| Admissions | Accreditation | A to Z Degree Fields | Booksellers | Catalog | Colleges | Contact Us | Continents/States/Districts | Contracts | Distance Education | Emergency | Emergency Medicine | Examinations | Forms | Grants | Hostels | Honorary Doctorate degree | Human Services | Internet | Investment | Instructors | Login | Lecture | Librarians | Membership | Observers | Professional Examinations | Programs | Progress Report | Recommendations | Research Grants | Researchers | Students login | School | Search | Seminar | Study Center/Centre | Sponsorship | Tutoring | Thesis | Universities | Work counseling |
|
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 air/fuel mixture. FADECs have been produced for both piston engines and jet engines. FADEC works by receiving multiple input variables of the current flight condition including air density, throttle lever position, engine temperatures, engine pressures, and many other parameters. The inputs are received by the EEC and analyzed up to 70 times per second. Engine operating parameters such as fuel flow, stator vane position, bleed valve position, and others are computed from this data and applied as appropriate. FADEC also controls engine starting and restarting. The FADEC's basic purpose is to provide optimum engine efficiency for a given flight condition. Safety With the operation of the engines so heavily relying on automation, safety is a great concern. Redundancy is provided in the form of two or more, separate identical digital channels. Each channel may provide all engine functions without restriction. FADEC also monitors a variety of analog, digital and discrete data coming from the engine subsystems and related aircraft systems, providing for fault tolerant engine control. Applications The flight crew first enters flight data such as wind conditions, runway length, or cruise altitude, into the flight management system (FMS). The FMS uses this data to calculate power settings for different phases of the flight. At takeoff, the flight crew advances the throttle to a predetermined setting, or opts for an auto-throttle takeoff if available. The FADECs now apply the calculated takeoff thrust setting by sending an electronic signal to the engines; there is no direct linkage to open fuel flow. This procedure can be repeated for any other phase of flight. In flight, small changes in operation are constantly made to maintain efficiency. Maximum thrust is available for emergency situations if the throttle is advanced to full, but limitations can’t be exceeded; the flight crew has no means of manually overriding the FADEC. Advantages Better fuel efficiency Automatic engine protection against out-of-tolerance operations Safer as the multiple channel FADEC computer provides redundancy in case of failure Care-free engine handling, with guaranteed thrust settings Ability to use single engine type for wide thrust requirements by just reprogramming the FADECs Provides semi-automatic engine starting Better systems integration with engine and aircraft systems Can provide engine long-term health monitoring and diagnostics Number of external and internal parameters used in the control processes increases by one order of magnitude Reduces the number of parameters to be monitored by flight crews Due to the high number of parameters monitored, the FADEC makes possible "Fault Tolerant Systems" (where a system can operate within required reliability and safety limitation with certain fault configurations) Can support automatic aircraft and engine emergency responses (e.g. in case of aircraft stall, engines increase thrust automatically). Disadvantages Full authority digital engine controls have no form of manual override available, placing full authority over the operating parameters of the engine in the hands of the computer. If a total FADEC failure occurs, the engine fails. In the event of a total FADEC failure, pilots have no way of manually controlling the engines for a restart, or to otherwise control the engine. As with any single point of failure, the risk can be mitigated with redundant FADECs. High system complexity compared to hydromechanical, analogue or manual control systems High system development and validation effort due to the complexity Requirements Engineering processes must be used to design, manufacture, install and maintain the sensors which measure and report flight and engine parameters to the control system itself. Software engineering processes must be used in the design, implementation and testing of the software used in these safety-critical control systems. This requirement led to the development and use of specialized software such as SCADA. 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. 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 capable of providing all engine and propeller functions without limitations. |
|
Why are aircraft noisy and what can be done about it?
What generates noise on conventional aircraft? What can we do about these noise sources? The departure check list The landing checklist |