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Malaysian Institu te of Aviation Technology

FLY BY WIRE

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FLY BY WIRE

A method of control used by some modern aircraft inwhich control movement or pressures exerted by the pilotare directed into a digital computer.

They are input into a program tailored to the flightcharacteristics of the aircraft.The computer output signal is sent to actuators at the

controls surfaces to move them the optimum amount forthe desired maneuver.

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Aircraft flight control systemsconsist of flight control surfaces,the respective cockpit controls,connecting linkages, and thenecessary operating mechanisms

to control an aircraft's direction inflight. Aircraft engine controls arealso considered as flight controls asthey change speed.
http://en.wikipedia.org/wiki/Flight_control_surfaceshttp://en.wikipedia.org/wiki/Aircraft_engine_controlshttp://en.wikipedia.org/wiki/Aircraft_engine_controlshttp://en.wikipedia.org/wiki/Flight_control_surfaces

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"Fly-by-Wire" - imply an electrically-

signaled only control system.However, the term is generallyused in the sense of computer-configured controls, where a

computer system is interposedbetween the operator and the finalcontrol actuators or surfaces. Thismodifies the manual inputs of thepilot in accordance with controlparameters. These are carefullydeveloped and validated in order toproduce maximum operationaleffect without compromising safety.

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A method of control used by somemodern aircraft in which controlmovement or pressures exerted bythe pilot are directed into a digitalcomputer where they are input into

a program tailored to the flightcharacteristics of the aircraft. Thecomputer output signal is sent toactuators at the controls surfaces to

move them the optimum amount forthe desired maneuver.

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MAIN ADVANTAGES:Saving in weight.

Requires less maintenance.More responsive.More economic.Easier to provide in-built protection systems.

DISADVANTAGES:All electrical/electronic and is supply critical.

Magnetic interference (lightning strikes)

TO OVERCOME:Backup facilities duplication or triplication of

hardware and softwareMechanical standby mode

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DIGITAL ELECTRONICS

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ELECTROMECHANICAL FLIGHT INSTRUMENT

What is electromechanical?

Example of electromechanical flight instrument?

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Elctromechanical devices are those that combineelectrical and mechanical parts.

One example of electromechanical flight instrument isHorizontal Situation Indicator (HSI).

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FLY BY WIRE SYSTEM

THE A320 SYSTEM

Consist of Primary and Secondary system.

Primary system include of aileron, spoiler, elevator , horizontalstabiliser and rudder.

Secondary system include of leading edge slats and trailing edgeflaps for low speed flight handling, airbrakes/ load alleviation

spoiler for deceleration.

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Electrical control is achieved by three types of computers:

i. ELAC (Elevator and Aileron Computers).

ii. SEC (Spoilers and Elevator Computers).

iii. FAC (Flight Augmentation Computers).

In addition the Flight Control Data Concentrator acquires data from

the ELACs and SECs and sends this to ECAM (Electronic Centralised

Aircraft Monitor the flight deck screen displays and CFDS).

The Electrical Flight Control System (EFCS) includes the ELACs, SECs,

Flight Control Data Concentrator (FCDC) and vertical accelerometers.

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The Electrical Flight Control System (EFCS) includes the ELACs, SECs,

Flight Control Data Concentrator (FCDC) and vertical accelerometers.

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FLY BY WIRE SYSTEM

THE B777 SYSTEM

Unlike the A320 it uses conventional flight deck controls.

Signalling is via ARINC629 data buses and various computers and

control units.

It has 3 Primary Flight Computers;

i. Left

ii. Centre

iii. Right
http://../DIGITAL%20TECHNIQUE/DAT.ppthttp://../DIGITAL%20TECHNIQUE/DAT.ppt

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LAWS OF RECONFIGURATION

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BASIC AUTOPILOT OPERATION

A sophisticated autopilot systems can land the airplane in weather

condition that are so bad that the human pilot could not legally landthe aircraft.

The capabilities of a modern autopilot go way beyond simplycontrolling the aircraft during cruise operations.

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SMALL AIRCRAFT AUTOPILOTS

The sensor is a gyro turn coordinator which controls the pneumaticpower applied to the servos.

This simple autopilot uses pneumatic servos to actuate theailerons.

The source of power is a dry air vacuum pump which is engine

driven.

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Diagram of a 3-axis autopilot that can be coupled to radio navigation receivers

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The pitch, roll and yaw servos receive electrical signals from thecomputer that activate electric motors to move the control surfaces.

A three axis autopilot with electric motor servos is illustrated infigure above.

The sensor used with the this system include gyro sensors and analtitude sensor.

The altitude sensor shows that this autopilot would have an altitudehold capability.

Radio signals from the aircraft navigation radios can be used by the

autopilot to steer the aircraft along a desired VOR or localizercourse.

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PRIMARY FLIGHT CONTROL SURFACE OPERATION

The Primary Flight Control System (PFCS) consists of;

i. Various automatic control

ii. Warning

iii. Indicating subsystems that are principallyconcerned with manual aircraft control

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These subsystems provide means for operating and monitoring themany control surfaces that are necessary for the safe and efficient

flight of a large airplane.

These systems operate for both automatic and manual flight.

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The positions of flight control surfaces is shown to the pilots by thecontrol surface position indicator.

Control and trim positions are provided for spoilers, rudder, stabilizerand aileron.

The rudder control limiting system automatically restricts the rudderauthority and limits rudder hydraulic power capability during highspeed flight.

The system mechanically limits rudder deflection as a function ofairspeed when the flaps are retracted.

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PRIMARY FLIGHT CONTROL SURFACE OPERATIONThe spoiler mode control system automatically changes theconfiguration of the roll and speedbrake inputs to the spoiler tooptimize roll, direct lift control and speedbrake control for low and

high speed flight.

The spoilers are used to control lift, speed and roll.

The system mechanically limits rudder deflection as a function ofairspeed when the flaps are retracted.

The stall warning system artificially vibrates the control columns to

warn of an impending stall.

PFCS d f ti

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Malaysian Institu te of Aviation TechnologyPFCS mode of operation

a) Normal - operates when all the necessary data is available for theprimary flight computers (PFCs) and the actuator controlelectronics (ACEs). All the control laws, protection functions, andthe autopilot flight director computers (AFDCs), operate.

b) Secondary - When the PFCS detects the loss of important air andattitude data, the PFCS operation changes to secondary mode.The PFCs and the ACEs operate but the PFC control laws andprotection functions downgrade. The autopilot cannot operate insecondary mode.

c) Direct - the PFCs are not used. The ACEs set the position of thecontrol surfaces in direct response to analog pilot input.

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BENEFITS OF THE FLY BY WIRE PHILOSOPHY

Since early 20th century, aircraft designers realized of the advantagesof replacing the heavy mechanical or hydraulic flight control systemwith an electrical system.

Mechanical systems have limited ability to amplify the pilots strength.

Both systems require redundant backup.

Hydraulic systems can develop leaks.

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BENEFITS OF THE FLY BY WIRE PHILOSOPHY

Both systems have limited ability to compensate for changingaerodynamic conditions.

By replacing mechanical and hydraulic linkages with electrical

systems, saved a lot of weight and improve reliability.

By putting circuitry between the pilot and the aircraft could providevarious safety improvements. Eg, the control system could prevent astall and can stop the pilot from overstressing the airframe.

Electronic requires less maintenance.

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