15.18 Flashcards
Fin case of a fire on apu what’s the quickest way to shut down the APU
Activate fire switch
Why’s it important that the APU shows a smooth acceleration during start sequence
Indicates the starter is operating properly and fuel metering from the fuel control unit is correct
What happens to the ac battery during apu start
Voltage decreases and after starts cut out it increases again
What 3 limitations do APU starters have
Starter duty time
Starter cool down time
Starter duty cycle
What happens while the APU start switch is activated
Apu control unit energises the starter relay which would allow dc power from aircraft battery to become available
What happens at the cut off speed at the APU control unit
Opens starter relay which disconnects the batttey from the apu starter motor
What do brush wear indicators do
Indicates if brushes are worn
What Type of motor is the APU starter
Brush type DC motor
What does the additional vent valve installed in the centre line of the apu exhaust duct do
Pressurises the gearbox to 4-5psi
What 3 types of supply pumps are used in the apu oil system
Gerotor
Gear type
Vane type
Where the oil reservoir in the apu located
In lower part of apu gearbox
What’s the two main differences of apu oil systems over engine oil systems
Deoiling valve
Oil system used to cool APU generator
What’s the airflow in the compressor dicscharge duct equal to
Difference between the static and total pressure
What two pressure pick ups does airflow sensors in a compressor surge protection system have
Static pressure pick up
Total pressure pic up
Is the surge protection system with or without load compressors better
With load compressors
What disadvantage does an anti surge valve have
Not fuel efficient as air is also bled off when there’s no surging
Why can’t a load compressor be switched off
Because it’s fixed to the apu rotor shaft
How controls the airflow into the load compressor
Variable inlet guide vanes
What benifit does the load compressor have
Reduces fuel consumption
What does the apu load compressor control system control
Amount of air going into the overload compressor to meet the bleed demand of the aircraft pneumatic system
What two subsystems is the apu air system divided into
Cooling and and bleed air
What’s an advantage of the vent push button being able to bypass the apu master switch
As they can purge the apu fuel feed line without someone in the cockpit
Why’s it important to have a positive feel pressure in the apu fuel feed line
Prevents cavitation of the hp fuel pump of the apu
How many boost pumps are in each fuel tank
Two