15.18 Flashcards
What does the APU do?
Provide pneubleed air and electrical power for aircraft systems
The APU can be split up into three main sections
Power
Bleed
Accessory gearbox
What does the power section of the APU do?
Drive the compressor and the gearbox
What is the compressor called that provides sufficient bleed air to the pneumatic system
Load compressor
What type of compressor will you find on APU
Centrifugal flow compressor
On modern APUs the combustion chamber is what type
Annular type
What is the air pressure for the APU
30-45psi
What are the two methods of APU bleed air supply
Compressor of the the power section
Individual load compressor
The airflow into the load compressor can be controlled by what?
Variable inlet guide vanes
Why does the APU generator not need a constant speed drive when running as a back up
Because the APU is always controlled to a constant speed by the APU fuel control unit
Where is the APU compartment located
In aircraft tail sections
What does the APU equipment compartment house hold
Air intake actuator
APU fire extinguisher bottle
Fuel supply line
Bleed air duct
How many APU mounts are there to support the APU
3 one is fixed the other 2 are flexible
How many mounts transmit vertical loads and forces from the APU
2
How many mounts transmit lateral loads and forces from the APU
1
How many mounts transmit vertical loads and forces from the APU
All 3
What equipment is used to remove the APU
Hoist equipment
What is another name for the air intake door
Air intake flap
What voltage is need to drive the APU air intake door actuator
28V DC power
What does the APU inlet (diffuser) do?
Guides the air to the APU
What does the APU air intake elbow do?
Forms the air duct between the air inlet duct and the APU air inlet
What are the two types of drains
Direct and indirect
What does the APU drain mast do
Collects the leakage and drains the fluid overboard during flight
What two actions are needed to start the APU
Start initiation
Start activation
What are the two APU control signals for constant speed control
APU speed signals
Torque motor signals
How many ways can you turn off the APU
3 ways
What is the cool down period of an APU
Between 0 and 120s
How is automatic stut down of an APU activated
By the APU control unit
What is the name of the primary fuel system of the APU
Low pressure fuel systems
Where does the primary fuel system start and end
Starts at the fuel tanks and ends at the FCU of the APU
Where does the secondary fuel system of the APU start and end
Starts at the FCU and ends at the fuel nozzle of the combustion chamber
What are the sub-systems for the APU air system
Cooling air system and bleed air system
What are the three main tasks of a bleed air system
Bleed supply
Surge procreation
Load compressor control
Can a load compressor be switch off
No because it is fixed to the rotor shaft
How can compressor surging be prevented
Bleeding off the air that is blocking the compressor discharge
When would the surge control valve open
If the airflow behind the load compressor decrease or stops
What are the two pressure pick ups in the surge protection system
Total pressure and static press
What are the three types of supply pumps which can be used in the APU oil system
Gerotor type
Gear type
Vane type
What pressure is the gearbox in the APU oil vent system pressurised to
4-5psi
What does the APU starter lead do
Transmit the battery power to APU starter motor
What type of motor is the starter motor
Brush type DC motor
What are the three starter limitations for a APU battery
Duty time
Cool down time
Duty cycle
The APU ignition system is usually powered by what?
DC
What are the most important indication you will see during APU start
Battery voltage
Speed indication
EGT indication
