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Pratt Raises Stakes In JSF Engine Battle
Aug 27, 2010
WEST PALM BEACH, Fla. Pratt & Whitney is upping the ante in the ongoing F-35 Joint Strike Fighter engine war by revealing the F135 has achieved combat-rated thrust 20% higher than the specification.
The disclosure raises the demonstrated sea-level thrust for the F135 above 50,000 lb., and follows results from the General Electric/Rolls-Royce Fighter Engine Team earlier this month that indicate the F136 alternate engine has in excess of 15% margin against the same specification.
Pratt & Whitney Military Engines President Warren Boley says the F135 result proves we have demonstrated margin and that we have the right core size. Thrust growth is not a specific requirement for the Lockheed Martin F-35; however, the provision of additional margin either for trading for longer operating life or for future growth is considered an important bargaining chip by the contenders.
Nevertheless, Boley says even though Pratt has demonstrated measured thrust with the conventional-takeoff-and-landing (CTOL) engine variant well in excess of the F135s advertised 43,000-lb.-thrust capability, the focus remains on providing a systems-level solution to the F-35 thrust requirement. So when someone says an engine can produce more thrust, if the lift fan cant produce more, then you cant use that thrust, he says.
Another thrust-limiting factor is the Pratt-developed exhaust duct, Boley adds. As a result, if someone says their thrust module can produce more thrust, it is interesting but not applicable, he says.
Overall F135 thrust margin also varies depending on engine variant and altitude. For example, tests show that the CTOL engine has around 12% excess against specification at higher Mach numbers, and the short-takeoff-and-vertical-landing (Stovl) variant has demonstrated much less margin owing to configuration limitations placed by the lift fan.
Although Boley outlined plans at the recent Farnborough air show to start tests of a higher-thrust F135 in January 2011, and later next year starting rig tests of a growth fan, he says this strategy is aimed at 5-10% thrust growth for later F-35 development if needed. Questions remain over what thrust will be needed, and when, because the baseline thrust assumption for the F-35 is that it is not going to grow and grow like the F-16.
The F-16 thrust requirement, like other fourth-generation fighters such as the F-15, has grown in lockstep with heavier weapons and stores payloads. This is not the case with the F-35, Boley says, which for stealth reasons is designed to accommodate the majority of its payloads and future growth internally. Fifth-generation fighter optimization is different from the optimization used for the fourth generation. Requirements drove the 43,000 lb. thrust to begin with, and its not one that is going to grow from 24,000 to 29,000 to 32,000 lb. thrust, he says. This is one reason the GE-Rolls great fighter engine war argument is irrelevant, Boley asserts.
Boley spoke at Pratts facility here, where the engine maker is closing on the final set of initial service release (ISR) tests for the F-35B Stovl engine. Were at the end of the development cycle, he says.
ISR clearance work is focused on accelerated mission and crosswind tests on two engines at West Palm Beach, and inlet operability tests on an engine at the Arnold Engineering Development Center in Tullahoma, Tenn. With the completion of these, we will write 3,000 verification reports to the JSF Program Office, and late in the fall the system program office will stamp off the ISR for the F-35B engine, he adds. Actual clearance is expected around Dec. 1.
The tests mark the conclusion of the F135 development phase, the CTOL engine having achieved ISR clearance in early March.
Pratt Raises Stakes In JSF Engine Battle | AVIATION WEEK
Aug 27, 2010
WEST PALM BEACH, Fla. Pratt & Whitney is upping the ante in the ongoing F-35 Joint Strike Fighter engine war by revealing the F135 has achieved combat-rated thrust 20% higher than the specification.
The disclosure raises the demonstrated sea-level thrust for the F135 above 50,000 lb., and follows results from the General Electric/Rolls-Royce Fighter Engine Team earlier this month that indicate the F136 alternate engine has in excess of 15% margin against the same specification.
Pratt & Whitney Military Engines President Warren Boley says the F135 result proves we have demonstrated margin and that we have the right core size. Thrust growth is not a specific requirement for the Lockheed Martin F-35; however, the provision of additional margin either for trading for longer operating life or for future growth is considered an important bargaining chip by the contenders.
Nevertheless, Boley says even though Pratt has demonstrated measured thrust with the conventional-takeoff-and-landing (CTOL) engine variant well in excess of the F135s advertised 43,000-lb.-thrust capability, the focus remains on providing a systems-level solution to the F-35 thrust requirement. So when someone says an engine can produce more thrust, if the lift fan cant produce more, then you cant use that thrust, he says.
Another thrust-limiting factor is the Pratt-developed exhaust duct, Boley adds. As a result, if someone says their thrust module can produce more thrust, it is interesting but not applicable, he says.
Overall F135 thrust margin also varies depending on engine variant and altitude. For example, tests show that the CTOL engine has around 12% excess against specification at higher Mach numbers, and the short-takeoff-and-vertical-landing (Stovl) variant has demonstrated much less margin owing to configuration limitations placed by the lift fan.
Although Boley outlined plans at the recent Farnborough air show to start tests of a higher-thrust F135 in January 2011, and later next year starting rig tests of a growth fan, he says this strategy is aimed at 5-10% thrust growth for later F-35 development if needed. Questions remain over what thrust will be needed, and when, because the baseline thrust assumption for the F-35 is that it is not going to grow and grow like the F-16.
The F-16 thrust requirement, like other fourth-generation fighters such as the F-15, has grown in lockstep with heavier weapons and stores payloads. This is not the case with the F-35, Boley says, which for stealth reasons is designed to accommodate the majority of its payloads and future growth internally. Fifth-generation fighter optimization is different from the optimization used for the fourth generation. Requirements drove the 43,000 lb. thrust to begin with, and its not one that is going to grow from 24,000 to 29,000 to 32,000 lb. thrust, he says. This is one reason the GE-Rolls great fighter engine war argument is irrelevant, Boley asserts.
Boley spoke at Pratts facility here, where the engine maker is closing on the final set of initial service release (ISR) tests for the F-35B Stovl engine. Were at the end of the development cycle, he says.
ISR clearance work is focused on accelerated mission and crosswind tests on two engines at West Palm Beach, and inlet operability tests on an engine at the Arnold Engineering Development Center in Tullahoma, Tenn. With the completion of these, we will write 3,000 verification reports to the JSF Program Office, and late in the fall the system program office will stamp off the ISR for the F-35B engine, he adds. Actual clearance is expected around Dec. 1.
The tests mark the conclusion of the F135 development phase, the CTOL engine having achieved ISR clearance in early March.
Pratt Raises Stakes In JSF Engine Battle | AVIATION WEEK
