The Rotax 912 is a horizontally-opposed four-cylinder, naturally-aspirated, four-stroke aircraft engine with a reduction gearbox. It features liquid-cooled cylinder heads and air-cooled cylinders. Originally equipped with carburetors, later versions are fuel injected. Dominating the market for small aircraft and kitplanes, Rotax produced its 50,000th 912-series engine in 2014.[1] Originally available only for light sport aircraft, ultralight aircraft, autogyros and drones, the 912-series engine was approved for certified aircraft in 1995.[2]
The Rotax 912 was first sold in 1989 in non-certificated form for use in ultralights and motorgliders.[3] The original 80 hp (60 kW) 912 UL engine has a capacity of 1,211 cc (73.9 cu in) 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 100 hp (75 kW) 912 ULS variant has a compression ratio of 11:1, and requires 91-octane ("premium") auto gas (100LL leaded avgas can be used, sparingly).[4]
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[5] 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.[3] On the 912A, F and UL the standard reduction ratio is 2.27:1 with 2.43:1 optional. Lubrication is dry sump, and fuelling is via dual CV carburetors or fully redundant electronic fuel injection. The electronic fuel injected Rotax 912iS is a recent development.[5]
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.[3]
The 912 is more fuel efficient and lighter than comparable older engines, e.g., Continental O-200, but originally had a shorter time between overhaul (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 certificated aircraft initially restricted its worldwide market potential. However, the engine received US Federal Aviation Administration (FAA) certification in 1995, and by 1999, the TBO had increased to 1,200 hours;[3] 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.[6] 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.[5] 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 which cannot hold lead in suspension; consequently, the use of leaded fuel mandates additional maintenance.[3]
A turbocharged variant rated at 115 hp (86 kW), the Rotax 914, was introduced in 1996. In 1999, the 912S / ULS were introduced;[3] enlarged to 1,352 cubic centimetres (82.5 cu in) with a compression ratio of 10.8:1, yielding 100 hp (75 kW). The 912S is certified, as are the A and F, which are used in the Diamond DA20, which is quite popular in Europe. The 912's popularity was greatly enhanced by the introduction of the light-sport aircraft 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.[3] The 100 hp (75 kW) versions are used in many light sport aircraft, such as the Zenith STOL CH 701 and the Tecnam P2002 Sierra. The 80 hp (60 kW) versions are sufficient to power the new generation of efficient motorgliders, such as the Pipistrel Sinus and the Urban Air Lambada. It is also fitted to some light twins, such as the Tecnam P2006T.
On 8 March 2012 the company displayed its 912 iS variant, a 100 hp (75 kW) version with fuel injection and an electronic engine management unit.[7] The version weighs 63 kg (139 lb), which is 6 kg (13 lb) 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 to start.[8]
On 1 April 2014 the company announced its new 912 iS Sport upgrade with greater power and torque and reduced fuel consumption.[9] A further derivative, the 135 hp (101 kW) Rotax 915 iS, was announced in July 2015.[10]
Unusually for a manufacturer of small aero-engines, 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:
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.[11]
The engine is available in the following versions; coloured cylinder head caps are used to easily identify the different horsepower ranges:[citation needed]
Green cylinder head caps
The # in the designation stands for:
Power density: 48.71 kW/L
Specific power: 0.98 kW/kg
Comparable engines
Related lists
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