Turbine Engines  Full Authority Digital Engine Control (FADEC)  Types of Turbine Engines  Turbojet  7-20  Figure 7-22.  Eclipse 500 VLJ.  FADEC is a system consisting of a digital computer and  ancillary components that control an aircraft’s engine  and propeller. First used in turbine-powered aircraft, and  referred to as full authority digital electronic control, these  sophisticated control systems are increasingly being used in  piston powered aircraft.  In a spark-ignition reciprocating engine, the FADEC uses  speed, temperature, and pressure sensors to monitor the status  of each cylinder. A digital computer calculates the ideal pulse  for each injector and adjusts ignition timing as necessary  to achieve optimal performance. In a compression-ignition  engine, the FADEC operates similarly and performs all of  the same functions, excluding those specifically related to  the spark ignition process.  FADEC systems eliminate the need for magnetos, carburetor  heat, mixture controls, and engine priming. A single throttle  lever is characteristic of an aircraft equipped with a FADEC  system. The pilot simply positions the throttle lever to a  desired detent, such as start, idle, cruise power, or max power,  and the FADEC system adjusts the engine and propeller  automatically for the mode selected. There is no need for the  pilot to monitor or control the fuel-air mixture.  The path the air takes through the engine and how power is  produced determines the type of engine. There are four types  of aircraft turbine engines—turbojet, turboprop, turbofan,  and turboshaft.  Turbine engines are classified according to the type of  compressors they use. There are three types of compressors—  centrifugal flow, axial flow, and centrifugal-axial flow.  Compression of inlet air is achieved in a centrifugal flow  engine by accelerating air outward perpendicular to the  longitudinal axis of the machine. The axial-flow engine  compresses air by a series of rotating and stationary  airfoils moving the air parallel to the longitudinal axis. The  centrifugal-axial flow design uses both kinds of compressors  to achieve the desired compression.  An aircraft turbine engine consists of an air inlet, compressor,  combustion chambers, a turbine section, and exhaust. Thrust  is produced by increasing the velocity of the air flowing  through the engine. Turbine engines are highly desirable  aircraft powerplants. They are characterized by smooth  operation and a high power-to-weight ratio, and they  use readily available jet fuel. Prior to recent advances in  material, engine design, and manufacturing processes, the  use of turbine engines in small/light production aircraft was  cost prohibitive. Today, several aviation manufacturers are  producing or plan to produce small/light turbine-powered  aircraft. These smaller turbine-powered aircraft typically  seat between three and seven passengers and are referred to  as very light jets (VLJs) or microjets.  [Figure 7-22]  Detonation and preignition often occur simultaneously and  one may cause the other. Since either condition causes high  engine temperature accompanied by a decrease in engine  performance, it is often difficult to distinguish between the  two. Using the recommended grade of fuel and operating  the engine within its proper temperature, pressure, and rpm  ranges reduce the chance of detonation or preignition.  During aircraft starting, the FADEC primes the cylinders,  adjusts the mixture, and positions the throttle based on engine  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.  The turbojet engine consists of four sections—compressor,  combustion chamber, turbine section, and exhaust. The  compressor section passes inlet air at a high rate of speed to  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. 