Among a pilot’s responsibilities is to understand the basics of each system on the aircraft f lown. Sometimes this seems excessive to pilots in training (especially those attending ground school for a new aircraft). It’s important, though, that a pilot be able to identify, understand, and rectify failures and problems that may occur in emergency situations. Therefore, most systems training emphasizes understanding of each system’s operating sequence, with special focus on what happens if various components fail. The systems of most modern turbine aircraft are similar in operating principles and components. However, they differ greatly in the details of implementation. The result is that, once you’ve learned the systems on one turbine aircraft, others are much easier to comprehend. Let’s take a look at the basics of the major turbine aircraft systems. Then when you attend ground school, you can concentrate not on “What is it?” but on “How is it implemented here?”
Introduction to Gas Turbine Engines The basic operating principle of a gas turbine engine is simple. Jet propulsion is described by Isaac Newton’s third law, which states that for every action there’s an equal and opposite reaction. In the broadest sense, gas turbine engines share jet propulsion with party balloons that have been inf lated and released. In each case pressurized gases escaping from a nozzle at one end create an equal and opposite force to drive each of these “reaction engines” in the opposite direction (Figure 3.1). The main difference between the balloon and the engine is in the source of the propulsive gases. The balloon is an energy storage device. Someone blows
CHAPTER 3
Turbine Engine and Propeller Systems
air into it, and once the stored air has escaped, the propulsion is over. Gas turbine engines, on the other hand, are heat engines. Through combustion of fuel with intake air, they continuously create expanding gases, the energy of which is converted into propulsive force to move an aircraft. For this reason, the core of a turbine engine is known as the gas generator; it generates the expanding gases required to produce thrust. A nozzle is then used to accelerate the velocity of the high-energy gases escaping from the gas generator. By increasing gas pressure through its tapered chamber, a nozzle forces gases to exit through its smaller exhaust opening. The effect of this process is an increase in the momentum of air passing through the engine, producing thrust (Figure 3.1). The gas turbine engine may be compared in basic stages of operation to its distant heat engine relative, the internal combustion engine (also known as the “piston” or “reciprocating engine”). As you remember, most aircraft reciprocating engines operate in four-stroke sequence: intake, compression, power (or combustion), and exhaust. Power developed by a piston engine is intermittent since only one stroke in four (the power stroke) actually creates power. Parallel stages occur in gas turbine engines but with a fundamental difference: turbine engines operate under more efficient continuous-flow conditions (see Figure 3.2). Instead of compressing intake air with a piston, turbine engines use one or more rotating bladed “wheels” in the compressor section known as compressors. Another set of wheels, known as turbines, is driven by the exhaust gases passing through the turbine section. Compressors and turbines are similar in that each is basically an extremely sophisticated fan, composed of a large number of hightolerance blades turning at very high speeds inside a 11
