115 Questions
What is the fundamental characteristic of a starter motor?
Smooth acceleration from rest to engine self-sustaining speed
What is a typical engine self-sustaining speed defined as?
When the engine will continue to accelerate without assistance
What features are present in the engine start panel from a four-engine aircraft?
Fuel and ignition switches, start button, indicator lights
Which of the following is NOT a type of gas turbine starter motor mentioned in the text?
Mechanical
What is the main purpose of an engine start selector switch on the multi-engine start panel?
Choose which engine to start
What does a starter system indicator light on the multi-engine start panel indicate?
Status of the starter system
What happens when the engine accelerates up to self-sustaining speed in terms of the starter motor?
It begins to turn faster than the starter motor.
Why do the pawls slip out of the tapered slots of the engine drive gear under the influence of the disengage springs?
To prevent over-speeding the starter beyond its design limits.
Why are starter-generator units desirable in gas turbine engines?
They reduce the total weight of starting system components.
What is the purpose of the heavy series winding in a starter-generator unit?
To produce a strong field and high torque for starting.
How does a starter-generator unit function after the engine has reached self-sustaining speed?
It operates as a generator to supply electrical system power.
Why does an overrunning feature exist in the engine start system?
To prevent the engine from driving the starter beyond its design speed.
What are the two types of starters mentioned in the text for gas turbine engines?
Hydraulic and electric starters
Which type of starter involves the use of compressed air to start a gas turbine engine?
Pneumatic starters
What is the function of an electric starter in the context of gas turbine engines?
To provide electrical power to start the engine
Which type of starter can act as both a starter and a generator for a gas turbine engine?
Starter-generator
What is the main advantage of an air impingement starter system for gas turbine engines?
It offers quicker engine start times compared to other starters
In the context of gas turbine engines, what does the term 'start sequencing' refer to?
The sequence of events for starting the engine components in a specific order
What is the primary role of the actuator piston in the hydraulic starter system described in the text?
To open the butterfly valve
At what engine rotational speed does the starter speed sensing switch open to reset the pilot valve in the hydraulic starter system?
Between 57-64% RPM
What prevents damage from excessive air pressure in the hydraulic starter system?
Relief valve
What is the main function of the regulator piston in the hydraulic starter system?
To regulate starter air pressure
When does the actuator return spring close the butterfly in the hydraulic starter system?
After starter speed sensing switch opens
What happens when the engine accelerates beyond self-sustaining speed in relation to the starter motor?
The pawls slip out of the tapered slots disengaging the starter motor.
What is the primary purpose of the series winding in a starter-generator unit?
To produce a strong field and high torque for starting.
How does a starter-generator unit function differently as a generator compared to a starter?
It supplies electrical system power after reaching self-sustaining speed.
What type of engines are electric starters primarily used on?
Turbo-propeller engines
In which situation would an electric starter-generator be used?
To start an Auxiliary Power Unit
What distinguishes an electric starter from an electric starter-generator?
The presence of a generator function
Which engines are most likely to use an electric starter?
Engines with low starting torque requirements
What type of electric starter motor typically develops high starting torque?
Series-wound motor
How do electric starters differ from hydraulic starters in terms of power source?
Electric starters use battery power, hydraulic starters use engine-driven pumps
Which component is NOT typically part of an electric starting system for gas turbine engines?
Generator unit
How is the torque of the starter motor transmitted to the clutch in an electric starter system?
Via reduction gears
What disengages the starter drive from the engine drive in some electric starters when the engine reaches self-sustaining speed?
Release clutch mechanism
How does the starter jaw engage the engine cranking jaw in an electric starter system?
By moving vertically
What happens automatically once the engine of an aircraft reaches a specific speed in relation to the starter motor?
The starter disengages
In an electric starter system, what is responsible for moving the starter jaw to engage the engine cranking jaw?
Helically splined shaft
What prevents the engine from driving the starter beyond its design speed?
The slip of the pawls out of the tapered slots
Why is a starter-generator unit considered beneficial for gas turbine engines?
It reduces the total weight of starting system components
What is the function of the series winding in a starter-generator unit?
To provide a strong field and high torque for starting
In a starter-generator unit, what happens after the engine has reached self-sustaining speed?
It transitions to act solely as a generator
What role does the actuator piston play in a hydraulic starter system?
To reset the pilot valve after self-sustaining speed is reached
Why is an overrunning feature necessary in engine start systems?
To avoid driving the starter beyond its design speed
What prevents the engine from driving the starter beyond its design speed in a gas turbine engine equipped with a starter-generator system?
The overrunning feature
What happens when a gas turbine engine equipped with a starter-generator system reaches self-sustaining speed?
The unit operates as a generator to supply power
In what way does the series winding contribute to the starting process in a starter-generator unit for gas turbine engines?
By producing a strong field and high torque for starting
Why do pawls slip out of tapered slots in the engine drive gear when a gas turbine engine accelerates up to self-sustaining speed?
To disengage the starter from driving beyond its design speed
What is the purpose of turning the engine master switch to the on position in the starter-generator circuit?
To energize the motor relay and close the circuit to the starter-generator
What happens once the battery and start switches are turned to the on and start positions in the starter-generator circuit?
The B-4 relay opens the circuit to disconnect the battery from the main DC bus
In a starter-generator unit, what does energizing the throttle relay initiate?
Starting the fuel pumps
What role does the motor relay play in the starter-generator electrical circuit?
Closes the circuit to engage the starter-generator with the main bus
What is controlled by energizing the ignition relay in a starter-generator system?
Closing the circuit to engage the ignition unit
When does the B-4 relay open in a starter-generator unit's operation?
When disconnecting battery from main DC bus after startup
What is the primary purpose of the undercurrent controller in a starter-generator system?
To control the electrical input to the starter
What is the function of the motor relay in the undercurrent controller of a starter-generator system?
To control input to the starter
Why does the aircraft designer not allow for a self-contained start in a starter-generator system configuration?
To prevent reliance on external power sources
What is the role of the undercurrent relay in a starter-generator system?
To control the operation of the motor relay
Why is it preferable to use external electrical power instead of an aircraft battery for engine starts in some configurations?
To preserve the aircraft battery for emergencies
What is the main function of the starter-generator controller in a typical starter-generator system?
To manage electrical power generation and engine starting operations
What is the primary role of the regulator piston in the pneumatic starter system described?
To control the airflow through the starter control valve
Why is the relief valve incorporated in the pneumatic starter system?
To release excess air pressure
What initiates the resetting of the pilot valve in the pneumatic starter system?
Starter speed sensing switch
In the pneumatic starter system, what role does the solenoid spring play when the engine rotates at 57-64% RPM?
Resets the pilot valve and vents the actuator to atmosphere
Which component ensures that at a certain engine rotational speed, the actuator closes the butterfly in the pneumatic starter system?
Actuator return spring
What is the primary function of the butterfly valve in the pneumatic starter system?
To control airflow into the starter
What is the purpose of the start air solenoid in the pneumatic starter system?
To allow air from the inlet side of the valve to pass through the regulator to the actuator piston
In the pneumatic starter system, what role does the holding coil play once the start button is pressed?
Activating the holding coil keeps the switch down and activated
Why does the pilot release the start button after the holding coil activates in the pneumatic starter system?
To keep the switch down and activated
What component is electrically completed to the starter control valve solenoid in the pneumatic starter system?
Starter Control Valve Solenoid
After pressing the start button in the pneumatic starter system, what initiates the opening of the pilot valve?
The start air solenoid
What happens when an electrical signal is sent to the start air solenoid in the pneumatic starter system?
The holding coil activates
What is the purpose of the poppet valve set at 2 PSI in the pneumatic starter system?
To decrease air pressure to prevent gearbox seal damage
How does the multiple disc clutch in the pneumatic starter system protect the engine accessory gear train?
By acting as a torque-limiting device
In the pneumatic starter system, what role does the tube that collects air from the turbine play?
Engages the starter coupling
Why is a portion of air directed to the starter gearbox in the pneumatic starter system?
To engage the starter coupling with the drive coupling
What does the reduction gearing do in a pneumatic starter system?
Reduces rotational speed and increases torque
What is the function of the clutch located between the starter coupling and reduction gearing in a pneumatic starter system?
To protect against overload and reduce impact force
What function does the solenoid spring perform when the engine rotates at 57-64% RPM in a pneumatic starter system?
Releases air pressure after starting
What is the primary purpose of the regulator piston in a pneumatic starter system?
To control air flow to the engine
How does an air impingement starter system differ from other pneumatic starters for gas turbine engines?
It eliminates the need for a starter gearbox
What does the operation of the control (throttle) lever do during the start of a gas turbine engine?
Selects an appropriate position for engine start-up
In a turbo-propeller engine, how is the throttle lever interconnected with the propeller control unit?
Maintains single lever operation of the engine
What function does the power lever serve in an aircraft's powerplant controls?
Controls propeller pitch (hence power)
What is the role of the speed lever in an aircraft's powerplant controls?
Controls engine speed
How is the output from the power and speed levers transferred to the powerplant in an aircraft?
Through cable and pulley mechanisms
What initiates the rotation of the engine in air impingement starting?
Air directed by a shut-off valve
How is self-sustaining speed achieved in gas turbine engines using air impingement starting?
By directing air onto the turbine blades
What is the purpose of the shut-off valve in air impingement starting?
To direct air onto the turbine blades
Why might some gas turbine engines not be fitted with starter motors?
To rely on air impingement for rotation
What role do non-return valves play in air impingement starting?
Prevent air from escaping the system
When does the speed switch close in air impingement starting?
When the engine reaches self-sustaining speed
What is the purpose of the actuator piston in the air impingement starter system?
To open the butterfly valve
What role does the starter speed sensing switch play when the engine rotates at 57-64% RPM in the air impingement starter system?
Removes the earth circuit from solenoids
What prevents damage from excessive air pressure in the air impingement starter system?
Relief valve
What allows external air sources to provide airflow in the air impingement starter system?
Turbine wheel
In the air impingement starter system, what initiates the closure of the butterfly when the engine reaches 57-64% RPM?
Actuator return spring
What converts airflow into torque in the air impingement starter system?
Turbine wheel
What happens when the engine self-sustaining RPM is established in the Allison T56 engine start sequence?
The engine starter automatically disengages
At what percentage of RPM does the engine stabilize within a low-speed ground idle range in the Allison T56 engine start sequence?
69% to 75%
What action is taken when the high-pressure fuel shut-off cock is activated open in the Allison T56 engine start sequence?
Fuel delivery begins
What is the final stage in the Allison T56 engine start sequence?
Start peak exhaust gas temperature
At approximately what percentage of RPM does the ignition system get deactivated in the Allison T56 engine start sequence?
65%
During what phase of the Allison T56 engine start sequence does combustion begin?
Approximately 60%
Why is it important to control the starting and ignition sequences of a gas turbine engine?
To avoid damage due to combustion over-temperature and unstable airflow.
Why does ignition in a gas turbine engine only begin after the engine is capable of meeting certain airflow requirements?
To ensure sufficient airflow for combustion when the fuel/air mixture ignites.
What is a potential consequence of not effectively sequencing ignition and fuel flow during engine starting?
Turbine damage due to combustion over-temperature and unstable airflow.
Why is it necessary for the pilot to manually place the throttle into the idle position following switch selection in certain engine configurations?
To increase the airflow through the engine during starting.
What can happen if the fuel flow rate during initial engine cranking is not sufficient for combustion?
Satisfactory combustion will not occur.
Why is it critical to ensure that there is sufficient airflow through the engine at the time of ignition?
To support combustion when the fuel/air mixture ignites.
What is the purpose of a shut-off cock in the fuel system of an aircraft engine?
To start and stop fuel flow to the engine
How is the high-pressure shut-off cock in the fuel control unit typically operated?
By a lever interconnected with the throttle lever
When must fuel flow commencement and ignition selection be carefully sequenced during engine start?
To coincide with sufficient compressor airflow
What controls the operation of a high-pressure cock that is electrically actuated in an aircraft engine?
A switch on the pilot's instrument panel
In some configurations, what happens automatically once a predetermined engine RPM is reached during starting?
Fuel flow and ignition are sequenced
Learn about the fundamental characteristics of a starter motor in aircraft engineering, including its purpose to produce high torque and provide smooth acceleration to the engine rotating assembly.
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