APU Flashcards
APU
Auxiliary Power Unit
The APU provides the means for engine starting without the need for an AGPU. It is located just inboard of the right engine nacelle in the aft equipment bay.
APU indirectly supplies
Hydraulic pressure and electrical power for operations
APU directly supplies
Pressurized air for the operations of systems
APU Fuel systems
The aft fuel cell provides all fuel for APU operation. The APU fuel control automatically regulates fuel flow. The APU burns approximately 175 lb of fuel per hour.
Lubrication System
The APU has a self con-tained oil system. An oil filler cap is on the left side of the unit. Oil cooling is provided by airflow over cooling fins at the compressor inlet. The sight gauge can be in-spected through a door in the bottom of the right engine nacelle.
Electrical System
The APU electrical system requires DC power. This power is normally delivered by the helicopter battery when the MSTR IGN switch is set to BATT.
What happens when the APU push button is pressed?
When the APU pushbutton is selected ON:
• DC power is applied to energize the APU boost pump
• The APU fuel shutoff valve is opened
• A signal is sent to the APU ECU to initiate the start sequence
When will the APU push button illuminate?
When the APU speed reaches 95%, the ON label in the button illuminates and the APU ON advisory is displayed.
APU Electronic Control Unit (ECU)
The start valve opens when the APU pushbutton is pressed to ON and closes automatically at 60% APU speed. The ECU monitors the APU for the following:
• Loss of thermocouple
• Overtemperature
• Overspeed
• Overcurrent
• Low oil pressure
• Percent RPM
• Exhaust gas temperature
Utility Hydraulic Accumulator
The accumulator, on the deck of the aft equipment bay below the APU, provides hydraulic pressure to the APU hydraulic starter through a solenoid operated hydraulic start valve.
Main Transmission Low Oil Temperature Sensor
The main transmission low oil temperature sensor provides transmission oil temperature information to the mission processor for cold start of the APU.
What burns more fuel power levers at ideal with APU on or power levels at fly? (When in the ground)
Power levels at fly burns less fuel than idle with APU on.
Also safer because you have control authority and it’s quicker to get off the ground.
APU FUEL BURN
175 lbs/hour
When both engines are at fly and APU is on what is supplying IPAS air?
APU will provide low pressure when it is on
Engine will provide high pressure.
Engines are the primary source of IPAS except when the APU is on.
APU fuel Subsystem
consists of an electrically driven APU boost pump which draws fuel from the aft fuel cell and provides pressurized fuel to the APU. The APU shut-off valve controls the flow of fuel from the aft cell to the APU via the boost pump.
