15.14 Engine Indication Systems Flashcards
What is the purpose of exhaust gas temperature (EGT) indication in gas turbine engines?
To monitor high temperatures to prevent thermal damage and indicate when a limit is exceeded.
Where is the highest temperature, known as Turbine Inlet Temperature (TIT), located in a gas turbine engine?
Directly behind the combustion chamber where hot gas hits the high-pressure turbine.
What is the typical range for EGT indications in gas turbine engines?
Between 600 °C and 900 °C (1100 °F and 1650 °F).
What are the relative temperatures used to monitor exhaust gases entering the first stage turbine inlet guide vanes?
- Exhaust Gas Temperature (EGT)
- Turbine Inlet Temperature (TIT)
- Turbine Gas Temperature (TGT)
- Interstage Turbine Temperature (ITT)
- Turbine Outlet Temperature (TOT)
Why is it impractical to measure turbine inlet temperature (TIT) in most engines?
It is especially challenging in large engines.
Where are temperature thermocouples typically inserted in gas turbine engines?
At the turbine discharge.
How does the EGT indicator in the flight deck show temperature?
It shows the average temperature measured by individual thermocouples.
What is the scale range of a typical EGT indicator?
From 0 °C to 1200 °C (0 °F to 2190 °F).
What components are included in a turbine inlet temperature (TIT) indicating system?
- Bridge circuit
- Chopper circuit
- Two-phase motor
- Feedback potentiometer
- Voltage reference circuit
- Amplifier
- Power off flag
- Over temperature warning light
What feature does a dual thermocouple system provide?
Dual-system reliability with electrically independent junctions.
True or False: Digital flight deck instrumentation systems use resistance-type indicators.
False.
Fill in the blank: The temperature of the gases entering the first stage turbine inlet guide vanes is the most critical of all the engine _______.
variables.
How are thermocouple voltages typically processed in digital flight deck systems?
They are input to a computer for adjustment, processing, monitoring, and output.
What does the over temperature warning light indicate?
That the TIT has reached a predetermined limit.
What is the role of the feedback potentiometer in the TIT indicating system?
To provide a humming signal to stop the drive motor when the correct pointer position has been reached.
What is the function of the external test switch in the TIT indicating system?
To test over temperature warning lights for all engines simultaneously.
What is the significance of the relationship between EGT and TIT?
EGT provides a relative indication of the TIT.
What is the purpose of amplifying thermocouple voltages in EGT measurement?
To energize a servomotor that drives the indicator pointer.
What are the three groups of engine indications?
- Performance indications
- System indications
- Engine trend monitoring
Performance indications monitor engine performance and limits; system indications monitor engine system operations; trend monitoring detects engine problems early.
What is EPR and how is it generated?
EPR stands for Engine Pressure Ratio, generated by comparing engine turbine discharge pressure to ram air pressure at the inlet.
EPR is an important measure of thrust developed by the engine.
What are primary indications in engine monitoring?
Primary indications monitor the performance and limits of the engine and set thrust for different flight phases.
Primary indications are crucial for safe engine operation.
What do secondary indications monitor?
Secondary indications monitor the operation of engine systems such as oil and fuel systems and detect malfunctions.
They help ensure the engine is functioning correctly.
What is the function of the Exhaust Gas Temperature (EGT) indication?
EGT indication measures the temperature of the exhaust gases from the engine, reflecting engine performance.
Monitoring EGT is critical for understanding engine health.
What is the role of the Aircraft Condition Monitoring System (ACMS)?
ACMS records engine parameters automatically to monitor engine trends and detect problems early.
It aids in proactive maintenance and safety.
What does the Engine Indication and Crew Alerting System (EICAS) display?
EICAS displays engine performance and system indications, and shows warnings and cautions.
EICAS is crucial for pilot awareness of engine status.
What are the main analyses conducted in engine trend monitoring?
- Thermodynamic analysis
- Mechanic-dynamic analysis
- Oil consumption analysis
These analyses help identify trends that may indicate engine issues.
How does the thermodynamic analysis function?
It checks pressures and temperatures along the gas flow path and monitors feedback signals from components like VSV and VBV.
This analysis is vital for assessing engine component condition.
What does the mechanic-dynamic analysis check for?
It checks for failures in the rotor system, such as imbalances and bearing failures.
Engine vibration and rotor speed signals are analyzed.
What triggers an alert in the oil consumption analysis?
An alert is triggered when oil consumption exceeds a certain level.
Monitoring oil consumption is essential for engine longevity.
What is the significance of the EPR indicator?
The EPR indicator measures the thrust being developed by comparing turbine discharge pressure and ram air pressure.
It is a critical tool for monitoring engine performance.
How is EPR displayed on the flight deck?
EPR is shown in analogue and/or digital format, with indicators for maximum thrust and actual throttle position.
This allows pilots to easily assess engine thrust.
What is Flexible Take-off (FLEX)?
FLEX is a standard take-off thrust setting used to reduce engine wear, unless performance constraints exist.
It helps prolong engine life by using assumed temperature thrust reduction.
What is the alternate method of limiting engine thrust production known as?
N1, which is based on compressor/fan speed.
N1 provides an alternative indication of engine thrust.
Fill in the blank: The indication located at the top of the engine display is used to monitor and set the engine _______.
[thrust]
True or False: Engine trend monitoring is primarily done in the flight deck during flight.
False
Engine trend monitoring is typically done on the ground.
What is the purpose of monitoring the oil supply system in an engine?
To guard against engine failure resulting from inadequate lubrication and cooling of the various engine components.
What does the oil pressure indicator typically show?
The engine oil pump discharge pressure.
What does a differential oil pressure system measure?
Pressure downstream of the oil pump outlet and at the inlet of the oil scavenge pump.
How does high chamber air pressure affect oil flow?
It reduces the oil flow through the jets.
How does very low chamber air pressure affect oil flow?
It increases the oil flow through the jets.
What are the two main types of oil pressure transmitters?
- Bourdon Tube type
- Strain Gauge type
Describe the Bourdon tube type oil pressure transmitter.
A tube that changes shape under pressure, causing a movement that deflects an indicator needle.
What materials can Bourdon tubes be made from?
- Copper
- Brass
- Aluminium
- Nickel alloy (e.g., Monel)
What is the principle behind a strain gauge?
It measures mechanical strain or deformation by detecting changes in electrical resistance.
What is the most common material used for strain gauges?
Metallic foil, like constantan or nickel-chromium.
What configuration is commonly used for strain gauges?
Wheatstone bridge configuration.
What happens to the Wheatstone bridge output voltage when strain is applied?
It becomes unbalanced, leading to a voltage difference proportional to the strain.
What is the role of the low oil pressure switch in an engine?
To initiate a low oil pressure warning if the oil pressure decreases below a certain limit.
What happens when the low oil pressure switch closes?
A signal is sent to the flight warning computer, displaying a warning message.
What is indicated by the oil inlet temperature indicator?
The temperature of the oil as it enters the oil pressure pump.
What is the primary component responsible for measuring engine oil temperature?
The oil temperature sensor.
What are the most common types of oil temperature sensors used in aircraft engines?
- Resistance Temperature Detector (RTD)
- Thermocouple
What does the output signal from the oil temperature sensor often require?
Amplification and processing for accurate measurement.
What is the function of signal conditioning in oil temperature measurement?
To filter, amplify, and calibrate the signal for accurate representation of oil temperature.
What happens if the oil temperature exceeds safe operating limits?
An over-temperature warning is triggered, which can be visual and audible.
What systems are required for monitoring engine fuel pressure, temperature, and flow?
Measurement and instrumentation systems.
Where is the low-pressure sensor typically positioned in an engine?
After the outlet from the low-pressure filter.
What can cause low fuel pressure in an engine?
Cavitation caused by high fuel pump demand.
What type of sensor is fitted across the fuel filter?
Differential pressure sensor.
What do the sensors provide warnings about?
Impending filter blockage and risk of cavitation.
How is low fuel pressure displayed to the flight crew?
As a warning lamp or EICAS status message.
What visual indication is critical for the fuel system?
That the fuel system is delivering fuel to the fuel metering device.
What type of pressure gauge is typically used in light reciprocating engine aircraft?
Direct reading Bourdon tube pressure gauge.
What does the differential fuel pressure gauge compare?
Fuel inlet pressure to air inlet pressure at the fuel metering device.
What types of sensors may modern aircraft use for fuel pressure?
Solid-state types with digital output signals.
What type of devices are used for warning signals related to fuel pressure?
Visual and audible warning devices.
Where are low fuel pressure warning switches typically located?
At the outlet of each fuel boost pump.
What is critical to monitor regarding fuel temperature?
To inform the flight crew when ice may form in the fuel system.
What type of sender is often used to monitor fuel temperature in large turbine aircraft?
Resistance type electric fuel temperature sender.
How can low fuel temperature be corrected in aircraft?
With the use of a fuel heater.
What does the fuel flow indicating system provide to the flight crew?
Actual fuel flow to the engines and fuel used since engine start.
How is the fuel used indicated?
In kg, lbs, or tons.
What does the fuel flow indication allow the flight crew to monitor?
Performance and economic operation of the engines.
How is actual fuel quantity calculated?
By subtracting used fuel from the amount of fuel in the tanks at take-off.
What resets the fuel-used indication to 0?
When the engine master switch is switched to ON and the aircraft is on the ground.
What must be present to generate fuel flow and fuel used indications?
A fuel flow transmitter on each engine.
What fundamental law of physics do fuel flow transmitters operate on?
Force = Mass x Acceleration.
What type of flow meters are common today?
Synchronous mass flow and motorless mass flow.
How does the synchronous mass flow transmitter measure fuel flow?
By measuring the turbine angle turned by the fuel mass.
What does the motorless mass flow transmitter utilize to generate acceleration?
The fuel itself.
What is the function of the fixed straightener in the motorless mass flow transmitter?
To stop all possible fuel spin.
What indicates the angle of the mass fuel flow in the motorless mass flow transmitter?
The angle between the rotating drum and the rotating impeller.
How does the FADEC system computer calculate mass fuel flow?
By calculating the time between two voltage pulses.
What does N1 indicate in turbine engines?
N1 indicates the low-pressure rotor speed.
What does N2 indicate in turbine engines?
N2 indicates the high-pressure rotor speed.
What is the expression of engine rotor speed indications?
Engine rotor speed indications are expressed as a percentage of a 100% design speed.
What are the three main parts of rotor speed indications?
- The sensor
- The data transmission
- The indication
Name the two types of sensors used to measure rotor speed.
- Variable reluctance type sensor
- Tachometer generator type
What principle does a variable reluctance sensor operate on?
A variable reluctance sensor operates on the principle of magnetic reluctance.
Where is the speed probe of a variable reluctance sensor typically positioned?
On the compressor casing in line with either a phonic wheel or the actual fan blades.
What happens to the magnetic flux in a variable reluctance sensor as the spool rotates?
The magnetic flux in the probe is altered, changing the current in the coil.
What is crucial for the operation of a variable reluctance sensor?
The air gap between the permanent magnet and the ferromagnetic target.
What does the induced voltage in a variable reluctance sensor relate to?
The induced voltage is directly proportional to the rate of change of the magnetic flux.
What does a tachometer generator generate?
A tachometer generator generates a 3-phase AC voltage proportional to the N2 rotor speed.
What is the role of the eddy current clutch in older generation aircraft rotor speed indicators?
It transfers the speed into a proportional torque to move the gauge pointer.
How does the FADEC computer utilize the signal from the tachometer generator?
It calculates the speed signal and provides electrical power.
What additional function can the tachometer generator provide during engine start?
It can illuminate a warning lamp to indicate engine rotation direction.
What are the three types of rotor speed indication displays?
- A display with a clock-type scale
- A display with a moving vertical bar
- The classical electromechanical indicator
What indicates the maximum permitted rotor speed on speed displays?
A red line limit indicates the maximum permitted rotor speed.
What happens if the actual N1 exceeds the redline limit?
It can cause severe damage to the engine and requires an unscheduled inspection.
What is recorded if the engine speed exceeds the N1 redline limit?
The N1 speed and duration of the overspeed is recorded.
Fill in the blank: The speed indications on modern engines change to _______ when N1 exceeds the redline limit.
red
What is the significance of engine vibration indication?
It allows the flight crew and maintenance to identify a rotor imbalance, which can be the first sign of engine damage
What are the main components of the engine vibration monitoring system?
- Indication in the flight deck showing vibration level
- One or two vibration sensors delivering electrical signals
- A computer for collecting and filtering vibration data
What does EVMU stand for?
Engine Vibration Monitoring Unit
Where are vibration sensors typically located on an engine?
- Near the N1 rotor shaft in the compressor area
- On the turbine frame in the turbine area
What types of accelerometers are used in engine vibration measurement?
- Electromagnetic accelerometer
- Piezoelectric-crystal type sensor
How does an electromagnetic accelerometer work?
A magnet held by springs induces an AC voltage when the coil moves due to vibration
What is the principle of a piezoelectric crystal sensor?
It generates a voltage when a force is applied to the crystal by an inertia mass
What does the monitoring unit do with the signals from the accelerometers?
Filters and analyses the signals for indication and trend monitoring
How is vibration indication displayed on modern aircraft?
Automatically controlled by the engine vibration monitoring unit and shown in digital format
What happens when the N1 or N2 speed signal fails?
The rotor identification shows BroadBand (BB) vibration
What does the vibration display show if the vibration level is equal to or more than 4.0 scalar units?
It automatically shows on the secondary engine display in reverse video format
What does the engine monitoring system do in case of vibration limits exceedance?
Records the exceedance and reviews it for necessary engine inspection
What is the purpose of a computerized Engine Balancing System?
To change or decrease engine vibration
What does the Engine Balancing System calculate?
Balance weights that need to be removed or replaced to decrease engine vibration
Fill in the blank: The vibration sensors send a signal to the monitoring unit with a voltage that is proportional to the level of acceleration and a frequency that is equivalent to the _______.
vibration frequency
True or False: The vibration display shows the lowest vibration signal for indication.
False
What happens to the vibration data when an engine is shut down?
The secondary engine display will show 0.0 and the performance maintenance page will show 0.00
What is the purpose of a torque meter in a turboshaft engine?
To measure the torque being delivered to the rotor or propeller
Torque meters are essential for estimating power production in turboshaft engines.
What are the two types of torque meters mentioned?
Electrical and hydraulic
These systems are used to measure torque in turboshaft installations.
What components make up a typical electrical torque meter system?
Torque meter assembly, phase detector, and indicator
These components work together to measure and display torque.
What does the inner shaft of a phase comparison torque meter connect to?
The drive from the engine to the gearbox
The inner shaft twists in proportion to the applied torque.
What is the function of the toothed gear wheels in a torque meter assembly?
To detect angular displacement and measure torque
They are situated on both the inner and outer shafts.
How is Electromotive Force (EMF) induced in the pick-up coil of a torque meter?
By the teeth of the exciter wheels cutting the magnetic lines of flux
This occurs as the gear turns.
What happens under no-load conditions in a torque meter?
No relative movement between the toothed wheels and no difference in output signals
This indicates that no torque is being applied.
What indicates the application of torque in a phase comparison torque meter?
Angular displacement of the output shaft relative to the datum shaft
This movement causes a phase difference in the output signal.
What does a hydraulic torque meter use to measure torque?
Engine oil pressure metered through a valve
The valve is controlled by a helical ring gear responding to applied torque.
What is the function of the piston in a hydraulic torque meter?
Controls the opening of a valve that regulates oil pressure flow
This ensures that oil pressure is proportional to the torque applied.
What unit is torque typically read in on the flight deck instrument?
lb/ft of torque or percent horsepower
This provides pilots with essential information for power settings.
Why is calibration of the torque meter important?
To ensure its accuracy
Regular calibration is necessary for reliable performance.
What is the purpose of the power assurance test?
To check that the engine can accelerate from idle to a given Engine Pressure Ratio (EPR) value within a specific time and de-accelerate back to idle within a specific time period.
What must be done before carrying out the power assurance test?
Position the aircraft in the engine run-up enclosure or a dedicated area, ensuring it points into the wind and wheel chocks are placed in front of and behind the wheels.
How long should the engine operate at idle before starting the power assurance test?
5 minutes.
What is the maximum EPR for the day used in ground tests?
The lowest EPR value of the two values for all pressure altitude and Total Air Temperature (TAT) conditions.
If the EPR of the day is lower than 1.4, what value should be used for the engine test?
Use the EPR of the day.
What value should be used for the engine test if the EPR of the day is above 1.4?
Use 1.4 EPR.
What should be turned off to ensure the engine can accelerate correctly?
Engine anti-ice and engine-bleed air switches.
How long should it take to slowly increase the engine speed to the maximum EPR?
30 seconds.
What is the maximum duration to operate the engine at the maximum EPR for stability?
30 seconds.
How long should it take to slowly decrease the engine speed back to idle speed?
30 seconds.
For how long should the engine operate at idle after the test to decrease temperature?
10 minutes.
What is the time requirement for the engine to accelerate to the required speed?
Within seven seconds or less.
What is the time requirement for the engine to decelerate to idle speed (N1)?
In eight seconds or less.
Fill in the blank: The aircraft must be pointing into the ______ during the power assurance test.
wind.
True or False: The power assurance test is applicable to all engine types and models.
False.
