Aircraft Systems

Detonation and preignition often occur simultaneously and Turbine Engines one may cause the other. Since either condition causes high An aircraft turbine engine consists of an air inlet, compressor, engine temperature accompanied by a decrease in engine combustion chambers, a turbine section, and exhaust. Thrust performance, it is often difficult to distinguish between the is produced by increasing the velocity of the air flowing two. Using the recommended grade of fuel and operating through the engine. Turbine engines are highly desirable the engine within its proper temperature, pressure, and rpm aircraft powerplants. They are characterized by smooth ranges reduce the chance of detonation or preignition. operation and a high power-to-weight ratio, and they use readily available jet fuel. Prior to recent advances in Full Authority Digital Engine Control material, engine design, and manufacturing processes, the (FADEC) use of turbine engines in small/light production aircraft was FADEC is a system consisting of a digital computer and cost prohibitive. Today, several aviation manufacturers are ancillary components that control an aircraft’s engine producing or plan to produce small/light turbine-powered and propeller. First used in turbine-powered aircraft, and aircraft. These smaller turbine-powered aircraft typically referred to as full authority digital electronic control, these seat between three and seven passengers and are referred to sophisticated control systems are increasingly being used in as very light jets (VLJs) or microjets. [Figure 7-22] piston powered aircraft. Types of Turbine Engines In a spark-ignition reciprocating engine, the FADEC uses Turbine engines are classified according to the type of speed, temperature, and pressure sensors to monitor the status compressors they use. There are three types of compressors— of each cylinder. A digital computer calculates the ideal pulse centrifugal flow, axial flow, and centrifugal-axial flow. for each injector and adjusts ignition timing as necessary Compression of inlet air is achieved in a centrifugal flow to achieve optimal performance. In a compression-ignition engine by accelerating air outward perpendicular to the engine, the FADEC operates similarly and performs all of longitudinal axis of the machine. The axial-flow engine the same functions, excluding those specifically related to compresses air by a series of rotating and stationary the spark ignition process. airfoils moving the air parallel to the longitudinal axis. The centrifugal-axial flow design uses both kinds of compressors FADEC systems eliminate the need for magnetos, carburetor to achieve the desired compression. heat, mixture controls, and engine priming. A single throttle lever is characteristic of an aircraft equipped with a FADEC The path the air takes through the engine and how power is system. The pilot simply positions the throttle lever to a produced determines the type of engine. There are four types desired detent, such as start, idle, cruise power, or max power, of aircraft turbine engines—turbojet, turboprop, turbofan, and the FADEC system adjusts the engine and propeller and turboshaft. automatically for the mode selected. There is no need for the pilot to monitor or control the fuel-air mixture. Turbojet The turbojet engine consists of four sections—compressor, During aircraft starting, the FADEC primes the cylinders, combustion chamber, turbine section, and exhaust. The adjusts the mixture, and positions the throttle based on engine compressor section passes inlet air at a high rate of speed to temperature and ambient pressure. During cruise flight, the FADEC constantly monitors the engine and adjusts fuel flow and ignition timing individually in each cylinder. This precise control of the combustion process often results in decreased fuel consumption and increased horsepower. FADEC systems are considered an essential part of the engine and propeller control and may be powered by the aircraft’s main electrical system. In many aircraft, FADEC uses power from a separate generator connected to the engine. In either case, there must be a backup electrical source available because failure of a FADEC system could result in a complete loss of engine thrust. To prevent loss of thrust, two separate and identical digital channels are incorporated for redundancy. Each channel is capable of providing all engine and propeller functions without limitations. Figure 7-22. Eclipse 500 VLJ. 7-20