Rolls-Royce hopes better-than-expected early test results from its newest and largest engine, the Trent XWB, will bolster its market position as it recovers from a difficult year.

Although flight trials of the latest Trent variant are yet to begin, bench tests of the engine for the Airbus A350 have yielded “very positive results,” says program director Chris Cholerton. Specific fuel consumption (SFC) “is better than expected.” Flight tests on the first A380, now an Airbus testbed, are due in the late summer or early fall.

“Most of that performance benefit is on the compressor,” adds chief engineer Chris Young, noting that early design studies “underestimated the benefits we would get.” Several factors are cited, including the decision to go with a rising line compressor, which effectively increases compressor blade-tip speed.

Furthermore, a change to the bearing load management system, which relocates the low-pressure system support from the center of the engine to the front, creates a stiffer core and improved clearance controls in the compressor. The new bearing load management system weighs more; but for the long-haul A350, the fuel-burn benefit offsets that penalty, Young suggests.

In addition, Rolls is seeing high surge margin in the engine, which could allow designers to trade some of that performance for a higher pressure ratio. That approach will be tested before year-end, which promises a 0.25% boost in SFC. It is not certain at what stage this adjustment could be introduced, but Cholerton indicates it could materialize on the flight-compliance engines that will be used during the A350 certification process.

Because of good intermediate-pressure-compressor surge margin, Rolls also was able to replace the last of four stages of variable vanes with nonmoving vanes to reduce complexity and weight.

Rolls sees other areas of improvement, with Young crediting the high level of processing and up-front work that went into the engine's design for the positive outcome.

The increased thrust potential could be critical, as customers signal they would like Airbus to boost performance of the A350-1000, which the aircraft maker appears to be planning (see p. 34).

Progress being made on the Trent XWB also may be fed into upgrades of the Trent 1000, which powers the rival Boeing 787. In particular, Rolls engineers see Boeing's discussions over the 787-10X, the possible stretch of the twin-widebody, as an opportunity to phase in new technologies.

“We are just starting the conversation with Boeing,” says Simon Carlisle, director of the Trent 1000 program. Although the aircraft configuration is far from set, Rolls expects the Trent 1000 to be able to cover the thrust demanded for the largest version of the 787.

The Trent XWB technology cut-off came a few years after that for the Trent 1000, so there are advances that could be fed back into the sister program. One of the big areas where Rolls is considering Trent XWB-related technology insertion into the 787 engine is in the compressor, says Trent 1000 chief engineer Andy Geer, although the “rising line” design may be too much of an architectural change to deliver, he adds.

Boeing and Rolls, meanwhile, have begun flight testing the upgraded Package B for the Trent 1000, which is aimed at closing a fuel-burn gap between what has been promised and what the initial build standard has delivered.

Package B should bring SFC within 1% of specification, says Geer. The fan system has been optimized around a different geometry, the air system has been tweaked and the low-pressure turbine (LPT) blades have been modified.

In particular, Package B includes improved aerodynamics in the six-stage LPT, better cooling flow for the intermediate-pressure turbine (IPT) and changes to the secondary air system to siphon off sealing and cooling air at a lower pressure stage. The root-to-tip twist of the fan blade also has been altered slightly to match changes in the pressure ratio caused by a concurrent reduction in nozzle area.

The enhanced engine is due to enter service on the fifth All Nippon Airways (ANA) airliner toward year-end. Initially, there was concern that a far greater number of higher-fuel-burn Package A engines would be fielded, but delays in delivering 787s have effectively minimized that situation. Carlisle expects all Package A units to be out of service within 12-18 months.

Both Package A and B engines also have been modified following last year's failure of a Trent 1000 on a test bench. Geer concedes it was an “unfortunate event,” but says that in the end, it took only six months to fully understand and fix the problem. Hardware and software changes to the engine management systems have resulted, but Geer notes that those did not come with an SFC penalty. However, the engine maker did run tests on other Trent-architecture powerplants to ensure there was not a systemic problem.

General Electric also has had to introduce a GEnx performance-improvement package to deal with its own SFC shortcomings.

Although meeting SFC targets has been a challenge, in other areas Rolls says it has ample margin. On noise, for example, the company has delivered a 20-db margin over Stage 4 levels, double what was required.

Rolls is also starting work on an outline Package C engine-enhancement program. Having closed out a concept review last month, Geer says “we are moving into the detailed design phase.” But there is still fluidity to the plans. The package, which will be defined more by the needs of the 787-9 than the -10X, could crystallize this year, he notes.

The 787-9, which is set to enter service in the second half of 2013, could see Trent 1000s with SFC cut by a further 2%. Several improvements, including elements of Package B, were run in a test engine at the manufacturer's Derby, England, facility in February 2009. Additional modifications to be introduced into the engine for the -9 version include better air sealing, optimized high-pressure turbine (HPT)cooling flows and aerodynamics. The engine could also incorporate an advanced case-cooling system for the HPT and IPT.

Owing to delays in the 787 program, Rolls is hopeful that it has been able to address maturity issues before the beginning of ANA's operations in the third quarter; more than 1,000 flights and 2,800 hr. have already been logged. “We are confident we have a mature product,” says Carlisle.

Following the certification of the Trent 1000 for 787 ETOPS in May, the main technical issues to sort out are completion of system-level extended twin-engine operations, plus function and reliability testing. The latter tests simulate regular airline service and are in addition to a route-proving operation planned by Boeing and ANA in early July. Carlisle notes that Rolls will treat those flights as if they were real in-service ops. He also says A380 lessons are being applied by making sure that adequate spares support is in hand. As with the A380, Carlisle expects that early operations will receive a lot of attention.

Spares support for these flights will be eased somewhat by the fact that ANA will focus initially on using the 787 in domestic service before expanding into international routes.

Rolls has secured 50% of 787 customers, although GE has a higher number of engines on contract. However, Carlisle notes that the Trent 1000 has won six of seven recent competitions, and he attributes the improvement partly to Boeing's 787 performace figures, which now show a smaller difference in SFC between the Rolls and GE powerplants than had been the case earlier.