Airplanes are built to fly using a variety of different types of engines. The engines serve as the means to move the aircraft and provide power to components such as the electric power supply, heating and pressurization. Smaller single-engine and some twin-engine airplanes are powered by reciprocating engines, while larger corporate, commuter and large commercial aircraft are flown using turbojet, turbofan or turboprop engines.
A reciprocating engine in an airplane is similar to a car engine when comparing the basic operating principles. The engine’s power output is the result of pistons moving up and down in cylinders. The up and down movement of the pistons turns a device called a crankshaft. The spinning crankshaft spins the propeller, which provides the thrust to move the airplane. A majority of reciprocating engines are powered by a fuel known as avgas, which is a 100-octane synthetic fuel. Some models have been converted to use automobile gasoline, and others have been developed to use diesel or jet fuel.
The turbojet is the first developed jet engine used on airplanes. The jet engine produces its thrust by sucking in air through the front by the rotation of compressor blades. The air moves from the compressor to the combustion chamber, where it is mixed with fuel and ignited. The hot expanded air from the combustion chambers flows toward the back of the engine, spinning large discs called turbines. The air then flows out the back of the engine, providing the thrust that pushes the airplane forward. The spinning turbine is connected to the compressor blades at the front of the engine to keep bringing in more air.
A turboprop engine is essentially a turbojet engine that is connected to a propeller. Instead of the gases pushing out of the back to provide power, the spinning turbine is connected by gears to a propeller. This provides more power than a reciprocating engine, allowing the aircraft to operate at much heavier weights and faster speeds. Compared with a turbojet aircraft, a turboprop is slower but far more fuel efficient, and has the ability to operate at airports with runways too short for many turbojet aircraft.
The turbofan engine is similar to a turbojet with an additional feature that passes some of the air around the inner portions of the engine. The rerouted air provides additional thrust, which requires less power compared with a straight turbojet. The turbofan engine is quieter and more fuel efficient than a turbojet and is becoming more common on commercial aircraft.
The turboshaft engine is similar to a turbojet with the main difference being that the gases are used to spin a shaft rather than producing thrust. Many helicopters use turboshaft engines to move the rotors.
