CHAPTER 6 AIRCRAFT POWER PLANTS INTRODUCTION All naval aircraft are engine driven. The early engines were all reciprocating engines. Today, almost all are jet propulsion engines. Therefore, this chapter covers only jet propulsion engines. The jet propulsion principle is the basic concept for the gas turbine engine. This principle is not a new concept. Sea creatures use jet propulsion to propel themselves through the water. The Egyptians built the first reaction engine around 250 BC. Between 1700 and 1930, technical achievements in engineering, manufacturing, and metallurgy made the reaction principle applicable to the development of the gas turbine engine for jet propulsion. In 1939, the Germans flew the first aircraft powered by a gas turbine engine, followed by the British in 1941, and the Americans in 1942. During World War II, Germany was the only nation to fly a gas turbine-propelled aircraft in actual combat. There are four types of jet propulsion engines: the rocket, the ramjet, the pulsejet, and the gas turbine engine. Of these, the gas turbine engine powers almost all naval aircraft. There are four types of gas turbine engines: the turbojet, the turbofan, the turboprop, and the turboshaft. The turbojet and turbofan engines use thrust directly. The turboprop and turboshaft engines use thrust to deliver torque (turning power) to an airplane propeller or a helicopter rotor. Regardless of the type, the purpose of an engine is to develop thrust. This chapter will give you basic information on jet propulsion engines. JET PROPULSION ENGINES LEARNING OBJECTIVE:  Recognize the basic operating principles for the four types of jet  propulsion  engines,  and  identify  the components and functions of each type of engine. A jet propulsion engine projects a column of air to the rear at extremely high speeds. The resulting thrust pushes the aircraft in the opposite (or forward) direction. Jet propulsion engines are grouped into four main types: 1. Rocket. These are jet propulsion systems that do not use atmospheric air. 2. Ramjet. The ramjet operates as a continuous thermal duct or athodyd. 3. Pulsejet. The pulsejet operates as an intermittent impulse duct. 4. Gas turbine. The gas turbine engine operates as a continuous turbine-compressor unit. ROCKET ENGINES The rocket uses a form of jet propulsion that differs in basic ways from thermal gas turbine systems. The rocket does not draw air from the outside to fuel the combustion process. It carries with it both the fuel and the oxidizer for combustion. This is a disadvantage for atmospheric flight, but it is the only way at present to fuel flight outside the earth's atmosphere. The rocket is a true jet reaction unit. A brief examination of its functions clarifies the reaction principle by which all thermal jet units operate. If you burn a hydrocarbon (compound containing only hydrogen and carbon) in a closed container (fig. 6-1), the heat of the burning fuel is released, causing the trapped gases to expand rapidly. Because the container has a closed volume, the temperature and pressure rises and is uniformly distributed (balanced) in all directions. Since the force of the rising pressure cannot be released and is balanced, the container does not move. 6-1 Figure 6-1.—Combustion in a closed container.