Engine redesign aimed at increasing performance in STOVL mode and addressing overheating and weight issues
As the first flight-test engine enters assembly, the Lockheed Martin F-35 Joint Strike Fighter (JSF) powerplant suppliers have unveiled a long-term plan to introduce major design changes to address a potential overheating problem and weight growth issues.
Pratt & Whitney expected by last week to combine the eighth and ninth stages of the high-pressure compressor rotor for the first F-35, named A-1. The completed engine should arrive at Lockheed’s Fort Worth, Texas plant by 21 December, with first flight of the “non-optimised” conventional take-off and landing F-35A scheduled around 28 August 2006.
But programme officials admit the first flight-test engine cannot meet the F-35A’s requirements, with the most serious deficiency requiring a redesign of the engine’s thermal management system, says Bill Gostic, P&W’s F135 programme manager. The JSF uses its fuel system to absorb the heat from the aircraft’s onboard electronics, which must be managed carefully to avoid overheating the engine’s combustor fuel nozzles.
P&W is addressing the concern by switching to dual-vane pumps that reduce heat loads through two pumping elements, says Gostic. The redesigned system will be introduced in the final two flight-test engines to be delivered in 2009. More design changes are required for the short take-off and vertical landing (STOVL) F-35B propulsion system scheduled for delivery in February 2007. Although Lockheed was initially reluctant to address weight growth by boosting engine thrust, propulsion eventually became involved with the ground rule that operating temperature could not be increased, as this would increase operating costs and limit future engine growth.
The changes are focused on increasing engine performance in both the short take-off and vertical landing modes, says Gostic. In the short take-off mode, the programme found a quick way to add a 2,000lb-thrust (8.9kN) improvement on initial roll.
The change involves closing both roll-post nozzles and instead channelling the heated air of out the main aft nozzle. After clearing initial roll at the ship’s edge, the roll-post nozzles would open to preserve stability.
A second major change for the STOVL variant involves reducing the exhaust nozzle diameter by 76mm (3in), says Gostic. This will reduce weight and drag and also allow the aft fuselage structure to shrink, saving further weight. However, as this change will cause a small reduction in “up-and-away” performance, the F-35A and F-35C carrier variant will retain the original nozzle size.
Gostic says the weight growth solutions were developed in collaboration with the General Electric/Rolls-Royce Fighter Engine Team, which last week secured a $2.4 billion system development and demonstration phase contract for the rival F136 engine.
STEPHEN TRIMBLE/WASHINGTON DC
Source: Flight International
