Pratt & Whitney's JSF engine effort is moving forward into the $4 billion SDD phase under the leadership of Tom Farmer, the vice president formerly in charge of the F119 engine for the F-22. Under its SDD contract P&W is "..responsible for the production-capable main propulsion system called the F135, and we are to provide a Rolls-Royce-designed and -developed lift system to our customer," says Farmer. As prime contractor, P&W's responsibilities extend to developing propulsion systems for all three variants of the F-35 and also ensuring interoperability with the General Electric F136 alternate engine.

Based on the F119 now in production for the F-22, the SDD version of the F135 engine (formerly known as the JSF119-611), is essentially unchanged from the powerplant used in the X-35 concept demonstrator. What is different, however, is P&W's contractual position within the programme. In the CDP, P&W "helped Lockheed Martin with integration of the propulsion lift system. Now, in SDD, we are responsible from the outset as partners with R-R, and we will facilitate the application of its lift system," explains Farmer.

Unlike former P&W military engine programmes which have been virtually exclusive in-house efforts, the F135 forms the basis of an entirely new level of external relationships. These include the close working relationship with R-R, and a raft of upcoming European partners on the F135, as well as a rather more unique relationship with its arch-rival GE. "Right now we're meeting weekly with GE technical personnel. We are talking about common hardware that must be compatible for all three versions, so we are working this diligently," says Farmer.

Intense discussions are also underway in Europe with potential industrial partners as part of the JSF programme office's plan to garner a 17% overseas financial contribution to the SDD phase. Under a P&W team led by international programme manager Ed O'Donnell, agreements with FIAT Avio in Italy and possibly Fokker Elmo and Interturbine of the Netherlands are expected to be sealed by year-end. Partnership agreements on a smaller scale are being sought for 2002 with companies in other countries.

R-R plays a significant role on the STOVL variants of both the F135 and F136 engines, and gained with the selection of Lockheed Martin's lift-fan-augmented JSF over Boeing's direct-lift design. The UK company's contribution to the F135 is led from its military headquarters in Bristol and includes the lift fan, drive shaft, gearbox, clutch, roll posts and three-bearing swivel duct for the engine's vectoring nozzle.

The shaft-driven fan produces almost half of the total lift power in STOVL mode, or more than 18,000lb thrust. Enhancements during development are likely to include a lighter design of 'hooded' lift-fan nozzle, and possibly a lighter low-pressure turbine for non-STOVL versions of the engine. R-R is also engaged in less-publicised work on the competing F136. The UK company has responsibility for the engine's advanced three-stage fan, combustor-diffuser system and gearboxes. The high pressure-ratio fan design features long-chord, hollow titanium blisks. The two companies are jointly developing an integrated high-pressure/low-pressure counter-rotating "coupled" turbine system. R-R says tests on the three-stage fan, conducted at its Indianapolis site last year, successfully demonstrated operation at full speed and pressure ratio.

The transition to SDD has finally allowed the newly named F136 engine to be openly recognised as a part of the JSF programme despite GE having lost out to P&W at the outset of the CDP. In November, following the main JSF contract awards, the Ohio-based engine maker was given a $411 million add-on contract to continue work on the F136. The agreement is a modification to a previously awarded contract for pre-SDD work on the engine. Awarded through the USNavy, the contract is divided between GE with 60%, R-R North America 13%, and Rolls-Royce (UK) 27%. GE says that around $20 million is included for work with P&W on the common engine installation.

The latest award follows completion of the last stages of development work conducted under a four-year Phase II contract awarded in 1996. This covered development of a core engine based on the high-flow, high-pressure compressor and turbine of the original F120,GE's contender to power theF-22. The core engine ran in 2000 and, according to a tight-lipped GE, "achieved all performance objectives." Phase III, the bulk of which comes under an initial $460 million contract running through to 2005, covers more component and subsystem tests as well as the first full engine tests, due to start in 2004.

The JSF programme office is expected to fund development of a production-standard engine almost immediately after the tests start, with initial service readiness of the F136-powered F-35 slated for 2010-11.

Source: Flight International