M15.13 Start and Ignition Flashcards
What is essential for starting a gas turbine engine?
Two separate systems:
* Compressor and turbine rotation
* Ignition of the air/fuel mixture
These systems must operate simultaneously during the starting cycle.
What must occur before the ignition is turned on during engine starting?
The starter must accelerate the compressor sufficiently to establish airflow through the engine
This airflow is necessary to support combustion.
What is the consequence of cutting off starter assistance below self-accelerating speed?
The engine may fail to accelerate to idle speed or decelerate
This could lead to a hot or hung false start.
What is a cartridge starter?
A starter that uses high velocity gases from a burning cartridge to rotate the engine
It is an independent method of starting gas turbine engines.
What initiates the burning of the cartridge in a cartridge starter?
An electrically fired detonator
This ignites the cartridge charge to generate gas for starting.
What is the typical air supply pressure required for air starters?
Around 30–50 pounds per square inch (psi)
This pressure is necessary for a complete start.
What controls the air supply to the starter in an air turbine starter?
An electrically operated control and pressure reducing valve
The valve opens when an engine start is selected.
What happens when the starter reaches cutout speed?
The turbine switch opens, interrupting the electrical signal to the start valve
This closes the valve and shuts off the air supply to the starter.
What are the typical maintenance tasks for air turbine starters?
Checking the oil level, inspecting the magnetic chip detector, and checking for leaks
Oil can be added through a port in the starter.
What is the function of the pressure regulating and shutoff valve in the starter system?
To regulate air pressure and control the starter operation
It consists of a valve housing containing a butterfly-type valve.
What are the two types of electric starting systems used on gas turbine engine aircraft?
- Direct cranking electrical systems
- Starter-generator systems
Each type has different operational characteristics.
What is a starter-generator system?
A system that functions as both a starter and generator after the engine reaches self-sustaining speed
It contains additional windings for generator function.
What is the typical voltage and current required for starting with a starter-generator?
A source of 24 volts and 1500 peak amperes
This is necessary for effective starting.
What is the role of the undercurrent controller in a starter-generator?
To assure positive action of the starter and keep it operating until sufficient engine speed is achieved
It contains relays for controlling the starter input.
Fill in the blank: The starter must continue to assist the engine until it reaches _______.
self-sustaining speed
This ensures the engine can sustain its own rotation.
True or False: The air starter valve has a manual valve override for emergencies.
True
This allows for engine start even if the valve fails to open automatically.
What is the function of the undercurrent controller in a starter-generator?
To assure positive action of the starter and keep it operating until the engine is rotating at a speed sufficient to sustain combustion.
What components are controlled by the control block of the undercurrent controller?
- Motor relay
- Undercurrent relay
What is the first step to start an engine equipped with an undercurrent relay?
Close the engine master switch.
What relays close when the battery and start switch are turned on?
- Motor relay
- Ignition relay
- Battery cut-out relay
Why is it necessary to open the battery circuit during starter operation?
To prevent the heavy drain of the starter motor from damaging the battery.
What happens when the current draw of the motor decreases to less than 200 amps?
The undercurrent relay opens, breaking the circuit to the motor, ignition, and battery cut-out relays.
What is a probable cause if the engine does not rotate during start attempt?
Low supply voltage to the starter.
What should be checked if the power switch is suspected to be defective?
Check the switch for continuity.
What is the function of the ignition system in turbine engines?
To ignite the fuel in the combustion chamber.
When is continuous ignition used in turbine engines?
During take-off, landing, and abnormal situations like flying through hailstorms.
What type of ignition system do most turbine engines use?
High-energy, capacitor-type ignition system.
What is the primary function of the exciter box in the ignition system?
To supply high voltage to the igniter plugs.
What is the purpose of the storage capacitor in the ignition system?
To store energy for ignition discharge.
What is the maximum voltage the storage capacitor can charge to?
Approximately 4 joules.
What distinguishes the igniter plug of a turbine engine from a conventional spark plug?
It must withstand a much higher energy current and has a larger electrode gap.
What is the typical design of an igniter plug in a turbine engine?
Annular gap igniter plug or constrained gap plug.
What should be done if there is no igniter spark when the system is turned ON?
Check the ignition relay and transformer unit.
What is the recommended action after shutting down the ignition system before removing components?
Wait at least 20 minutes to allow residual charge to dissipate.
What is a safety precaution when performing maintenance on the starting system?
Ensure relevant circuit breaker switches are open/off and tagged.
What should be used when handling components of a turbine ignition system?
Insulated tools.
What is the role of the transformer in the ignition system?
To step up the voltage for igniter spark generation.
What indicates that the igniter is functioning correctly during a test?
Listening for a clicking noise as the engine begins to turn.
What should be followed when working on engine ignition systems?
All manufacturer’s instructions
This is crucial for safety and to prevent accidents.
What can be present in the ignition exciter that poses a risk?
Residual high voltage and current
These can lead to injury or death if released.
What is the most likely way for an accidental discharge to occur?
By touching the igniter
This emphasizes the need for caution during maintenance.
What is the standard procedure for igniter maintenance?
Disconnect the igniter lead coupling nuts at the exciter end first
This helps ensure safety during maintenance.
What type of tools must be used when working on ignition systems?
Insulated tools
This reduces the risk of electric shock.
What should not be touched with bare hands in ignition maintenance?
Coupling nuts or connectors
This is to prevent accidental discharges.
What is the voltage level in the engine ignition system?
Very high voltages
This is a significant safety concern.
What could happen if ignition units are touched without precautions?
Serious injury or death
This underscores the importance of safety measures.
What should be ensured before touching ignition units?
No electricity left in the ignition units
This is crucial for safety.
How long should one wait after opening circuit breakers before touching ignition units?
At least three minutes
This allows any residual charge to dissipate.
