The two teams developing engines for the Joint Strike Fighter have avoided hitches besetting the rest of the programme, with CTOL and STOVL variants under test
Lockheed Martin's F-35 Joint Strike Fighter programme may have hit a series of technical snags, but as far as propulsion goes, progress has been smoother. The two competing engine teams are on or ahead of schedule and, for the first time since the programme began, will be simultaneously testing propulsion systems by mid-year.
Pratt & Whitney's F135 development team, including Hamilton Sundstrand and Rolls-Royce, is sticking to a virtually unchanged timetable. By mid-April it will have production-configuration engines for the conventional take-off and landing (CTOL) and short take-off and vertical landing (STOVL) F-35 variants under test. The General Electric/Rolls-Royce Fighter Engine Team, meanwhile, plans to fire up its first F136 by the end of July.
With funding secured, hardware coming in and efforts being made to trim weight where possible, both engine teams remain focused on testing without trying to second-guess possible F-35 schedule changes in the future. "I just keep telling our people to keep their heads down and work hard. We've got the programme back in shape, and that's how we want to keep it," says GE's F136 JSF programme general manager Bob Griswold.
P&W, which is further along than its rival, is on track to complete tests to support first flights for the CTOL F-35A in October 2005 and the STOVL F-35B in April 2006. "We're under contract and that hasn't changed," says director international programmes Ed O'Donnell.
The F135 ran for the first time at its West Palm Beach test site in Florida in October 2003, marking the start of a massive development effort involving three CTOL and four STOVL ground test engines. P&W designates the CTOL and CV (carrier variant) engines the F135-100 and 400 respectively, while the STOVL engine is dubbed the F135-600. The first STOVL test engine, FX641-1, ran on April 14 following the delivery of the lift system from R-R.
Clutch assembly
The lift system, which is common to the F135 and the F136, consists of a lift fan, clutch and driveshaft, three-bearing swivel duct (3BSD), and roll control ducts and nozzles. The 1.3m (50in)-diameter, two-stage counter-rotating lift fan was developed by R-R Indianapolis, as was the sophisticated clutch assembly that transmits up to 27,000shp (20,100kW) from the drive shaft to the fan. The current design completed 1,500 engagements in mid-February with a single set of clutch plates, a tenfold life increase over the unit tested in the X-35B concept demonstrator flights in 2001. The 3BSD was developed by R-R Bristol, while the roll control ducts and nozzles were jointly produced by R-R and Spanish company ITP, in which R-R holds a 49% share.
"We have three more STOVL engines in build, and all four will be in test by mid-summer," says O'Donnell. "This is the year of the STOVL." While FX641-1 begins tests in Florida, the second F135-600, FX642-1, will go to the Arnold Engineering Development Center (AEDC) in Tennessee for altitude tests in the "up and away mode without the roll posts and fan", O'Donnell says. The third STOVL engine, FX643-1, will undergo accelerated mission testing (AMT), beginning around August 2004, while the fourth engine, designated FX640-1, will be the last to join the effort at Florida, where it will be mated to the F-35 aircraft systems for full integration tests.
The initial results from tests of the first three CTOL engines show that to date "we are hitting all our pre-test predictions", says O'Donnell. "Although we are finding some minor problems, there's been nothing significant," he says, describing them as "minor tweaks to the design". The issues appear to be related to durability and result from the fact that the pre-system development and demonstration (SDD) or concept demonstrator aircraft (CDA)-phase designs "are not focused on the maturity aspects", he adds. P&W believes that lessons learned from the development of the F119, the direct "father" of the F135, will lead to rapid solutions to durability issues.
The first CTOL test engine, FX631-1, has completed the first block of testing, which covered 250h, including 5h in afterburner. A maximum thrust of 39,750lb (177kN) was achieved before the engine was pulled out for inspections and fitted with additional instrumentation for a second 150h test phase that is set to run from around now until June.
The second engine, FX632-1, has also completed its "Build 1" tests at AEDC with Lockheed Martin inlets to check distortion characteristics, and following changes to "Build 2" standard will be shipped to Florida in May for AMT work. The third engine, FX633-1, is being transported to AEDC for 225h of altitude testing that are set to be completed by the end of June.
Design review
A post-test critical design review (CDR), originally set for August, will be held in October. "This will be the first design review targeted towards final release configuration for service," says P&W F135 SDD manager Dan Tennant. The slip to October allows P&W "to inject more test data" into the review, but also reflects the fact that Lockheed Martin's original airframe CDR, scheduled for the August timeframe, has also "moved out", he adds.
¼"We're fully committed to bringing the CTOL configuration through to initial flight release in the third quarter of 2005, and we are on track to start and build that first CTOL engine in the first quarter of 2005," Tennant says. Work on the first STOVL engine for flight testing is, meanwhile, due to begin around mid-2005, with its first flight targeted for April 2006.
For the GE/R-R Fighter Engine Team, as the joint limited liability company is officially named, this year is particularly significant for many reasons. Primarily, funding is secured through 2004 to guarantee the continued development of the F136 through to SDD in 2005.
Furthermore, the JSF Programme Office (JPO) has now formally recognised the projected SDD milestones for the F136 programme for the first time. To the outsider, this may sound trivial, but to the F136 team it represents a quantum leap in its credibility and officially establishes the engine as a funded part of the overall JSF programme structure.
To cement this further, the JPO is also "very close" to approving - and recognising - the jointly held GE/R-R limited liability company arrangement. "We are wrapping up the final negotiations," says Griswold, who adds that although the company was formed "some time ago", it is "like we've had the store open but no-one has been coming in".
Two key milestones recognised by the JPO include the first SDD engine to test target of the third quarter 2007, and the first flight of a F136-powered F-35 in the fourth quarter of 2009. Assuming no more dramatic schedule changes occur, the F136 is expected to be available for the Lot 4 production batch in late 2011 or early 2012. Although this is around a year later than originally planned, the slippage of the whole JSF programme means it makes no difference in terms of when the first F136 will be available as an option.
The most dramatic development this year, however, is the assembly and running of the first F136. "The majority of the hardware is already here," says GE F136 supply chain manager Jean Lydon-Rodgers. "The core compressor through the HP turbine is all assembled, and the hardware for the second engine to test is right behind it. By the middle of April all the hardware will have arrived and by early July we will have completed assembly. We will then have first fire at the end of that month," she says.
F136 threat lifted
As recently as last year the sight of parts rolling into GE's Evendale, Ohio site was something that several on the programme feared would not be seen. In 2003 the JPO, looking urgently for money to keep the overall JSF effort on track, reluctantly targeted the F136 as the quickest option. The move threatened to delay SDD for the F136 by a year and the availability of the engine by a further two years. Not only would this have been bad news for the GE/R-R marketing effort and prospective customers hoping for a competitive engine choice, but it also posed massive questions over how to hold the development team together.
Through the middle of last year the team lobbied furiously with both the government and customers and secured victory. "Through Congressional support we got back about $53 million of the money that was taken away from us [$56 million] for 2004, plus an additional $14 million of risk reduction money. So we are fully funded for 2004 and for the next 'transition' phase, which will be a bridge between these engines and the start of SDD," says Griswold. He says that a further $60 million is being given "to us sooner so, as a result, we got it back on track for Lot 4 deliveries".
According to Lydon-Rodgers, "over the last two months we've been involved in the core assembly, and the fan frame assembly, combustor diffuser nozzle and HP turbine rotor is all one". R-R, which has 40% of the programme, is due to deliver the fan module around 23 May "so we can put it on the front end of the engine", Lydon-Rodgers adds. Other than the fan module, containing three blisk stages, R-R also has responsibility for the combustor, stages two and three of the LP turbine and the gearboxes. The two engine companies jointly developed the integrated high- and low-pressure counter-rotating turbine design that incorporates a single-stage HP turbine and three-stage LP turbine. The HP turbine and first stage of the LP turbine form part of the coupled, vaneless counter-rotating system.
GE, with 60% of the overall effort, is developing the core compressor and turbine system components as well as the afterburner. Philips Aerospace in the Netherlands provides the fan casing and stage one and two HP compressor blisks. Italy's Avio is expected to be participating in the structural components of the LP turbine and the accessory gearbox.
Assembly of the first full CTOL test engine No 652002 (001 being designated to the initial pre-SDD core), will be followed by the second (STOVL) engine (003) in October. The first STOVL test runs are not scheduled to start at Peebles, Ohio until February, however, to allow time for the installation of the lift system. In the meantime, a series of risk-reduction rig tests are under way, says F136 development manager Tom Maxwell. "We have completed a full annular combustor test and have several controls rigs working. We are pre-testing all the software that goes into the configuration, which is extra complex because when you are in the hover mode it is actually the engine control system that is controlling the aircraft."
Another major test just completed was on the hybrid ceramic bearing being used for the first time in the critical No 3 (main thrust) bearing. "We've had experiences with legacy bearings where, if they got contaminated or lost lubrication, they would fail. We have tested this for up to 2h under load without oil and it was OK, and have now run 10,000h without a problem," says Maxwell adding that a back-up bearing design has been dropped as a result.
The CTOL engine will initially go on test at GE's own altitude test site in Evendale before going to AEDC after the start of SDD in August 2005. During the transition to SDD "we will release long-lead materials for four engines, and when we get the actual SDD contract we will release additional material for another 10 engines and nine flight-test engines", adds Maxwell.
Production ramp-up
Within two months of this, the first P&W F135-powered F-35 should be taking to the air, marking the start of the company's enormous ramp-up to support the assembly of almost 90 aircraft in the first three lots of low-rate initial production. The next two years therefore set the scene for what promises to be one of the most fiercely contested combat-engine battles in the industry's history.
GUY NORRIS / LOS ANGELES
Source: Flight International
