Systems Flashcards
(26 cards)
234 Engines
Avco Lycoming AL5512 gas turbine engines
Fuel Capacity
UT two 500gal tanks (489 usable)
Cargo hook assembly is rated for
28,000lbs
Drive system consists of
5 transmissions, 2 engine drive shafts, 9 synchronizing shafts, and a vert shaft
Dimensions rotors turning
99ft long
60ft wide
How many oil coolers in the aft pylon
4
APU
Solar T62-T-2C
95 SHP
Includes a hydraulic motor/pump, a fuel control unit, and an automatic electronic sequencing unit
AGB
Auxiliary Gearbox
Provides complete electrical and hydraulic power for main engine start, and for flight control and electrical checks on ground
Reduction Drive Assembly
Drives the accessory drive, APU oil pump, APU speed detector and fuel control, and reduces RPM from 56,000 to 6000 and 4200.
Hydraulic APU Motor/Pump
Acts as a motor to start the APU
Acts as a pump to turn the AGB
What happens when the pilot moves the APU switch to the START position?
The airframe fuel pump takes fuel from the LH tank and pressurizes it to the fuel control assembly
This action also opens the hydraulic start valve, activating the hydraulic motor pump.
At what engine speed does the start fuel valve open?
5% engine speed
This is when a single igniter is activated to ignite vaporized fuel.
What occurs at 14% APU rated speed?
The APU main fuel solenoid valve opens, allowing maximum fuel flow to the fuel manifold
This flow is directed to six vaporizing tubes in the combustor.
How is fuel flow controlled after the main fuel solenoid valve opens?
By engine compressor discharge pressure acting on the diaphragm in the APU governor section
Fuel flow increases in proportion to increasing compressor pressure.
What happens at 70% rated speed?
The igniter, hydraulic pump, and start fuel solenoid are all switched off
Main injectors continue to supply fuel for combustion.
What indicates a failure to start the APU?
A fault indicator on the ESU will indicate ‘Fail to Start’ if the engine fails to reach 90% rated speed in 40 seconds
This is part of the fault logic in the ESU.
How is engine speed governed in the APU?
By a flyweight assembly within the governor housing
The assembly reacts to changes in centrifugal force as the APU is loaded.
What happens when the APU rotor shaft slows down?
A reduction of centrifugal force acting on the flyweights occurs
This reduction is felt through a bearing plate and valve assembly.
Fill in the blank: The governor control spring expands, moving the fuel metering valve to _______.
increase fuel flow
This action continues until normal engine speed is regained.
True or False: The same action that increases fuel flow can also protect the engine from overspeed.
True
The governor mechanism works in reverse to protect the engine.
What happens when the engine is suddenly offloaded?
A minimum flow orifice installed in the fuel control housing bypasses the governor, allowing a small amount of fuel under pump pressure to flow to the main fuel nozzles.
What is the function of aneroid bellows in the fuel system?
They register changes in ambient air pressure and increase or decrease the fuel flow accordingly.
How does a pilot shut down the APU?
The pilot moves the OFF/RUN/START switch from RUN to OFF position.
