M14.2 - Systems
M14.2
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- Created by: Bikboi
- Created on: 02-10-24 16:17
What does EGT monitoring prevent?
Thermal damage to the engine
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Where are the highest temperatures recorded in the engine?
*** - Turbine Inlet Temperature
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What can the *** temperature exceed?
1400°C (2550°F)
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Where is EGT measured?
Between HPT and LPT or directly behind LPT
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What is the maximum expected EGT?
600 - 900°C
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Where are EGT thermocouples placed to provide relative indication of ***?
Turbine discharge
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How many EGT thermocouples are used?
Several placed at intervals around engine exhaust duct and average gives indication
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Thermocouple voltages are very small, therefore what is required?
They must be amplified to energise the servomotor to drive the pointer
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What is the range of the hermetically sealed EGT indicator?
0 to 1200°C
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What is contained within the indicator to show power off?
Power off warning flag at lower portion
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What types of thermocouples are used for *** indication?
2 electronically independent junctions within 1 probe
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What is used to stop the motor when the correct pointer position is reached?
Humming signal
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How is input voltage variation to indicator within *** indicator precluded?
Voltage reference circuit in bridge circuit
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When does the over temp warning light illuminate on the *** indicator?
When *** reaches predetermined limit
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How does the test switch of the *** indicator work?
Tests all engines by simulating over temp signal in temp control bridge circuit
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When is N3 displayed?
When the engine has 3 rotors
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What unit is used to express engine speed?
%
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What are the 3 main parts of the turbine engine speed indication?
Sensor, Data transmission and Indication
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What are the 2 types of speed sensor?
Variable reluctance and tachometer generator on the gearbox
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How are variable reluctance sensors also referred to?
Magnetic reluctance sensors or magnetic pickups
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What principle does variable reluctance sensors work on?
Magnetic reluctance - Opposition of magnetic circuit to flow of flux
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Where are variable reluctance sensors located?
Compressor casing inline with phonic wheel or fan blades
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What parameter of the induced signal within a speed sensor is related to spool speed?
Frequency
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What is the critical part of the variable reluctance sensor?
Air gap between magnet and target
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What does reluctance mean?
How much opposition the magnetic circuit offers to the magnetic flux
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If the air gap between the target and the magnet is larger, what is true of the reluctance?
High
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What is faradays law of electromagnetic induction?
Changing magnetic flux induces a voltage across a coil wound around sensor
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What is true regarding the relationship between rate of change of flux and induced voltage?
Directly proportional
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Rotating magnetic field of the tachometer generates a phase AC voltage, what is proportional to the input speed?
Frequency
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In older aircraft, how is the tachometer indication driven?
Voltage direct from tachometer generator
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What does the tachometer generator supply power to?
FADEC computer
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How is the tachometer generator also referred to?
Dedicated generator or control alternator
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What does the warning lamp that is powered by the tachometer generator used for?
Indication of engine rotation and correct direction of movement (Only used in start cycle)
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Why is engine movement indication important?
To inform the pilot when to open the HP fuel ****
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What are the 3 types of rotor speed indication?
Clock, moving vertical bar and electro-mechanical indicator
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What is the red line limit on the speed indication?
Speed limit (Maximum permitted rotor speed) indication
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What is required when speed limit exceedances occur?
Unscheduled maintenance required to inspection internal sections
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What happens when a speed exceedance occurs?
Indications turn red and accompanied by warnings from CWS
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What happens on modern engines exceedances occur?
N1 speed and duration of overspeed is recorded and initiates a report in trend monitoring
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What does the speed exceedance report in trend monitoring of modern engines provide?
Information to determine depth of inspection required
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What are the 3 groups of engine indication?
Performance, systems and trend monitoring
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What engine indication is always located at the top?
Performance
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What is engine trend monitoring?
Alerts operator to a problem at early stage by analysing data in a workshop that is recorded by ACMS during flight.
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What are the 3 types of analyses?
Thermodynamic, Mechanic-dynamic and oil consumption
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What is thermodynamic analyses used for?
Pressures and temperatures along gas flow path
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What is mechanic-dynamic analyses used for?
Failures in rotor system via VIB and rotor speed
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What is oil consumption analyses used for?
Alert when certain limit of oil consumption is exceeded
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What does engine pressure ratio (EPR) compare?
Turbine discharge pressure to pressure of ram air at inlet
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What does a differential pressure gauge?
Compares 2 different pressures
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What does the EPR system compensate for?
Airspeed and altitude
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What is the normal mode of displaying thrust?
EPR
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What is the alternate mode of displaying thrust?
N1
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The EPR value is the EPR required for flexible take off, how is it set?
Adjusted manually by knob on flight deck
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What does the blue circle correspond to on thrust indication?
Actual throttle position
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What is flexible takeoff?
Uses assumed temperature thrust reduction to preserve engine wear and extend engine life
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What is shown on oil pressure indication?
Oil pump discharge pressure
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What is a differential oil pressure system?
Direct indication taken downstream of pump outlet and inlet of oil scavenge pump
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What does a differential oil pressure system compensate for?
Bearing chamber air pressure
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What would be the effect of higher chamber air pressures?
Reduced oil flow through the jets
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What are the 2 types of oil pressure transmitters?
Bourdon tube and strain gauge
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What can the closed end of a bourdon tube be connected to in order to provide electrical indication?
Potentiometer
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What is the construction of a bourdon tube?
C shaped/helical with oval cross section
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What material can a bourdon tube be made from?
Copper, Brass or nickel alloy like monel
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What is the most common makeup of a strain gauge?
Metallic foil like constantan or nickel-chromium
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Why is the strain gauge usually made from metallic foil like constantan or nickel-chromium?
Excellent electrical properties
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What changes within strain gauge when undergoing strain or deformation?
Resistance
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What is used to maximise sensitivity to strain of strain gauges?
Wheatstone bridge
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What happens to the resistance of a strain gauge arm when stretched?
Resistance increases when stretched
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What level is the output voltage when no strain is being experienced?
Minimum
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What is required to be carried out with the output voltage of the strain gauge?
Amplification and filtering
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When oil pressure increases, what happens to the contacts within low oil pressure switch?
Contacts open
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What always accompanies low pressure warning?
Acoustic warning
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What part of the system is oil temperature measured?
Oil pressure pump inlet
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What other information can be deduced from oil temperature?
Correct operation of engine oil cooler
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How many times a minute does the oil circulate?
3 to 4
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What are the 2 most common types of oil temperature sensor?
Resistance temperature detector or thermocouple
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What is involved with signal conditioning for the oil temperature indication?
Filtering, amplification and calibration
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Where is the low fuel pressure sensor located?
Outlet of low pressure filter
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What is fitted across the fuel filter to show impending filter blockage and cavitation?
Differential pressure sensors
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What is used on light piston aircraft for fuel pressure indication?
Bourdon tube
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If an aircraft is fitted with an aux fuel pump, what is displayed on startup?
Auxiliary pressure and then EDP pressure when startup complete
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What is used to compare fuel inlet pressure to air inlet pressure at fuel metering device?
Bellows type pressure gauge
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What types of sensors are used on modern aircraft fuel pressure indications?
Solid state and digital output signals
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Where is the low fuel pressure indication found?
Annunciator adjacent to on/off switch on fuel panel
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What is used in the main fuel tank for fuel temperature measuring?
Resistance type electric fuel temp sender
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What also be equipped to the fuel system for low oil temperatures?
Fuel heaters
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Why are computer corrections required to fuel temperature?
Due to viscosity changes affecting fuel flow indication
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What are the 2 indications provided by fuel flow systems?
Fuel flow and fuel used
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What is additional function of the fuel flow indication?
Redundant calculation of actual fuel quantity by subtracting fuel used from fuel in tanks at takeoff.
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When is fuel used indication reset?
Master switch set to on and A/C on GND.
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What point of the system does the fuel flow transmitter measure fuel flow?
Between FCU and nozzles
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What are the common types of fuel flow transmitter?
Synchronous mass flow and motorless mass flow type
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How does a synchronous mass flow transmitter work?
Fuel mass turns a turbine against a spring and deflection angle is measured
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What is measured within a motorless mass flow transmitter?
Angle between drum and impeller magnets due to impeller lagging behind
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What is the manifold pressure in piston aircraft engines?
Pressure inside induction system
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What type of gauge is used to measure manifold absolute pressure?
Direct reading type gauge
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When throttle increases, what happens to MAP?
Increase
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What is the MAP when engine is not running?
Ambient
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When engine is at idle, what is the MAP?
Lower than ambient
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How is engine failure indicated on the MAP?
Increases to a value of the ambient pressure when the failure occured
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What is the atmospheric pressure at 10,000ft in relation to sea level?
1/3 of sea level pressure
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What is used to increase pressure and mixture denstity at altitude?
Supercharging/Boosting
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Where is the engine driven centrifugal air pump fitted?
Between carburetor and cylinders
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What device is NOT used to carry out electrical/electronic manifold pressure reading?
Direct type reading gauge
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What device is NOT used to carry out electrical/electronic manifold pressure reading?
Bellows type
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What does an electrical torque meter consist of?
Torque meter assembly, phase detector and indicator
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How many shafts make up a torque meter?
Inner (drive shaft twists proportional to torque) and Outer (Connected to engine output only)
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How is torque detected by the pickups of the electrical torque meter?
Phase difference
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What is used to give a signal to drive the indicator within an electrical torque meter?
Phase comparator
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How does a hydraulic torque meter work?
Oil pressure moves a gear against a piston that allows oil pressure flow and the pressure is proportional to torque applied
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What units are used to indicate engine torque?
Lb/ft or % horsepower
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Why must hydraulic torque meters be calibrated at intervals?
Used to set power settings
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What is the efficiency of a propeller driven aircraft reliant on?
Thrust provided by the prop at specific RPMs
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What is used to monitor propeller speed?
Tachometer
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In a fixed pitch propeller, what is used to indicate engine power?
Tachometer
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What is the green arc on a tachometer indicator for?
Maximum continuous RPM
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Where are mechanical tachometers usually found?
Small, single engine light aircraft
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What is used to move the indicator of a tachometer?
Flyweights
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What is used to limit the rotation of the drag cup in a hydraulic tachometer?
Calibrated restraining spring
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How does the magnetic drag cup tachometer work?
Eddy currents from rotating magnet on the end of flexible drive shaft interacts with magnet of cup which causes it to rotate
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What is the speed of the shaft proportional to within electric tachometers?
EMF induced in the coil
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What are the 2 parts of the tachometer generator?
Tachometer generator attached to crankshaft and indicator near pilot
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What is the output frequency of the tachometer generator proportional to?
Speed of the engine
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How is the indication of an electric tachometer generated?
Synchronous motor that mirrors the generator
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What are the 2 types of tachometer?
AC and DC
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What does the EMF generated of the DC tachometer generator dependent on?
Flux link and speed of shaft
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What does the polarity of the induced voltage relate to?
Direction of shaft motion
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How is heavy current of the armature controlled?
Resistance connected in series with voltmeter
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What is the main advantage of AC tachometer generators when compared to DC?
Reduces problems with commutator and bushes
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What is used in the place of a commutator in an AC tachometer generator?
Stationary armature and rotating magnetic field
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What is used to measure the angular velocity of the shaft?
Frequency or amplitude
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How are ripples of rectified voltages smoothened?
Induced voltages are rectified and passed to capacitor filter
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Other cards in this set
Card 2
Front
Where are the highest temperatures recorded in the engine?
Back
*** - Turbine Inlet Temperature
Card 3
Front
What can the *** temperature exceed?
Back
Card 4
Front
Where is EGT measured?
Back
Card 5
Front
What is the maximum expected EGT?
Back
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