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Aircraft Gas Turbine Engines


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Aircraft Gas Turbine Engines

  1. 1. 11•History•Types Of Engines used on Aircraft•Basic understanding of their operation•Sections / Modules of a Gas Turbine Engine.•Significant Components installed on the Engine.For Flight Operation OfficersEngr, Zafar I. Jami
  2. 2. 22Short History The engine that Wright Brothers used to power thefirst aircraft was a standard automobile piston enginebased on Otto Cycle. Later, engines were made lighter and more powerful.These requirements lead to development of severalversions. More common types in use were: HO, V type liquid cooled and Radial air cooled. World War II brought rapid developments and adventof the Jet age. These also blossomed into several types: Turbojet, Turboprop and Turbofans.
  3. 3. 33Piston Engines.Piston Engines are based on Otto Cycle.Which is same as that used for mostautomobile engines. It normally works on aFour Stroke Cycle consisting of:1. Intake2. Compression3. Power and4. Exhaust strokes.There are three most common types which arenamed according to the arrangement ofcylinders around the crankshaft. These are• Horizontally Opposed (4 to 8 Cylinders)-80 to 400 Hp range, aircooled,• Vee type ( 8-12 cylinders) usually watercooled. Used on high performanceaircraft in WW II due lower Drag.• Radial (7 to 11 in Single Row or) 14 to 18 inDouble Row. Aircooled. -900 to 4000 Hprange.
  4. 4. 44Gas Turbine Engines.•They work on Brayton Cyclewhere:• The air is compressed inthe Compressor.•Then it is burned in theCombustor.•The hot gasses pass throughthe turbines that extractenergy to run theCompressor, Fan andaccessories installed on theEngine.•Then the gasses exhaust atvery high velocity producingthe required Thrust. Typical Brayton Cycle fora Gas Turbine.ExhaustNozzle
  5. 5. 55Types of Gas Turbine Engines• The first generation Gas Turbine Engines wereTurbojets that sucked air from the front andexhausted them at high speed from rearproducing reaction that pushed the aircraftforward.•Next came the Turbofans where a part of air wasexhausted without going through the coreproducing additional thrust. These are also calledBypass Jets and are more efficient than theturbojets.•Concurrently, for lower speed application, theenergy from exhaust was used to drive thepropeller after reducing its speed through aGearbox. These are called Turboprops.• The same engine, when used to power theHelicopter’s Rotor instead of a Propeller, is calleda Turbo shaft Engine.Early Bypass jetFan/LPC Core LPT
  6. 6. 66How an Engine powers theaircraft to fly? Propeller Aircraft: Propellers have airfoil shapedblades that generate Lift inforward direction when rotatedby the Engine. Jet Aircraft: It works on the Newton’s ThirdLaw of Motion: Every Action Has a Reaction. It discharges a jet of fast movinggas backward whose reactionpushes the aircraft forward.
  7. 7. 7Engines and Powerplant The Engine in the form that is Ready For Installation(RFI) on an Aircraft, is commonly called aPowerplant. It consists of Engine + QEC (Quick Engine Change): QEC – consists of Plumbing, Harness and Componentspeculiar to a position on an aircraft. Commonly installedComponents on the engine include: Starter Hydraulic Pump/s. IDG (or CSD + Generators). Anti-icing valves and ducts. Customer Bleeds.7
  8. 8. Note: - All OEMs have their own divisions and namesfor Modules.8Basic Sections (or Modules ) of aModern Turbofan Engine – (1).A. Fan and LPC: It consists of a Single Stage fan which has a muchlarger diameter than other stages and pushes the bypass air outwithout passing through the “Core” of the engine. In additionit has a few (usually 3-5 stages) of Low pressure compressor toreduce load on HPC.B. Core Module: This consists of:a. High Pressure Compressor (HPC): This usually has 7-14 stages ofalternate rows of blades and vanes that progressively increase thepressure to desired value.b. Diffuser and Combustor: In this section, the passage is widened toslow down the airflow and increase its static pressure. The air isthen led to Combustor unit where it is mixed with atomized fuelwhich burns to provide high energy.
  9. 9. 9Basic Sections (or Modules) of aTurbofan Engine (2).c. High Pressure Turbine (HPT): It consists of One orTwo Stage of Vanes and Blades. First stage vanes facethe highest temperature. It extracts power to run theHPC and the Accessory Gear Box.C. Low Pressure Turbine(LPT): This usually has 3-6stages of alternate rows of blades and vanes thatprogressively extract power to rotate the Fan/LPC.D. Accessory Drive Gear Box (AGB): It provides a drivefor all components and accessories installed on theengine. It gets power from the HP Shaft through aseries of gears and shafts.
  10. 10. 10Some significant Componentsinstalled on a Jet Engine…. (1)Fuel Pump : It gets fuel from the aircraft when thefuel shut off valve is in ON position. It usually have twostages. It delivers more fuel than required in theengine. The next unit bypasses the excess fuel back tooutput of the first (centrifugal) stage. Engine Fuel Control: In general, it receives fuelfrom the fuel pump, then computes the fuel required bythe engine and bypasses the remaining fuel back to FuelPump. It can be Fully Mechanical, Hybrid or FullyElectronic (Digital)- which are also called EEC or FADEC .
  11. 11. 11Some significant Componentsinstalled on a Jet Engine…. (2) Starter : They are either Electric or Pneumatic driven.Pneumatic starters are more common on larger engines. But thelatest trend is again towards Electric starters. They are mounted on Accessory Gear Box and drive Engine’s(HP) shaft through a gear train till the engine reaches a selfsustaining RPM. Pneumatic supply can be obtained from following sources. Ground Start Cart Auxiliary Power Unit Which itself has an electric starter that can be run on Aircraftbatteries. Through Cross Bleed from another running engine. Through air bottles in emergency.
  12. 12. 12Significant Engine Components..(3)Electric Generator: They are also mounted on the Accessory DriveGearbox. As they have to run at constant RPM, power to run theGenerator is transmitted from engine’s HP shaftthrough a Constant Speed Drive Unit. On newer aircraft, this unit is integral with theGenerator and housed in the same unit. Together, theyare called IDG. Usual supply from the generator is at 115V /400Hz.
  13. 13. 13Significant Engine Components… (4)Hydraulic Pumps and Plumbing. Hydraulic power is needed in aircraft to operateLanding Gears and several other components. Larger twin engined aircraft usually have two pumpson each engine, while the smaller ones have a singlepump. On most aircraft they provide hydraulic fluid at 3000psi. There are three tubes for pressure, scavenge and drainfluids which are joined with tubing from aircraft neartop of the pylon.
  14. 14. 14Significant Engine Components… (5)Engine Anti-icing and Customer Bleeds. As engine compressor is a ready source of hightemperature and high pressure air, some of it is bledout for different uses. Anti-icing air is bled from later sages, which is veryhot. As and when selected, it runs through the lip ofnose cowl or wing Leading edge and exhausts toatmosphere after heating it. Customer Bleed air is often taken from alternatelyfrom one of two stages in compressor (dependingupon requirement), and fed to the aircraft’s air-conditioning and pressurization system for controllingCabin’s pressure and temperature.
  15. 15. 1515What a Flight Dispatching Officer mustknow about the Engines. As the weight of the aircraftincreases, the engine has towork harder, not onlyduring takeoff, but alsoduring Cruise and Landing. This can result in twothings:1. Engine under certainconditions may fail.2. Repeated applications ofhigher power will lower itslife on wing. So remember, the Enginesthat work harder die young. Also, when such engines go tothe Shop, they are in moredepilated condition and costmuch more. As such, always try tominimize All Up Weightand ensure that it neverexceeds the weight permittedby the OEM’s manuals.
  16. 16. 1616How to be a good ‘Weight watcher’of an AircraftBe very vigilant to look for thefollowing: Unaccounted weightsspecially in passengers’baggage and hand-carries. Higher temperatures thanexpected at the time oftakeoff. Specially, a delayedmorning flight.o Excess fuel load evenwithin spec limits is bad forengines’ health. .Avoid fuel tankering foreconomic reasons unless itwill pay for added enginemaintenance costs. Consider safety first. If therecommended weight isbeing exceeded, neverhesitate to recommendoffloading of passengers,baggage or cargo even if itmeans loss of revenue anddelays.
  17. 17. 17Thank You!WarningThe presentation has been specifically prepared by the author for aPakistan CAA approved course conducted at Academy forAviation Excellence and material or pictures may not be copiedor used without specific authority from the author the Academy.Some material may also have a copyright.