The Rotax 912 is a family of four-cylinder, four-stroke aircraft piston engines combining liquid and air cooling with a propeller reduction gearbox. Its carburetted versions include the 80 hp UL, A and F and the 100 hp ULS and S. Later fuel-injected iS models extended the family.[1]912 UL, A and FBRP-Rotax · flyrotax.com · Accessed 2026-09-13Open source details[2]912 ULS and SBRP-Rotax · flyrotax.com · Accessed 2026-09-13Open source details[3]Rotax aircraft engine historyBRP-Rotax · flyrotax.com · Accessed 2026-09-13Open source details
Development
Rotax began developing the 912 in 1984. The A1 and A2 received their original certification on 25 September 1989. The F versions followed in 1994, and the S versions in November 1998. Rotax introduced the fuel-injected 912 iS in 2012 and the iS Sport in 2014, retaining the family name while changing its fuel and engine-management systems.[3]Rotax aircraft engine historyBRP-Rotax · flyrotax.com · Accessed 2026-09-13Open source details[4]EASA.E.121 type certificateEASA · flyrotax.com · Accessed 2026-09-13Open source details
Carburetted architecture
The ULS and S employ two carburettors, a mechanical fuel pump and dual electronic ignition. Hydraulic tappets adjust the valve mechanism automatically. Lubrication uses a dry-sump system with a separate oil tank, so the installation includes plumbing and an external reservoir rather than storing all working oil beneath the crankcase.[2]912 ULS and SBRP-Rotax · flyrotax.com · Accessed 2026-09-13Open source details
The engine runs faster than the propeller. The reduction gearbox accommodates this speed difference: Rotax lists a 2.43:1 ratio for the 100 hp version, whose peak rating occurs at 5,800 rpm. Its displacement is 1,352 cubic centimetres, with an 84 mm bore and 61 mm stroke.[2]912 ULS and SBRP-Rotax · flyrotax.com · Accessed 2026-09-13Open source details
Weight and installation
The 80 hp version is listed at 55.4 kg with its 2.27:1 gearbox, with a 2.43:1 option also available. Rotax itemises the exhaust, engine frame, external alternator and other equipment separately. These components become part of the installed propulsion system even when they are excluded from the basic engine-and-gearbox figure.[1]912 UL, A and FBRP-Rotax · flyrotax.com · Accessed 2026-09-13Open source details
The 100 hp ULS/S listing gives 56.6 kg with gearbox and overload clutch. Its electric starter and geared propeller drive form part of a compact installation intended for light aircraft.[2]912 ULS and SBRP-Rotax · flyrotax.com · Accessed 2026-09-13Open source details