In order to perform their characteristic functions of vertical flight and hovering, helicopters rely on rotors to generate lift and thrust. The power for the rotors is generated by the engine, which can be either a turboshaft engine or a piston engine depending on the helicopter. Although piston engines have been used for longer, the release of the turboshaft engine in the late 1950s revolutionized helicopter performance. These engines are lighter, more reliable, and provide sustainable high-power output when compared to previously used four-piston cylinder engines. However, light utility helicopters still benefit from piston engines as they can still be an advantageous choice. This blog will delve into seven types of engines that have been used in helicopters from both categories so you can better understand the benefits and applications of each.
Currently, most helicopters are powered by turboshaft engines, with a select few small helicopters depending on radial piston engines. The piston, or reciprocating, engine is the older of the two engine types and has been used since helicopters were in the prototype stage. Multiple types of reciprocating engines have been developed and used for helicopters over the years, but the turboshaft engine is most widely used today.
The first turboshaft-powered helicopter was released in 1951 and relied on gas turbine engines to produce shaft power. In this engine design, compressed air mixes with fuel in the combustion chamber, which then ignites and expands. The energy produced powers the turbine wheels and rotates the rotor system. The turboshaft engine produces more power than piston engines, which is why the majority of helicopters today rely on turboshaft power, but it is helpful to understand the differences among piston engines and why each design is outdated for most helicopters.
The earliest style of engine we will cover are in-line piston engines. The predecessor of the modern piston engine, the in-line engine gets its name from the configuration of its cylinders in a narrow row. This design limited airflow over the engine for cooling, which in turn led to the development of rotary piston engines during World War I. In this adapted design, the cylinders are housed in a rotating cylinder block that extends around a central, stationary crankshaft. These engines were placed vertically in early helicopter prototypes, but they proved more beneficial in airplanes; this led to the employment of a new reciprocating engine design for helicopters.
Early helicopter designs in the 1940s, including the Sikorsky VS-300 and many others, relied on opposed-piston engines. This engine gets its name from its two cylinder rows that are placed opposite one another in the horizontal position. By positioning the cylinders across from one another, the engine operates with better air cooling and a lower center of mass, which are a few reasons this design made it past the prototype stage. Opposed-piston engines were not the only engines used in the first helicopter designs; radial piston engines were introduced in the late 1940s and functioned as a small, highly efficient alternative engine for other helicopter models.
Similar to rotary piston engines, radial engines have one or more rows of cylinders extending from a central crankshaft, but the crankshaft of the rotary engine rotates rather than remaining stationary. This engine is the only reciprocating engine still used in helicopters today, but most have been replaced by turbine engines. Looking ahead, manufacturers and engineers are working to develop electric engines that can power entire helicopters with electricity, but these engines currently only appear in toy helicopters and small unmanned aircraft, as electric motors typically lack the power needed to generate enough vertical thrust for a manned helicopter.
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