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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
Q

What does a auto shut down mean and do

A
  • Auto activated by control unit
  • Prevents damage from exceedances
  • No cool down period
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26
Q

Automatic shut down operating limits

A
  • Excessive EGT
  • Over speed
  • Low oil ox
  • High oil temp and surge
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27
Q

Primary fuel system start and finish

A

Starts at fuel tank and ends at APU FCU

28
Q

HP fuel system start and finish

A

FCU to fuel nozzles

29
Q

Why is a positive fuel pressure in the APU fuel feed needed

A

Prevents cavitation at the HP pressure fuel pump

30
Q

APU fuel system controls

A
  • APU master switch
  • APU fire switch
  • External APU shut off switches
31
Q

Where does the On signal go before reaching the fuel pump

A

AND gate

32
Q

What information is needed with a AND gate before fuel pump activation

A
  • No emergency shut down signal
  • Pump only runs if the fuel pressure in the CX feed manifold is too low
33
Q

When does the APU fuel boost pump run

A

When there are no tank boost pumps that can feed the APU

34
Q

What can be found in the APU compartment of an Airbus aircraft

A

APU fuel line vent switch

35
Q

What does the APU fuel line vent switch do

A

Turns on the fuel boost pump

36
Q

Advantage of APU fuel line vent switch

A

Can purge fuel line with out cockpit interaction

37
Q

Where is the APU fuel boost pump located

A

In the main or centre tank

38
Q

What powers the APU fuel boost pump

A

DC battery

39
Q

Methods of DC fuel pump power delivery

A
  • APU battery
  • Normal battery
40
Q

What converts battery power to the single phase AC motor for the APU boost pump

A

Static inverter

41
Q

Types of APU fuel lines

A
  • Shrouded
  • Un-shrouded
42
Q

APU air sub-systems

A
  • Cooling
  • Bleed
43
Q

APU bleed air system main tasks

A
  • Bleed supply
  • Surge protection
  • Load compressor control
44
Q

APU bleed valve position on start

A

Closed

45
Q

When does APU bleed valve open

A

APU is at 95%

46
Q

How is compressor stall or speed oscillation avoided on APU shut down

A

Load vents overboard via a orifice

47
Q

What moves the hydraulic actuator for the APU load compressor control

A

Fuel pressure

48
Q

Position of IGV when APU is starting

A

Closed

49
Q

When does the APU IGV system arm

A

100%

50
Q

When does the APU typically surge

A

When bleed load changes

51
Q

What APU surge protection is used on aircraft with out a load compressor

A

Anti-surge system

52
Q

Position of anti surge during flight

A

Open

53
Q

When does the surge control valve open

A

If the airflow behind the load compressor decreases or stops

54
Q

What usually controls the APU surge valve

A

Electronically controlled via a torque motor

55
Q

APU cooling air goes where

A
  • APU cases
  • APU compartment
  • APU oil cooler
56
Q

Types of supply pump in a APU oil system

A
  • Gerotor type
  • Gear type
  • Vane type
57
Q

How is the oil always cooled in the APU

A

AOHE

58
Q

When does a low oil pressure trigger a automatic shut down

A

When pressure is low but APU is at correct speed

59
Q

Generally what type of pumps are the scavenge pumps

A

Gerotor type

60
Q

Purpose of APU de-oiler system

A

To help support the APU start sequence

61
Q

When does the APU control unit activate the de-oiler valve

A

Shut down

62
Q

Advantages of a pressurised gearbox

A
  • Supports the oil supply pump
  • Minimise oil foaming
63
Q

What usually is the type of starter motor

A

Bush type DC motor

64
Q

Types of starter clutch in starter motors

A
  • Sprag type
  • Pawl type
65
Q

APU starter limitations

A
  • Starter duty time
  • Starter cool down time
  • Starter duty cycle
66
Q

Indication during APU start

A
  • Battery voltage
  • Speed indication
  • EGT

Module 15 (20 decks)

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