Turboprop Engines

Turboprop Engines

Propulsion Devices (Engines)

Air-BreathingUse atmospheric air (+ some fuel) as main propellantRocketsCarry entire propellant (liquid/solid fuel + oxygen)Piston, Gas Turbine and Ramjet EnginesJet-engine.ppt, 10-7-01Gas Turbine Engines (most aircraft jet engines): Use high-temperature gases to power a propeller or produce direct thrust by expanding and accelerating the exhaust gases through a nozzle. Three main types: Turboprop , Turbofan and Turbojet

Jet Engines Basic Operation Air enters the trough the intake duct (cowl). Air compressed by passage through the compressor. Mixed with fuel in the combustion chamber. Fuel is ignited, Pressure and Temperature raised Some of the pressure used to turn a turbine; Turbine shaft drives the compressor. Hot, high pressure air forced through a nozzle. The reaction force is the engine thrust.

Schematic of a Turboprop engine

Turboprop20 to 25% of Thrust produced by Nozzle75 to 80% of Thrust produced by PropellerOperating Mach No: 0.4 to 0.65Subsonic Aircraft (0.1 to 0.8)

Examples

Super Hercules C-130JEngine: 4 Rolls-Royce AE 2100D3 turboprop, 3,458 kW eachPropellers: Dowty R391 6-blade composite propeller, 1 per engineMaximum speed: 362 knots (417 mph, 671 km/h)Service ceiling: 28,000 ft (8,615 m) with 19,090 kilograms payload

Turbofan20 to 40% of Thrust produced by Nozzle60 to 80% of Thrust produced by FanOperating Mach No: 0.4 to 0.8High Subsonic Aircraft (0.3 to 0.8)

ExamplesAirbus A380

Boeing 777

Turbojet

Chemical energy is converted into mechanical energy100% Thrust produced by NozzleOperating Mach No: 1 to 2Supersonic Aircraft (1 to 5)

Examples Sukhoi-Su-30MKI

Engine: 2 Lyulka AL-31FP turbofans with thrust vectoring, 123 kNMaximum speed :Mach 1.9 (2,100km/h or 1,300mph)Service ceiling: 17,300 m (56,800 ft)Max. takeoff weight: 38,800 kg

LCA Tejas Mark-II

Engine :1 F404-GE-IN20 turbofan thrust 89.8 kNMaximum speed : Mach 1.6 (1,350km/h)Service ceiling: 15,240m or (50,000 ft)Max. takeoff weight: 13,200 kg

A Turboprop engine differs from a turbofan and turbojet as it produces the thrust required for the aircraft by using a propeller rather than the exhaust gases of the turbine itself.The exhaust gases itself cannot provide enough thrust for the aircraft as most of the power is directed towards the propeller.The propeller is coupled to the turbine through areduction gearthat converts the highRPM, lowtorqueoutput to low RPM, high torque.Turboprop engines are mostly used in subsonic aircrafts and work most efficiently at speeds under 450 mph (390 knots)They are mostly used when there is a requirement of a high-performance take-off and landing and efficiency at moderate speeds.

Turboprop engines usually contain at least one stage ofcentrifugal compression. Centrifugal compressors have the advantage of being simple and lightweight, at the expense of a streamlined shape.

Greater power and reliability compared to reciprocating engines.Turboprop airliners operate at near the same speed as smallturbofan-powered aircraft but burn two-thirds of the fuel per passenger.It can use shorter runways for take off and landingAdvantages of Turboprop engines

Disadvantages of Turboprop engines

Compared to aturbojet(which can fly at high altitude for enhanced speed and fuel efficiency) a propeller aircraft has a much lower ceiling.Lower thrust-to-weight ratio when compared to a Turbojet engine.

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