APU Flashcards
(75 cards)
1
Q
A
2
Q
What is the rated power of the Solar T62-T-2C turbine engine?
A
95 SHP
SHP stands for Shaft Horsepower.
3
Q
Where is the Solar T62-T-2C turbine engine mounted?
A
Aft of the fuselage, aft of station 594.
4
Q
What is the primary purpose of the APU?
A
To provide electrical and hydraulic power for ground operations and starting.
5
Q
From which fuel tank does the APU pull fuel?
A
LH fuel tank.
6
Q
What does the motor/pump do during the start of the APU?
A
Acts as a motor to start the engine.
7
Q
What does the motor/pump become after starting the APU?
A
A pump to drive the AGB on the aft transmission.
8
Q
How many major sections does the engine have?
A
6 major sections.
9
Q
What are the major sections of the engine?
A
- Inlet
- Compressor
- Combustion
- Turbine
- Accessory
- Reduction drive
10
Q
How is the compressor supported?
A
By a single forward ball bearing and an aft roller bearing.
11
Q
What does the compressor pressure force the circular seal to do?
A
Force the seal rearward against a shoulder on the turbine nozzle.
12
Q
What is the function of the combustion section in the APU?
A
Air flows from the compressor past the combustion burner for burning.
13
Q
Where is the igniter mounted in the combustion housing?
A
Aft left side of the housing.
14
Q
How many fuel injectors are mounted to the combustion housing?
A
Six evenly spaced fuel injectors.
15
Q
What component directs expanding hot gas to the turbine wheel?
A
The combustion section.
16
Q
What is the speed reduction ratio from the APU?
A
9.33:1.
17
Q
What is the output speed of the APU after reduction?
A
6,000 RPM.
18
Q
What does the fixed displacement motor pump produce when starting the APU?
A
372 in/lbs of torque at 500 RPM.
19
Q
What pressure can the pump produce when driven at 6,000 RPM?
A
4,400 PSI.
20
Q
Fill in the blank: The APU’s output drives ___ planetary gears.
A
3.
21
Q
True or False: The accessory gear drives the APU speed detector and fuel control assembly.
A
True.
22
Q
What protects people from thermal radiation and hot surfaces around the combustion housing?
A
A thermal blanket.
23
Q
What is the purpose of the oil pump in the APU?
A
To drive the APU lubrication system.
24
Q
What is the inlet pressure when the APU is operating at 100%?
A
2,000 PSI.
25
What is the primary source of fuel for the APU?
Fuel comes from the LH tank
## Footnote
LH tank refers to the left-hand tank in the aircraft's fuel system.
26
What components are involved in the APU fuel system?
* DC boost pump
* APU fuel shutoff solenoid valve
* 10 micron filter
* Engine mounted pump
* Control unit
## Footnote
These components work together to supply fuel to the APU.
27
How is the APU fuel shutoff valve controlled?
Controlled by the ESU
## Footnote
ESU stands for Electronic Control Unit.
28
What is the normal state of the APU fuel shutoff valve?
Normally closed
## Footnote
The valve opens during APU start and remains open until the switch is off or the APU fire button is pressed.
29
What is the full fuel flow rate for the APU?
115 lb/hr
## Footnote
Fuel flow is reduced to 50 lb/hr when the APU is unloaded.
30
What happens to the fuel flow during APU start?
Fuel is allowed to flow through start solenoid valve to a start fuel nozzle
## Footnote
This is controlled by the ESU.
31
At what APU speed is the start solenoid energized open?
5% APU speed
## Footnote
The solenoid is de-energized off at 70% APU speed.
32
What energizes the main fuel solenoid?
28 volt DC from the ESU
## Footnote
This occurs when the APU reaches 14% speed.
33
What is the process for starting the APU?
Go to Run then hold START for 3 seconds
## Footnote
This activates the airframe pump and other components necessary for APU start.
34
What component opens at 5% engine speed during APU start?
Start valve
## Footnote
This allows fuel to flow to the APU.
35
What happens if the engine fails to reach 90% speed in 40 seconds?
ESU will shut engine down and indicate 'failed to start'
## Footnote
This is a safety feature to prevent prolonged unsuccessful attempts to start the APU.
36
What governs the engine speed of the APU?
Flyweight assembly within the housing
## Footnote
This assembly adjusts fuel flow based on load conditions.
37
What is the capacity of the oil sump in the APU?
6 pints
## Footnote
The sump is located on the lower portion of the reduction drive housing.
38
What type of filter does the oil pass through?
10 micron disposable filter
## Footnote
This filter has a spring-loaded ball type bypass set for 15-40 PSI.
39
How many oil jets are in the jet ring around the high-speed input pinion?
Three oil jets
## Footnote
These jets direct oil to mesh points of the input pinion and planetary gears.
40
What is the function of the centrifugal oil separator plates?
Remove oil from the air before venting to the atmosphere
## Footnote
This is crucial for maintaining system efficiency.
41
What relieves excess pressure in the system?
Pressure relief valve
## Footnote
This valve dumps some oil back to the sump.
42
Where is the dumped oil directed to cool it?
Into the side surface of air inlet housing as it flows back to sump
## Footnote
This helps maintain optimal oil temperature.
43
What does the APU control panel include?
Switches for operation and three lights: overspeed, fail, and overtemp
## Footnote
Some panels also have a normal/alternate switch for using an external DC power source.
44
How is the APU fuel shutoff relay controlled?
By the ESU via 28 VDC power to airframe fuel pump and shutoff valve
45
What does the APU 90% speed relay control?
APU hydraulic start valve and hydraulic AGB valve
## Footnote
Relay is energized with APU switch in start and de-energized when APU reaches 90% plus 1.5 seconds.
46
What are the functions of the APU overspeed and overtemp light relays?
Controlled by ESU, supplies ground for fail light if impending failure or test switch is made
47
What is the purpose of the ESU?
Sense and control operations of APU and APU system
## Footnote
Monitors APU speed, EGT, and compares that data with its program.
48
What capabilities does the ESU provide for APU operation?
* APU start sequence
* Malfunction indication and shutdown during start and operation
* Resequence itself to restart condition
* APU condition monitoring for fault isolation
49
What do the ESU bit indicators show?
15 different codes with a key on the side of the ESU box
50
How does the APU mag pickup function?
Generates AC voltage based on accessory gear rotational speed, providing APU RPM to the ESU
51
What is the function of the APU ignition exciter?
Converts DC input into HT AC current output for igniter, providing spark for ignition during start sequence
52
What is the spark rate during the APU start sequence?
4 sparks per second, can operate 1 minute on then needs 5 minutes off
53
Where is the APU thermocouple located and what does it do?
Single element unit on top of aft section of combustion, senses EGT and sends data to ESU
54
What does the APU hour meter record?
Total operating hours
55
What is required to start the APU?
* Fuel from LH tank (more than 200 lbs)
* Battery connected, battery CB and battery bus CB depressed, APU CB depressed
* 3,000 psi in the 200" utility hydraulic accumulator
56
What happens when the APU switch is set to RUN?
Sends 28 V DC through de-energized contact for No 1 and 2 gen main line contactors, reducing load on AGP during APU crank
57
What does the APU switch to START position do?
Allows the start cycle to begin and energizes 90% relay and APU hydraulic start valve
## Footnote
De-energizes the AGB valve.
58
How is the utility system pressure related to APU operation?
200 cubic inch accumulator pressure is released to the APU motor/pump to crank the P
59
Fill in the blank: The APU ignition exciter is a _______ type exciter.
capacitor discharge
60
What happens at 5% APU speed?
ESU energizes start fuel solenoid open and provides voltage to ignition exciter
## Footnote
All actions are monitored by the ESU.
61
What occurs at 14% APU speed?
200 cubic inch accumulator pressure is depleted; APU motor/pump circulates hydraulic fluid from the reservoir rather than the accumulator
## Footnote
Fluid bypasses utility hydraulic cooler through the pump.
62
What is the function of the ESU at 70% APU speed?
De-energizes start fuel solenoid closed and ignition exciter
## Footnote
This indicates the transition in APU operation.
63
What happens at 90% APU speed?
ESU de-energizes the 90% relay, energizing the AGB valve closed and de-energizing the hydraulic APU start valve closed
## Footnote
Hydraulic pressure builds to drive the AGB motor.
64
What is indicated when the APU switch releases from START to RUN?
28 volt DC is disconnected from No 2 flight control hydraulic pump solenoid
## Footnote
This allows No 2 pump to produce normal 3,000 psi pressure.
65
What does the ESU monitor during APU operation?
Oil pressure, EGT, speed, and oil pressure
## Footnote
If oil pressure drops below 7 psi, the ESU will shut down the APU.
66
What happens if APU acceleration from 5-90% does not occur within 40 seconds?
An APU fail light appears on the overhead console
## Footnote
There will also be an OTEMP and OSPD light.
67
What is the power output of the APU for engine start and ground power?
95 SHP
## Footnote
This is used for all systems without engines running.
68
What are the different installations for UT and LR APU systems?
UT has an open intake screen; LR has a fire resistant stove pipe intake
## Footnote
This affects the design of the APU.
69
What components are included in the APU accessory assembly?
* Reduction drive assembly
* Compressor assembly/intake
* Combustion assembly
## Footnote
These are key parts of the APU.
70
How is air processed in the APU?
Air comes in, goes through a single stage compression rotor, and is ignited by a single ignitor
## Footnote
Six main fuel nozzles are equally spaced in the combustor housing.
71
What is the output speed reduction from the magnesium reduction drive housing?
Reduces 56,000 RPM output speed of APU to 42,000 RPM at accessory drive gear
## Footnote
This is essential for compatibility with accessory systems.
72
Where does the fuel for the APU come from?
LH tank
## Footnote
It is powered by a DC mounted airframe pump.
73
What does the 90% relay control?
* HYD start valve
* AGB valve
* Provides a ground for overspeed fail light
## Footnote
It is crucial for ESU sensing and control of APU functions.
74
What does the mag pickup do?
Generates AC power to indicate RPM of the APU
## Footnote
This is important for monitoring APU performance.
75
What do the two APU lights indicate?
* Green light when APU is on and ECLs are not in fly
* Amber light when ECLs are in fly
## Footnote
These lights provide visual status of the APU.
