PAUL LEWIS / MONTREAL & HARTFORD
Airframe and engine refinements follow concept phase
Joint Strike Fighter (JSF) prime contractors Lockheed Martin and Pratt & Whitney have unveiled a number of important changes and refinements to the F-35 airframe and F135 powerplant as the programme works towards final design and incorporates lessons learned during the concept demonstration phase.
JSF is eight months into a $30 billion full-development phase and at its first major milestone with the start of preliminary design review (PDR). "This is a series of events, with the engine having already completed PDR. Major suppliers will start next month, rolling up in March 2003 with the air system PDR," says Tom Burbage, Lockheed Martin JSF general manager.
The decision has already been taken to modify the internal weapons bay of the short take-off vertical landing (STOVL) F-35 variant to accommodate 900kg (2,000lb) munitions, bringing it in line with that of the conventional take-off landing and carrier versions (CV). This has required internal rearranging of items such as the liftfan's digital electronic controls and includes fitting the aircraft with the same heavier doors and actuators as on the other versions.
"On STOVL weight is king and so the requirement was to go with lighter weapons which allow for smaller doors and actuators to save weight. When we did our demonstration we had so much margin it opened up the possibility of a common bay on all three versions," says Burbage. The change could have an important bearing on the UK's pending decision between the STOVL and CV versions.
Lockheed Martin is working with P&W to improve the design of the liftfan doors, which on the demonstrator opened and folded to the side. "With the liftfan directly behind the cockpit, that has induced some aero distortion in the inlet. We've just tested a rear-opening hatch," says Tom Farmer, P&W F135 engine programme vice-president.
The axisymmetric aft nozzle on the end of the STOVL's version's three-bearing swivel duct has been shortened by 75mm (3in) to improve ground and ship deck clearance during vertical landings. There is a slight increase in induced drag as a result.
Other improvements to the STOVL propulsion system include new hollow liftfan blades from Rolls-Royce, a refined clutch incorporating new material and two fewer plates, a straddle-mounted drive shaft offering better rigidity and lower vibration and the elimination of variables vanes from the low-pressure turbine.
Source: Flight International
