First Stovl Engine Shipped For F-35B

Pratt & Whitney and Rolls-Royce have shipped the first production short take-off and vertical landing (Stovl) propulsion system to Lockheed Martin for installation in the F-35B.

The lift fan unit, produced at Rolls’ Indianapolis facility, will be integrated with Pratt & Whitney’s F135 initial production Stovl engine and remaining elements of the lift system in the first production Stovl aircraft, BF-6.

The lift-fan, a 50-in., two-stage counter-rotating fan capable of generating around 24,000 lb. of thrust, is driven via a gearbox and shaft from the main engine, and produces the forward vertical lift. Rolls-Royce U.K. is responsible for other elements of the lift system including the three-bearing swivel module, a swiveling jet pipe that redirects the main engine thrust downward to provide the rear vertical lift, as well as two roll posts in the wings, each of which provide a further 1,950 lb. of thrust.

Although originally aimed at a March 2010 delivery target, development issues with the planned hollow second-stage “blisked” lift fan rotor contributed to an overall delay. Other improvements are believed to have been retained, however, including a lift fan case made of titanium instead of aluminum and an inlet guide-vane ice protection system. The upgrades were made as part of efforts to cut extra weight from the earlier Block 3 development configuration, itself 150 lb. lighter than the original lift-system design.

The complete system includes the variable-area vane-box nozzle (Vavbn), which vectors the lift-fan exit flow as well as back-pressures the fan to control stall margin. As the nozzle box is also an integral part of the Stovl aircraft’s structure, it is one of the earliest modules to be delivered, while the lift fan is almost the last.

Delivery to Lockheed’s Joint Strike Fighter assembly site in Fort Worth comes as Pratt and Rolls complete final paperwork and verification tasks in the run-up to initial service release (ISR) clearance for the Stovl propulsion system. “We expect initial ISR before the end of the year,” says Bennett Croswell, vice president of F119/F135 Engine Programs for Pratt & Whitney.

Although flight tests of the initial F-35Bs at the U.S. Navy’s Patuxent River, Md., test site have been slowed considerably by airframe-related issues, Croswell says “the engines have been doing well there.” Engine availability has been “well above 98 percent and in fact in terms of mission readiness metrics they have demonstrated numbers in flight test that are higher than that.”

Pratt is meanwhile set to deliver another four F135 engines in the next three weeks for a 2010 total of 15 as it ramps up to meet the higher schedule demands of 2011. “We will be bringing more engines into the program through the TBR [technical baseline review] process,” Croswell says, referring to the program’s recent redirection on schedule and costs. As the TBR adds extra aircraft to the flight test effort late in 2011, Pratt “will need to add more spare engines into the program,” he says.

Production for 2011 is therefore scheduled to cover more than 30 engines, some of which will be for low rate initial production (LRIP) 4 batch aircraft toward the end of the year. “We expect to get a handshake by the end of the year,” on LRIP 4, Croswell says.

Pratt proposed a fixed-price, incentive cost-based agreement for this batch based on prices it believes are achievable from a cost-reduction plan aimed at getting the F135 down to the same cost as the F-22’s F119 engine by the 250th unit. “That’s for an engine that weighs 1,500 pounds more and produces 25 percent more thrust,” Croswell adds. Although initially working toward the Pentagon’s Joint Assessment Team-validated “should-cost” curve, Croswell says Pratt is working to get underneath a lower “should-cost” curve.

“We can take the price of the engine even below that original ‘will cost’ curve, and we’re feeling optimistic we will be finding more opportunities.” Croswell adds that, in addition to “the natural leaning [of cost] from the manufacturing process,” Pratt is working with suppliers as well as with its own internal shops to seek further reductions. As an example, he says Pratt is sourcing integrally bladed rotors from Turkey, reducing costs and increasing international industrial participation.

Croswell says Pratt is driven independently to reduce costs, even without the competitive pressures brought about by the alternate General Electric/Rolls-Royce F136. “We did it on the F119 for the F-22. It’s a decision to drive cost out of the product because when we do it, that enables our customer to buy more product and gives us more efficiency.”