500. I need more practice to be more specific.

    From someone who owns both a Ximango and a Dimona, he observes also that the air-start speed is considerably lower on the Ximango. We think this is because the MT-hydraulic prop has a much thinner blade chord than the fat Hoffman.

    Closing an already too-long answer, I'll add that even with modest airspeed and a nearly-dead battery, the starter will spin the engine much more easily and faster than it normally ever does on the ground.

    Thank you said by: RotaxOwner Admin

  • Re: Engine Air-Start Survey

    by » 5 months ago

    Here's a Ximango air-start with altitude and speed recorded.



    Thank you said by: Bill Hertzel

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