Powerplant Flashcards
Reduction Gear Box Items
Prop brake Prop pump and over speed governor ACW generator Aux feather pump Propeller Valve Module Fuel Cooled Oil Cooler
Accessory Gear Box
DC starter/generator
HP fuel pump
Engine oil pumps
Power Plant Overview
Aircraft fitted with
– two Pratt & Whitney, PW 127 E (42-500)
– two, six blades propellers (Hamilton 568F)
It’s a free turbine engine, composed of 3 concentric shafts and spools:
– The shaft of the HP spool composed of the HP turbine and the HP compressor (rotation speed of the HP spool: NH). The HP spool drives the accessory gear box (AGB)
– The shaft of the LP spool composed of the LP turbine and the LP compressor
– The Power shaft composed of 2 power turbines (Free turbines). The 2 power turbines drive the propeller through the reduction gear box (RGB)
Fuel System
Fuel from the tanks flow through:
- A fuel heater (heat transferred from engine oil) to
- The HP pump and filter to
- The HMU (Hydro Mechanical Unit) that meters fuel and provides motive flow to the tank’s jet pump to
- A fuel flow meter to
- The FCOC (Fuel Cooled Oil Cooler) to
- The Flow Dividers containing the fuel nozzles.
Lubrication System
A single system serves both engines. The tank holds 14.4L and is fitted with a filler cap and sight gauge. A gear pump driven by the AGB supplies oil through an air cooler and a filter while RGB oil is cooled by the fuel heater and the FCOC. Pressure is controlled by a regulating valve and a low temperature valve provides protection against surges during cold starts. A pressure transducer and a low pressure switch are also installed. Most scavenging is accomplished by blow down or gravity, but pumps are used to clear the RGB and bearing cavities #6 and #7.
Ignition System
2 engine mounted ignition exciters and 2 spark igniters per engine provide ignition for:
- Ground starting using either A or B system or both.
- In flight, A+B is used regardless of start selection.
- When Nh drops below 60% automatically except when Nh falls below 30%, the EEC is deselected (MAN IGN available), CL is in feather or fuel shut off.
- On a failed engine in case of ATCPS sequence.
Propeller
Driven by a free power turbine. Pitch change is hydro mechanically controlled by the PVM (Propeller Valve Module) which is controlled by the PEC (Propeller Electronic Control) and provides synchro phasing between the props. The control system takes inputs from the PLs, the CLs, and the PWR MGT Selectors to achieve pitch change. The system is protected against:
- low pitch in flight
- overspeed
- hydraulic pressure loss
Propeller Valve Module
The PVM provides: -basic prop speed setting (-14*(reverse) to 78.5* (feather)) -beta scheduling -reversing -synchro phasing -feathering -low pitch protection The PVM also works in conjunction with the overspeed governor to contain prop overspeed.
Propeller Electronic Control
The PEC controls the prop speed control system by detecting, isolating and accommodating system faults. Prop speed is calculated by the PEC using altitude and airspeed data from the EEC and the Np sensors.
Propeller Interface Unit
An electronic box that serves as a go between for the PEC and the cockpit instruments for prop speed selection and PEC fault signalization.
Propeller Brake
A hydraulic prop brake fitted to only the right engine RGB in order to stop prop rotation (power turbine rotation is stopped) for use in Hotel Mode. The right engine may then be used as an aux power unit running the DC electric system and the air conditioning system.
Prop Brake Ready Light
The prop brake may only be engaged when the ready is illuminated. To get the ready light, four conditions must be met:
- the aircraft must be on the ground
- the gust lock must be engaged
- the CL must be in either feather or fuel shutoff
- blue hydraulic system pressure must be available (2900psi)
Hydro-Mechanical Unit
The HMU performs several functions
- meters fuel to the engine
- commands a rotor speed per the top or base laws
- includes a stepper motor to adjust flow as commanded by the EEC
- ensures engine shut down (HPSOV)
- delivers motive flow to the tank jet pump
Engine Electronic Control
- Regulates a given power by controlling the HMU’s stepper motor to obtain a calculated torque as function of PLA, PWR MGT selector, flight conditions, position status of the bleed valves.
- Ensures minimum prop speed control on the ground and low power settings.
- Delivers uptrim to the good engine in conjunction with the ATPCS during engine failure.
- Controls the Handling Bleed Valve (HBV) to ensure correct LP Compressor operation.
Top Law (EEC ON)
Is a TQ(PLA) control law to produce a constant power backed up by an Nh(PLA) law that takes over at low power, in case of engine torque control failure, or in Hotel Mode. The EEC commands a determined power (torque value) for a given prop speed and PL setting depending on rotary selector position. Power is maintained at maximum automatically within mechanical and thermodynamic limits.
