CRJ Systems > APU > Flashcards

APU Flashcards

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1
Q

What is the primary purpose of the APU?

A

To provide electrical power to
the aircraft buses as a backup to the engine generators.

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2
Q

What is the APU

A

Fully automated gas powered turbine engine

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3
Q

APU secondary purpose

A

supply bleed air for engine start and air conditioning

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4
Q

APU automatic fault detection and shutdown

A

The APU has an automatic fault detection and shutdown feature.
The APU also has automatic fire extinguishing protection when the aircraft is on the ground

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5
Q

How does the APU generate power

A

Controlled by a Electronic Control Unit, or ECU, the APU turns an accessory gearbox that drives the 40 kVA APU generator.

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6
Q

What altitude can the APU be operated up to?

A

41000

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7
Q

What is the maximum altitude for starting the APU?

A

37000

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8
Q

What altitude can the APU generator be used up to?

A

41000

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9
Q

What altitude can the APU supply bleed air up to?

A

25000

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10
Q

What altitude can APU bleed air be used for engine start?

A

21000

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11
Q

Where is the APU located in the aircraft?

A

In a fireproof compartment in the tail cone of the aircraft. Can be accessed through two clamshell doors located on the bottom side of the tail cone

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12
Q

APU air inlet door location

A

An APU air inlet door is located on the upper, right side of the aft fuselage section.

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13
Q

What happens after air is let into the inlet

A

From the APU air inlet door, air is supplied to the APU compressor and the APU oil cooler.
The oil cooler heats the air which is then discharged into the APU compartment for ventilation purposes

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14
Q

APU Componets

A
  • single-stage centrifugal compressor,
  • annular reverse flow combustor,
  • two-stage axial flow turbine,
  • accessory gearbox,
  • self-contained oil system,
  • exhaust duct,
  • eductor,
  • Fuel Control Unit (FCU),
  • and Electronic Control Unit (ECU).
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15
Q

what does the single-stage centrifugal compressor do

A

A single-stage centrifugal compressor is used to create the high pressure air used for combustion.

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16
Q

Combustion section

A

Compressed air from the centrifugal compressor is mixed with vaporized fuel.
This mixture is then ignited in the combustor section of the APU.

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17
Q

2 stage axial turbine

A

The expansion of gases in the combustor section drive a two-stage axial flow turbine.
The turbine rotor drives a shaft.
In turn, the shaft rotates and transfers mechanical power to drive the compressor and the accessory gear box.

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18
Q

What components are mounted on the APU accessory gearbox?

A

The ECU
speed sensor, starter motor, fuel control unit, 40kVA APU generator, fuel
pump, and the oil pump

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19
Q

Exhaust eductor

A

When the APU is operating on the ground, an exhaust eductor located on the aft part of the power section induces cooling airflow across the oil cooler and into the APU compartment.

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20
Q

APU oil cooler

A

The cooling airflow flows over the fins of the oil cooler.
Air is then exhausted into the APU enclosure, thereby providing ventilation for that area.

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21
Q

10.What is the function of the APU air inlet door?

A

Combustion air for the APU enters the aircraft through the APU air inlet located on the upper right side of the aft fuselage, just above the APU compartment.

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22
Q

What controls the position of the APU air inlet door?

A

The APU Electronic
Control Unit (ECU) controls the position of the APU air inlet door. The door
is moved via a DC powered actuator.

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23
Q

12.What is the purpose of the APU exhaust eductor

A

Induces cooling airflow
across the oil cooler and into the APU compartment

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24
Q

What happens to the APU exhaust/ ventilation air

A

The ventilation air is exhausted through the outer sleeve in the APU exhaust eductor, by means of venturi force from the APU exhaust.
The air is literally sucked out the end of the aircraft by the pressure of the exhaust exiting the APU.

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25
Inlet door position on the ground
Top On the ground, the APU inlet door is in the full open position whenever the PWR/FUEL switchlight on the APU control panel is selected. In flight, the APU inlet door is opened when the START/STOP switchlight is selected. The APU air inlet door is closed when the APU is shutdown.
26
APU inlet door position in flight
In flight, the APU inlet door is opened when the START/STOP switchlight is selected.
27
APU shutdown position
The APU air inlet door is closed when the APU is shutdown.
28
Inflight the apu inlet door open depends
on how fast the plane is goin
29
Where is the inlet door EICAS message
ED 2 bottom left
30
Inlet door postion unknown and apu is not operating
220 or less
31
APU Exhaust
The hot gases produced by the APU are exhausted through the tailpipe. The high velocity of this exhaust gas produces a venturi effect that draws the cooling air flow through the eductor.
32
Where does APU get its fuel
When the APU is operating, it receives a steady supply of fuel from the left collector tank. The APU fuel system utilizes a dedicated fuel manifold and APU fuel pump.
33
How is fuel metered
The accessory gearbox mounted fuel control unit meters the flow of fuel to the APU, as commanded by the ECU. Commanded fuel flow is based on electrical and bleed air demands, as well as the APU's RPM and EGT.
34
26.What is the purpose of the load control valve?
It will open up based on bleed requirements when the pneumatic system is operating in the automatic mode
35
27.What happens if the APU EGT remains high?
The load control valve (LCV) will shut completely to reduce EGT and protect the APU from shutdown
36
28.What prevents the reverse flow of bleed air into the APU?
A one-way check valve. It is between the load control valve (LCV) and the bleed air cross feed
37
Bleed isolation valve
After the APU load control valve opens, the bleed isolation valve will be automatically opened to allow the APU to supply bleed air to both sides of the pneumatic system.
38
Can we use the APU for anti ice
NO, The APU load control valve automatically closes and the engine bleed air valves are commanded open when either cowl or wing anti-ice is selected ON.
39
14.What is the purpose of the surge control valve?
The purpose of the surge control valve is to prevent compressor surges. The APU works harder at altitude due to the lower air density. This results in an increase in temperature in the combustion chamber, as well as an increase in pressure downstream of the compressor. This increase in pressure could result in a compressor surge. When the compressor surges, the impeller continues to turn but does not compress additional air.
40
15.When does the surge control valve operate?
When the APU is supplying electrical power above 17,000 feet
41
Does the surge control valve operate on the ground?
no
42
What is to start and operate the apu
Both the APU battery and the main battery are required to start and operate the APU.
43
16.What is the minimum battery voltage required to start the APU?
22 volts (for both the APU battery and the main battery) ON DC ELEC PAGE
44
Starting the APU...
the PWR FUEL switch light on the APU Control Panel is pressed first, initiating the APU pre start sequence. status message APU SOV OPEN status message APU BITE status message DOOR OPEN APU RPM and Temp gauge appears APU fuel pump automatically turns on to provide fuel (if pumps fails to do so we get amber light on ED 1) Once BITE test goes away press Start switch ECU now energizes the apu starter(status message APU START ) Start stop switch on panel now illuminates Ignition-At 5% RPM, a fuel solenoid will open to allow fuel into the combustion chamber, and ignition will be introduced... 46% RPM ECU de-energizes (ground, 46-60 in air) Start stop switch deilluminates and apu start status message goes away At 95% rpm the ignition is deenergized 2 seconds after 99% rpm, the AVAIL will illuminate mesning itd ready for electrical loading APU SOV status message is removed Once the APU is operating, the APU GEN switch can be moved to the AUTO position. The APU generator will come online and supply power to all of the aircraft AC buses. After electrical power is established, APU bleed air can be used for air conditioning and engine starts. Check AC page TRU under 120 and DC synoptic page buses are powered
45
26.What is the purpose of the load control valve?
It will open up based on bleed requirements when the pneumatic system is operating in the automatic mode
46
APU after electric is established
use for AC and engine starts
47
Pneumatics using APU
Bleed valves in AUTO L and R pack on Recirc fan on APU load control valve will open based on bleed air requirements. The ECU controls the operation of the APU load control valve. APU load control valve is open, APU bleed air will be delivered to the left side of the pneumatic system, and an APU LCV OPEN status message When the APU load control valve is open, the bleed isolation valve will automatically open as well to bring to the right side Engine bleeds will be closed you will see APU LCV OPEN ISOL OPEN L ENG BLEED CLOSED R ENG BLKEED CLOSED
48
APU start in flight difference
identical to the ground start with one exception. On the ground, the APU air inlet door opens when the PWR FUEL switchlight is pressed. In flight, however, the APU air inlet door does not open until the START/STOP switchlight is depressed. This prevents the APU from windmilling before it is started.
49
APU inhibit start
if the apu is spinning more than 5% on ground or 12% in flight
50
What monitiors the apu for faults or malfunctions
ECU
51
What will happen if a fault or malfunction of the apu happens on the ground or inflight
automatic shut down, except for some cases in flight it will stay on until landing or manual shut off
52
what happens with an APU fire
the APU will shut down automatically on the ground or in flight. If the aircraft is on the ground, the APU fire bottle will discharge automatically five seconds after shutdown.
53
Normal APU shut down
Press start stop switch The ECU senses the signal from the switch, the APU generator trips, and the AVAIL light in the START/STOP switchlight extinguishes. In addition, the ECU closes the APU fuel solenoid valve. As the APU spools down, the air intake door closes, and a DOOR CLSD message is displayed on the EICAS
54
When is apu shutdown complete
APU shutdown is complete after the PWR FUEL switchlight is pressed. The APU RPM and EGT gauges are removed from the EICAS status page 10 seconds after pressing the switchlight.
55
Other ways to shutdown apu
There are two additional APU remote shutoff switches installed in the aircraft. these switches can be used in the event of an emergency. When the APU is operating unattended on the ground, these switches can be used to shut down the APU from the outside of the aircraft.
56
APU remote shut off switches locations
forward firewall of the APU compartment. The second is located on the external services panel, on the right forward section of the fuselage.
57
41.What is the purpose of the APU combustor section?
This is where compressed air from the centrifugal compressor is mixed with vaporized fuel and ignited
58
42.What drives the accessory gearbox?
ECU
59
43.What is the function of the APU ECU?
The ECU controls and monitors APU operation, including the recording of operating hours and start cycles. The DC-powered ECU controls the fuel flow and EGT and sends operating data to the EICAS displays (this answer is copy and pasted directly from the PRM)
60
44.What happens if the APU inlet door position is unknown and the APU is not operating?
Then we are limited to 220 knots
61
45.What is the function of the APU oil cooler?
Heats the air which is discharged into the APU compartment for ventilation purposes
62
46.What happens to the bleed isolation valve when the APU load control valve opens?
Automatically opens to supply bleed air to both sides of the system
63
47.What happens if the APU fuel pump fails during operation?
An internal bypass valve opens, allowing the accessory gearbox mounted high pressure pump to draw the fuel, permitting continuous operation.
64
48.What is the purpose of the APU's automatic fire extinguishing protection?
To automatically extinguish a fire
65
49.What does the APU ECU do during the prestart sequence?
The ECU schedules starter disengagement as a function of altitude
66
50.What happens to the APU air inlet door during an in-flight start? it
it does not open until the START/STOP switch light is selected
67
54.IF the APU fuel pump fails while the APU is running:
The APU will continue to run via an internal bypass valve that allows the fuel pump to suction feed fuel from left collector tank
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