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M15 Lewis > 15.18 > Flashcards

15.18 Flashcards

1
Q

Fin case of a fire on apu what’s the quickest way to shut down the APU

A

Activate fire switch

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2
Q

Why’s it important that the APU shows a smooth acceleration during start sequence

A

Indicates the starter is operating properly and fuel metering from the fuel control unit is correct

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3
Q

What happens to the ac battery during apu start

A

Voltage decreases and after starts cut out it increases again

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4
Q

What 3 limitations do APU starters have

A

Starter duty time

Starter cool down time

Starter duty cycle

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5
Q

What happens while the APU start switch is activated

A

Apu control unit energises the starter relay which would allow dc power from aircraft battery to become available

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6
Q

What happens at the cut off speed at the APU control unit

A

Opens starter relay which disconnects the batttey from the apu starter motor

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7
Q

What do brush wear indicators do

A

Indicates if brushes are worn

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8
Q

What Type of motor is the APU starter

A

Brush type DC motor

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9
Q

What does the additional vent valve installed in the centre line of the apu exhaust duct do

A

Pressurises the gearbox to 4-5psi

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10
Q

What 3 types of supply pumps are used in the apu oil system

A

Gerotor
Gear type
Vane type

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11
Q

Where the oil reservoir in the apu located

A

In lower part of apu gearbox

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12
Q

What’s the two main differences of apu oil systems over engine oil systems

A

Deoiling valve
Oil system used to cool APU generator

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13
Q

What’s the airflow in the compressor dicscharge duct equal to

A

Difference between the static and total pressure

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14
Q

What two pressure pick ups does airflow sensors in a compressor surge protection system have

A

Static pressure pick up
Total pressure pic up

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15
Q

Is the surge protection system with or without load compressors better

A

With load compressors

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16
Q

What disadvantage does an anti surge valve have

A

Not fuel efficient as air is also bled off when there’s no surging

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17
Q

Why can’t a load compressor be switched off

A

Because it’s fixed to the apu rotor shaft

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18
Q

How controls the airflow into the load compressor

A

Variable inlet guide vanes

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19
Q

What benifit does the load compressor have

A

Reduces fuel consumption

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20
Q

What does the apu load compressor control system control

A

Amount of air going into the overload compressor to meet the bleed demand of the aircraft pneumatic system

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21
Q

What two subsystems is the apu air system divided into

A

Cooling and and bleed air

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22
Q

What’s an advantage of the vent push button being able to bypass the apu master switch

A

As they can purge the apu fuel feed line without someone in the cockpit

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23
Q

Why’s it important to have a positive feel pressure in the apu fuel feed line

A

Prevents cavitation of the hp fuel pump of the apu

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24
Q

How many boost pumps are in each fuel tank

A

Two

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25
Q

What do the fuel switches in the apu fuel system do

A

Primary - monitors the fuel pressure in apu feed line
Secondary- control the apu fuel boost pump

26
Q

What does the apu feul shut off valve act as

A

An isolation valve

27
Q

Where the fuel taken from for the apu

A

Main engine fuel feed system

28
Q

What’s the primary fuel system of the apu also known as?
What’s the secondary fuel system of the apu also known as ?

A

Primary= Lp feul system
Secondary= Hp fuel system

29
Q

Where are the apu shut down switches located

A

In areas of ac that are easily accessible to ground personnel

30
Q

How longs the cooling period in emergency apu shut down

A

Isn’t one in an emergency

31
Q

What does the automatic apu shut down prevent?
How longs the cooling period?

A

Prevents apu damage due to exceeding operating limits
Isn’t one

32
Q

What’s the main componentsof the inlet guide vane

A

IGV actuator assembly
Transmission assembly
Inlet guide vanes

33
Q

What’s a safe shut down
How long do apu take to cool down

A

When apps allowed to shut down after its operated for a sufficient time without pneumatic or electric load

Varies from 0-120s and can be adjusted in maintenance if needed

34
Q

What are the 3 different ways to shut down the apu

A

Emergency shut down
Automatically
Manually turned off with apu MASTER SWITCH

35
Q

What two signals does the apu control unit use for constant speed control

A

Torque motor signal
Apu speed signal

36
Q

What happens to the apu air inlet door and fuel shut off valve when pre start test is successfully performed

A

Both open

37
Q

What does the pre start test do

A

Makes sure the apu control unit itself operates properly and all importwnt sensor signals are available

38
Q

What two actions are necessary to start the apu

A

Start initiation and start activation

39
Q

How many apu control switches are on Boeing ac?
Airbus ac?

A

2 on airbus ( master and start )
1 on Boeing ( two switch positions )

40
Q

What 3 different modes does the apu have

A

Start mode ( from activation until it’s reached 100%)
Normal speed mode ( keeps apu at 100% regardless of load changes )
Apu shut down mode ( monitors and controls apu shut down )

41
Q

What are the two different types of apu drain valves

A

Direct-

Indirect-

42
Q

What does the apu drain system help to prevent

A

Fire, operating malfunction, corrosion

43
Q

What does the air intake nose form on the lower apu air intake

A

Optimum aerodynamic surface

44
Q

What type of power is the apu air intake door driven by

A

28 v dc

45
Q

What does the apu air intake door do

A

Supplies air to the apu or shuts off inlet if apu isn’t running

46
Q

Wheres the air intake located on airbus ac located?
Boeing?

A

Lower intake door on airbus
Right hand upper side fuselage on Boeing

47
Q

What’s the equipment called used to remove the apu

A

Fish pole hoist

48
Q

How many mounts support the apu?
What’s are the mounts connected by?
What purpose do these mounts serve?

A

3

Mount links

One fixed for stability and strength
2 flexible to permit limited movement for thermal expansion

49
Q

How many apu access doors are located on ac

A

2
1 on smaller ac

50
Q

What characteristic does the apu compartment housing have

A

Entirely fire proof to prevent any possible fire proper gait on to the fuselage

51
Q

Where’s the apu located

A

In ac tail section

52
Q

Why do APU generators not require a constant speed drive

A

Because apu is controlled to a constant speed by the apu fuel control unit

53
Q

What benifits do apu with load compressors have

A

Fuel efficient
Airflow can be changed on demand from pneumatic system

54
Q

What are two methods of apu bleed air supply

A

Use compressor of power section
Use individual load compressors

55
Q

What psi does the apu bleed air supply

A

30-45psi

56
Q

What type of combustion chamber are on modern apu

A

Annular

57
Q

What does the bleed section of the apu do

A

Makes sure that sufficient bleed air is supplied of ac pneumatic system

58
Q

How many ac generator are found on large apu

A

2#

59
Q

What 3 sections are apu split up into

A

Power sections
Bleed sections
Accessory gearbox

60
Q

What must modern twin engine ac provide

A

Bleed air and electrical power in flight in case of engine bleed air or generator failure

61
Q

Where’s the apu mainly used

A

On ground

M15 Lewis (18 decks)

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