PUTTING F135 TO THE TEST

Pratt & Whitney's F135 system and development demonstration (SDD) test program is quickly gaining momentum with seven engines planned to be under evaluation by midsummer.

FX631--the first of the SDD F135s--began running at the company's West Palm Beach, Fla., test center in October and has accumulated more than 246 hr. Initial trials examined sea-level operability, fan performance and augmentor operability of the conventional takeoff and landing (CTOL) configured powerplant.

To date, the engine has completed 182 tactical cycles and 164 afterburner lights. Accumulated time in reheat is 5 hr., and 39,750 lb. of thrust has been generated in maximum afterburner. Additional operability tests with this powerplant are scheduled, and its evaluation program should conclude in 2006 after running up some 500 hr.

Also in test at West Palm Beach is FX633, another powerplant configured for CTOL operations. According to Pratt officials, "the F-35's low-observability inlets are not your traditional aircraft inlet," so the engine is heavily engaged in aircraft/engine-inlet compatibility studies. As a result, Pratt engineers--working with Joint Strike Fighter prime Lockheed Martin--fabricated both a sea-level aircraft inlet and an "up and away" inlet, and are running the engine behind them.

"We're studying how the engine acts in each of those conditions, looking at the airflow from the aircraft inlet to the engine fan, so that we can avoid any fan deficiencies popping up later in the program. We're also trying to validate our high-cycle fatigue predictions and determine if there will be any high-cycle fatigue issues," explained William Gostic, Pratt & Whitney's director of F135 programs. Other objectives of this testing are to validate computational fluid dynamics models used to predict fan interactions.

Trials with FX633 began in mid-January and are expected to wrap up this month. Once fan evaluations are concluded, the powerplant will reenter the program for accelerated mission testing--another attempt to identify and resolve any performance and operability problems as early as possible.

According to Gostic, three of the seven SDD test engines will be in the CTOL configuration, while four will be built as short takeoff/vertical landing (Stovl) versions. Overall, the seven engines should accumulate approximately 2,000 hr. this year, with half of that time dedicated to endurance trials. Another 500 of those 2,000 hr. will be altitude tests conducted at the U.S. Air Force's Arnold Engineering Development Center (AEDC) near Tullahoma, Tenn.

The third CTOL engine, FX632, will be outfitted with telemetry instrumentation and will perform altitude development work at AEDC. Of the four Stovl powerplants:

* FX641 will be used in initial operability trials.