Engine Flashcards
General
AVCO Lycoming AL 5512
Direct drive shaft turbine engines with 2 stage free type power turbine, external annular combustor, and 2 stage gas producer turbine that drives a combination axial centrifugal compressor
Rated at 2975shp MCP and 4355shp 30 min OEI
6 Sections of Engine
- Air inlet
- Accessory drive
- Compressor
- Diffuser and combustor
- Gas producer
- Power turbine and exhaust
Air Inlet Housing
Divided into outer and inner housing
Inner housing has mounts for:
- Engine oil supply tank
- Engine transmission nose box
- Torque meter box
- Starter drive
- Oil tank filler
- Accessory drive gearbox
Inner housing encloses:
- Output shaft support housing
- Power turbine overspeed governor drive
- All accessory drive gearing
- No. 1 and 3 bearings and supports
- No. 6 and 7 bearings
Overspeed control is mounted externally on housing at 11 o clock
Compressor
Housing is split into 2 halves and encloses 7 stage axial compressor and single stage centrifugal compressor
6th stage stator location accommodates bleed band which covers air bleed holes in housing
Compressor rotor consists of 7 compressor rotor discs, 7 spacers, and a centrifugal impeller
Compressor rotor encloses but doesn’t connect to power turbine shaft
Diffuser
Moves air from compressor to combustion chamber, reverse annular flow design
Supports:
- No. 2 main bearing housing
- First turbine nozzle
- Diffuser curl
- First turbine rotor cylinder
- 2nd turbine nozzle
External oil lines connect to tubes in air diffuser, providing No. 2 bearing housing with pressure and scavenge oil flow
Oil pressure measured at tee attached below No. 2 bearing strainer housing externally on air diffuser
Combustion Chamber
Composed of:
- Housing
- Vanes
- Liner
- 2 drain valves
Air from diffuser flows through outer air case to rear of assembly at which it is changed 180*
Slots cut in surface of flame tube allow air to enter and maintain good fuel/air mixing
28 fuel nozzles, 2 manifolds fitted to rear of flame tube facing forward. Once ignited hot expanding gas reverses flow direction 180*
Dump valve and flow divider allows excess fuel to drain from combustor assembly when engine is stopped
N1 Gas Producer Turbine
2 stage axial flow air cooled system mounted on rear of compressor shaft
Each turbine has set of guide vans, one set of nozzles, and one turbine wheel which forms a complete turbine stage
Power Turbine
2 stage axial flow assembly supported on rear by dual set of main engine bearings
Assembly includes No. 3 and 4 turbine discs and turbine nozzles
Power transmitted by power turbine is transmitted forward through compressor shaft via power turbine shaft and terminates within air inlet assembly
Torque meter head splined to front end of shaft coverts twisting moments into electrical signals to drive cockpit gauges
PTIT is measure at stage 3 nozzle section by 5 thermocouple probes mounted circumferential around nozzle
Accessory Drive Gearbox
Located at bottom of air inlet housing
Drive by by shafts located with 6 o’clock strut of air inlet housing
Gear on top of section of each shaft driven by N1 and N2 respectively
Bottom of shafts drive following components within accessory drive:
N1: fuel pump, oil pump, N1 tach, FCU
N2: N2 tach, overspeed generator, FCU speed sensor
Chip detector installed in lower left side of gearbox
Fuel Flow
Start fuel flows into combustion chamber through 2 starting fuel nozzles and ignited by 4 spark plugs
N1 increases, causing metered main fuel to go from fuel control to fuel/oil heat exchanger, onwards to high pressure side of fuel preheater, where fuel is heated as it passes through low pressure side
Fuel then passes in line fuel filter to flow divider, which provides primary and secondary fuel flow separation to 28 fuel nozzles.
Fuel is then ignited
Fuel Control
FCU is a computer supplied with 6 variable inputs with an output in the form of metered fuel supply. T2 and P3 adjust the output as atmospheric conditions vary. N1 and N2 speeed sensing maintains stable engine running relative to power and speed demands made by pilot. Demand by ECL when set to FLIGHT will always be for FULL gas generator power. Demand by Logic N2 control box will always be for LESS THAN THAT CALLED FOR BY ECL. FCU responds to LOWEST figure, therefore N2 will be governing factor
Protects engine from over temperature or compressor surge during accelerations by automatic acceleration limiter and compressor air bleed system
Deceleration limiter protects against flameout during deceleration
N1 and N2 controlled by FCU by varying fuel to engine fuel nozzles.
Each fuel control includes:
- Single element fuel pump
- Gas producer speed governor
- Fuel flow limiter
- Fuel control fuel shutoff valve
- Main metering valve
Engine Oil System
Oil tank integral with air inlet housing which supplies an engine driven pump assembly made up of one pressure pump and 2 scavenge pumps
Oil tank contains 3.75 gallons, ENG OIL LEVEL annunciator illuminates when contents fall to 1.6 gallons
ENG OIL PRESS LOW comes on when oil pressure falls below 15-19psi
Oil flows from tank to pressure pump, through a filter and then to fuel/oil heat exchanger. Oil then goes 2 separate paths, one to the front section of engine and other to rear section. Pressure relief valve protects the system and a cooler bypass valve insures adequate oil circulation at low temps or if cooler is blocked
Oil from front section drains into accessories drive gearbox. Oil is returned to reservoir by paddle type scavenge oil pump. Oil draining from No. 4 and No. 5 bearing in rear section of engine, along with oil from No. 2 bearing, is passed to engine accessories drive gearbox with assistance of a paddle pump. From there, the main element of scavenge pump returns oil to passages within air intake, where the oil is cooled by inlet air and then drained into main reservoir
During start, when oil is cold, a valve opens to allow scavenged oil to bypass the air inlet passages and return directly to tank
Venting system bleeds air/oil vapor from accessories gearbox and oil tank, to the engine starter gearbox where it is separated by a centrifuge. Air is vented to atmosphere, oil returned to tank
Chip detector in accessory gearbox attracts metal and illuminates associated ENG CHIP DET light. Rear bearing oil from No. 4 and No. 5 bearings and scavenge oil line from No. 2 bearing flows separately into a housing containing dual chip detectors which have no cockpit indication
Engine Condition Levers
ECL moves position sensor, resulting in movement of N1 actuator. Actuator mechanically operates a lever which controls fuel control shutoff valve and operating speed of gas producer.
In event of high side N2 governor malfunction, ECL can be used to control engine power output. Retarding ECL from FLIGHT hands N2 control over to N1.
If electrical power is lost a built in mechanical brake holds the actuator at its last selected position .
Ignition and Starting System
Engine start uses hydraulic power from utility hydraulic system.
Consist of:
- Ignition exciter
- Igniter plugs
- Coil and cable assembly
- Hydraulic starter
- Start solenoid valves
- Hydraulic relief valves
- Engine starter switch
Engine Start Notes
To start engine ECL must be in STOP with boost pumps on and switch to MOTOR
28 volt DC will be directed to engine from either EMERGENCY BUS for No. 1 engine or No. 2 DC ESS BUS for No. 2 engine, causing start valve to open. This allows utility hydraulic pressure to power engine start motor and crank engine. Simultaneously, utility system ISOLATION VALVE will close, isolating all of utility subsystems, giving engine start exclusive priority of available fluid pressure. Additionally, power to left, right, and center windshield anti icing circuits, cabin heater and blower circuits, avionics cooling fan, and right and left aft fuel boost pumps are removed to reduce electrical load
- subsystems will remain isolated until engine start switch is placed OFF*
- when engine is being started, start valve for other engine is kept de energized by open contacts from energized start relay. This prevents trying to start both engines at once*
When ECL set to GROUND and starter switch moved to START, 28vdc power is routed through engine ignition unit and ignition coil and cable to the 4 spark plugs. Additionally, start fuel solenoid valve is energized open
Once N1 stable at 50-55%, place switch OFF. This will close engine start valve, re open utility system isolation valve, and cause ENG START light to extinguish. Start relay cross-tie will also permit other engine to be started.
Overspeed Protection System
Reduces engine power turbine speed to safe operating level in event of overspeed
System will active when N2 rises above 114%, and consists of:
- Overspeed harness
- Overspeed controller
- Fuel limiting valve
- Power turbine mag speed pickups
Overspeed controller receives speed info from mag speed pickups on tach drive shaft. At predefined pulse repetition frequency (aka 114% N2) the controller will power fuel limiting valve, which reduces fuel flow until N2 drops below 114%
To prevent any false signals from activating the overspeed system, signal discrimination and the use of separate digital AND analog speed sensing channels much both agree that an overspeed condition exists before controller will actuate
Fire Detection Circuitry
3 circuits, 2 identical for engines and 1 for APU compartment
Circuit consists of a dual loop detector containing a sensor and responder routed around each engine
When fire detector is energized by abnormal temp, the corresponding fire handle (for engine) or push button (for APU) is activated. Both circuits in the dual loop engine system must sense and over temp condition before FIRE PULL handle eliminates
Power for fire detection system is supplied from 28vdc emergency bus through FIRE DET CB on overhead panel
Torque Sensing System
Output shaft of engine, rotating within the electric torquemeter head, acts as the core of a transformer and magnetic properties vary with torque
Inverter provides reference signal for primary winding of torquemeter head assembly, and current produced in transformer secondary winding is proportion to torque developed by engine
Power to operate indicators (gauges) is provided from No. 1 and No. 2 AC essential busses
Power for inverters for No. 1 and 2 engines is provided by No. 1 DC essential buses through the ENG NO. 1 TORQUE and ENG NO. 2 TORQUE CB
Junction box on the engine air inlet housing converts transformer secondary output to DC signal for operation of torquemeter
PTIT System
System monitors the gas temp of each engine upon exiting gas producer turbine assembly and prior to entering power turbines
10 thermocouples are installed on each engine measuring heat as electro magnetic frequencies
Signal goes to both the PTIT gauge and engine monitor
Fuel Pressure
Transducer measures fuel pressure at input side of engine fuel control
Power is supplied from the No. 1 and 2 DC essential buses
Loss of 28vdc power to indicator will cause associated pointer to indicate less than zero
Fuel Temp
Sensed between output end of fuel pump and input end of barrier filter
Engine Monitor System
Designed primarily for recording performance during OEI testing
Panel receives 28vdc power from the No. 1 DC bus and 115 VAC power from No. 1 AC bus
In event of instrument failure, engine monitor panel can be used for normal readout
