Tests at the U.S. Air Force’s Arnold Engineering Development Center (AEDC) in Tullahoma, Tennessee reveals that General Electric/Rolls-Royce F136 alternate engine has more than 15% thrust margin against specification, significantly exceeding the power of the baseline Pratt and Whitney F135 of the F-35 Joint Strike Fighter.
It is the first to officially calibrate the combat-rated thrust of a production-representative F136 at sea level condition. Although the test program is only a matter of days old, it already appears to be showing greater performance margin in afterburner than expected, says the General Electric Rolls-Royce Fighter Engine Team.
Defense Secretary Robert Gates has made killing the second engine a centerpiece of his crusade to cut unnecessary defense spending. With the Obama administration promising to veto any defense bill that prolongs the F136, U.S. Congress has defied Gates and passed provisions that fund the engine. The Senate has not weighed in, but key committee chairmen have voiced support for competitive engines. Details of the F136’s test performance could strengthen support and more broadly undermine Gates’s efforts to reform the Pentagon.
In March this year, following the first maximum afterburner test of a system development and demonstration engine, the team quietly expressed confidence the F136 would exceed the thrust of the baseline F135 by 5%. Actual thrust achieved in the test remains undisclosed, but it is in excess of 40,000 lbs.
Pratt and Whitney, which derived its F135 from the F-22 Raptor’s F119 engine, remains confident its own growth plans will stave off the challenge from the F136 without getting ahead of the need or increasing development costs. The company, which begins final qualification tests of the short-takeoff-and-vertical-landing (Stovl) engine in Florida this month, plans to start tests of a higher-thrust F135 in January 2011 and begin rig tests of a growth fan later next year.
Although the F135’s thrust meets specification for the Lockheed Martin F-35 as currently configured, future growth potential is becoming an important part of the ongoing alternate engine debate. Thrust growth, and the engine life and maintenance cost benefits if traded for lower operating temperatures, are recognized as key factors by both sides. Thrust growth is considered particularly important for the performance of the F-35B Stovl variant, while the ability to use additional temperature margin to cut long-term support costs is applicable to all models, including the conventional-takeoff variants.
Pratt and Whitney Military Engines President Warren Boley says growth testing is part of a medium- to long-term strategy to increase F135 thrust by as much as 20%. “There is no doubt Pratt and Whitney has the suite of technology, and we are dedicated to do that,” he says. Although initial growth is aimed at satisfying F-35 thrust requirements, Boley says more power will also accommodate future applications on other platforms including unmanned aircraft.