Module 1

Flight Control Systems

Primary and Secondary Flight Control

Flight Control Linkage Systems

The pilot’s manual inputs to the flight controls are made by moving the cockpitcontrol column or rudder pedals in accordance with the universal convention:• Pitch control is exercised by moving the control column fore and aft; pushing the column forward causes the aircraft to pitch down, and pulling the column aft results in a pitch up• Roll control is achieved by moving the control column from side to side or rotating the control yoke; pushing the stick to the right drops the right wing and vice versa• Yaw is controlled by the rudder pedals; pushing the left pedal will yaw the aircraft to the left while pushing the right pedal will have the reverse effect

There are presently two main methods of connecting the pilot’s controls to therest of the flight control system. These are:• Push-pull control rod systems• Cable and pulley systems

Cable and Pulley System

High Lift Control Systems

Flight Control ActuationThe key element in the flight control system, increasingly so with the adventof fly-by-wire and active control units, is the power actuation. Actuation hasalways been important to the ability of the flight control system to attainits specified performance. The development of analogue and digital multiplecontrol lane technology has put the actuation central to performance andintegrity issues. Addressing actuation in ascending order of complexity leadsto the following categories:• Simple mechanical actuation, hydraulically powered• Mechanical actuation with simple electromechanical features• Multiple redundant electromechanical actuation with analogue control inputs and feedbackThe examination of these crudely defined categories leads more deeply intosystems integration areas where boundaries between mechanical, electronic,systems and software engineering become progressively blurred.

Conventional Linear Actuator

Blue channel

Green channelHydaulic power

Mechanical Signalling Summing link

Hydraulic piston actuator

Feedback link

SV SV

Mechanical Screwjack Actuator

Advanced Actuation Implementations

The actuation implementations described so far have all been mechanical orelectro-hydraulic in function using servo valves. There are a number of recentdevelopments that may supplant the existing electro-hydraulic actuator. Thesenewer types of actuation are listed below and have found application in aircraftover the past 10–15 years:

Direct Drive ActuationFly-by-Wire (FBW) actuationElectro-Hydrostatic Actuator (EHA)Electro-Mechanical Actuator (EMA

Direct Drive Actuation

In the electro-hydraulic actuator a servo valve requires a relatively small elec-trical drive signal, typically in the order of 10–15 mA. The reason such lowdrive currents are possible is that the control signal is effectively amplifiedwithin the hydraulic section of the actuator. In the direct drive actuator theaim is to use an electrical drive with sufficient power to obviate the need forthe servo valve/1st stage valve. The main power spool is directly driven bytorque motors requiring a higher signal current, hence the term ‘direct drive’.Development work relating to the direct drive concept including comparisonwith Tornado requirements and operation with 8 000psi hydraulic systemshas been investigated by Fairey Hydraulics see reference [9]. This paper alsoaddresses the direct digital control of aircraft flight control actuators.

Fly-By-Wire Actuator

Electro-Hydrostatic Actuator (EHA)

Electro-Mechanical Actuator (EMA)

Module 2

Engine Control Systems

Engine Technology and Principles of Operation

Illustrations of single and multiple spool engines

Two and three shaft turbofans

Fuel Flow Control

Air Flow Control

Engine air management

Bleed air control – RR Trent 800 example

Control SystemsThe number of variables that affect engine performance is high and the nature of the variables is dynamic, so that the pilot cannot be expected constantly to adjust the throttle lever to compensate for changes, particularly in multi-engined aircraft. In the first gas turbine engined aircraft, however, the pilot was expected to do just that. A throttle movement causes a change in the fuel flow to the combustion chamber spray nozzles. This, in turn, causes a change in engine speed and in exhaust gas temperature. Both of these parameters are measured; engine speed by means of a gearbox mounted speed probe and Exhaust Gas Temperature (EGT), or Turbine Gas Temperature (TGT), by means of thermocouples, andpresented to the pilot as analogue readings on cockpit-mounted indicators. The pilot can monitor the readings and move the throttle to adjust the conditions to suit his own requirements or to meet the maximum settings recommended by the engine manufacturer. The FCU, with its internal capsules, looks after variations due to atmospheric changes.

In the dynamic conditions of an aircraft in flight at different altitudes, temperatures and speeds, continual adjustment by the pilot soon becomes impractical. He cannot be expected continuously to monitor the engine conditions safely for a flight of any significant duration. For this reason some form of automatic control is essential.

Control System Parameters

Engine control systems – basic inputs and outputs

5 Input Signals

• Throttle position• Air data – Airspeed and altitude• Total temperature• Engine speed• Engine temperature• Nozzle position• Fuel flow• Pressure ratio

6 Output Signals

• Fuel flow control• Air flow control

Example Systems

A simple engine control system – pilot in the loop

A simple limited authority engine control system

Engine control system with NH and TGT exceedence warnings

Full authority engine control system with electrical throttle signalling

The RB199 control system in the BAE Systems EAP

A modern simplified engine control system

Turbojet Engine (EJ200 in Eurofighter Typhoon)

Turbofan (Trent 1000 in Boeing B787) Turboprop (EPI TP400 in A400M)

Helicopter (T800 in EH101 & NH-90)

Engine StartingTo start the engines a sequence of events is required to allow

fuel flow, to rotatethe engine and to provide ignition energy. For a particular type

of aircraft thissequence is unvarying, and can be performed manually with

the pilot referringto a manual to ensure correct operation, or automatically by

the engine controlunit. Before describing a typical sequence of events, an

explanation of some ofthe controls will be given.

Fuel Control

Typical location of LP and HP Cocks

Ignition Control

Engine ignition

Engine Rotation

APU functional diagramAPU – airborne rating example

Throttle LeversThe throttle lever assembly is often designed to incorporate HP cock switchesso that the pilot has instinctive control of the fuel supply to the engine.Microswitches are located in the throttle box so that the throttle levers actuatethe switches to shut the valves when the levers are at their aft end of travel.Pushing the levers forward automatically operates the switches to open thefuel cocks, which remain open during the normal operating range of the levers.Two distinct actions are required to actuate the switches again. The throttlelever must be pulled back to its aft position and a mechanical latch operatedto allow the lever to travel further and shut off the fuel valve.

Starting SequenceA typical start sequence is:Open LP cocksRotate engineSupply ignition energySet throttle levers to idle – open HP cocksWhen self-sustaining – switch off ignitionSwitch off or disconnect rotation power source

Together with status and warning lights to indicate ‘start in progress’, ‘failedstart’ and ‘engine fire’ the pilot is provided with information on indicatorsof engine speeds, temperatures and pressures that he can use to monitor theengine start cycle. In many modern aircraft the start cycle is automated so that the pilot has onlyto select START for the complete sequence to be conducted with no furtherintervention. This may be performed by an aircraft system such as VehicleManagement, or by the FADEC control unit. In future this sequence may beinitiated by an automated pre-flight check list.

Engine IndicationsEngine speed – NH and NLEngine temperaturePressure ratioEngine vibrationThrust (or torque)

Some examples of engine synoptic displays

Engine Oil Systems

Module 3

Hydraulic and Environment Control Systems

Hydraulic Circuit Design

Hydraulic system loads

• Pressure• Integrity• Flow rate• Duty cycle• Emergency or reversionary use• Heat load and dissipation

A simple hydraulic system

Hydraulic Actuation

Hydraulic FluidThe working fluid will be considered as a physical medium for transmittingpower, and the conditions under which it is expected to work, for examplemaximum temperature and maximum flow rate are described. Safety regulations bring about some differences between military and civilaircraft fluids. With very few exceptions modern military aircraft have, untilrecently, operated exclusively on a mineral based fluid known variously as:

DTD 585 in the UK

MIL-H-5606 in the USA

AIR 320 in France

H 515 NATO

Fluid Pressure

Fluid Temperature

Fluid Flow Rate

Hydraulic Piping

Hydraulic Pumps

Characteristic curve for a ‘constant pressure’ pump

Examples of hydraulic pump technology

Working principle of a piston pump

Need for a Controlled Environment

Ram Air Cooling

Fuel Cooling

Engine Bleed

Use of fuel as a coolant for hydraulic or engine oil

Closed loop cooling system

Bleed Flow and Temperature Control

Mixing hot air with heat exchanger outlet

Cabin temperature control system

Air Cycle Refrigeration

• Humidity Control• Hypoxia

Tolerance