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Thrust advance

All three engine manufacturers have found a home on the A380 – and two have formed an unprecedented alliance.

When the first A380 begins its take-off roll along the runway at Toulouse Blagnac, its four engines will be producing a total of 280,000lb (1,250kN) of thrust - more than any previous commercial airliner and 100,000lb more than the first Boeing 747 in 1969.

The story of the A380's engines goes back to mid-1994, when the consortium envisaged a 480t aircraft powered by simple derivatives of the powerplants developed for the A330. This suited the engine manufacturers, who were in the middle of a hugely expensive development programme for the Boeing 777 powerplants.

As it transpired, the subsequent growth of the A3XX during its transformation into the A380 moved the power requirement away from that of the A330 range. All-new designs were therefore mooted, one of which was to emerge from an unprecedented Engine Alliance teaming deal between General Electric and Pratt & Whitney.

Family milestone

For its first flight in January 2005, the A380 will be powered by Rolls-Royce's Trent 900. The A380 marks the fourth milestone in the UK engine manufacturer's successful Trent family development strategy as well as its third Airbus application after the Trent 700 on the A330 and the Trent 500 on the A340-500/600.

Originally drawn up around the thrust requirements of the Boeing 747-500X/600X, the Trent 900 was conceived as a combination of the 2.9m diameter Trent 800 (Boeing 777) fan and the core of the Trent 500 (Airbus A340-500/600). With growing uncertainty over the growth 747, the Trent 900 joined the A3XX programme in October 1996 when a memorandum of understanding was signed between R-R and Airbus. Over time, the thrust requirement grew from 67,000lb to 70,000lb, culminating in the changes for the London airports' stringent QC2 noise regulations evoked after the Airbus customer symposium in January 2000.

"We had to change the LP system within only a few months, but our design people had lots of options under their belt," says R-R marketing vice-president Robert Nuttall. The most dramatic and immediate change was the adoption of a much larger 3m diameter fan based around the advanced Trent 8104 design. This three-dimensional fan, parts of which are forward swept, had been originally aimed at the 777-200X/300X, but had ended up as a technology demonstrator following the subsequent weight growth requirement of the Boeing long-range twins.

The thrust growth associated with the QC2 noise and weight changes provided R-R with an ideal opportunity to introduce the fan into the Trent 900, the technology having been judged "too early" for the preceding Trent 500. The intermediate pressure (IP) compressor aft of the fan in the Trent 900 is also a scaled version of the larger unit developed for the Trent 8104. The LP system changes also extended aft, resulting in a scaling-up of the LP and IP turbines, while the fan case also grew to fit the larger bypass requirements. The LP turbine is approximately the same diameter as the fan on the RB211-535, and measured in terms of fan diameter, the Trent 900 is the largest engine ever made by R-R.

As with the Trent 500/800, the Trent 900 consists of a single fan stage, an eight-stage IP compressor, six-stage HP compressor, single-stage HP and IP turbines and a five-stage LP Turbine. The Trent 900 also marks the first use by R-R of a counter-rotating HP turbine which, in tests, has demonstrated up to a 2% improvement in overall efficiency. Like the advanced fan, the concept was also mooted for the Trent 500 but was not considered sufficiently mature for implementation until now. The HP turbine rotates counter-clockwise to optimise the flow as it enters the IP turbine, requiring fewer nozzle guide vanes. The existing vanes are also subjected to much lower stress so have a smaller cross-section and are therefore lighter. Tests will focus on the performance of the revised flow regime, and particularly on oil system temperatures resulting from the related bearing changes in the area.

The Trent 900 ran for the first time at Derby in the UK on 18 March 2003, achieving its certification thrust level of 81,000lb on 2 April and passing the 88,000lb thrust level around seven days later. "The higher thrust level was not for bravado. It was literally to push the engine for data on extreme operating conditions," says Nuttall. The second and third test engines are scheduled to fire up in June. Test engines four and five will be complete by August, and will be allocated to performance and the 150h block endurance tests as well as some birdstrike work. Engine number six, after some initial performance cross calibration tests, will be used for the 3,000 cycle initial maintenance interval tests. The final dedicated test engine, number seven, will be used for the fan blade off test.

Testing also includes some production-standard engines, with the first - number 91000 - being allocated to the Airbus A340-300 flying testbed. This is expected to make its first flight on the aircraft at Toulouse around mid-May 2004. A further set of 'build one' Trent 900s will follow to support the actual A380 flight test programme. The test effort, which is being conducted to ETOPS standards despite the four-engined configuration of the A380, is expected to culminate in October 2005 with European JAA certification, with US FAA certification due around a month later. The initial Trent 970 version will be rated at 70,000lb thrust for entry-into-service on the A380-800 passenger version with launch customer Singapore Airlines in early 2006. Provision is being made for certification to the higher thrust levels required for the -800 Freighter and growth versions, and the Trent 900 has baseline growth capability to 84,000lb.

R-R remains confident that its past experience with the Trent family as a whole, and the Trent 500 in particular, stands it in good stead for the A380 flight test and service entry. Nuttall says: "It's derivative and low- risk. When it flies for the first time it will have 20 million hours of experience behind it, some of which is from the Trent 500, which has had the most reliable entry-into-service of any engine."

Partnership

The mid-1990s also saw the birth of Boeing's proposed 747-500X/600X, another large aircraft that would require new or highly derived engines. Although aimed exclusively at Boeing's proposal, GE and P&W declared their intention to team up in August 1996 to "develop, manufacture, sell and support a family of modern technology engines for high-capacity, long-rage aircraft".

The 50:50 GE/PW partnership, hatched the previous February in a radical cost-saving move, was focused on the GP7000 - a baseline design that combined P&W's low-pressure (LP) PW4000-based expertise with GE's GE90-derived high-pressure (HP) core technology. Less than four months after the birth of the Alliance, however, the stretched 747 plan was abandoned, and in 1997 the GP7000 was refocused squarely on the A3XX. Although a proposed GP7100 version was later aimed at the 747-400X and 767-400ERX models studied by Boeing, the main focus remained on the GP7200 defined for the A3XX.

As configured by 1999, the GP7200 was designed with a 2.8m (110in) diameter fan (versus 2.6m for the Boeing applications), a four-stage LP compressor, nine-stage HP compressor, a single annular combustor, two-stage HP turbine, and five-stage LP turbine. The engine was rated at between 67,000 and 80,000lb thrust, and was designed around an initial A3XX-100 range requirement of 14,230km (7,690nm).

The following year brought significant changes, however, as A3XX customer review meetings revealed the need to bring the aircraft in line with QC2 requirements. To play its part, the Engine Alliance extended the fan diameter to 2.9m, raising the bypass (fan pressure) ratio from 8:1 to 9:1. The changes added stages to the LP compressor and LP turbine, and were accompanied by several specific noise reduction features. These included sweeping the hollow wide-chord fan, increasing the axial spacing between the fan blades and the associated (contoured) exit guide vanes, and optimising blade and vane counts in the LP compressor and turbine.

Tests of a 42%-scale GP7200 fan on Pratt & Whitney Canada's (P&WC) advanced technology fan integrator verified a predicted performance benefit of around 1% from the swept fan over a conventional design. Testing of a larger 94% scale hollow titanium swept fan on a PW4098 started in Florida in 2003, and will focus on performance and aeromechanical work, while preparations continue for the start of rig tests on the first full-scale versions. These include a series of bird strike tests in a spin rig in the second quarter. Blades used in the 1.1kg (2.5lb) and 2.5kg strike tests will then be fitted to a development engine to check performance in a damaged condition. "The main objective is to leave 2003 with a fully validated blade," says GP7200 chief engineer Bob Saia.

The first full GP7200 engine is expected to run on 15 February 2004, two months earlier than planned, building extra contingency time into the schedule. In all, the certification plan will accumulate over 23,000 endurance cycles and 7,000h of test time on seven engines. The Alliance says this represents the most extensive testing prior to service entry of any commercial engine, and represents 5,000 more cycles than the GE90 or PW4084 certification programmes. The engine is also due to fly on GE's 747 flying testbed by the end of 2004, while the crucial final blade-out containment test is set for mid-September 2004.

This test will also provide a valuable evaluation of the frangible bearing support (FBS), a new technology introduced to reduce peak vibratory imbalance loads transmitted to the engine in the event of a blade separation in-flight. Derived from the PW6000 programme, the FBS consists of a specially designed bolted flange integral with the fan rotor static support structure. Fuse bolts connecting the FBS bolt flange are sized to separate under the enormous loads that would follow the loss of a blade. Fuse bolt separation transfers the fan radial imbalance load path to a fan stub shaft and number two bearing support structure, reducing the loads transmitted to the engine mounts and wing pylon.

In 2005 the Alliance plans to certificate the engine concurrently at take-off thrust ratings of 76,500 and 81,500lb, the latter to accommodate A380 growth plans. The baseline engine will be certificated as the GP7270 at 70,000lb thrust for the 560t passenger version, and as the GP7277 rated at 76,500lb for the 590t A380-800 freighter. Both ratings are flat rated to 30°C at sea level.

Auxiliary power

P&WC plans to make the first run of the newly assembled PW980 auxiliary power unit (APU) for the A380 by June. Not surprisingly for the world's largest airliner, the PW980 is the biggest commercial APU ever made and is rated at the equivalent of 1,270kW (1,700shp). The two-spool design is based on the PW901 used on the 747-400, which is itself derived from the P&W JT15D-5, but is scaled up thermodynamically by around 10% for the A380.

To accommodate the higher mass flow requirements of the Airbus application, the design is slightly enlarged over the 901 and incorporates some new materials such as single crystal nickel alloy PW8-1484 in the turbine to help retain similar durability levels as the 747 APU. Design of the PW980 is headed by Hamilton Sundstrand Power Systems Division's San Diego, California-based unit, while manufacturing, assembly and test is being led by P&WC in Montreal, Canada.

The APU consists of centrifugal HP and LP compressors driven by single-stage HP and LP turbines. The LP spool drives a gearbox with two 120KVa oil-cooled generators attached to it. Unlike some other large aircraft APUs, the PW980 does not need additional features such as oil heaters. "Because of the two-spool design we don't have the starting loads you get with a single-shaft design," says P&WC APU programme manager Mark Badger, who adds the design is simpler and easier to maintain as a result.

As well as a focus on reliability and durability, the programme includes a huge focus on reducing noise and other emissions. "We have a new effusion-cooled combustor design which allows us to control the flow through the combustor, and helps us put a finger on noise," says Badger, who adds that the resulting 3dBA improvement is "our biggest success on the programme so far".

A mock-up of the APU is currently being installed into the aft section 19.1 by the Airbus España division, after which the combination will be sent for tests in San Diego. The mock-up APU will be replaced by a real PW980 in the last quarter of 2003 and tested in a new test cell at Montgomery Field, California. A further four APUs will be delivered for durability and flight tests in 2004, while Technical Standing Order certification is scheduled for March 2005.

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