Helicopter Piston Engine Specifications
Helicopters can, in theory, be powered by anything from two-stroke piston or diesel engines to turbine-powered or rotary-combustion versions. In practice, Lycoming is the only FAA certified maker of helicopter piston engines. Its specifications are the same as other four-stroke piston engines with a few exceptions because they are aviation-based.
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Engineering Specifications
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The basic design of Lycoming or non-FAA certified engines used in helicopters, such as ROTAX, are essentially the same as those used in a car or motorcycle. Four-stroke engines are most common. They tend to be multi-cylindered engines with overhead cams. However, many special considerations are taken with piston aircraft engines.
Engine Design
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The configuration of the engine, like in other vehicles, is matched to the application. A helicopter engine, for example, requires the ability to withstand greater loads than a small propeller aircraft. The rotors are larger, the airframe is heavier and all the lift is under load. This requires much more torque, so fundamental engine design and layout reflects the load requirements of a helicopter.
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Manufacturing Standards
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The consequences of engine failure in an aircraft are far more serious than a car or other gas-powered vehicle, so regulations governing the manufacture of aircraft engines and their component parts are far more stringent. Manufactures comply with a number of international manufacturing and materials standards, such as SAE International. Additional safety procedures, such are x-raying parts to verify structural integrity, are also employed.
Compression and Fuel
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A few key difference between aircraft and auto piston engines are their fuel and compression. While octane is often misunderstood and thought to be a measure of a fuel's power, it is really a measure of the fuel's stability. Lower octane fuels will unintentionally combust if compressed too tightly. Excess compression can result from and engine being out of tune. As a result, instead of the "high" 92 octane fuel used in cars, aviation fuel or "avgas" is typically over 120 octane. It is a much more stable fuel. Fuel mixtures are also different. Just as with cars, some engines are fuel injected and some are carburetted. But all aircraft piston engines fuel delivery systems are designed for the rapid increases and decreases in elevation. There is some mechanism so the air-fuel ratio doesn't change too dramatically or adjusts with altitude.
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