Powerplant Flashcards
What engine is on the B4?
Turbomeca Arriel 2B1
Horse power
2B1 and 2D
2B1 - 728 MCP, 747 TO
2D - 856 MCP, 952 TO
What engine is on the T2?
Turbomeca Arriel 2D
Describe the engine
Features a:
- free turbine engine
- gas generator shaft and power turbine shaft are completely independent
- speed governor = adjusts free turbine to a constant RPM by acting on the gas generator
- Modular design = main components can be inspected/replaced without returning engine to factory
Conditions the governor uses to make adjustments to the free turbine speed
- respective of altitude and pedal positioning
- irrespectice of collective pitch/phase of flight
Gas generator turbine speed (Nr/N1)
B4(Nr): 52,110 RPM at 100% (counter clockwise)
T2(N1):
Free turbine speed (Nf/N2)
B4(Nf): 39,095 RPM at 100% (clockwise)
T2(N2):
Output shaft rotation speed?
B4: 6,000 RPM (clockwise)
T2:
Where is the engine located?
In a fireproof compartment aft of the MGB and above the rear cargo compartment
How is the engine connected to the MGB?
via a shaft mounted between two flexible (Thomas) couplings
How many indepented modules make up the engine?
5
Mod1
Output shaft and Accessory Gearbox
Transmits power to MGB and Accessory drive couplings
Mod2
Single-stage Axial Compressor with bleed valve
What type and composition is the impeller?
Centrifugal Compressor
Composition is a single piece of forged titanium
Purpose of impeller vanes going from axial to centrifugal?
Axial to centrifugal vanes aid in the acceleration of the air rearward and rotationally. As the vanes transition to centrifugal the air continues to accelerate and gain velocity as it is propelled outward.
Stators are not necessary as they are replaced by the diffuser.
Air flow in the compressor
5.5 lbs/sec
What is the diffuser and its purpose?
The diffuser is a scroll with a series of divergent ducts
Its purpose is to trade the flow’s kinetic energy (high velocity) for increased potential energy (static pressure) by gradually slowing (diffusing) the gas velocity.
Mod3
Gas Generator Module
- centrifugal compressor
- annular combustion chamber
- single-stage gas generator turbine
What type of gas generator turbine do we have?
Single-stage, Axial, gas generator turbine
Mod4
Free Turbine
What type of power turbine do we have?
Single-stage, axial, power turbine
Mod5
Reduction Gear Module
Reduces the free turbine speed from
39,158 RPM to 6,000 RPM
Describe the Gears in the Reduction Gear Box
3 stage, steel helical gears
Drive gear - Intermediate gear - output gear
RPM Reductions at 100%
52,110 RPM - Gas Generator turbine (Nr)
39,095 RPM - Free Turbine (Nf)
6,000 RPM - Output shaft
3,568 RPM - Nominal TR RPM
386 RPM - Nominal MR RPM
How is the engine mounted?
Installed in a fireproof compartment
- Rear mounted by securing the torque tube to a support which is mounted to the floor via 2 rubber shock mounts
- Forward secured to the MGB via a flared coupling
How is T4 measured?
Measure at the free turbine inlet by 8 dual thermocouple sensors.
- 4 to the VEMD
- 4 to the FADEC
T4 confirmation box mounted below the torque tube
How is torque measured?
Measuring and comparing the drive torque and the drive resistance R (MGB)
- datum shaft has 4 integrated equally spaced teeth (outer ring)
- drive shaft (inner ring) has 4 equally spaced teeth
- 8 teeth form a speed sensor that induces a magnetic field
Whats included in the fire detection system?
- (ENG FIRE) red light
- 3 fire detectors
How do the fire detectors work?
Thermal bimetallic detector
- contacts open when an abnormally high temp is detected, contact opening brakes detection circuit
Where are the fire detector located?
3 fire detectors located at critical points outside the engine
1. RH side - 400C
2. RH side - 200C
3. Lower - 200C
What is the engine air system?
3 Systems in one
- Internal - pressurizes/seals oil lines, cools internal parts, balances forces on rotating assemblies
- Tappings - start injector ventilation, pressure measurement
- Compressor Bleed Valve
What does the Compressor Bleed Valve do?
The compressor has a high compression ratio = engine has good thermodynamic efficiency at operating RPM
During start/post start acceleration, airflow is too high - must be reduced to precent airsteam disturbances (stall or surge)
Bleed Valve provides airflow reduction automatically by comparing P3 (pressure internal, intake and filtered through air system) and P0 (ambient)
How are power changes in the engine accomplished?
Varying Ng speed via fuel flow
What does delta Ng refer to?
Difference between the actual (indicated) take-off power and the max computed take-off power
What 3 engine values are displayed on the FLI?
T4
Torque
Ng
What type of Bleed Valve do we have?
Pneumonic, butterfly valve
Controlled by P3/P0 pressure ratio
Components of the fuel control
- Engine Electronic Control Unit (EECU/FADEC)
- Fuel pumps and metering unit (HMU)
- Engine Back-up Control Ancillary Unit (EBCAU)
- Fuel Valve Assembly
What kinds of injectors do we use?
- Dual injectors used for start
- Centrifugal main injectors Ng >48
What is fuel flow governed by?
2 fuel metering valves/units in the HMU
- Main Fuel Metering Unit
- Back-up Fuel Metering Valve (EBCAU)
Describe the Main Fuel Metering Unit
- Needle assembly which regulates fuel flow
- Dual actuators (2 step motors - Channel A and B) drive the needle assembly based on ECU signals
- Position transmitter send needle info to ECU
Describe the Back-up Fuel Metering Valve
EBCAU. Purpose: back-up governing and fuel metering valve
- composed of a back-up electrical actuator
- actuator controls a valve
- valve allows flow of additional fuel
Where is the Fuel Valve Assembly located
Top of engine, aft of the bleed air valve
