propulsion systems with controls
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Propulsion Systems Propulsion Systems With ControlsWith Controls
http://www.hill.af.mil/museum/info/C-17.jpg
Modern Turbofan EnginesModern Turbofan Engines
Utilize air bypassing the core to increase Utilize air bypassing the core to increase engine efficiencyengine efficiency
Trade off of kinetic energy for greater Trade off of kinetic energy for greater mass flow as bypass ratio increasesmass flow as bypass ratio increases
Two general classifications: Low Bypass Two general classifications: Low Bypass and High Bypassand High Bypass
Low Bypass TurbofansLow Bypass Turbofans
Bypass ratios less than 2 (twice as much air Bypass ratios less than 2 (twice as much air around the core as through the core)around the core as through the core)Enables much higher speeds (up to M~3), more Enables much higher speeds (up to M~3), more compact dimensions, and practical usage of compact dimensions, and practical usage of afterburners at an expense of fuel efficiency and afterburners at an expense of fuel efficiency and noise, making these engines suitable for fightersnoise, making these engines suitable for fightersTypical thrust class for this engine type is 10500-Typical thrust class for this engine type is 10500-22000lb, with the F119 putting out 35000lb with 22000lb, with the F119 putting out 35000lb with afterburnersafterburnersTypical T/W ratios of almost 8:1Typical T/W ratios of almost 8:1SFC:~.75 lb/lbf*hSFC:~.75 lb/lbf*h
High Bypass Ratio EnginesHigh Bypass Ratio Engines
Bypass Ratios 10+:1 (if any larger it is usually more Bypass Ratios 10+:1 (if any larger it is usually more efficient to mount a prop) utilizing large diameter fansefficient to mount a prop) utilizing large diameter fans
Have much larger thrust classes than low bypass Have much larger thrust classes than low bypass engines:30,000lb to as much as 130,000lbengines:30,000lb to as much as 130,000lb
The 75-100,000lb thrust class has become a popular The 75-100,000lb thrust class has become a popular choice for airliners as only two engines are requiredchoice for airliners as only two engines are required
Takes advantage of the Law of Conservation of Takes advantage of the Law of Conservation of Momentum to obtain large thrust values at the expense of Momentum to obtain large thrust values at the expense of top speed (larger air mass at a slower velocity)top speed (larger air mass at a slower velocity)
Average T/W from 5-6Average T/W from 5-6
SFC:~.37 lb/lbf*hSFC:~.37 lb/lbf*h
Engine ControlsEngine Controls
Compensators: Electronically limit an Compensators: Electronically limit an engines thrust to match an engine to engines thrust to match an engine to another in pairs, so that mounting 2 another in pairs, so that mounting 2 engines on different sides of an aircraft engines on different sides of an aircraft with not create yaw (usually utilize a with not create yaw (usually utilize a closed feed back system)closed feed back system)Engines must be individually tested to Engines must be individually tested to calibrate compensators and for information calibrate compensators and for information for FADEC usagefor FADEC usage
Engine Controls ContinuedEngine Controls Continued
FADEC: Full Authority Digital Engine Control (or FADEC: Full Authority Digital Engine Control (or DEEC Digital Electronic Engine Control)DEEC Digital Electronic Engine Control)
Controls Fuel Flow rates for precise control of Controls Fuel Flow rates for precise control of thrust, controls variable stator vanes, monitors thrust, controls variable stator vanes, monitors engines heath, and startingengines heath, and starting
Usually small enough to fit on engine (for larger Usually small enough to fit on engine (for larger engines) otherwise requires mounting in aircraft engines) otherwise requires mounting in aircraft fuselagefuselage
InletsInlets
Turbofan engines require airspeeds below Turbofan engines require airspeeds below M=1 to operate properlyM=1 to operate properlySupersonic inlet designs must incorporate Supersonic inlet designs must incorporate diffusers (normal or oblique shock) to slow diffusers (normal or oblique shock) to slow supersonic air to subsonic speedssupersonic air to subsonic speedsEngine ducting must feature smooth Engine ducting must feature smooth transitions from inlet shape to the engines transitions from inlet shape to the engines inlet shape to prevent turbulent air from inlet shape to prevent turbulent air from entering the engineentering the engine
NozzlesNozzles
The nozzle is used to The nozzle is used to accelerate the hot gas accelerate the hot gas from the combustion from the combustion chamber into the chamber into the atmosphere to produce atmosphere to produce thrustthrust
Some nozzles can adjust Some nozzles can adjust exit area to achieve the exit area to achieve the best thrust efficiency best thrust efficiency
Vectored thrust for Vectored thrust for maneuverabilitymaneuverability http://www.pr.afrl.af.mil/win/nozzle.jpg
AfterburnersAfterburners
Require high specific thrust operate efficientlyRequire high specific thrust operate efficiently
Lower specific thrust engines ie high bypass Lower specific thrust engines ie high bypass engines will not provideengines will not provide
Trade off of engine efficiency for large short term Trade off of engine efficiency for large short term gains in thrustgains in thrust
SFC:~2 lb/lbf*hSFC:~2 lb/lbf*h
www.enginehistory.org/P%26W/J58/J58_Afterburner.jpg
Necessary Propulsion HardwareNecessary Propulsion Hardware
EngineEngineStarter: takes bleed air from another source and Starter: takes bleed air from another source and transmits power through the engines gearboxtransmits power through the engines gearboxAPU: Auxiliary Power Unit provides electrical APU: Auxiliary Power Unit provides electrical power from aircraft subsystems and provides power from aircraft subsystems and provides bleed air for engine startingbleed air for engine startingCan also be started using a ground cart or Can also be started using a ground cart or explosive cartridge starting methods (B-52)explosive cartridge starting methods (B-52)Fuel tanks, lines, and possibly auxiliary fuel Fuel tanks, lines, and possibly auxiliary fuel pumps to pump from tank to tankpumps to pump from tank to tank