Powerplant Flashcards
Max Takeoff Power SHP
5071 SHP
Normal Takeoff Shaft Horsepower
4,580 SHP
Describe Nl
Low pressure axial compressure
Describe Nh
High pressure centrifugal compressor
What is the engine accessory gear box driven by?
high pressure (Nh) compressor rotor
What components are on the engine accessory gear box?
Fuel Metering Unit (FMU)
Oil Pump
DC Starter-Generator
Permanent Magnet Alternator (PMA)
What drives the propeller reduction gear box?
power turbine shaft
How much extra power does the FADEC deliver when the power levers are over-traveled past the rating detent?
25%
What components are mounted on the propeller reduction gear box?
Hydraulic Pump (main engine-driven pump)
AC Generator
Pitch Control Unit (PCU)
Propeller Overspeed Governor (POG)
Maximum reverse thrust SHP
1500 SHP
Describe the FMU.
The electro-mechanical Fuel Metering Unit is mounted on and driven by the engine accessory gearbox and controls fuel flow to the engine based on signals from the FADEC.
How many fuel pumps are in the FMU?
two integral engine driven fuel pumps; a low pressure pump and a high pressure pump
What are the functions of the FADEC?
controls engine fuel flow
controls various engine bleed valves to prevent compressor surges and stalls
prevents engine overspeed
controls automatic start and shutdown
supplies voltage to the Propeller Electronic Control (PEC)
detects and indicates powerplant faults
Electrical power source for the FADEC
Permanent Magnet Alternator (PMA) driven by the accessory gearbox when Nh is above 20%; essential DC bus initially
Describe how the FMU uses fuel pumps to meter fuel.
The low pressure pump receives low pressure fuel from the fuel tank boost ejector pump and sends it to the heater/filter element. After being heated and filtered the fuel is routed to the high pressure pump which sends it to the metering valve and then to the engine fuel nozzles. A portion of the high pressure fuel returns to the fuel tank to provide the motive flow necessary for the operation of the fuel tank ejector pumps.
Describe a FADEC critical fault.
FADEC will automatically respond to a critical fault with either a power stabilization to flight idle or engine shutdown.
Describe a FADEC Cautionary Fault.
condition that requires caution when applying control inputs; may result in either the necessity to reposition power levers to maintain symmetrical torque, or power lever movement that causes engine surge
Describe a FADEC Advisory Fault.
automatically accommodated by the FADEC and does not result in the illumination of warning lights or caution lights; transmits fault code to the Engine Monitoring Unit (EMU)
When does the Automatic Takeoff Power Control System (ATPCS) automatically arm?
both power lever angles “high” and torque on both engines at least 50%
An uptrim condition is indicated in the cockpit by:
“UPTRIM” message on ED
change in power rating from NTOP to MTOP on ED
change in torque bug position from NTOP to MTOP
A power uptrim will occur when either of the following conditions exist:
torque on the failed engine falls below 25% with the power levers in the RATING detent and MTOP not selected
power turbine speed (NPT) falls below 80% with the power levers in the RATING detent and MTOP not selected
Describe the Nh overspeed protection.
powerplant has an independent overspeed protection circuitry (dual channel) built into the FADEC which has the capability to cut off fuel flow to the engine through the Fuel Shutoff Solenoid (inside the FMU)
Propeller system components
Propeller Electronic Control (PEC) Pitch Control Unit (PCU) Propeller Overspeed Governor Unit (POG) Auxiliary Feathering Pump Automatic Propeller Synchrophase System
Describe the PEC.
The Propeller Electronic Control is a dual channel microprocessor based controller which uses inputs from the airplane, propeller control system sensors, and the engine control system to control propeller pitch and speed. The PEC is soft mounted aft of the propeller reduction gearbox and performs a number of safety functions.
Describe the functions of the PEC.
Autofeather
Automatic Underspeed Propeller Control
initiates power UPTRIM command to the FADEC
Describe the PCU.
The Pitch Control Unit is a hydromechanical device that interfaces with the propeller to meter high pressure engine oil to a two stage servo valve mounted on the PCU which controls propeller speed by directing the flow of high pressure oil into the fine pitch or course pitch chambers of the prop pitch change cylinder as directed by the PEC. It also controls the minimum blade pitch that can be obtained in flight.
Describe the POG.
The Propeller Overspeed Governor unit is an independent mechanical system used to limit the propeller speed in case of a propeller overspeed malfunction; incorporating a high pressure pump (driven by the reduction gearbox) to provide the PCU with high pressure oil from the engine gearbox. The Governor is a flyweight design, driven directly from the drive gear of the pump.
Describe the Auxiliary Feathering Pump.
The Auxiliary Feathering Pump consists of a 28 volt DC electrical motor driving an external gear pump which is mounted on the aft side of the propeller reduction gearbox and provides a secondary source of oil pressure for feather the propeller. The pump is automatically activated when autofeather occurs and is manually activated when alternate feather is selected.
Describe the Propeller Synchrophase System.
When the speeds of both propellers are within a predetermined difference of one another in flight, the PEC automatically enters a synchrophase mode to reduce propeller noise. The phase angle is calculated by timing the differences between the master prop (left) and slave prop (right) Magnetic Pickup Unit signals over a complete propeller revolution. Does not operate during takeoff.
When does the autofeather system arm?
autofeather system select ON
torque of both engines exceeds 50% and both power levers are advanced beyond a 60 degree angle.
When does the autofeather system trigger?
torque of the failed engine falls below 25% for at least three seconds
How long does the Auxiliary Feathering Pump activate after an autofeather?
approximately 30 seconds
Explain how the POG works.
incorporates hydraulic and electronic section to reduce high pressure oil supply when prop speed exceeds 1071 rpm and/or uses FADEC Np overspeed circuitry to signal FMU to reduce amount of fuel being supplied to the engine when prop speed reaches 1122 rpm
Describe the engine ignition system.
consists of one dual channel exciter unit and two igniter plugs in the combustion chamber; controlled by FADEC
Name and describe the start malfuntions.
Hot start - ITT exceeds 920C
No light off - engine does not light within 16 seconds of fuel intro
Hung start - Nh does not reach 50% within 70 seconds
No starter cutout - START light remains illuminated (QRH)
Starter Failure - SELECT light remains illuminated (QRH)
Describe the difference between an air start and ground start.
Air start:
both igniters are activated
FADECs auto abort circuits are disabled
FADECs automatic ITT limiting feature is disabled
When does the START SELECT switch automatically center itself during at start?
Nh reaches approximately 50%
How is engine oil cooled?
automatic routing of oil through an air cooled oil cooler (cooler door located on the underside of the engine nacelle)
1 or #2 ENGINE OIL PRESS warning light
engine oil pressure below 44 psi
1 or #2 ENGINE FADEC FAIL warning light
FADEC has malfunctioned
1 or #2 ENG FUEL PRESS caution light
pressure at engine driven fuel pump inlet is low, ejector pump failure or loss of motive flow to the ejector pump
1 or #2 ENG FADEC caution light
FADEC sensed a condition that requires caution when applying control inputs
1 or #2 PEC caution light
PEC senses a beta mode malfunction
Describe the autofeather process.
Following a 3-second delay, the propeller of the failed engine will then automatically feather. Immediately after the autofeather of the failed engine’s propeller is initiated, the autofeather system automatically disarms and the AF/ARM advisory message on the ED disappears. The disarming of the system prevents any possible occurrence of a dual autofeather. The associated Auxiliary Feathering pump is activated for approximately 30 seconds to assure adequate oil pressure is available to feather the failed engines propeller. The associated Alternate Feather switchlight (guarded) on the Propeller Control panel will illuminate indicating activation of the Auxiliary feather pump.
The Autofeather system then sends an Np underspeed cancel signal to the failed engines FADEC preventing the FADEC from increasing NH in an attempt to maintain propeller speed as the feathering propeller speed decreases below 660 rpm.
The Auxiliary feathering pump also serves as a backup source of oil pressure to the propeller pitch-change mechanism in the event of a loss of engine oil pressure. The pump is supplied with oil from an auxiliary oil reservoir built into the case of the propeller reduction gearbox.
