Rotax Engines

Rotax was established in 1920 in the city of Germany, Dresden, but its manufacturing operations were relocated to Gunskirchen, Austria in 1943.

After World War II, the company achieved high sales figures beginning in 1962 by producing small engines for various applications, including snow motorcycles.

Rotax Type 936/ year 2000

Bombardier acquired Rotax-Werk AG and renamed it Bombardier-Rotax GmbH.

The Rise of Rotax

Rotax also achieved great success with its very light and light aircraft engines. This began in 1982 with two-stroke single and inline twin-cylinder engines, production of which continues today.

Type 593/ year 1985-1999

In the mid-1980s, they began developing larger four-stroke engines for light aircraft. Rotax is now a leading international supplier of engines to manufacturers of very light and light aircraft worldwide. They have reported delivering more than 100,000 aircraft engines. Today, Rotax is the undisputed leader in the light aircraft industry, supplying approximately 80 percent of the engines in new LSA models sold in USA, with other estimates suggesting market shares as high as 90 percent.

Rotax four-stroke engines are used in many models and brands of light aircraft sold in the United States. Other well-known brands in the market include Lycoming and Continental engines that power more advanced models.

Continental’s IO-520: Big, slow turning.

Rotax’s Success and Underlying Factors

"They appeared on the scene suddenly and quickly dominated the ultra-light aircraft industry," engineers worked to produce various configurations adaptable to numerous aircraft airframes, exhaust systems and installation types.

Starting with reliable four-stroke engine series, Rotax launched the 80-horsepower 912UL engine in 1989, which could be purchased by end users. This was followed by the 100-horsepower 912ULS variant. As the company’s market share grew, so did its product range, allowing OEMs and experimental aircraft builders to choose not only the carbureted UL and ULS versions of the 912, but also the fuel-injected 100-horsepower 912iS Sport, the 115-horsepower 914UL, or the company’s most powerful unit, the turbocharged 141-horsepower 915iS.

The 141-horsepower turbo Rotax is now also used in the Sling TSi, delivering impressive results. The Sling is an excellent four-seat aircraft, achieving approximately 435 kg of useful load with the 141-horsepower Rotax engine.

One of the key factors in Rotax motors becoming the gold standard among LSA manufacturers has been their consistent focus on producing lightweight engines with exceptional power-to-weight ratios from the outset.

Rotax 912 is sport

They designed engines capable of sustained operation between 5,000 and 5,500 rpm, reaching their TBO (time between overhaul) under these conditions. Every aspect of the engine, from the metallurgy of its components to the lubricants used, was engineered to enable high-rpm operation.

When compared to a 100 to 125-horsepower Lycoming or Continental, Rotax engines deliver similar power at roughly half the weight, enabling much lighter and more compact aircraft designs.

Rotax 915 is Sport

In older aircraft engines, fuel entering the cylinders was not precisely controlled electronically and operated with rich mixtures at maximum rpm. Rotax’s electronically controlled fuel injection system promises improved performance, increased power, greater efficiency and long life.

The production quality of Rotax engines manufactured in Only Austria is very high. With this infrastructure, the company has focused on developing new engines with higher power outputs.

As a result, Rotax achieved significant success with the 916 engine. Although expensive, the increase from 141 hp to 160 hp opened the door to new performance levels in several designs that were already good on the 915 but improved substantially with the newer engine.

Rotax embraces the view that its products must operate worldwide and is developing engines capable of running on lower-octane fuels.

In traditional engines without a gearbox, propeller speeds cannot exceed 2,700–2,900 rpm, limiting high-rpm engine performance. Powerful engines driving large propellers at high rpm generate significant noise levels.

Rotax’s application of a gearbox system to its 900-series engines allows the motors to produce more power while turning the propeller at lower rpm, reducing noise and providing some aerodynamic benefit. The disadvantage is a slight increase in weight, but this is offset by the simplicity and compact size of the design.

Another advantage of the 900-series design lies in its combustion chambers and valve mechanisms. The older combustion chambers found in Continental and Lycoming engines require high-octane fuels to produce high power.

Peak Performance: The Rotax 916

Rotax needs to produce an engine in the 200–220 hp range. The 900 series has reached its limits. The 912iS produces 100 hp at just under 83 cubic inches without turbocharging, equivalent to 1.2 hp per cubic inch—more than double the power density of a Lycoming. To achieve this, it must produce 91 pound-feet of torque at 5,800 rpm, requiring a BMEP (brake mean effective pressure) of 165 psi in the combustion chamber. Although the hp per cubic inch figure appears impressive, this is actually a very high BMEP, comparable to that of a 180-horsepower Lycoming.

Rotax 916

The Rotax 916, however, meets this demand. For takeoff, it delivers 160 horsepower (limited to five minutes, then 137 hp continuous), working extremely hard. First and foremost, the power per cubic inch is an impressive 1.93 hp per cubic inch. To achieve this power, the engine must produce 145 foot-pounds of torque at 5,800 rpm—a significant leap from the 912’s figures—requiring a BMEP of 263 psi. This is an extremely high figure, pushing the engine’s ability to withstand detonation to its limits, which is achieved solely through precise electronic control. For such power, a six-cylinder engine may be preferred over a four-cylinder one, but this only affects weight and cost.

It is worth noting that Rotax is not the only player in this field. The ULPower 520T engine itself demonstrates impressive performance. The ULPower 520T is a six-cylinder, 321-cubic-inch engine with two pushrods per cylinder. The 520T produces 220 hp at 2,700 rpm using only a modest 38 inches of manifold pressure. To achieve this, it generates 428 pound-feet of torque from a bore/stroke ratio of 1.056:1—even a Lycoming with a 1.717:1 bore/stroke ratio produces less torque. A disadvantage of ULPower is its lack of liquid cooling. Although liquid cooling systems appear to add weight and complexity, they offer greater efficiency.

The Future of Rotax Engines

Rotax is working on an engine for the next horsepower class—perhaps two classes higher. The next engine could be designed to allow production of both four- and six-cylinder versions using the same cylinder blocks. Rotax is proceeding with careful and cautious steps. The 900 series has been on the market for over thirty years, during which its power output has been carefully developed and doubled.