Guy Norris / Los Angeles

Powerplant development is well under way, with the big three unusually engaged in "co-opetition"

Propulsion system development is ramping up rapidly for the F-35, with tests of the first Pratt & Whitney F135 development engines getting under way in Florida, and plans for the start of tests on the General Electric/Rolls-Royce F136 in July 2004. But as with so many other aspects of the JSF, the propulsion story is complex and unusual.

For example, although the F135 and F136 engines will compete head-to-head for later production batches, the three engine makers have been involved in unprecedented joint interoperability studies - dubbed "co-opetition" - to ensure all F-35 variants will be able to use either engine seamlessly .

The common denominator in engine programmes is that all short take-off and vertical landing (STOVL) variants, be they F135- or F136-powered, will use the R-R shaft-driven lift-fan system. Developed at R-R's Indianapolis site where special fan and gear system test rigs have been built, the lift system is married to the roll posts, offtakes and three-bearing swivel duct developed and produced by R-R in the UK.

P&W's F135 began runs at its West Palm Beach, Florida test complex in October and reached military-power thrust levels ahead of schedule. The engine, designated FX631-1, is the first of seven conventional take-off and landing (CTOL), carrier variant (CV) and STOVL F135 development engines to be introduced into the tests next year.

FX631 will be used to assess CTOL sea-level performance and operability, as well as to map out fan characteristics and for afterburner development. The second engine, FX633-1, will join the effort by December, with the third engine, FX632-1 due the following month.

P&W has designated the CTOL engine as the F135-100, the CV as the -400 and the STOVL the -600. The first test engine series, led by FX631, is representative of the -100 and -400 standard engines, while the requirements of the F135-600 STOVL engine will be met with tests of a series beginning on or before April 2004 with engine FX641-1.

STOVL tests are expected to be more complex and critical to the overall programme than tests of the CTOL/CV version. Tests of the first STOVL engine will focus on control-system logic development and special afterburner operation.

Accelerated tests

A second STOVL test engine, FX642-1, is expected to join the effort by June 2004, followed by engines 643-1 and 640-1 in August and October 2004, respectively. The third engine will focus on accelerated mission tests, while the fourth will face integrated systems tests and STOVL sea-level performance and operability work.

The test programme is starting despite three open items hanging over from the propulsion critical design review last May relating to vulnerability, radar cross-section and thermal management. But according to P&W F135 programme director Bill Gostic: "These are really system-wide requirements, so we got the agreement of Lockheed Martin and the JPO to clear the engine configuration for the start of ground tests."

Gostic is confident the F119 (the engine powering the F/A-22 fighter) heritage of the F135 will keep the programme on or ahead of schedule, and says lessons learned from that engine F119 will help. "We're feeding back hot-section cooling from the F119 to improve margins in the F135, and we are introducing affordability/durability improvements in the compressor," he says.

The baseline F135 has a three-stage fan with hollow first-stage blades, composite fan inlet guide-vanes and first-stage stators. Aft of the fan is a six-stage high-pressure (HP) integrally bladed rotor or blisk compressor, a single-stage HP turbine with advanced cooling and a two-stage low-pressure (LP) turbine.

The GE/R-R team won a rearguard action to keep its F136 funding on track for 2004, and is confident the US government will formally recognise it as a standalone entity within the next two years. Modelled on the GE-Snecma CFM partnership, the team provides the platform for GE and R-R to develop and support the engine over a predicted 50-year-plus service life.

Based on GE's variable cycle YF120 engine, the F136 is split between GE with 60% and R-R with 40% - the latter responsible for the front fan, part of the LP turbine and combustor. Responsibility for a counter-rotating integrated HP/ LP turbine is shared.

GE is prime on the HP compressor and afterburner, with Philips ETG providing elements of the LP compressor, and FiatAvio supplying LP turbine components and the accessory gearbox. The F136 has a three-stage fan made of long wide-chord titanium blisks, the first stage of which is hollow.

Although starting behind the F135 and F136, the GE/R-R team is hopeful it will stay on track for initial system release in mid-2010, making it available for the fourth JSF production lot. "There will be fewer than 100 aircraft flying [with the P&W engine] at that time, only a small part of the thousands that will be out there," says GE JSF general manager Bob Griswold.

"One advantage is we haven't yet had to cut off the configuration for the production engine, so we can let it evolve to better suit the aircraft. I'd like to believe the combination of R-R and GE will therefore give us the edge," he says.

Source: Flight International