Ground runs of engine for conventional take-off F-35A show overtemperature problems have been resolved

Pratt & Whitney has begun ground testing its F135 engine in the configuration that will power initial production Lockheed Martin F-35 Joint Strike Fighters. Contracts will be signed shortly for the first two production F-35s and three F135s to be delivered in 2009.

The engine in ground runs at P&W's West Palm Beach, Florida test centre is in the initial service release (ISR) configuration planned for the F135-100 powering the conventional take-off and landing F-35A. The engine incorporates modifications to reduce higher than expected operating temperatures (Flight International, 1-7 June 2006).

"It has all the fixes for RIT [rotor inlet temperature] margin," says Bill Gostic, vice-president F135 programmes. RIT is the flow temperature coming out of the combustor and was about 90ºC (190ºF) above the target. Fixes include improving the efficiency of the fan, eliminating turbine leaks to reduce the cooling air required and re-optimising bypass ratio.

"The CTOL engine has adequate RIT margin for production. The short take-off and vertical landing engine has demonstrated adequate up-and-away RIT margin," says Gostic. The 40,000lb thrust-class (178kN) F135 runs hotter in STOVL mode, and P&W has not yet demonstrated the powered-lift temperature margin.

P&W is now ground testing the complete STOVL propulsion system, aiming for final flight release in the first quarter of next year, to support the planned first flight of the STOVL F-35B in May 2008. Rolls-Royce, meanwhile, has completed a crucial overtorque test on the gearbox for the shaft-driven lift fan for the STOVL aircraft.

"We have demonstrated at the lift-fan subsystem level the performance needed. We need to couple that with the ISR fan and turbine changes and demonstrate the STOVL RIT," says Gostic. "But testing to date says we will be okay."

Source: Flight International