The Rotax 912 was first sold in 1989 in non-
certificated form for use in
ultralights and
motorgliders. The original 912 UL engine has a capacity of and a compression ratio of 9.1:1, and is designed to work with regular automotive gasoline, with up to 10% ethanol. The later certified
912 ULS variant has a compression ratio of 11:1, and requires 91-octane ("premium") auto gas (100LL leaded
avgas can be used, sparingly). The engine differs from previous generation aircraft engines (such as the
Lycoming O-235) in that it has air-cooled cylinders with liquid-cooled heads and uses a 2.43:1 PSRU reduction gearbox to reduce the engine's relatively high 5,800 rpm shaft speed to a more conventional 2,400 rpm for the
propeller. The gearbox has proven to be generally trouble-free. The 912's lubrication system differs from most dry-sump designs in that oil is forced into the storage tank by
crankcase pressure rather than by a separate scavenge pump. This requires a novel preflight inspection procedure: before checking the oil level with the
dipstick, the engine is "burped" by removing the oil filler cap and turning the propeller until a gurgling sound is heard, which indicates that all oil has been forced into the tank and the oil level can now be checked accurately. A torsional shock absorber consisting of 2
dog gears serves to smooth the power pulses and reduce gearbox wear during startup and shutdown. In addition to the lower fuel consumption, the 912 is certified to run on automotive fuel (mogas), further reducing running costs, especially in areas where
leaded avgas is not readily available. with ECUs supplied by
Rockwell Collins. The version weighs , which is more than the standard 912S. The non-certified 912 iS targets the light sport and homebuilt aircraft market and 912 iSc will be
certified. Production started in March 2012, and the engine has a 2000-hour recommended time-between-overhaul. On 1 April 2014, the company announced its new 912 iS Sport upgrade with greater power, torque, and reduced fuel consumption. A derivative, the
Rotax 915 iS, was announced in July 2015, and a further upgrade, the
Rotax 916 iS was announced in March 2023.
Rotax's warnings to flyers Rotax publishes extensive warnings in the owner's manual about both the certified and non-certified versions of the engine design. Pilots are cautioned that the 912 engine is not suitable for: • use in situations where a safe landing cannot be made • use in
rotorcraft • night flying (unless equipped with redundant electrical power), or •
aerobatics. ==Variants==