85 Questions
What is the main reason for performing continuous operation with low joule HEIUs?
To increase igniter plug life
In which scenario would the persistent operation of high joule units be recommended?
To minimize maintenance costs
What is the primary drawback of using high joule units for continuous operation?
Decreased igniter plug life
Why is it common to use low joule HEIUs for continuous operation?
To extend the life of the igniter plug
Which of the following is a possible consequence of using high joule units for continuous operation?
Shortened lifespan of the igniter plug
What impact does persistent operation of high joule units have on igniter plug life?
It shortens the igniter plug life
What receives power from the DC bus through the fuel shut-off valve circuit breaker?
Fuel control relay
Which switch energises the ignition relay in the example discussed?
16% switch
Where is the ignition relay usually located?
In an equipment compartment in the engine nacelle
What controls fuel scheduling during engine start and deceleration?
94% switch
What supplies electrical power to the HEIU?
Ignition relay
What de-energises the ignition relay in the speed sensitive control system?
65% switch
What is the main function of an aircraft bus?
Supply electrical power to various components
How can circuit breakers protect aircraft electrical circuits?
By preventing short circuits or power surges
What advantage do circuit breakers have over fuses?
Circuit breakers give visual indication of circuit limits
What happens when the white collar becomes exposed in a circuit breaker?
The circuit is open or disconnected
What type of power supply do low tension current ignition systems receive?
DC voltage from the battery bus
How are high tension current ignition systems powered?
AC voltage from the aircraft AC bus
What is the main difference between low tension and high tension current ignition systems?
The type of power supply they receive
In terms of duty cycles, what defines an intermittent duty cycle ignition system?
It has a time limit placed on its operation
What does the term 'duty cycle' refer to in relation to ignition systems?
The time limit on operation to prevent damage
Where does a high tension current ignition system draw its power from?
Aircraft AC bus
What is a key advantage of a continuous duty cycle ignition system for aircrew?
Continuous engine relight capability during critical flight maneuvers
What is the main difference between AC and DC igniter systems?
Operating voltages
Which component is typically found in a dual high energy ignition system for gas turbine engines?
Dual high energy ignition system
What is the purpose of the 'fuel control relay' in an ignition system?
To regulate fuel flow
In a typical ignition system, what component protects against circuit overloads?
Circuit breaker
What is the significance of 'ignition and relight switches' in an ignition system?
Initiate engine relight sequence
What is the purpose of the ignition and relight switches in an aircraft?
To connect bus voltage to the High Energy Ignition Unit (HEIU)
What is the role of the relight switch in the ignition system?
To restart engine combustion after an in-flight flame-out
Which component generates the high voltage necessary for engine ignition?
High Energy Ignition Unit (HEIU)
What happens when the relight switch is turned on in an aircraft?
28 volt DC is directly supplied to the HEIU
Why is it necessary to have both AC and DC voltage options for the HEIU?
To optimize ignition under different conditions
Which part of an aircraft's ignition system receives power directly from the HEIU?
Igniter Plug
How do intermittent duty cycle systems differ from continuous duty cycle systems?
In the duration of operation before switching off
What is the main concern addressed by implementing a duty cycle for ignition systems?
Avoiding damage to system components
How does high joule unit operation impact igniter plug life in an intermittent duty cycle system?
Decreases igniter plug lifespan
Which type of duty cycle system would be more suitable for an aircraft that requires frequent engine restarts?
Intermittent duty cycle system
In an aircraft, what defines the duration an ignition system can operate without causing harm to its components?
'Duty cycle'
What is the duty cycle of the ignition system mentioned in the text?
2 minutes on, 3 minutes off
At what RPM range does the ignition system operate continuously?
16% to 65%
What is the action of the 'above 65%' switch in the ignition system?
De-energises the ignition relay
What happens when the ignition system is de-energised by the 'above 65%' switch?
Manifold drain valve opens
What component connects the high tension ignition leads to the igniter plugs?
HEIU
Which speed-sensitive control system is activated above 65% RPM according to the text?
'Above 65%' switch
What is the primary reason for implementing intermittent duty cycle ignition systems in aircraft?
To manage current draw and prevent overheating during limited periods
How are intermittent duty cycle ignition systems managed by aircrew?
Manually by selecting ignition on when needed
In intermittent duty cycle systems, what happens after the restricted duty cycle based on operating time?
A cooling off period following the operating time
Which feature distinguishes intermittent duty cycle ignition systems from continuous duty cycle systems?
Limited operating time followed by a cooling off period
How do some aircraft enhance their intermittent duty cycle ignition systems for critical operations like take-off?
By using additional plugs at full capacity for short periods
What distinguishes DC and AC igniter systems in terms of components, according to the text?
Ignition leads
In a gas turbine engine, what is the purpose of the speed-sensitive control component in the ignition system?
Ignition and relight switches
Which component in the typical ignition system ensures proper fuel scheduling during engine start and deceleration?
Fuel control relay
What protects aircraft electrical circuits from overload in an ignition system?
Circuit breaker
Which component is responsible for generating the high voltage required for engine ignition?
High energy ignition unit
What is the primary function of the ignition leads in an aircraft's ignition system?
Connect high tension ignition leads to igniter plugs
Where does a low tension current ignition system receive its power from?
Battery bus
What determines whether an ignition system is classified as having an intermittent duty cycle or continuous duty cycle?
Operation time limit
In an aircraft's ignition system, where are the high-voltage, high-amperage discharges across igniter plugs dissipated?
Combustion chamber
What is the primary function of the High Energy Ignition Unit (HEIU) in the ignition system?
Generate high voltage for engine ignition
Which component varies in type and position within a combustion chamber in different engine designs?
Igniter plug
What is the source of power for high tension current ignition systems in aircraft?
AC bus
What is the duty cycle of the ignition system when operating above 65% RPM?
2 minutes on and 23 minutes off
Which component de-energises the HEIU, paralleling valve, and manifold drain valve in the ignition system?
Above 65% switch
How does the ignition system differ when operating below 65% RPM compared to above 65% RPM?
It has a different duty cycle
In the context of the text, what is the purpose of high tension ignition leads?
To connect the HEIU to the igniter plugs
What effect does de-energising the ignition relay have on the parallel valve and manifold drain valve?
They remain closed and inactive
Which switch is responsible for halting the operation of the ignition system above 65% RPM?
'Above 65%' switch
What is the purpose of the trembler mechanism in a DC HEIU?
To open and close the primary circuit rapidly
Which component in a DC HEIU extends the duration of spark by delaying the reservoir capacitor discharge?
Choke
What does the reservoir capacitor do in a DC HEIU?
Charges up and discharges high voltage
In a DC HEIU, what does the glass sealed discharge gap contain?
Two metallic contacts separated by an air gap
What is the role of the high voltage rectifier in a DC HEIU?
To convert AC to DC voltage
Which component in a DC HEIU converts AC voltage to DC voltage for charging the reservoir capacitor?
Transformer
What is the function of the High Energy Ignition Unit (HEIU) in an aircraft's ignition system?
Generates the high voltage required for engine ignition
Where does an igniter lead connect to in an aircraft's ignition system?
HEIU
What determines whether the HEIU is supplied with DC or AC voltage?
The type of HEIU fitted
In an aircraft's ignition system, what component connects the igniter plug to the High Energy Ignition Unit (HEIU)?
Igniter lead
What is the purpose of supplying 28 volt DC directly to the HEIU when the relight switch is closed?
To continue rotating the engine in case of flame-out
What occurs when the relight switch is selected to 'on' in an aircraft's ignition system?
28 volt DC is supplied directly to the HEIU
What differentiates low tension current systems from high tension current systems in terms of power source?
Low tension systems are DC voltage systems receiving power from the battery bus, while high tension systems are AC voltage systems receiving power from the aircraft AC bus
What role does the engine starting system play in relation to the High Energy Ignition Unit (HEIU)?
It provides a voltage supply to the HEIU
Which statement accurately describes how the HEIU interacts with igniter plugs during operation?
HEIU stores energy and dissipates it as a high-voltage discharge across igniter plugs at a predetermined value
In what way does the High Energy Ignition Unit (HEIU) contribute to engine design variation?
By influencing the positioning and type of igniter plugs within the combustion chamber
How do low joule High Energy Ignition Units (HEIUs) differ from high joule units in terms of operation?
Low joule units prevent damage by operating within restricted duty cycles, unlike high joule units
Study Notes
Ignition System Types
- Two common types of gas turbine ignition systems:
- Low tension (DC voltage)
- High tension (AC voltage)
Ignition System Duty Cycles
- Two types of duty cycles:
- Intermittent duty cycle: used for short periods, usually during ground starting
- Continuous duty cycle: provides continuous engine relight capability during critical flight maneuvers
Ignition System Components
- Typical components of an ignition system:
- DC or AC bus
- Ignition circuit breaker
- High Energy Ignition Unit (HEIU)
- Fuel control relay
- Ignition relay
- Speed sensitive control
- Ignition leads
- Igniter plugs
- Ignition and relight switches
High Energy Ignition Unit (HEIU)
- Generates high voltage required for engine ignition
- Can be supplied with either DC or AC voltage
- Components of a DC HEIU:
- Induction coil
- Trembler mechanism
- Reservoir capacitor
- Glass sealed discharge gap
- High voltage rectifier
- Choke
Igniter Plugs
- Types of igniter plugs vary between engine designs
- Positioned within a combustion chamber
Ignition Relight Switches
- Located in the aircraft cabin, near the throttles
- Connect bus voltage to the HEIUs
- Allow pilots to regain combustion in case of in-flight flame-out### Ignition System Overview
- Each system is connected to a High Energy Ignition Unit (HEIU), which receives a voltage supply controlled by the engine starting system.
- The HEIU stores electrical energy until it reaches a predetermined value, then dissipates it as a high-voltage, high-amperage discharge across an igniter plug or plugs.
Igniter Plug
- Igniter plug types and their position within a combustion chamber vary between engine designs.
Ignition System Types
- There are two common types of gas turbine ignition systems: low tension (DC voltage) and high tension (AC voltage).
Low Tension Current (DC) System
- Receives power from the battery bus.
High Tension Current (AC) System
- Receives power from the aircraft AC bus.
Ignition System Duty Cycles
- There are two types of ignition system duty cycles: intermittent and continuous.
- The term 'duty cycle' refers to the time limit placed on the operation of the ignition system to prevent damage to its components.
Test your knowledge on aircraft ignition systems with this quiz. Learn about the operation of high and low joule HEIUs and their impact on igniter plug life. This quiz is a helpful resource for those studying aviation technology or maintenance.
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