Full Authority Digital Engine Control - FADEC

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Full Authority Digital Electronic/Engine Control

FADEC Full Authority Digital Engine Control

As the world is moving towards automation, so is the aviation industry. Gone are those days when a pilot used to push and pull mechanical levers with all their might to actuate the various functions on the aircraft. Pratt and Whitney JT8D is a good example of the complete engine being controlled by mechanical linkages.

History of FADEC

FADEC - Full Authority Digital Engine Control
FADEC box
During the early development of aircraft control systems mechanical linkages were the most common method used by almost all the major aviation manufactures around the globe but as the electronics age kicked in researches were carried around all the globe to use electronics in aircraft controlling system. The first major advancement was the analog electronic control system in which simple electronic signals bearing either of the values 0 or 1 were used, though more efficient than the mechanical control system this system was not was reliable.

After the mechanical and analog electronic engine control systems, came the digital electronic engine control system. In diginal electronic control system electronic signals were used to control the aircraft. Lets take a very simple example to understand this, you want to ask a question in the comment section at the end of this article what would your brain do it will frame the question with help of your eyes by reading the article it means it is collectinv signals from your eyes and then it will direct your hand accordinly to write, so it will send a signal to your hand muscles through your nerves. 

Kudos! You got it right EEC being the brain of the aircraft, airlerons being the hands and temprature and pressure sensors being the eyes. Let's understand the working of FADEC in a more technical way.

Aircraft Engine

What is FADEC and how does it works?

As the name suggests FADEC is concerned about some very sophisticated and precise combinations of various electronic devices together. FADEC is a computer system coupled with sensors and actuators which is completely capable of controlling the complete engine by itself.

FADEC versus EEC/ECU



The most common confusions which blow up the mind of almost all the nerds who read about FADEC, What is EEC? How it is related to FADEC? and many more.....!

Let's understand it in a very simple way. Assume you are on a dinner with your girlfriend and mother. You being the EEC your mother being the FADEC computer and your girlfriend being the pilot. Your girlfriend tells you to order 2 plates of dal makhni you make calculations and decide that only 1.5 plates of dal makhni would be enough and tell your mother about the same. Now your mother overrides your girlfriend's decision and tell you to order only 1.5 plates of dal makhni, then its a FADEC system. But if your mother is not present then you will have to order 2 plates of dal makhni only, then its not FADEC. 

Let's get a bit technical

The electronic engine control or the engine control unit is an electronic computer system which performs all the computation in the FADEC system. In simple language if we use EEC alone then the pilot can override the decision taken by the EEC hence manual controlling is available but when the EEC becomes a part of the FADEC system, then decision of EEC cannot be overridden by the pilot making it the supreme controller of the aircraft.

Sensors

Sensors in aviation industry are nothing but devices which are used to collect data about various operating conditions of the aircraft such as pressure and temperature at various engine stations. The other types of sensors are the ones which give the information about the exact location of various components of the aircraft such as the control surfaces. 


Actuators

Actuators are the devices which are used to control the various components of the aircraft such as the control surfaces, bleed valves etc. For example if the pilot wants increase the angle of attack he would use the torque motor actuator to move the aileron accordingly. 




Now you can easily understand the working of a FADEC system, consider an example that the pilot wants to change the angle of rudder by some degrees the FADEC computer would use its sensor to get the exact information about the location of the rudder at that instant and would use various computing operations to analyze the data coming from the sensor as well as given by the pilot and then use its actuator to move the rudder accordingly. You may think that this process is time consuming but it is very quick as the FADCEC computer has the capability of computing at a speed of 70 times per seconds.


The example given here is a simpler one, I am providing an image with the block diagram depicting working of FADEC system.




Functions carried out by FADEC

1.  Power Management Control- Always making the aircraft engine to work at most optimum speeds so that engine works at the most optimum levels i.e. max power in min fuel consumption.

2. Starting Shut down and Ignition Control and the fuel system - The complete starting shut down and ignition of the engine is controlled by the FADEC system after sensing the various thermodynamic and chemical aspects of the air and fuel mixture.

3. Active Clearance Control- The ACC system is also controlled by the FADEC system in which cold bleed air is circulated around the turbine casing so that the expansion of casing due to hot exhaust is compensated.

4. Variable Geometry Control

5. Thrust Reversal Control- Apart from the braking action provided by the flaps, thrust reversing technique is also used for aerodynamic braking. The Thrust Reversal braking is also controlled by the FADEC system.

All in all the prime function of the FADEC system is minimum Fuel consumption minimum Operating costs and minimum Emissions into the environment.

Always stay away from the FOE.

Though FADEC is a fabulous advancement in the field of aviation but every coin has two faces sk let us look at some of the disadvantages of FADEC.

Disadvantages of FADEC system

1.     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.
2.     If a total FADEC failure occurs, the engine fails. (both the channels fail)
3.     Upon total FADEC failure, pilots have no manual controls for engine restart, throttle, or other functions.
4.     Single point of failure risk can be mitigated with redundant FADECs (assuming that the failure is a random hardware failure and not the result of a design or manufacturing error, which may cause identical failures in all identical redundant components).
5.     High system complexity compared to hydro mechanical, analogue or manual control systems.
6.     High system development and validation effort due to the complexity.
7.     Whereas in crisis (for example, imminent terrain contact), a non-Fadec engine can produce significantly more than its rated thrust, a FADEC engine will always operate within its limits.

Thanks for reading!


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