Rotax 912

Rotax 912 installation in a 3Xtrim 3X55 Trener

The Rotax 912 is a normally-aspirated, air- and water-cooled, horizontally-opposed, four-cylinder, four-stroke, gear reduction-drive engine commonly used on light sport aircraft and ultralight aircraft. The engine is available in the following versions:

• 912A# - Certified to JAA 22, 80 hp
• 912F# - Certified to FAR 33, 80 hp
• 912S# - Certified to FAR 33, 100 hp
• 912UL# - Uncertified, 80 Hp
• 912ULS# - Uncertified, 100 Hp

Where the # in the designation stands for:

1. Prop shaft with flange for fixed pitch prop, P.C.D 100 mm
2. Prop shaft with flange for fixed pitch prop, P.C.D 75 mm, P.C.D. 80 mm and 4" P.C.D.
3. Prop shaft with flange for constant speed propeller P.C.D. 75 mm, P.C.D. 80 mm, P.C.D 4" and drive for hydraulic governor for constant speed propeller
4. Prop shaft with flange for constant speed propeller P.C.D. 75 mm, P.C.D. 80 mm, P.C.D 4" and prepared for retrofit of a hydraulic governor for constant speed propeller

The initial versions were 80 hp with 100 hp variants added later, using higher compression ratios and different parts to achieve the increase in power. The 912A was used in aircraft like the Diamond DA20-A1 Katana, which is quite popular in Europe. The 100 hp versions are used in many light sport aircraft, such as the Flight Design CTSW, the Tecnam P2002 and the Titan T-51 Mustang.

The engine is different from conventional aircraft engines (such as the Lycoming O-235) in that it has air-cooled cylinders with water-cooled heads and uses a gearbox to reduce the engine's relative high shaft speed (5,800 RPM for 100 hp versions) to a lower speed for the propeller.

The 912 series has a lower time between overhaul (TBO) than traditional engines but is more fuel efficient than similarly sized engines (e.g., Continental O-200). It is not clear whether the 912 series will be more economical than traditional engines in the USA, but the engines are very popular in Europe due to the lower fuel consumption and lower noise generated.

Specifications (Rotax 912 UL)

General characteristics

• Type: 4-cylinder, 4-stroke liquid / air cooled engine with opposed cylinders, dry sump forced lubrication with separate oil tank, automatic adjustment by hydraulic valve tappet, dual CD carburetors, mechanical diaphragm pump, electronic dual ignition, electric starter, integrated reduction gear 1 : 2.273
• Bore: 79.5 mm
• Stroke: 61 mm
• Displacement: 1211.2 cm³
• Length: 561 mm
• Width: 576 mm
• Dry weight: 60 kg with electric starter, carburetors, fuel pump, air filters and oil system

Components

• Valvetrain: OHV, hydraulic lifters, pushrods, rocker arms
• Fuel type: premium unleaded: 90 octane or higher leaded or unleaded or AVGAS 100 LL
• Oil system: dry sump with trochoid pump, camshaft driven
• Cooling system: liquid cooled cylinder heads, air cooled cylinders

Performance

• Power output: 59.6 kW @ 5800 RPM
• Specific power: 48.71 kW/L
• Compression ratio: 9:1
• Fuel consumption: 19.2 liters/h @ 5000 RPM (75% power)
• Specific fuel consumption: 285 g/(kW·h) @ 5500 RPM (maximum continuous power)
• Power-to-weight ratio: 0.98 kW/kg

Related content

German Wikipedia entry

Related development:

Comparable engines: ULPower UL260i, Jabiru 2200

References

• The official Rotax® Aircraft Engines Website
• FAA Type Certificate Data Sheet E00051EN
• Horizontally-Opposed Piston Aero Engines: Rotax