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BV234 > APU > Flashcards

APU Flashcards

1
Q

Engine

A

Solar T62-T-2C gas turbine rated at 95shp

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2
Q

Sections of APU Engine

A
  1. Annular air inlet
  2. Compressor section
  3. Combustion
  4. Turbine section
  5. Engine accessories section
  6. Reduction drive assembly
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3
Q

Air Inlet

A

Annular air intake screen

Air inlet DUCT assembly is contoured cylindrical casting is is bolted to APU

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4
Q

Compressor Section

A

Single stage centrifugal compressor
Fixed guide vanes
Bolted onto flange which is integral to APU rotor shaft
Rotor shaft is supported by forward ball bearing and at aft end with roller bearing
Forward bearing resists THRUST and RADIAL loads
Aft bearing resists RADIAL loads only

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5
Q

Combustion Section

A

Annular combustion burner assembly, air flows between walls of combustion housing and liner and reverses direction to flow forward through burner section

Single igniter mounted at the AFT LEFT side of combustor housing ignites fuel air mixture supplied by start fuel nozzle during starting

6 equally spaced main fuel injectors mounted on combustor housing supply fuel to 6 vaporizing tubes
Tubes direct fuel into chamber of combustion liner for burn
Port in sump on lowest portion of combustor housing vents excess fuel after false starts and malfunctions

Exhaust gas temp monitored by single thermocouple on aft section of combustor housing

2 section thermal blanket laced around combustor housing and exhaust duct to protect people from heat

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6
Q

Turbine Section

A

Turbine wheel is pressed onto aft end of rotor shaft

This connection causes the turbine rotor shaft to turn the compressor and output pinion in to the reduction drive assembly

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7
Q

Reduction Drive Assembly

A

Single piece reduction drive housing made of magnesium

APU output pinion enters reduction drive and moves 3 planetary gears that drives short output shaft

Output shaft drives accessory drive gear and oil pump drive gear

Accessory drive gear drives APU speed detector and fuel control assembly

Oil pump drive gear drives APU lube system, which consists of:

  1. Pump
  2. Filter
  3. Pressure relief valve
  4. Oil jets
  5. Connecting passages
  6. Oil sump
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8
Q

Hydraulic APU Motor/Pump

A

Mounted to front of reduction drive housing and splined to reduction drive output shaft

Acts as a motor to start APU

Acts as a pump to turn the AGB

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9
Q

APU Fuel

A

Fuel comes from LH tank and is sucked by APU fuel booster pump (DC powered) and then pushed through APU fuel shutoff solenoid valve and filter, then to the engine mounted pump and control unit

Booster pump operates when APU switch is at start and continues operating until switch is off

Shutoff valve is energized open during APU start and remains open until start switch is OFF or APU button is pressed

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10
Q

APU Fuel Control System

A

Engine driven fuel pump pushes fuel to engine governor assembly

From the governor fuel is split into:

  1. Start fuel
  2. Main fuel

During start, fuel flows through a start solenoid valve (energized open by ESU) to the start fuel nozzle (only 1). During normal ops the start solenoid valve is closed and main fuel solenoid is open

Fuel is then provided via main fuel line to 6 main fuel injectors

Fuel control system is mounted to at top section of reduction drive assembly

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11
Q

APU Start Fuel Solenoid Valve

A

Energized open by 28vdc from ESU at 5% rated APU speed

Valve de energized off at 70% rated APU speed

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12
Q

APU main Fuel Solenoid Valve

A

Energized open by 28vdc from ESU triggered at 14% APU speed

Normal shutdown of APU is accomplished by de energizing this valve

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13
Q

APU Fuel System Operation

A

APU switch moves from RUN to START:

  1. Airframe fuel pump takes fuel from LH fuel tank and pressurizes fuel through airframe shutoff valve
  2. A. Hydraulic start valve opens, causing motor pump to turn, which turns compressor
  3. As turbine speed increase APU fuel pump output increases, forcing fuel through start fuel valve, which opens at 5%
  4. Single igniter is activated at 5%, causing combustion
  5. At 14% the main fuel solenoid opens, allowing max fuel flow to fuel manifold and to 6 vaporizing tubes
  6. A. All fuel flow is controlled in proportion to compressor pressure
  7. At 70%, igniter, hydraulic pump, and start fuel solenoid are all switched off
    * if engine fails to reach 90% in 40 seconds, ESU will shut engine down with “Fail to Start” indication*

APU speed is governed by flyweight assembly within the governor housing. APU slows causes more fuel to flow, APU goes to fast it restricts the fuel flow to APU

If APU load is significantly reduced, a minimum flow orifice in fuel control housing bypasses the governor, which allows a small amount of fuel under pump pressure to flow to fuel nozzles, which is enough to maintain combustion

Moving APU switch to OFF position removes 28vdc from airframe fuel pump solenoid and ESU. Fuel pump stops, fuel solenoid closes the valve, and starves APU of fuel

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14
Q

APU Oil Pump

A

2 gear pump housed in reduction drive housing

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15
Q

APU Oil Filter

A

Contains bypass, located on reduction drive housing

Angled tube on No. 2 side of reduction gear housing

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16
Q

Pressure Relief Valve

A

Mounted internally in main oil gallery, relieves by passion small portion of pump output back to sump

17
Q

Oil Sump

A

6 pint capacity, lower portion of reduction drive housing, has filler cap with dipstick and sight gauge on No. 1 side

18
Q

Oil Pressure Switch

A

Normally closed but opens as pressure increases with APU operating above 90% speed

Reduction in pressure closes switch, allowing current to flow back to ESU, which will shut down the APU

19
Q

Lube System Operation

A

Pump draws oil from sump to filter housing and onwards to 4 jets

3 of those jets lubricate high speed input pinion and planetary gears within reduction gearbox

The 4th jet is directed between end of output shaft and high speed pinion to create a mist for rotor shaft bearing lubrication

This oil flows through the hollow rotor shaft to the end where I reverses flow and lubricates the outside of the rotor shaft, back to reduction drive housing and into the sump

20
Q

APU Relays

A

Fuel shutoff relay…controlled by ESU, controls 28vdc power to airframe fuel pump and shutoff valve

90% speed relay…controlled by ESU, controls 28vdc to APU hydraulic start valve and AGB valve. Energized with APU switch in start and de energized when APU reaches 90% plus 1.5 seconds

Overspeed light relay…controlled by ESU, supplies ground for overspeed fail light and is energized when impending failure exists or when test switch is made

Over temp light relay… controlled by ESU, supplies ground for over temp light and is energized when impending failure exists or when test switch is made

21
Q

Electronic Sequence Unit (ESU)

A

Senses and controls all operational functions of APU and APU system components

Control is achieved by monitoring APU speed and EGT

Functions of ESU:

  1. APU start and sequence operation
  2. Malfunction indication and shutdown during start
  3. Malfunction indication and shutdown during normal operation
  4. Resequence itself to restart condition on reapplication of power after shutdown
  5. APU condition monitoring for fault isolation
22
Q

Magnetic Pickup

A

Located on RH side of accessory drive housing, generates AC voltage proportional to accessory gear rotational speed

This voltage is transmitted to ESU to indicate APU RPM

23
Q

Ignition Exciter and Igniter

A

Capacitor discharge type exciter converts DC input to sparks for ignition during start sequence

24
Q

Thermocouple

A

Single element positioned of top aft section of combustor

Senses EGT and sends signal to ESU

Over temp signal to ESU will result in APU shutdown

25
Q

Starting Requirements

A
  1. Fuel supply from LH tank, cannot be less than 200lbs
  2. Battery connected with CB and battery bus CB in, APU CB in
  3. 3,000psi in 200 cubic inch utility hydraulic accumulator
26
Q

APU Switch to RUN

A
  1. 28vdc through de energized contacts of No. 1 and 2 generator main line contractors to No. 1 flight control hydraulic pump solenoid and ESU. Energizing solenoid on each flight control hydraulic pump reduces pump output. At same time utility hydraulic system isolation valve closes which removes utility hydraulic pressure from utility hydraulic sub systems. These actions reduce load on AGB during APU crank cycle
  2. Electrical power supplied to ESU
  3. 28vdc supplied to airframe fuel pump and shutoff solenoid
27
Q

APU Switch to START

A

Start cycle begins

ESU energizes 90% relay and APU hydraulic start valve, de energizes AGB valve

200 cu inch accumulator pressure is released to APU motor/pump to crank APU. Fluid is then exhausted through open AGB valve to utility hydraulic reservoir

5% APU speed…ESU energizes start fuel solenoid open and provides voltage to ignition exciter

14% APU speed…200 cu inch accumulator is depleted, APU motor/pump now act as pump and circulates hydraulic fluid from reservoir, bypassing utility hydraulic cooler through the pump with pressurized fluid returning back to reservoir through open AGB valve

70% APU speed…ESU de energizes the start fuel solenoid and ignition exciter

90% APU speed…ESU de energizes 90% relay, energizes AGB valve closed, and de energizes hydraulic APU start valve closed

Hydraulic pressure now buds up and drives AGB motor, which turns:

  1. Transmission AGB
  2. No. 1 and 2 AC generators
  3. No. 1 and 2 flight control hydraulic pumps
  4. Utility hydraulic pump
  5. Aft transmission lube pump

At this point, ESU provides ground to APU ON light indicating APU at 100% and working

BV234 (18 decks)

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