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Module 15 > M15.18 APU > Flashcards

M15.18 APU Flashcards

1
Q

APU Main section

A
  • Power
  • Bleed
  • Accessory gearbox
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2
Q

What does the gearbox drive in the APU

A
  • Fuel pump
  • Oil pump
  • Cooling fan
  • Ac generator
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3
Q

Power section parts

A
  • Compressor
  • Combustion chamber
  • Turbine
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4
Q

What type of compressor is generally found in an APU

A

Centrifugal flow compressor

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5
Q

What type of combustion chamber is commonly found in an APU

A

Annular

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6
Q

APU air pressure delivery

A

30-45 psi

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7
Q

Methods of APU bleed air supply

A

Compressor from power section
Dedicated load compressor

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8
Q

Do APUs require a CSD and why

A

They run at one speed

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9
Q

APU mounts

A
  • Right aft
  • Left aft
  • FWD
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10
Q

How many fixed mounts on an APU

A

One

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11
Q

What mounts transmit what loads

A
  • One mount transmits lateral loads
  • Two mounts transmit axial loads
  • All 3 mounts transmit vertical loads
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12
Q

What is used to remove the APU

A

Fish pole hoist

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13
Q

Why is the APU inlet door movable

A
  • To increase aerodynamic efficiency
  • Prevent birds and fod ingress
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14
Q

Purpose of air intake flap diverter

A
  • Increase ram air into the duct
  • Stops fluid running along the APU from entering the intake
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15
Q

What moves the diverter

A

Mechanical push pull cable

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16
Q

Types of APU drains

A

Direct and indirect

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17
Q

APU control unit operating modes

A

Start - Up to 100%
Normal - Maintains 100%
Shut down

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18
Q

What speed is the APU starter switched off

A

50%

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19
Q

What speed are all control and protection circuits for normal ops armed

A

95%

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20
Q

What speed is fuel supplied

A

10%

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21
Q

APU control unit signals for constant speed control

A
  • APU speed
  • Torque motor signal
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22
Q

What signals are used for the normal speed mode on modern APU

A
  • Air inlet temp
  • Air inlet pressure
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23
Q

APU shut down modes

A
  • Normal
  • Auto shutdown
  • Emergency shut down
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24
Q

How long is the cool down period

A

Between 0 and 120s

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25
What does a auto shut down mean and do
- Auto activated by control unit - Prevents damage from exceedances - No cool down period
26
Automatic shut down operating limits
- Excessive EGT - Over speed - Low oil ox - High oil temp and surge
27
Primary fuel system start and finish
Starts at fuel tank and ends at APU FCU
28
HP fuel system start and finish
FCU to fuel nozzles
29
Why is a positive fuel pressure in the APU fuel feed needed
Prevents cavitation at the HP pressure fuel pump
30
APU fuel system controls
- APU master switch - APU fire switch - External APU shut off switches
31
Where does the On signal go before reaching the fuel pump
AND gate
32
What information is needed with a AND gate before fuel pump activation
- No emergency shut down signal - Pump only runs if the fuel pressure in the CX feed manifold is too low
33
When does the APU fuel boost pump run
When there are no tank boost pumps that can feed the APU
34
What can be found in the APU compartment of an Airbus aircraft
APU fuel line vent switch
35
What does the APU fuel line vent switch do
Turns on the fuel boost pump
36
Advantage of APU fuel line vent switch
Can purge fuel line with out cockpit interaction
37
Where is the APU fuel boost pump located
In the main or centre tank
38
What powers the APU fuel boost pump
DC battery
39
Methods of DC fuel pump power delivery
- APU battery - Normal battery
40
What converts battery power to the single phase AC motor for the APU boost pump
Static inverter
41
Types of APU fuel lines
- Shrouded - Un-shrouded
42
APU air sub-systems
- Cooling - Bleed
43
APU bleed air system main tasks
- Bleed supply - Surge protection - Load compressor control
44
APU bleed valve position on start
Closed
45
When does APU bleed valve open
APU is at 95%
46
How is compressor stall or speed oscillation avoided on APU shut down
Load vents overboard via a orifice
47
What moves the hydraulic actuator for the APU load compressor control
Fuel pressure
48
Position of IGV when APU is starting
Closed
49
When does the APU IGV system arm
100%
50
When does the APU typically surge
When bleed load changes
51
What APU surge protection is used on aircraft with out a load compressor
Anti-surge system
52
Position of anti surge during flight
Open
53
When does the surge control valve open
If the airflow behind the load compressor decreases or stops
54
What usually controls the APU surge valve
Electronically controlled via a torque motor
55
APU cooling air goes where
- APU cases - APU compartment - APU oil cooler
56
Types of supply pump in a APU oil system
- Gerotor type - Gear type - Vane type
57
How is the oil always cooled in the APU
AOHE
58
When does a low oil pressure trigger a automatic shut down
When pressure is low but APU is at correct speed
59
Generally what type of pumps are the scavenge pumps
Gerotor type
60
Purpose of APU de-oiler system
To help support the APU start sequence
61
When does the APU control unit activate the de-oiler valve
Shut down
62
Advantages of a pressurised gearbox
- Supports the oil supply pump - Minimise oil foaming
63
What usually is the type of starter motor
Bush type DC motor
64
Types of starter clutch in starter motors
- Sprag type - Pawl type
65
APU starter limitations
- Starter duty time - Starter cool down time - Starter duty cycle
66
Indication during APU start
- Battery voltage - Speed indication - EGT

Module 15 (20 decks)

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