Graham Warwick/WASHINGTON DC
Pratt &Whitney has exercised all short take-off and vertical landing (STOVL) modes of the propulsion systems under test for the Boeing and Lockheed Martin Joint Strike Fighter (JSF) concept demonstrators. All four JSF119 engine variants were on test by late November.
Programme manager Bob Cea says the shaft-driven lift fan on the JSF119-611S powerplant for the Lockheed Martin X-35B STOVL demonstrator has been run to full thrust, and the three-bearing main engine nozzle vectored through the full 108°. Meanwhile, the twin direct-lift nozzles on the JSF119-614S engine for Boeing's STOVL X-32B have been vectored past 90°, he says.
The Boeing engine has demonstrated fan efficiency "...beyond what we predicted, at temperatures lower than predicted and at SFCs [specific fuel consumption] better than anticipated," Cea says. In STOVL mode, the two-dimensional thrust nozzle closes, diverting the exhaust to "Pegasus- style" lift nozzles.
The "big unknown" with the Lockheed Martin engine was the lift fan, Cea says. Engaging the shaft-driven fan in STOVL mode "...doubles the work of the turbine," he says: "We've just run at maximum engine airflow and maximum lift fan thrust - and it works. Stresses were as expected, and fuel flows and efficiencies look better."
Tests of the basic F119-based engines for the conventional take-off and landing variants of the JSF demonstrators produced "outstanding results," says Cea, with "...maximum flow at rotor inlet temperatures lower than anticipated, compressor efficiency better than expected, low vibration, low stress and excellent behaviour."
P&W is now building two more sets of engines, for flight clearance testing. These will be less heavily instrumented, and will have flight-weight lift-system hardware. The company will then build two flight test engines, and refurbish one ground-test example as a spare, for each JSF team. Cea says 2,500h of testing will be done before the demonstrator first flights in 2000.
The demonstrator engines are built around a core identical to that of the F119s powering Lockheed Martin/Boeing F-22 development aircraft, but run at higher temperatures to produce more thrust. Cea says engines proposed for the JSF development phase will be based on the F119 core, but incorporating "supercooled" turbine blades and vanes to extend life at the higher temperatures.
Cea says P&W has just run JSF-type blades and vanes for 1,500 cycles in a testbed engine, with 500 more cycles planned by year end. Despite the apparent rapid progress in the 23 months since P&W won the JSF contract, Cea says 1999 "-holds a lot of challenges".
Source: Flight International
