CHAPTER 6AIRCRAFT POWER PLANTSINTRODUCTIONAll naval aircraft are engine driven. The earlyengines were all reciprocating engines. Today, almostall are jet propulsion engines. Therefore, this chaptercovers only jet propulsion engines.The jet propulsion principle is the basic concept forthe gas turbine engine. This principle is not a newconcept. Sea creatures use jet propulsion to propelthemselves through the water. The Egyptians built thefirst reaction engine around 250 BC. Between 1700 and1930, technical achievements in engineering,manufacturing, and metallurgy made the reactionprinciple applicable to the development of the gasturbine engine for jet propulsion. In 1939, the Germansflew the first aircraft powered by a gas turbine engine,followed by the British in 1941, and the Americans in1942. During World War II, Germany was the onlynation to fly a gas turbine-propelled aircraft in actualcombat.There are four types of jet propulsion engines: therocket, the ramjet, the pulsejet, and the gas turbineengine. Of these, the gas turbine engine powers almostall naval aircraft. There are four types of gas turbineengines: the turbojet, the turbofan, the turboprop, andthe turboshaft. The turbojet and turbofan engines usethrust directly. The turboprop and turboshaft enginesuse thrust to deliver torque (turning power) to anairplane propeller or a helicopter rotor. Regardless ofthe type, the purpose of an engine is to develop thrust.This chapter will give you basic information on jetpropulsion engines.JET PROPULSION ENGINESLEARNING OBJECTIVE: Recognize thebasic operating principles for the four types ofjet propulsion engines, and identify thecomponents and functions of each type ofengine.A jet propulsion engine projects a column of air tothe rear at extremely high speeds. The resulting thrustpushes the aircraft in the opposite (or forward)direction. Jet propulsion engines are grouped into fourmain types:1. Rocket. These are jet propulsion systems thatdo not use atmospheric air.2. Ramjet. The ramjet operates as a continuousthermal duct or athodyd.3. Pulsejet. The pulsejet operates as anintermittent impulse duct.4. Gas turbine. The gas turbine engine operates asa continuous turbine-compressor unit.ROCKET ENGINESThe rocket uses a form of jet propulsion that differsin basic ways from thermal gas turbine systems. Therocket does not draw air from the outside to fuel thecombustion process. It carries with it both the fuel andthe oxidizer for combustion. This is a disadvantage foratmospheric flight, but it is the only way at present tofuel flight outside the earth's atmosphere. The rocket isa true jet reaction unit. A brief examination of itsfunctions clarifies the reaction principle by which allthermal jet units operate.If you burn a hydrocarbon (compound containingonly hydrogen and carbon) in a closed container (fig.6-1), the heat of the burning fuel is released, causing thetrapped gases to expand rapidly. Because the containerhas a closed volume, the temperature and pressure risesand is uniformly distributed (balanced) in all directions.Since the force of the rising pressure cannot be releasedand is balanced, the container does not move.6-1Figure 6-1.—Combustion in a closed container.
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