Aircraft ECU and associated electrical systems 7720 Flashcards
requirments of a fuel system
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
purpose of the fuel managemnt panel
to allow the pilot to control fuel system
fuel tank construction
crashworthy construction, made from a polyurethene elastomeric material, which has self sealing properties
float switch assembly
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
purpose of the fuel distribution manifold
located on the transmission decking
controls fuel flow xfeed between 1,2,3 tanks
purpose of the jet/scavenge pumps
the jet pumps draws fuel from the bottom of the tank to ensure that all fuel is used up,
mechanical pump which feeds pressurised fuel from the booster pump manifold, into the primary inlet,
this comes out the jet at high speed creating a venturi effect
low pressure in the secondary inlet sucks fuel from the bottom of the tanks
booster pump operation CT diagram
booster pumps have their own pressure switch and controlled by its own indicator push button
when working normally the pump will be blank
a failure will cause the indicator to show OFF in green and low pressure will show LOW in yellow
with AC power on and booster pumps OFF the indicator will indicate OFF in green
when the booster pump push switch is pressed ON, the booster pump relay will energise, and its contacts will change over and three phase electrical power will be fed to the booster pump,
initially the pump pressure will be low and the pressure switch will cause a yellow LOW caption on the switch indicator to be illuminated
as the booster pump runs up, the pressure will increase and the contacts in the pressure switch will change over and a low caption will be removed
how is the pilot made aware of a booster pump failure
an indication will appear in the IDU as a YELLOW LOW caption
booster pump is selected to OFF by pressing the indicator switch
the pilot will need to consider reducing altitude and be aware of possible performance limitations
checked regularly to ensure contents do not fall below 45kgs reducing the possibility of cavitation
merlin auto fuel operation
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 swithces 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
high level float switch failure
if a HLFS fails to close its mortorised ball valve, the the auto system will cause an overflow of fuel
overspill switches fitted above the normal fuel tank full switches will operate and cause a SPILL indication on the IDU to show that overflow is taking place
the transfer pumps can then be manually selected OFF by switching the AUTO/MANUAL switch to the manual position
xfeed switch to pos 1, 2, 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
fuel xfeed operation during engine failure
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
what happens to the merlin fuel indications at 600kg, 200kg and 146kg
if contents of individual tanks fall below 200kg or the total content falls below 600kg the digital readout will change from green to yellow with a yellow box around it
when a reed switch in the LLFS falls below the 20min level, (146kg) a FUEL LOW caution caption appears in the WCA window
describe pressure refuel merlin
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
describe HIFR
located on the cabin bulkhead aft if the cabin door, provides the controls necessary to pressure refuel the aircraft in flight
the HIFR hose is a lightweight hose and cant operate the microswitchon the AC refuel point,
but the tanks full/refuel on indicator push switch bi-passes the normal refuel switch and when pressed, the ON light is displayed and the refuel system is allowed to operate
pressing the full/refuel switch to off will stop the refuel process
Describe defuel merlin
connect the pressure defuel hose to the aircraft refuel point, causes a microswitch to operate and a DC supply is fed to the REFUEL/OFF/DEFUEL
when the REFUEL/OFF/DEFUEL switch is selected to DEFUEL, the refuel/defuel valve in the transfer tank is energised open and allows fuel to be drawn from the transfer tank
when the transfer tank is empty, the LLFS operates causing the transfer tank refuel/defuel valaves to be energised open and allow the fuel to be dran out via the main fuel gallery,
as the No1, 2 and 3 fuel tanks empty, theirLLFS make and refuel/defuel valves are de-energised closed to prevent the ingress of air which would stop the defuel process
when each fuel tank has been defueled to its lowest point using the defuel bowser, the residual fuel is then drained using the manual fuel drained valves located at the base of the bowser
describe fuel jettison
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
describe fuel gauging system
allows the pilot to know exactly how much fuel is left on board
why is fuel measure in kg
so all of the weight of the aircraft can be calculated prior to take off
this ensures that take off limits are not exceeded
tank probe construction
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,
tank probe operation
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)
explain compensator
a secondary probe with a compensator unit on the bottom is fitted in the tanks 1,2 and 3
the compensator is an extra capacitor with two tubes and its own oscillator.
its purpose is to provide a reference and compensate for changes of specific gravity (density) of the fuel
the probe outputs are fed to the fuel indication electronic unit (FIEU) the fuel contents signals are processed for display on the cockpit display system (CDS)
how is fuel level displayed
fuel contents afe in KG in a histogram format with corrsponding digital readout
fuel signal failure wildcat
in the event of a signal failure of the SMD of the fuel tanks
a red F will Flash within the relevent display 5 times at 1 hertz and then remain steady
whats the LOW pressure drop caption and level
displays a GREEN ON caption when they are selected on and a YELLOW LOW caption when below 0.14 bar
buttons are black when pumps are off
wildcat quantity guaging system
fuel contents unit (FCU) converts the signal produced ny the probes into a DC voltage proportional to the fuel quantity
located in the nose bay and interfaces with the fuel probes to convert the fuel probe signals to a dc voltage
wildcat fuel operation
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 Cof 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
fuel safety precaution
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
functions of the EECU
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 swithc is seleceted 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
master? hot standby?
the EECU share their engine power information so that he output power of all engines is equal
eac EECU has two identical control channel A and B, both channel are equally capable of engine control
the operating channel is selected by the pilot, the selected channel becomes the MASTER channel and the other channel become the HOT STANDBY channel
if a failure occures in the master channel control is automatically transfered to the hot standby channel and an illumination on the selector pannel will show the transfer has happened
inputs and outputs of the EECU
controls the acceleration start sequence and acceleration of the engines up to ground idle
controls the rate of acceleration of the engine and rotor speed when the engine and rotor speed when the engine conditon switch is selected from GI to FLIGHT
controls the rotor speed - default datum speed is 102%
keeps the engines torque matched by sharing torque in formation with the other ECU’s
it limits the output power 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 feed engine speed, temperature and torque information to the EIS
pilots inputs to the EECU
engine condition switch VENT/OFF/GI/FLIGHT
control channel selection A/B
collective pitch (collective pitch resolver)
overspeed test switch (simulates engine overspeed)
contingency switch to overcome power limits
accessory drive selection (No1 engine)
neutral selection (No3 engine)
Nf trim
engine fadec sensor inputs
Gas turbine speed (Ng)
power turbine speed (Np)
turbine inlet temeperature (TIT)
engine Torque
position of the Throttle
how are EECU failures be indicated to pilot
a failure of an EECU will be indicated on the WCA, EECU FAIL attention getters flash with voice warning
other failures will be indicated as a caution captions ENG 1, 2 and 3 ECU SBY, ENG1, 2 and 3 ECU CTR
wildcat NP needed for lift off
from ground idle to 104%(Np) for takeoff
advantages of FADEC
better aircraft handling , less vibration, less component wear/damage and less pilot fatigue
turbojet operation
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
turbo prop operation
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
turbo shaft operation
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, powerfull, light weight engine
4 requirements, starting system
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
2 types of starter motor
electrical - wildcat
air turbine (low pressure) - merlin
ch c pg6 fig 7 diagram
basic starter circuit merlin
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
HEIU operation
when the HEIU is switched on, a dc current flows through the primary coil.
the primary coil acts as an electromagnet opening the contact.
the open circuited primary looses its magnetic effect and the contacts close under the influence of the spring.
this action is repeated at high speed and the pulses of current in the primary coil induce high voltage pulses into the secondary coil
the pulses in the secondary are half wave rectified by the diode bank and cause the reservoir capacitor to charge,
when the charge reached the break down value of the discharge gap, the capacitor will discharge to earth through the choke and igniter plug.
this action repeats itself. producing high energy sparks at the igniter plug at a rate of 100 - 120 per minute
all components of the HEIU explained
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
HEIU safety prec
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
ESU operation
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
merlin No 1 starter cycle
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
when motor ECU without fuel
replacement of a component in the starter systems
a compressor wash needs to be carried out
the fuel system or an oil system needs to be primed or bled
the engine needs to be vented to clear engine casing of compressor wash fluid post compressor wash, and unused fuel post flight
when FADEC shuts down engines
when the engine start sequence has been initiated, the ECU will control the engine fuel flow and acceleration bleed-air vlave
the ECU will auto shut engine if following conditions apply
EMSS is selected OFF
the engine does not light up within 30 seconds
the Ng is less than 50% within 60 seconds
the PTIT exceeds 850ºC
how long should pilot vent engines
15 seconds is the recommended cranking period for venting the engines
cautions when starting wildcat engines
wait 3 minutes between attempts to start and/or vent runs to allow the starter to cool (2 minutes if first start of the day)
after three starter/vent operations, a period of 30 minutes must elapse before another attempt to start is made
no more than three successive abortive attempts to start should be made using the same internal battey within a 24 hour period, to prevent overheating
vent runs should be terminated after 15 seconds
SMD how does it display info
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
EXP NG sensor
Gas generator speed (Ng) the speed of the gas generator is sensed by an NG sensor which is mounted on the accessory gearbox.
the sensor is a magnetic variable reluctance pickup speed sensor, which senses speed of the 76 tooth gear which drives the oil pump.
the sensor has two output windings that feed separate signals to the two ECUs for speed governing and cockpit indications
EXP power turbo speed sensor
the speed of the turbine is sensed by an Np sensor which is mounted on the engine rear support.
the sensor is a duel coil magnetic variable reluctance pickup speed sensor,
it senses the speed of the power tubine shaft from the passage of the lugs on the shaft as it rotates
the sensor has two output windings that feed separate signals to the two ECUs for speed governing and cockpit indications
EXP PTIT
the PTIT harness is made up of five dual thermocouple sensors which are electrically connected in parallel and arranged concentrically at the rear of the combustion chamber.
the thermocouples provide two outputs feeding separate signals to the ECUs for engine control and cockpit indications
Thermocouple principle
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
AC thermocouples use Alumel and chromel
alumel is a mixture of aluminium and nickel and chromel is a mixture of chromium and nickel
ECU torque
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 (only the power turbine shaft twists relative to the output power, the reference shaft does not twist
Oil PY/temp/low px
engine oil pressure and gearbox oil pressure are sensed by oil pressure transmitters on the engines and the gearbox which are displayed in the cockpit
oil temeprature of th engines and gearbox are sensed by oil temperature probes on the engines and gearboxes and displayed in the cockpit
oil pressure switches sense low pressure in the engines gearboxes and feed the caption on the WCA window
wildcat relight parameters
EMSS is selected to FLY or GI
the ECU BIT detects no failure that would result in an unsafe start
the starter master switch is set to ON
one channel remains functional
Ng is greater than 50%
indications on wildcat start
a green START and ignition (IGN) legend is displayed
a small red circle is also displayed at 850ºC on the PTIT scale of the starting engine to display the maximum temperature
