The Rotax 912 is a horizontally-opposed four-cylinder,

naturally-aspirated A naturally aspirated engine, also known as a normally aspirated engine, and abbreviated to N/A or NA, is an internal combustion engine in which air intake depends solely on atmospheric pressure and does not have forced induction through a turboc ...

four-stroke A four-stroke (also four-cycle) engine is an internal combustion (IC) engine in which the piston completes four separate strokes while turning the crankshaft. A stroke refers to the full travel of the piston along the cylinder, in either directio ...

aircraft engine An aircraft engine, often referred to as an aero engine, is the power component of an aircraft propulsion system. Aircraft using power components are referred to as powered flight. Most aircraft engines are either piston engines or gas turbin ...

with a

reduction gearbox An epicyclic gear train (also known as a planetary gearset) is a gear reduction assembly consisting of two gears mounted so that the center of one gear (the "planet") revolves around the center of the other (the "sun"). A carrier connects the ...

. It features liquid-cooled cylinder heads and

air-cooled Air-cooled engines rely on the circulation of air directly over heat dissipation fins or hot areas of the engine to cool them in order to keep the engine within operating temperatures. Air-cooled designs are far simpler than their liquid-cooled ...

cylinders. Originally equipped with

carburetor A carburetor (also spelled carburettor or carburetter) is a device used by a gasoline internal combustion engine to control and mix air and fuel entering the engine. The primary method of adding fuel to the intake air is through the Ventu ...

s, later versions are

fuel injected Fuel injection is the introduction of fuel in an internal combustion engine, most commonly automotive engines, by the means of a fuel injector. This article focuses on fuel injection in reciprocating piston and Wankel rotary engines. All co ...

. Dominating the market for small aircraft and

kitplane Homebuilt aircraft, also known as amateur-built aircraft or kit planes, are constructed by persons for whom this is not a professional activity. These aircraft may be constructed from "scratch", from plans, or from assembly kits.Armstrong, Kenn ...

Rotax Rotax is the brand name for a range of internal combustion engines developed and manufactured by the Austrian company BRP-Rotax GmbH & Co KG (until 2016 BRP-Powertrain GmbH & Co. KG), in turn owned by the Canadian Bombardier Recreational Prod ...

produced its 50,000th 912-series engine in 2014. Originally available only for

light sport aircraft A light-sport aircraft (LSA), or light sport aircraft, is a category of small, lightweight aircraft that are simple to fly. LSAs tend to be heavier and more sophisticated than ultralight (aka "microlight") aircraft, but LSA restrictions on weigh ...

ultralight aircraft Ultralight aviation (called microlight aviation in some countries) is the flying of lightweight, 1- or 2-seat fixed-wing aircraft. Some countries differentiate between weight-shift control and Aircraft flight control system, conventional three-a ...

autogyro An autogyro (from Greek and , "self-turning"), gyroscope, gyrocopter or gyroplane, is a class of rotorcraft that uses an unpowered rotor in free autorotation to develop lift. A gyroplane "means a rotorcraft whose rotors are not engine-d ...

s and drones, the 912-series engine was approved for

certified Certification is part of testing, inspection and certification and the provision by an independent body of written assurance (a certificate) that the product, service or system in question meets specific requirements. It is the formal attestatio ...

aircraft in 1995.

Design and development

The Rotax 912 was first sold in 1989 in non- certificated form for use in ultralights and

motorglider A motor glider is a fixed-wing aircraft that can be flown with or without engine power. The FAI Gliding Commission Sporting Code definition is: a fixed-wing Aircraft#Heavier-than-air – aerodynes, aerodyne equipped with a means of propulsion (M ...

s. 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 Avgas (aviation gasoline, also known as aviation spirit in the United Kingdom, UK) is an aviation fuel used in aircraft with spark-ignited internal combustion engines. ''Avgas'' is distinguished from conventional gasoline (petrol) used in moto ...

can be used, sparingly).Prizio, Dave
"Firewall Forward: Rotax service Training,"
July 19, 2013, ''Kitplanes,'' retrieved July 5, 2023 The engine differs from previous generation aircraft engines (such as the

Lycoming O-235 The Lycoming O-235 is a family of four-cylinder, air-cooled, horizontally opposed, piston aircraft engines that produce , derived from the earlier O-233 engine.Textron Lycoming: ''Operator's Manual, Textron Lycoming Aircraft Engines, Series O-2 ...

) 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 A propeller (often called a screw if on a ship or an airscrew if on an aircraft) is a device with a rotating hub and radiating blades that are set at a pitch to form a helical spiral which, when rotated, exerts linear thrust upon a working flu ...

. The gearbox has proven to be generally trouble-free. On the 912A, F and UL the standard reduction ratio is 2.27:1 with 2.43:1 optional. Lubrication is

dry sump A dry sump system is a method to manage the lubricating motor oil in Four-stroke engine, four-stroke and large Two-stroke engine, two-stroke Reciprocating engine, reciprocating internal combustion engines. The dry sump system uses two or more o ...

, and fuelling is via dual CV carburetors or fully redundant electronic fuel injection. The electronic fuel injected Rotax 912iS is a recent development. The 912's lubrication system differs from most dry-sump designs in that oil is forced into the storage tank by

crankcase A crankcase is the housing in a reciprocating engine, piston engine that surrounds the crankshaft. In most modern engines, the crankcase is integrated into the engine block. Two-stroke engines typically use a crankcase-compression design, res ...

pressure rather than by a separate scavenge pump. This requires a novel preflight inspection procedure: before checking the oil level with the

dipstick A dipstick is one of several measurement devices. Some dipsticks are dipped into a liquid to perform a chemical test or to provide a measure of quantity of the liquid. Since the late 20th century, a flatness/levelness measuring device trademark ...

, 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. The 912 is more fuel efficient and lighter than comparable older engines, ''e.g.'',

Continental O-200 The Continental C90 and O-200 are a family of air-cooled, horizontally opposed, four-cylinder, direct-drive aircraft engines of 201 in3 (3.29 L) displacement, producing between 90 and 100 horsepower (67 and 75 kW).''Federal Aviation Admini ...

, but originally had a shorter

time between overhaul Time between overhauls (abbreviated as TBO or TBOH) is the manufacturer's recommended number of running hours or calendar time before an aircraft engine or other component requires overhaul. On rotorcraft, many components have recommended or ma ...

(TBO). On introduction, the TBO was only 600 hours, which was double that of previous Rotax engines but far short of existing engines of comparable size and power. The short TBO and lack of certification for use in factory-built

type certificate A type certificate signifies the airworthiness of a particular category of aircraft, according to its manufacturing design (''type design''). Certification confirms that the aircraft of a new type intended for serial production is in compliance w ...

d aircraft initially restricted its worldwide market potential. However, the engine received US

Federal Aviation Administration The Federal Aviation Administration (FAA) is a Federal government of the United States, U.S. federal government agency within the United States Department of Transportation, U.S. Department of Transportation that regulates civil aviation in t ...

(FAA) certification in 1995, and by 1999, the TBO had increased to 1,200 hours; on 14 December 2009, the TBO was raised from 1,200 hours to 1,500 hours, or 1,500 hours to 2,000 hours, depending on serial number. 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

is not readily available. The 912 may be operated using leaded fuel, but this is not recommended as lead sludge tends to accumulate in the oil tank and reduction gearbox. Also, avgas is incompatible with the recommended

synthetic oil Synthetic oil is a lubricant consisting of chemical compounds that are artificially modified or synthesised. Synthetic oil is used as a substitute for petroleum-refined oils when operating in extreme temperature, in metal stamping to provide en ...

which cannot hold lead in suspension; consequently, the use of leaded fuel mandates additional maintenance. A

turbocharged In an internal combustion engine, a turbocharger (also known as a turbo or a turbosupercharger) is a forced induction device that is powered by the flow of exhaust gases. It uses this energy to compress the intake air, forcing more air into the ...

variant rated at , the

Rotax 914 The Rotax 914 is a turbo-charged, four-stroke, four-cylinder, horizontally opposed aircraft engine with air-cooled cylinders and water-cooled cylinder heads. It is designed and built by the Austrian company BRP-Powertrain, owned by Bombardier ...

, was introduced in 1996. In 1999, the 912S / ULS were introduced; enlarged to with a compression ratio of 10.8:1, yielding . The 912S is certified, as are the A and F, which are used in the

Diamond DA20 The Diamond DV20/DA20 Katana is an Austrian-designed two-seat general aviation light aircraft. Developed and manufactured by Diamond Aircraft, it was originally produced in Austria as the DV20. The DV20 shares many features from the earlier ...

, which is quite popular in Europe. The 912's popularity was greatly enhanced by the introduction of the

light-sport aircraft A light-sport aircraft (LSA), or light sport aircraft, is a category of small, lightweight aircraft that are simple to fly. LSAs tend to be heavier and more sophisticated than ultralight (aka "microlight") aircraft, but LSA restrictions on weigh ...

category in Europe and the United States, which resulted in the introduction of many factory-built aircraft designed to fully exploit the engine's small size and light weight. The versions are used in many light sport aircraft, such as the Zenith STOL CH 701 and the

Tecnam P2002 Sierra The Tecnam P2002 Sierra is a two-seat, low-wing, light aircraft designed and constructed by the Italian aircraft manufacturer Tecnam. Introduced during the early 2000s, the aircraft quickly became a staple of the company's product lineup, compr ...

. The versions are sufficient to power the new generation of efficient motorgliders, such as the

Pipistrel Sinus The Pipistrel Sinus is a two-seat, single-engine ultralight motor glider, developed and manufactured by Pipistrel in Slovenia and Italy.Vandermeullen, Richard: ''2012 Kit Aircraft Buyer's Guide'', Kitplanes, Volume 28, Number 12, December 2011, pa ...

and the Urban Air Lambada. It is also fitted to some light twins, such as the

Tecnam P2006T The Tecnam P2006T is an Italian high-winged twin-engined all-metal light aircraft, built by Tecnam, Costruzioni Aeronautiche Tecnam based in Capua, Italy, near Naples. The P2006T received airworthiness certification in the European Union by EASA u ...

. On 8 March 2012 the company displayed its 912 iS variant, a version with

fuel injection Fuel injection is the introduction of fuel in an internal combustion engine, most commonly automotive engines, by the means of a fuel injector. This article focuses on fuel injection in reciprocating piston and Wankel rotary engines. All c ...

and an electronic engine management unit. 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

. Production started in March 2012 and the engine has a 2000-hour recommended time-between-overhaul to start. On 1 April 2014 the company announced its new 912 iS Sport upgrade with greater power and torque and reduced fuel consumption. A further derivative, the

Rotax 915 iS The Rotax 915 iS is an Austrian aircraft engine, produced by Rotax of Gunskirchen for use in ultralight aircraft, homebuilt aircraft, light-sport aircraft, small helicopters and gyroplanes. The engine was type certified in 2017. The engine wa ...

, was announced in July 2015.

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 A rotary-wing aircraft, rotorwing aircraft or rotorcraft is a heavier-than-air aircraft with rotor wing, rotary wings that spin around a vertical mast to generate lift (force), lift. Part 1 (Definitions and Abbreviations) of Subchapter A of Chapt ...

*night flying (unless equipped with redundant electrical power), or *

aerobatic Aerobatics is the practice of flying maneuvers involving aircraft attitudes that are not used in conventional passenger-carrying flights. The term is a portmanteau of "aeroplane" and "acrobatics". Aerobatics are performed in aeroplanes and gl ...

s. The manual states that Rotax gives no assurances that the engine is suitable for use in any aircraft, and that the engine may seize or stall at any time, which could lead to a crash landing. The manual adds that non-compliance with such warnings could lead to serious injury or death.

Variants

The engine is available in the following versions; coloured cylinder head caps are used to easily identify the different horsepower ranges: ;912 A# :Certified to JAR 22, , with dual carburetors and electronic ignition. Black cylinder head caps ;912 F# :Certified to FAR 33, , with dual carburetors and electronic ignition. Black cylinder head caps ;912 iS :Uncertified, with direct fuel injection and an electronic engine management unit. Green cylinder head caps ;912 iSc :Certified, with direct fuel injection and an electronic engine management unit ;912 iS Sport :Uncertified, aluminum airbox, longer intake runners and eco-mode when operated below 97% power setting. Green cylinder head caps ;912 iSC Sport Green cylinder head caps ;912 S# :Certified to FAR 33, with larger bore than 912A/F/UL, with dual carburetors and electronic ignition. Green cylinder head caps ;912 UL# :Uncertified, , similar to the 912A/F. Black cylinder head caps ;912 ULS# :Uncertified, , similar to the 912S. Green cylinder head caps ;912 ULSFR# :Uncertified French Authority specification. The # in the designation stands for: # Shaft with flange for fixed pitch propeller, P.C.D. 100 mm # Shaft with flange for fixed pitch propeller, P.C.D. 75 mm, P.C.D. 80 mm and P.C.D. 4 inches # Shaft with flange for constant speed propeller P.C.D. 75 mm, P.C.D. 80 mm, P.C.D. 4 inches and drive for hydraulic governor for constant speed propeller # Shaft with flange for fixed pitch propeller P.C.D. 75 mm, P.C.D. 80 mm, P.C.D. 4 inches also can be fitted with an adaptor, drive and governor for a constant speed propeller.

Applications

Specifications (Rotax 912 UL/A/F)

References

External links

The aircraft engines section of the official Rotax company websiteFAA Type Certificate Data Sheet E00051EN

912 UL 80 hp Engine Datasheet912 ULS 100 hp Engine Datasheet914 UL 115 hp Turbocharged Engine DatasheetMotive.Aero Rotax Distributor
{{Rotax aeroengines Boxer engines Rotax engines 1980s aircraft piston engines