5Meridian – PA46-500TP Power Plant The PT6A engine consists of two main sections:Gas generator sectionPower section.
6Meridian – PA46-500TP Power Plant The gas generator section takes outside air, compresses it and delivers it to the combustion chamber.The gas generator is separated from the power turbine in the Meridian application.The gas generator drives accessories mounted at the rear of the power plant.
7Meridian – PA46-500TP Power Plant The Power or Turbine section is separated from the Gas Generator in the Meridian PT6A-42A.The separation occurs between the forward most component of the gas generator (the compressor turbine) and the beginning of the power turbines.The Power Section shaft is connected to a gear reduction unit which, in turn, is connected to the propeller shaft.
8Meridian – PA46-500TP Power Plant External air is drawn in through a duct section, through screens, turned 180 degrees into the gas turbine or compressor that consists of three axial stages and one centrifugal stage.From there, the compressed air leaving the compressor passes through diffuser pipes which turn the flow 90 degrees, reduce its speed and direct the air into the combustion chamber.
9Meridian – PA46-500TP Power Plant In the annular combustion chamber the air is mixed with fuel and burned.Initially, two igniter plugs are used to light the fuel/air mixture when the engine is started.Once started, the igniter are not required to maintain the combustion process and can be shut off once the engine has reached idle speed.
10Meridian – PA46-500TP Power Plant The expanding hot gases are directed first through the compressor turbine and then through the power turbine.After passing through the power turbine, the gases are exhausted through ports on each side of the engine.The exhaust stubs fitted to the engine are normally directed to utilize the remaining energy of the gases in the form of thrust for additional aircraft propulsion.
11Meridian – PA46-500TP Power Plant The expanding hot gases are directed first through the Gas Generators’ forward compressor turbine, which provides the ongoing power to spin the Gas Generator.Expanded gases then pass through the Power Turbines, rotating the forward shaft which is connected to the gear box and on to the propeller shaft.Gases are exhausted through ports on each side of the engine. These exhaust stubs fitted to the engine are designed to utilize remaining energy of the gases in the form of thrust for additional aircraft propulsion.
12Meridian – PA46-500TP Power Plant Two bleed air systems are incorporated in the PT6A engine.Automatic bleed air from the compressor prevents compressor stall during acceleration from low engine speeds or deceleration from high engine speeds.For aircraft use, air may be bled for heating or pressurizing aircraft cabins.
13Meridian – PA46-500TP Power Plant These valves are located on the sides of the compressor at the 3 and 9 o’clock positions.During acceleration and deceleration of the engine, the Gas Generator produces more air than the Power section can consume, which could lead to compressor stall.Simply put, to prevent this, low and high pressure valves are installed that allow excess pressure to be vented overboard.When Ng is at 69%, the low pressure valve is closed and at 91%, both valves are closed.
14Meridian – PA46-500TP Power Plant A shaft connects the power turbine to the two-stage planetary reduction gearbox.Bevel gears, located forward of the second stage planetary gears, drive the following accessories that are mounted on the forward reduction gearbox case:The first stage reduction ring gear floats axially against a hydraulic torquemeter cylinder.· propeller governor or constant speed unitThe oil pressure in this cylinder is proportional to output torque. That pressure is used to provide data for the torque indicator in the cockpit.· propeller over-speed governor· tachometer-generator
15Meridian – PA46-500TP Power Plant The accessory gearbox, mounted on the rear of the engine, is used to drive the following engine accessories:· High-pressure fuel pump· Fuel control unit· Oil scavenge and oil pressure pumps.Space is also provided for aircraft manufacturer provided accessories such as the starter-generator, gas generator tachometer-generator, fuel boost pumps or hydraulic pumps.
16Meridian – PA46-500TP Power Plant – Fuel System The fuel system is designed to deliver clean fuel to the engine at the pressure and flow that are necessary for all engine operating conditions.The airframe fuel system contains the necessary boost pumps, transfer pumps, selector/shutoff valves, strainers and filters required to supply fuel to the engine and to manage the fuel load distribution in the airplane.The engine is equipped with a fuel system which consists of a fuel heater, high- pressure fuel pump, fuel filter, fuel control unit, start control or flow divider unit and a manifold with fuel injection nozzles.The fuel control unit is either a hydro-pneumatic or a hydro-mechanical system which meters the correct amount of fuel to the engine to maintain the gas generator speed selected by the pilot via the power control lever. It also controls fuel flow scheduling during engine starting, acceleration and deceleration.The PT6A engine is approved for operation with all commercial jet fuels, JP-4, JP-5 and for a maximum of 150 hours during any overhaul period with all grades of aviation gasoline. Specific grades of diesel fuel are approved as alternate fuels for restricted use. No engine adjustments are required in changing from one fuel to another, nor is it necessary to purge the fuel system when changing fuels, except when using alternate fuels.For listings of approved fuels and fuel additives refer to the appropriate Service Bulletins for each PT6A engine model.
17Meridian – PA46-500TP Power Plant – Engine Instrumentation Incorporated into the design of the PT6A engine are accurate and reliable torque and ITT measuring systems that give the pilot an accurate indication of the primary engine operating parameters.Torque Pressure is sensed by a torque pressure transducer mounted on the reduction gearbox, to indicate the torque being developed by the engine. Torque is the primary parameter used to set power for takeoff and cruise operation for specified propeller speeds.ITT is monitored to ensure that combustion gas temperature limits of the engine are not exceeded.Two tachometer-generators are installed on the engine: one on the reduction gearbox monitors propeller speed (Np), and the other on the accessory gearbox monitors gas generator speed, (Ng).Pressure and temperature gauges monitor the oil system.
18Meridian – PA46-500TP Power Plant – Engine Instrumentation Torque GaugeITT Temp GaugeNp - Propeller RPMsNg – Gas Turbine Percent RPMsOil PressureOil TempVacuumElectricalRudder TrimFuel Information
19Meridian – PA46-500TP Power Plant – Engine Instrumentation NOTES:Fuel Flow data is based on fuel consumed by the engine which is a very accurate measure. However, the Fuel Remaining and Endurance Remaining numbers rely upon accurate INITIAL FUEL information input by the pilot.Fuel Gauges report fuel as measured in the tanks by the fuel transducers.OAT Toggle: F or COATFuel GaugesFuel TotalizerFUEL FLOW DATACurrent FLOWFuel USEDFuel REMAININGENDURANCEReset Initial FuelExceedances
20Meridian – PA46-500TP Power Plant – Engine Controls Prop Lever & GovernorPower Lever Cam Assembly(opposite side)Fuel Lever
22Meridian – PA46-500TP Power Plant – Engine Controls Condition LeverCut-OFF/FeatherRunPower LeverPower rangeIdleBetaReverseMOR Lever (manual override)StoredFriction Lever
23Meridian – PA46-500TP Power Plant – Engine Controls NotesWarningsPower lever not to be moved into reverse when engine is off – may cause damage to linkages.Moving power below idle in flight is PROHIBITED. Doing so may cause loss of aircraft control, engine overspeed leading to loss of engine power.
24Meridian – PA46-500TP Power Plant - Review Pratt & Whitney CanadaPT6A-42A500 shaft horse power (SHP)Reverse flow, free turbineTurbine Speed: rpmsMaximum allowable torque – 1313 ft poundsGeared to 2000 rpm propeller speedMajor ComponentsCompressor – Gas GeneratorHot Section – Power SectionReduction gear sectionFuel : Aviation JetA or JetA-1Accessories:Starter GeneratorAlternatorAC CompressorOil is synthetic turbine oilSite gauge on left side of engineCheck quantity within 15 minutes of shut downQuantity within green on site gauge – OKQty below green, use dipstick to determine qty to addControls consist ofPower leverCondition leverManual Overide leverFriction lever
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