AVIATION MERIT BADGE


	The operation of a turbine or jet engine can be summarized as “suck, squeeze, bang, blow.” A more detailed explanation is below.

	The turbojet uses a series of fan-like compressor blades to bring air into the engine and compress it. An entire section of the turbojet engine performs this function, which can be compared to the compression stroke of the reciprocating engine. In this section, there is a series of rotor and stator blades. Rotor blades perform somewhat like propellers in that they gather and push air backward into the engine. The stator blades serve to straighten the flow of this air as it passes from one set of rotor blades to the next.

	As the air continues to be forced further into the engine, it travels from the low-compression set of rotors and stators to the high-compression set. This last set puts what we might say is the final squeeze on the air.

	The combustion chamber receives the high-pressure air, mixes fuel with it, and burns the mixture. The hot, very high-velocity gases produced strike the blades of the turbine and cause it to spin rapidly. The turbine is mounted on a shaft, which is connected to the compressor. Thus, the spinning is what causes the compressor sections to function. After passing the turbine blades, the hot, highly accelerated gases go into the engine’s exhaust section.

	The exhaust section of the jet engine is designed to give additional acceleration to the gases and thereby increase thrust. The exhaust section also serves to straighten the flow of the gases as they come from the turbine. Basically, the exhaust section is a cone mounted in the exhaust duct. This duct is also referred to as the tailpipe. The shape of the tailpipe varies, depending on the design operating temperatures and the speed-performance range of the engine.

	With all the heat produced in the turbojet engine, you probably wonder how it is kept from overheating. Like most aircraft reciprocating engines, the jet is also air-cooled. Of all the air coming into the compressor section, only about 25 percent is used to produce thrust; the remaining 75 percent passes around the combustion chamber and turbine area to serve as a coolant.
	With better all-around performance at a lower ate of fuel consumption, plus less noise resulting from its operation, it is easy to understand why most new jet-powered airplanes are fitted with turbofan engines. This includes military and civilian types.