09-08-2012, 01:02 PM
FADEC
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What is FADEC?
Digital Electronic Controls
Design Requirements : Modern Engine Control System
Why is FADEC Preferred?
A Backgrounder
Location of FADEC
Electronic Aspects of FADEC
How does FADEC work?
FADEC : Functions
FADEC : Essential Features
FADEC : Infrastructure (Simplified)
Schematic Diagram
Advantages & Limitations
DESIGN REQUIREMENTS OF MODERN ENGINE CONTROL SYSTEM
Speed / Accuracy / Ease of Control (Least Aircrew Workloads)
Wide Operational Range
Reliability & Operational Safety
Low Operating & Maintenance Costs
Should Not Add Weight
Fuel Efficiency
Dependable Starts
A BACKGROUNDER
The FADEC systems were first used in the automotive Industry where it is well proven.
Now-a-days airlines and the militaries all over the world incorporate it on turbine powered aircraft.
FADECs are made for piston engine and jet engines both but they differ in the way of controlling the engine .
Advanced, intelligent & robust propulsion controls are critical for improving the safety and maintainability of future propulsion systems.
Propulsion system reliability is considered to be critical for aircraft survival. Hence, FADEC systems came into being.
FADEC is now common on many engines and semiconductor and equipment cooling technology has advanced so that control units can now be mounted on the engine and still provide highly reliable operation for long periods.
Developing and implementing modern intelligent engine systems requires the introduction of numerous sensors, actuators and processors to provide the advanced functionality.
The application of artificial intelligence and knowledge-based system for both software and hardware provides the foundation for building the intelligent control system of the future.
With time, control systems became more sophisticated with the introduction of additional engine condition sensors and multiple servo-loops.
The task of handling engines was eased by the introduction of electronic control in the form of magnetic amplifiers in early civil and military aircraft.
The mag-amp allowed engines to be stabilized at any speed in the throttle range by introducing a servo-loop with engine exhaust gas temperature as a measure of engine speed and an analogue fuel valve to control fuel flow.
Transistors, integrated circuits and high temperature semi-conductors have all played a part in the evolution of control systems from range temperature control through to full digital engine control systems.
This allowed the pilot to accelerate and decelerate the engine while the control system limited fuel flows to prevent over- speeds or excessive temperatures.
With modern FADEC systems there are no mechanical control rods or mechanical reversions, and the pilot can perform carefree handling of the engine throughout the flight envelope.
On modern aircraft the engine is supervised by a computer to allow the pilot to operate at maximum performance in a combat aircraft or at optimum fuel economy in a passenger carrying aircraft.
Today, each FADEC is unique and therefore is expensive to develop, produce, maintain, and upgrade for its particular application.
In the future, it is desired to establish a universal or common standard for engine controls and accessories. This will significantly reduce the high development and support costs across platforms.
Engine operating parameters such as fuel flow, stator vane position, bleed valve position and others are computed from this data and applied as appropriate.
For example, to avoid exceeding a certain engine temperature, the FADEC can be programmed to automatically take the necessary measures without pilot intervention.
The inputs are received by the EEC and analyzed up to 70 times per second.
HOW DOES FADEC WORK?
FADEC : ESSENTIAL FEATURES
Conrol & Monitoring of Engine Operations
Dual Channels & Redundancy
Engine Life Monitoring
Record of Engine Performance Parameters
Automated Troubleshooting
Memory Read or Recall of Engine Data
Control of Common Engine Problems
Display of Warnings
Adaptation
Isochronous Idle Speed
FADEC : INFRASTRUCTURE
CONTROL OPERATIONS IN GAS TURBINE ENGINES
- Air Control (Compressor Entry)
- Fuel Control (Main / AB / Starting System)
- Starting & Ignition Control
- Lubrication Control
- Surge Control (Through Bleed Valve)
- Thrust Control (Through Exhaust Nozzle)
- Vibration Control (Through Air / Fuel Control)
HARDWARE:
- Dual Power Supply
FADEC Computer (With Logic Circuit PCBs & Programmed / Programmable Memory)
A Set of Servo Actuating Motors / Solenoid Valves / Position Sensors (for every System Control Unit)
Dual Position Sensors for Actuators (of every System)
A Set of Electrical Harnesses (for every System)
Display Panel with Indicators / Warning Lights (in Cockpit)
Multiple Engine RPM, Pressure Sensors & Thermocouples
Pilot’s Throttle
SOFTWARE:
- EPR Schedules (For Thrust, over Entire Range of Engine Operation Without FADEC Computer Failure)
N Schedules (For Thrust as per Pilot’s Throttle, Engine Operation in case of Limited FADEC Computer Functionality)
Note: In case of certain degree of FADEC failure there is an automatic mode switch-over from EPR to N rating. However, if the failure disappears, the pilot can reset the mode to switch-back to EPR mode.
INPUTS:
From Aircraft.
Ambient Temperature
Altitude
Mach Number
Angle of Attack
Impact Pressure
Landing Gear Position
Missile / Rocket Firing Signals etc.
INPUTS:
From Engine.
Throttle Lever Position
RPM
Turbine Outlet / Exhaust Gas Temperature
Exhaust Nozzle Area
Fan Duct Flaps Position
Bearing Temperatures
Engine Vibration
Engine Pressures