Engine indicating systems Flashcards
What does N1 and N2 indicate in a gas turbine engine?
N1 indicates the speed of the low-pressure rotor, and N2 indicates the speed of the high-pressure rotor.
What are the three main parts of a rotor speed indication system?
The sensor, the data transmission, and the indication.
How is rotor speed expressed in gas turbine engines?
Rotor speed is expressed as a percentage of the 100% design speed.
How does a variable reluctance sensor generate a signal?
Changes in the magnetic flux cause variations in induced voltage, which is then amplified and conditioned to provide a usable output signal.
What is the role of a variable reluctance sensor in speed indication?
It detects changes in magnetic flux between a magnet and a ferromagnetic target to measure rotor speed.
Where is the variable reluctance sensor typically positioned?
It is positioned on the compressor casing in line with either a phonic wheel or the actual fan blades.
What does a tachometer generator do in older aircraft systems?
`It generates a 3-phase AC voltage proportional to the N2 rotor speed, which is directly used to drive rotor speed indicators.
How is the tachometer generator used in modern aircraft systems?
It sends 3-phase AC voltage to the FADEC computer for calculating speed and also supplies electrical power to the computer.
What additional function can a tachometer generator or speed probe serve during engine start?
It can provide a signal to illuminate a warning lamp indicating that the engine is turning and whether it’s turning in the correct direction.
What are the three types of rotor speed indication displays?
A display with a clock-type scale, a moving vertical bar, and the classical electromechanical indicator.
What happens when the N1 speed exceeds the redline limit?
The display indications turn red, warnings are issued, and the overspeed event is recorded for maintenance inspection.
What is the significance of the redline limit on rotor speed indications?
It represents the maximum permitted rotor speed to prevent engine damage.
How do modern engines handle N1 overspeed events?
The speed and duration of the overspeed are recorded, and a report is generated for maintenance to assess necessary inspections.
What principle does the variable reluctance sensor operate on?
It operates on the principle of magnetic reluctance, which is the opposition of a magnetic circuit to the flow of magnetic flux.
What is the role of the air gap in a variable reluctance sensor?
The air gap changes due to the target’s motion, affecting magnetic reluctance and thus inducing voltage changes in the sensor coil.
What is the primary purpose of the Exhaust Gas Temperature (EGT) indication in a gas turbine engine?
To monitor high temperatures in the turbine engine to prevent thermal damage and indicate when a limit is exceeded.
Why is it impractical to measure Turbine Inlet Temperature (TIT) directly in most engines?
Because the TIT can be higher than 1400 °C (2550 °F), making it difficult to measure directly.
Where is the highest temperature in a gas turbine engine measured, and what is it called?
The highest temperature is measured directly behind the combustion chamber, where the hot gas hits the high-pressure turbine. It is called the Turbine Inlet Temperature (TIT).
Where is the Exhaust Gas Temperature (EGT) typically measured in a gas turbine engine?
The EGT is measured at a colder location in the engine, either between the high- and low-pressure turbine or directly behind the low-pressure turbine.
What is the relationship between Exhaust Gas Temperature (EGT) and Turbine Inlet Temperature (TIT)?
The EGT has a direct relationship to the TIT, making it possible to use EGT as an indicator of the TIT.
Where are thermocouples typically placed in a gas turbine engine for temperature measurement?
Thermocouples are usually spaced at intervals around the perimeter of the engine exhaust duct near the turbine exit.
Why is temperature monitoring important in gas turbine engines?
Temperature monitoring is crucial for checking the mechanical integrity of the turbines and ensuring the engine operates within safe conditions.
What are the typical temperature ranges for Exhaust Gas Temperature (EGT) indications?
Maximum EGT indications can range between 600 °C and 900 °C (1100 °F and 1650 °F).
What are some of the different relative temperatures used to monitor gas turbine engines?
Exhaust Gas Temperature (EGT), Turbine Inlet Temperature (TIT), Turbine Gas Temperature (TGT), Interstage Turbine Temperature (ITT), and Turbine Outlet Temperature (TOT).
How does an Exhaust Gas Temperature (EGT) indicator function in the flight deck?
The EGT indicator shows the average temperature measured by individual thermocouples, with the tiny thermocouple voltages being amplified to drive the indicator pointer.
What does a Turbine Inlet Temperature (TIT) indicating system provide?
It provides a visual indication at the instrument panel of the temperature of gases entering the turbine, using multiple thermocouples to represent the average TIT.
Describe the range and features of a typical analogue EGT indicator.
The analogue EGT indicator ranges from 0 °C to 1200 °C (0 °F to 2190 °F) and includes a vernier dial, a power off warning flag, and is a hermetically sealed unit.
What components are included in the analogue Turbine Inlet Temperature (TIT) indicating system?
It includes a bridge circuit, chopper circuit, two-phase motor, feedback potentiometer, voltage reference circuit, amplifier, power off flag, and over-temperature warning light.
What is the function of dual thermocouples in a Turbine Inlet Temperature (TIT) system?
Dual thermocouples provide signals to both the flight deck indicator and engine monitoring/control systems, ensuring dual-system reliability.
How does the digital flight deck instrumentation system differ from analogue systems in temperature monitoring?
Digital systems use sensor resistance and voltage values input to a computer, which processes and displays the information, and sends it to other systems for control and monitoring.
What are the three main groups of engine indications?
Performance indications (primary), system indications (secondary), and engine trend monitoring.
What is the purpose of performance indications?
To monitor engine performance, set thrust for different flight phases, and monitor engine limits.
What are system indications used for?
To monitor the operation of engine systems like oil and fuel systems and to quickly detect malfunctions.
What does engine trend monitoring aim to do?
Detect engine problems early by analyzing engine parameters recorded by the Aircraft Condition Monitoring System (ACMS).
What types of displays are used for engine indications?
A combination of analogue gauge-type displays, digital readouts, and moving vertical bars.
Where are performance indications typically located, and what do they measure?
Located at the top, they measure equivalent engine power using N1 or Engine Pressure Ratio (EPR).
What parameters are monitored in the engine’s oil system through secondary indications?
Oil quantity, oil pressure, and oil temperature.
What sensors are used for engine performance indications, and how is data transmitted?
Specific sensors or probes measure data, which is electrically transmitted to indicators, often via the FADEC system.
What is the purpose of the nacelle temperature indication?
To monitor the temperature in the engine nacelle, which can increase due to hot air leakage.
What additional indications are provided on the ECAM/EICAS system?
Warnings and cautions when limits are exceeded, such as low oil pressure or a clogged filter.
How is engine trend monitoring data typically recorded and transmitted?
Recorded during flight by ACMS, printed out in the flight deck, and transmitted via ACARS to the ground for analysis.
What are the three types of analysis used in engine trend monitoring?
Thermodynamic analysis, mechanic-dynamic analysis, and oil consumption analysis.
What does the thermodynamic analysis in engine trend monitoring check?
Pressures, temperatures, and feedback from components like Variable Stator Vanes (VSV) and fuel flow.
What triggers an alert in the oil consumption analysis?
When the oil consumption exceeds a certain level.
What does the mechanic-dynamic analysis in engine trend monitoring primarily check?
Rotor system failures such as imbalances and bearing failures by monitoring vibration and rotor speed.
What is Engine Pressure Ratio (EPR), and what does it measure?
EPR is a differential pressure gauge measuring the ratio of turbine discharge pressure to engine inlet pressure, indicating engine thrust.
What additional features are shown on an EPR display?
An AMBER or RED line for maximum thrust, and a BLUE circle for the actual throttle position.
How is EPR data generated and displayed?
Pressure measurements from engine inlet and turbine exhaust are sent to a differential pressure transducer, with the ratio displayed on the flight deck.
What adjustments are made to EPR to ensure accurate thrust monitoring?
Adjustments for temperature, altitude, and other factors are made to reflect accurate thrust.
What is the “Flexible Take-Off” (FLEX) setting, and when is it used?
FLEX is a reduced thrust setting based on an assumed temperature to preserve engine life, used unless conditions require full thrust (TOGA).
