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http://gizmodo.com/the-next-f-35-lightnings-engine-adapts-for-flight-figh-1456423944
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"What we are looking at with adaptive engines are engines that can operate at multiple design points across a range of flight envelopes while maintaining optimal operating efficiency," Kenyon said.
This adaptive cycle engine will utilize a secondary bypass stream (three air streams in total) to act much like the gearing on a car's transmission, allowing the F135 engine to adjust and match its bypass ratio at will, whether it's high-thrust takeoffs or high-efficiency cruising at altitude. "That third stream is something that we have the ability to modulate, to change the conditions of that flow," Kenyon told Gizmodo. "How much flow, and flow characteristics so that we can kind of optimize the bypass ratio over the flight envelope."
"On top of that adaptive fan we’re also making improvements, tremendous improvements in the core system as well. We’re putting in a higher pressure ratio, higher efficiency compressor, leveraging a lot of our advanced commercially-derived, 3D aerodynamic design capability...We’re looking at increasing the temperature capability and the efficiency of the turbine stages, and then we’re also looking at the exhaust system. Having that adaptive third stream allows us to work with that stuff as well...we’re making improvements to the efficiency of the core engine, but we’re also using the adaptive architecture to give us a lot more design options in terms of how we can manage the engine over the flight envelope."
http://www.pw.utc.com/Press/Story/20130925-1100/2013/All Categories
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Similar to changing gears in a car or on a bicycle, changing an aircraft engine's bypass ratio allows the engine to be optimized for high thrust takeoffs, while maintaining the efficiency of a commercial airline's high bypass engine in cruise conditions. Unlike commercial airline engines which are attached to the wing, engines used in modern fighter aircraft must use smaller diameter turbofans and be embedded within the aircraft. Consequently, there is a performance tradeoff between high thrust capabilities and optimum efficiency experienced in cruise conditions. Developing a next generation variable cycle adaptive engine is therefore essential to meeting the evolving needs of the warfighter.
Modern military turbofan engines have two airstreams – one that passes through the core of the engine, and another that bypasses the core. Development of a third stream of airflow will allow for improved fuel efficiency and cooler heat sinks which improve thermal management of the air system and reduced heat signature.
"Developing an effective adaptive fan concept is a critical step in advancing technology that will ensure next generation air dominance for our military," said Jack Hoying, program manager, Air Force Research Laboratory. "We are working closely with our industry partners to develop game-changing technologies that will truly advance the state of the art for military engines in the 21st Century."
The adaptive fan variable cycle technology will leverage and improve upon Pratt & Whitney's baseline experience in building and fielding fifth generation fighter engines – the F119 that powers the F-22 Raptor, and the F135 powering the F-35 Lightning II, according to Bennett Croswell, president, P&W Military Engines.
"Pratt & Whitney has an innovative approach to achieving variable cycle features with a multiple flow path architecture," said Croswell. "We're building on our foundation of proven fifth generation capabilities, and we are now mastering adaptive technologies – really expanding the boundaries of state of the art engine technology critical for the next sixth generation aircraft."
Hope that explains something on Why Variable cycle engines are important & much sought after tech for fighters,
Achieving optimum thrust & SFC at various operating conditions spread through out the flight envelope , is the key of the new low bypass variable cycle engine tech, unlike the optimum SFC & thrust achieved by non varible cycle high bypass older tech engines at " A SINLGE PONIT IN THEIR OPERATING ENVBELOPE & FLIGHT CONDITIONS
Add to that
1.higher Engine Thrust to weight ratio for better over all fighter TWR,
2., lower frontal area for lower RCS,
3, nimbler response to throttle alterations key to close combat,
4. Capacity to achieve the designated thrust with lower temperature capable blades
we know why Kaveri even though unfinished has the DNA of a state of the art engine fit for any cutting edge 5th gen stealth fighter design" meaning the fighter performs closer to its optimum performance envelope through out it flight envelop
"
"What we are looking at with adaptive engines are engines that can operate at multiple design points across a range of flight envelopes while maintaining optimal operating efficiency," Kenyon said.
This adaptive cycle engine will utilize a secondary bypass stream (three air streams in total) to act much like the gearing on a car's transmission, allowing the F135 engine to adjust and match its bypass ratio at will, whether it's high-thrust takeoffs or high-efficiency cruising at altitude. "That third stream is something that we have the ability to modulate, to change the conditions of that flow," Kenyon told Gizmodo. "How much flow, and flow characteristics so that we can kind of optimize the bypass ratio over the flight envelope."
"On top of that adaptive fan we’re also making improvements, tremendous improvements in the core system as well. We’re putting in a higher pressure ratio, higher efficiency compressor, leveraging a lot of our advanced commercially-derived, 3D aerodynamic design capability...We’re looking at increasing the temperature capability and the efficiency of the turbine stages, and then we’re also looking at the exhaust system. Having that adaptive third stream allows us to work with that stuff as well...we’re making improvements to the efficiency of the core engine, but we’re also using the adaptive architecture to give us a lot more design options in terms of how we can manage the engine over the flight envelope."
http://www.pw.utc.com/Press/Story/20130925-1100/2013/All Categories
"
Similar to changing gears in a car or on a bicycle, changing an aircraft engine's bypass ratio allows the engine to be optimized for high thrust takeoffs, while maintaining the efficiency of a commercial airline's high bypass engine in cruise conditions. Unlike commercial airline engines which are attached to the wing, engines used in modern fighter aircraft must use smaller diameter turbofans and be embedded within the aircraft. Consequently, there is a performance tradeoff between high thrust capabilities and optimum efficiency experienced in cruise conditions. Developing a next generation variable cycle adaptive engine is therefore essential to meeting the evolving needs of the warfighter.
Modern military turbofan engines have two airstreams – one that passes through the core of the engine, and another that bypasses the core. Development of a third stream of airflow will allow for improved fuel efficiency and cooler heat sinks which improve thermal management of the air system and reduced heat signature.
"Developing an effective adaptive fan concept is a critical step in advancing technology that will ensure next generation air dominance for our military," said Jack Hoying, program manager, Air Force Research Laboratory. "We are working closely with our industry partners to develop game-changing technologies that will truly advance the state of the art for military engines in the 21st Century."
The adaptive fan variable cycle technology will leverage and improve upon Pratt & Whitney's baseline experience in building and fielding fifth generation fighter engines – the F119 that powers the F-22 Raptor, and the F135 powering the F-35 Lightning II, according to Bennett Croswell, president, P&W Military Engines.
"Pratt & Whitney has an innovative approach to achieving variable cycle features with a multiple flow path architecture," said Croswell. "We're building on our foundation of proven fifth generation capabilities, and we are now mastering adaptive technologies – really expanding the boundaries of state of the art engine technology critical for the next sixth generation aircraft."
Hope that explains something on Why Variable cycle engines are important & much sought after tech for fighters,
Achieving optimum thrust & SFC at various operating conditions spread through out the flight envelope , is the key of the new low bypass variable cycle engine tech, unlike the optimum SFC & thrust achieved by non varible cycle high bypass older tech engines at " A SINLGE PONIT IN THEIR OPERATING ENVBELOPE & FLIGHT CONDITIONS
Add to that
1.higher Engine Thrust to weight ratio for better over all fighter TWR,
2., lower frontal area for lower RCS,
3, nimbler response to throttle alterations key to close combat,
4. Capacity to achieve the designated thrust with lower temperature capable blades
we know why Kaveri even though unfinished has the DNA of a state of the art engine fit for any cutting edge 5th gen stealth fighter design" meaning the fighter performs closer to its optimum performance envelope through out it flight envelop
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