FADEC

A FADEC (Full Authority Digital Engine Control) is a system consisting of a digital computer, called an "Electronic Engine Control" (EEC) or Electronic Control Unit (ECU), and its related accessories that control all aspects of aircraft engine performance. The term FADEC is an acronym for either "Full Authority Digital Engine Control" or "Full Authority Digital Electronics Control". FADECs have been produced for both piston engines and jet engines, their primary difference due to the different ways of controlling the engines.

History

The goal of any engine control system is to allow the engine to perform at maximum efficiency for a given condition. The complexity of this task is proportional to the complexity of the engine. Originally, engine control systems comprised simple mechanical linkages controlled by the pilot. By moving throttle levers directly connected to the engine, the pilot could control fuel flow, power output, and many other engine parameters.

Following mechanical means of engine control came the introduction of analog electronic engine control. Analog electronic control varies an electrical signal to communicate the desired engine settings. The system was an evident improvement over mechanical control but had its drawbacks including common electronic noise interference. This system was pioneered in the 1960s and first introduced as a component of the Rolls Royce Olympus 593 engine. The 593 was the engine of the supersonic transport aircraft Concorde.

Following analog electronic control, the clear path was digital electronic control. Later in the 1970s NASA and Pratt and Whitney experimented with the first experimental FADEC, first flown on an F-111 fitted with a highly modified Pratt & Whitney TF30 left engine. The experiments led to Pratt & Whitney F100 and Pratt & Whitney PW2000 being the first military and civil engines respectively fitted with FADEC and later the Pratt & Whitney PW4000 as the first commercial "dual FADEC" engine.

Function

True 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. If the engine is controlled digitally and electronically but allows for manual override, it is considered solely an Electronic Engine Control or Electronic Control Unit. An EEC, though a component of a FADEC, is not by itself FADEC. When standing alone, the EEC makes all of the decisions until the pilot wishes to intervene. FADEC works by receiving multiple input variables of the current flight condition including air density, throttle lever position, engine temperatures, engine pressures, and many others. 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.

FADEC not only provides for efficient engine operation, it also allows the manufacturer to program engine limitations and receive engine health and maintenance reports. For example, to avoid exceeding a certain engine temperature, the FADEC can be programmed to automatically take the necessary measures without pilot intervention.

afety

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

To perhaps more clearly illustrate the function of a FADEC, explore a typical civilian transport aircraft flight. The flight crew first enters the data appropriate to the day’s flight in the flight management system or FMS. The FMS takes environmental data such as temperature, wind, runway length, runway condition, cruise altitude etc. and calculates power settings for different phases of flight. For takeoff, the flight crew advances the throttle (which contains no mechanical linkage to the engine) to a takeoff detent or opts for an auto-throttle takeoff if available. The FADECs know the calculated takeoff thrust setting and apply it. The flight crew notes that they have merely sent an electronic signal to the engines, no direct linkage has been moved to open fuel flow. This procedure is the same for climb, cruise, and all phases of flight. The FADECs compute the appropriate thrust settings and apply them. During flight, small changes in operation are constantly being made to maintain efficiency. Maximum thrust is available for emergency situations if the throttle is advanced to full, but remember, limitations can’t be exceeded. The flight crew has no means of manually overriding the FADECs, so if they make a decision the crew doesn’t like, it must be accepted.

FADECs today are employed by almost all current generation jet engines and increasingly in newer piston engines, on fixed-wing aircraft and helicopters.

In piston-engine powered aircraft, the system replaces both magnetos, making obsolete repetitive and costly magneto maintenance, and eliminates carburetor heat, mixture controls and engine priming. By controlling each cylinder of the engine independently for optimum fuel injection and spark timing, the need for the pilot to monitor and control mixture is eliminated. Because imprecise mixture operation can affect engine life, the FADEC has the potential to reduce operating costs and increase engine life for the average General Aviation pilot. Tests have also shown significant fuel savings potential. FADEC paid for itself in reduced operating costs.

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).

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 SCADE.

References

*cite web
url = http://www.hispano-suiza-sa.com/spip.php?article62&lang=en
title = Hispano-Suiza: Digital Engine Control
accessdate = 2007-03-09
*Moren, Chuck. Interview with student. FADEC. Embry-Riddle Aeronautical University, Daytona Beach. 2007-03-13.
*cite book
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date = 2007-03-10
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