ecu part 2

Question 1

requirments of a fuel system

Answer 1

hold sufficient fuel required for the flying task

supply the correct amount of fuel to all engines

supply fuel at the correct pressure

to be able to refuel from pressure or gravity refuellers

emergency jettison

isolate fuel from engines in an emergency

monitor fuel usage or fuel contents

transfer fuel to maintain the (C of G)

indicate fuel flow failure or low level

to be able to defuel by suction or gravity to any level required

Question 2

float switch assembly

Answer 2

fitted in each fuel tank and consists of a tube fitted with four float switches

float switch contains a reed switch operated by magnets

HLFS operates at 100% (tank full) and is used to close the refuel/defuel valve during refuel and provide a tank full indication

80% float switch is a transfer threshold float switch to allow automatic transfer of fuel in the fuel transfer automatic mode

17% float switch operates to indicate when the fuel level in the tank is at a LOW alert level

0% closes the refuel/defuel valve during defuel and switches off the transfer pumps in the transfer tank

Question 3

xfeed switch to pos 1, 2, 3

Answer 3

if all the xfeed switches are selected to pos 1. No 1 tank will supply all three engines and the indications for engines 2 and 3 will indicate TNK1

same for all engines

Question 4

wildcat fuel operation

Answer 4

the wildcat fuel system is configured to keep the CofG within limits during refuel/defuel and flight

fuel is used from the main tanks first and as the fuel drains to 2/3 level the C of G moves towards the fwd limit

fwd tank drains down to the mid position CofG moving rwd

main tanks now drain to the 1/3 level with CofG moving fwd

the remaining fuel in the fwd tank then empties with the CofG returning rwd

the main fuel tank now drains until empty with Cof G moving to the center

the collector tanks are then the last to be used

fuel LOW indication are shown at 100 kg for both or 50kg for one, these are yellow box around indications and histograms

low level float switch is activated at 47kg of fuel and FUEL LOW 1 or 2 will display on IDU

Question 5

merlin auto fuel operation

Answer 5

under normal conditions the No1, 2 and 3 fuel tanks motorised ball transfer valves are closed

until the contents of the fuel tanks has fallen to 80%

then float switch in the fuel tank will open the motorised ball transfer valve and allow fuel to enter the tank from the transfer tank

when the transfer tank is empty the LOW LEVEL FLOAT SWITCH (LLFS) operates and switches the transfer pumps off

transfer pumps in the transfer tank supply fuel to the main fuel gallery pipe which runs along the left side of the cabin

fuel transfer continues until the No 1, 2 and 3 fuel tanks high level float switch (HLFS) operate to close their respective motorised ball transfer valve

Question 6

describe fuel jettison

Answer 6

select master dump switch to open

a supply is fed to the master jettison switch, limit switch of the jettison valve, through coils of the motor and motor armature, to the limit switch of the jettision valve and master switch to earth

when the jettison valve is open the limit switch changes over, removing the supply to the motor and making the circuit to illuminate the yellow OPEN caption on the indicator and prepare the circuit for shut selection

when the jettison pump push switches are pressed to ON, the jettison pump relays are energised and contacts change over to feed 115v 3Ø to jettison pumps,

initially the pressure switch will cause a yellow LOW caption to be illuminated on the push switch indicator

when the jettison pumps are running the pressure switch contact will change over and a green ON caption will be illuminated on the push switch indicator

when the MASTTER DUMP switch is selected to shut, a supply is fed through the master jettison switch and the limit switch of the jettison valve, through the shut field coil of the motor and the motor armature, through the limit switch of the jettison valve and the master jettison switch to earth

when the jettison valve is shut, the limit switch changes over remeoving the supply of the motor and extinguishing the captions on the indicator and preparying the circuit for an open selection

Question 7

why is fuel measure in kg

Answer 7

so all of the weight of the aircraft can be calculated prior to take off

this ensures that take off limits are not exceeded

Question 8

tank probe construction

Answer 8

two primary probes and a secondary probe installed in each fuel tank,

made of two concentric tubes, one inside the other,

an oscillator unit is attached to the outer tube

installed at angles so they dont penatrate the fuel tanks during a crash,

more accurate guaging during flight manoeuvres

Question 9

tank probe operation

Answer 9

vairiable capacitors with the fuel acting as a dielectric (higher the fuel level the greater the capacitence)

the changing level of capacitance relative to the level of fuel causes a change in the frequency output of the local oscillator this is fed to the fuel indication electronic unit (FIEU)

FIEU processes the fuel quantity signals and feeds the information to the aircraft maintenance management computers (AMMC) and cockpit display system (CDS)

Question 10

fuel safety precaution

Answer 10

switch of all electrical supplies

ensure all tansk are drained and ensure area is well ventilated

only safety torches are to be used inside tanks

fit blanks to open pipes/conduits

deal with spillages immediately using ready available spill kits

no HP air blasts in the pressence of fuel vapor

fire extinguisher are to be available

appropriate clothing is to be worn

barrier cream is to be used

the TWO-MAN rule is observed

vehicles must not approach with 15 metres of an aircraft undergoing repairs to the fuel system

Question 11

functions of the EECU

Answer 11

controls the engine start sequence and acceleration of the engine up to ground idle

controls the rate of acceleration of the engine and rotor speed when the engine condition switch is selected from GI to flight

controls the rotor speed - default datum speed is 102%

keeps the engine torque matched by sharing torque information with the ECU’s

it limits the output of the engine so that limits of the transmission are not exceeded

it causes the engine to shut down if there is an overspeed of Ng or Np

it feeds engine speed, temperature and torque information to the EIS

Question 12

engine fadec sensor inputs

Answer 12

Gas turbine speed (Ng)

power turbine speed (Np)

turbine inlet temeperature (TIT)

engine Torque

position of the Throttle

Question 13

advantages of FADEC

Answer 13

1. better aircraft handling ,
2. less vibration,
3. less component wear/damage
4. less pilot fatigue

stand for full authority digital electronic control (FADEC) sytem

Question 14

4 components, starting system

Answer 14

A motor - to impart force to overcome inertia and friction of the rotating assembly of the engine amd its ancillary equipment

fuel system - to introduce the fuel/air mixture into the engine appropriatly metered for combustion

ignition system - able to provide a means of igniting the initial charge of fuel/air mixture

a control system - to programme the start sequence and to prevent design parameters from being exceeded

Question 15

2 types of starter motor

Answer 15

electrical - wildcat

air turbine (low pressure) - merlin

Question 16

5 HEIU safety prec

Answer 16

never touch an igniter unit output lead or the igniter plug whilst the HEIU is operating

wait at least one minute after switching off before touching any part of the system (to allow charge to dissipate)

always disconnect the LT lead at the HEIU (DC supply) before working on the system

always disconnect the LT lead before the HT lead when disconnecting the HEIU

always reconnect the HT lead before the LT lead when reconnecting the HEIU

Question 17

all components of the HEIU explained

Answer 17

parallel/series rectifier bank rectifies the charging current

the discarge resistors dissipate any charge remaining on the reservoir capacitor when the unit is switched off

the safety resistors provide a safe path for the energy if HT lead is disconnected

the choke extends the spark duration

the discharge gap ensures the reservoir capacitor has charged to the correct level before energy arc the gap

primary capacitor stops sparking at the contacts and ensures high voltage pulses are induced into the secondary

Question 18

ESU operation APU

Answer 18

batter master switch ON

engine master start switch ON

fuel switch selected to ON

press the start/stop button

ON caption will illuminate and start signal supplied to the ESU

ESU checks that all conditions are correct and energises the APU start contactor

power is supplied to the starter motor and the APU START caption is illuminated

starter motor accelerates the APU rotor to a speed of 5%, at this point the start fuel valve and igniter operates

at 14% APU rotor speed the main fuel valve opens and the rotor is further accelerated by the starter, with assistance from the engine combustion

at 70% rotor speed to the start fuel valve and ignition system are shut down and the APU START caption is extinguished

at 90% +5 seconds APU rotor speed, the main fuel valve is opened fully

at 90% +10 seconds APU rotor speed the ESU initiates a ‘ready for service’ signal indicating that the APU is operating at the correct conditons to supply bleed air and operate the APU AC generator

the ‘APU READY’ caption on the control panel is illuminated and the APU ‘ready’ advisory caption is displayed on the WCA window

Question 19

merlin No 1 starter cycle

Answer 19

before merlin No1 engine start, engine must be in accessory drive, blades spread, rotor break on

start master switch ON

bleed switch to APU/ENG

with APU running bleed switch set to APU, fuel switches selected to ON, engine condition switch to GI

when engine condition switch is moved to GI power is fed to the start control section of the EECU.

the ON solenoid of the FUEL SHUT OFF VALVE to energise

the ignition exciter to energise

the press/start valve in the engine fuel system to energise

the solenoid of the starting pressure shut of valve (SPRSOV) is energised OPEN allowing air pressure through to the engine

the start relay is energised causing the shut off valve in the environmental control system to close. (ensures all air is available for starting)

operation of the SPRSOV causes a green ‘START’ caption on the PPSD on IDU

Question 20

Thermocouple principle

Answer 20

when two dissimilar metals are joined at their ends to form a closed loop and heat is applied to one end, an EMF is produced.

the magniture of the EMF will depend upon the difference in temperature between the two ends of the loop and types of dissimilar metals used

the end of the loop to which heat is applied is called the HOT JUNCTION and the other end COLD JUNCTION

A/C thermocouples use Alumel and chromel

alumel is a mixture of aluminium and nickel and chromel is a mixture of chromium and nickel

Question 21

ch c pg 33 fig 38

SMD how does it display info

Answer 21

the systems managment display (SMD) shows fuel contents in the top left window

the ECU in the control of the engine is indicated in green and the serviceable standby in white

engine indications Ng, PTIT, Np, Nr and Tq are displayed in the centre window,

the WCA window on the right

the bottom windows display the temperatures and pressures of the engines and gearbox.

hydraulic pressures of the three systems on the bottom right window

Question 22

1. ECU torque

Answer 22

engine torque is a measure of the output power being developed by the engine.

the engine torque sensor is a dual coil variable reluctance magnetic pickup probe, which measure the engine torque on the power turbine output shaft, from which torque signals are fed to each ECU for engine control and cockpit display

the engine torque sensor is excited by two pairs of blades,

one pair of blades is fitted to the power turbibe shaft and the other is fitted to the reference shaft

the power turbine shaft twists linearly as it delivers power to the transmission.

the sensor probe detects the difference in angle between the blades to produce the torque signals

the engines torque indications are important to the pilot during tale off, landing, load lifting, engine torque matching and anoy other flight conditions where significant power demand placed on the engines

Question 23

describe pressure refuel merlin

Answer 23

pressure refuelled from a bowser which takes 9 mins

connecting the pressure refuel hose to the aircraft refuel point, causes a microswitch to operate allowing a DC supply to the REFUEL/OFF/DEFUEL switch on the control panel

when the REFUEL/OFF/DEFUEL SWITCH is selected to refuel, the refuel/defuel valves in No 1,2 and 3 fuel tanks are energised open allowing fuel from the main gallery into No1, 2, and 3 fuel tanks

as the fuel tanks 1,2 and 3 become full, their HLFS operate and remove electrical power from the refuel/defuel valves causing the valves to de-energise and close to shut off the supply of the fuel to No1 2, and 3 fuel tanks

with No1,2 and 3 tanks full and refuel/defuel valves close, power is then fed to transfer tanks refuel/defuel valves which opens to allow fuel from the main fuel gallery to refuel the transfer tank

as transfer tank becomes full HLFS de-energises refuel/de-fuel valves, the refuel control panel will illuminate to indicate tans are full

Question 24

describe fuel jettison

Answer 24

select master dump switch to open

a supply is fed to the master jettison switch, limit switch of the jettison valve, through coils of the motor and motor armature, to the limit switch of the jettision valve and master switch to earth

when the jettison valve is open the limit switch changes over, removing the supply to the motor and making the circuit to illuminate the yellow OPEN caption on the indicator and prepare the circuit for shut selection

when the jettison pump push switches are pressed to ON, the jettison pump relays are energised and contacts change over to feed 115v 3Ø to jettison pumps,

initially the pressure switch will cause a yellow LOW caption to be illuminated on the push switch indicator

when the jettison pumps are running the pressure switch contact will change over and a green ON caption will be illuminated on the push switch indicator

when the MASTTER DUMP switch is selected to shut, a supply is fed through the master jettison switch and the limit switch of the jettison valve, through the shut field coil of the motor and the motor armature, through the limit switch of the jettison valve and the master jettison switch to earth

when the jettison valve is shut, the limit switch changes over remeoving the supply of the motor and extinguishing the captions on the indicator and preparying the circuit for an open selection

Question 25

fuel xfeed operation during engine failure

Answer 25

if no one engine had failed. No 1 tank could be left with fuel when the other tanks were low,

the selection of No 2 and No 3 crossfeed switches to pos 1 would allow No1 tank to then feed the servicable No2 and No3 engines the crossfeed indicators for engines 2 and 3 would then indicate TNK1

Question 26

turbojet operation

Answer 26

compressor draws air into the engine and compresses it.

fuel is fed to the burners in the combustion chamber and lit by igniter plugs during the start cycle

some of the air from the compressor is used to support combustion

the rest of the air is heated and it expands to produce thrust which forces its way rearwards to form the thrust stream to drive a fixed wing A/C

Question 27

what happens in a merlin A/C when an individual fuel tank is at (or below) 200kg?

Answer 27

a digital readout will change from green to yellow with a yellow box around it

Question 28

what happens if a merlin A/C fuel is at or below 600kg

Answer 28

a digital readout will change green to yellow with yellow box around it

Question 29

what happens in a merlin A/C at or below 146KG

Answer 29

when the reed switch in any one of the low level float switches falls below the 20 minute level (146KG) a FUEL LOW caution will appear on the wca window

Question 30

turbojet operation

Answer 30

compressor draws air into the engine and compresses it.

fuel is fed to the burners in the combustion chamber and lit by igniter plugs during the start cycle

some of the air from the compressor is used to support combustion

the rest of the air is heated and it expands to produce thrust which forces its way rearwards to form the thrust stream to drive a fixed wing A/C

Question 31

turbo shaft operation

Answer 31

a turbo shaft engine has free turbine which is used to produce shaft power to drive machinery instead of producing thrust,

turboshaft engines are most used in applications that require a small, powerful, light weight engine

Question 32

turbo prop operation

Answer 32

turboprop has a free turbine which is used to drive an aircraft propeller

turboprop engines deliver more power and great efficiency at lower flying speeds than a traditional jet propulsion engine

they offer greater economic advantage on smaller aircraft and over shorter distances

Question 33

ch c pg6 fig 7 diagram

basic starter circuit merlin

Answer 33

a basic E- starting circuit for the engine consists of a starting motor and an igniter unit operated by start contactors and an igniter relay,

with the start master switch made an electrical supply will be available at the start button

start button pressed, start contactor energises, allowing DC power to the starter motor which turns the engine compressor, igniter relay energises supplying DC power to the HEIU which produces power required for the igniter plug

fuel is supplied to the engine and should start accelerate to ground idle speed

once the start cycle has started the pilot can release the button and start cycle will be held on by the engine speed sesning unit, this continues to feed power to the start motor and igniter unitl the engine starts or start cycle times out

a successful engine start will be detected by the engine speed sensing unit which removes the supply to the hold circuit and terminates the start cycles