APU Flashcards
Location of the APU
On the right side of the MWGB
Purpose of the APU
To provide power to the MWGB during ground operations for start and shutdown while the proprotors are not turning.
The ____ reduces the APUs operating speed to match the MWGBs operating speed
APU accessory/speed reduction gearbox.
The APU powers the MWGB which in turn powers what systems
Electrical, Pneumatic, and Hydraulic systems
How does the APU get fuel
Fuel is suctioned from the right feed tank by the APU fuel pump at approx. 300 lb/hour
APU power output
300 shp
Location of the APU Control Panel
Overhead console
What provides power to start the APU
28 VDC electric start motor that gets power from the battery or external power source
APU start limitations
Wait 15 seconds before each attempted APU restart. If it fails to start after 3 attempts than allow the start motor 55 minutes before an attempted restart
2 major sections of the APU
- Power Section2. Gearbox/Reduction Drive Assembly
APU Power section
Consists of a constant speed gas turbine with a single stage radial flow compressor, a combustion chamber, and turbine elements
APU Gearbox/Reduction Drive Assembly
Reduces APU rpm for use by the MWGB and drives the APU oil and fuel pumps. It houses the reduction drive assembly, accessory drive, integral clutch, and output drive.
APU Ignition and start system
Ignition exciter provides 5,000 volts to energize the 2 igniter plugs that ignite the fuel air mixture
5 subsystems of APU
- Ignition and Start System2. Lubrication System3. Fuel System4. Electronic Control Unit (ECU)5. Event Monitoring System (EMU)
How many chip detectors are in the APU oil system
2 located on the bottom of the gearbox reservoir
How many fuel nozzles are there in the APU fuel system
2 start nozzles which the ECU signals close and the 6 main fuel nozzles to open
ECU
Electronic Control Unit - full authority digital controller that performs APU sequencing, condition monitoring, fault isolation, and protection of the APU system.
Functions of the ECU
- Communication with the wing fire protection system to shut down APU in case of fire2. Enables APU to clutch to MWGB after reaching operation temperature or lapsed time interval3. Transmits malfunction indications4. Controls the APU start schedule, fuel flow, turbine speed, and shutdown
ECU Automatic Shutdown Criteria
- Turbine overspeed (103.2%)2. Turbine underspeed (95%)3. Low Oil Pressure (less than 20 +/- 5 psig)4. High Oil temperature (greater than 149 degrees C)5. High EGT6 Midwing Fire detected by wing fire protection system (WFPS)
EMU
Event Monitoring Unit - houses the hour meter, start counter, pressure transducer, and temperature detector.
CRANK position of APU control Panel
starter powered rotation without fuel or ignition.
CRANK position limitation
30 seconds
RUN/DISENG position of APU control Panel
Performs initial BIT and normal start but does not result in engagement of APU clutch to MWGB
RUN/ENGAGE position of APU control Panel
Performs initial BIT and normal start and allows the internal clutch to engage the MWGB
