Rolls-Royce's campaign to step up fuel-burn savings and reliability across its big fan engine family is reaching a key phase with tests starting of a second round of upgrades to the Trent 900 for the Airbus A380 and for design audits beginning on improvements to the A330's Trent 700, and delivery of the first updated Trent 800EP for the Boeing 777.

The upgrade programs are designed in most cases for retrofit, but in each instance, will also provide the production standard for new-build engines in the future. Collectively, they form a vital element of Rolls' competitive battle against the General Electric-Pratt & Whitney Engine Alliance GP7200 over the A380, and the engine options provided by both U.S. manufacturers for the A330.

The battle is particularly intense over the A380 market. The Trent 900-powered version has been in service six years and now powers 58 aircraft with six operators. Since 2012, all Trent 900s have been delivered to EP (enhanced performance) Block 1 standard to improve reliability and fuel burn. “We have the best reliability in the A380 fleet, and based on last month's numbers, we reckon we are ahead,” says Peter Johnston, head of customer marketing for civil large engines. Following the introduction of the EP Block 1 package, Airbus has changed its official fuel-burn specification (or “Orange Book” listing) for the Trent 900. “The EP has been better than we said it would be,” says Johnston. “It's around 0.3 percent better than we claimed it to be based on results of Airbus production flight tests, so with around a one percent improvement, that is a better starting point for EP2.”

Block 1, like the other upgrade packages, is based primarily around the introduction of elliptical leading edges in the compressor. Other changes include tighter low-pressure (LP) turbine tip clearances and a new hard coating for the high-pressure (HP) compressor drum. Reliability-driven upgrades include changes to the HP and intermediate-pressure (IP) turbine disc and blades, IP nozzle guide vanes, seal segments, turbine case cooling, an LP location-bearing package, an IP turbine shaft coupling nut and a software upgrade to the electronic engine controller.

“We have now moved into the test phase for the follow-on EP2,” says Johnston. Designed to provide up to a 0.8% fuel-burn improvement, Rolls says that together with the better-than-expected outcome of the production EP1 engines, the overall improvement could net more than 1%. Five EP2 test engines are involved in the evaluation with the third unit currently moving on to core certification testing at Rolls' 57-bed ground-test facility in Derby, England. A fourth engine, built to production standards, will be used for back-to-back testing.

The three other engines in the program include a structural test engine that is viewed using a powerful X-ray device to assess dynamic movement and clearances of parts. Another functional test engine is used for detailed air and oil systems evaluation, assessment of the bearing loads and confirmation of overall functional behavior. A fifth engine, built to production representative standard with all the EP2 core modifications fitted, is currently in assembly and will be used for cyclic endurance tests.

The EP2 configuration includes optimization of the fan blade tip clearance using technology features derived from the Trent XWB now in flight test on the A350, as well as from the Trent 1000 on the Boeing 787. It also incorporates a tighter turbine case cooling control system and better sealing of the LP turbine, both of which are mainly derived from the XWB. Other elements include air system changes, aerodynamic improvements to the IP compressor and lower-drag 'A-frame' engine section stators with elliptical leading edges between the core and fan duct.

A group of engineering auditors is meanwhile completing a review of a second package of planned improvements to the Trent 700, which are designed to provide a further 1% fuel savings to A330 operators worth $200,000 per year from 2015 onward. “We want to make sure we're happy with it before we launch into detailed design and development later this year,” says Johnston, adding that the focus this time is primarily on LP turbine system changes to maximize propulsion efficiency. “The LP turbine is a big improvement because it results in almost a one-to-one benefit, rather than core improvements, which tend to be more diluted.”

Specific changes for the EP2 package, which is timed to coincide with the introduction of the heavier-weight 242-ton A330 in 2015, include the debut of a lower-drag version of the anti-flutter bridge in the LP turbine. Similar in concept to a clapper or snubber on a fan blade, the bridge is located mid-span on the turbine nozzle guide vanes. The revised design introduces a thinner profile that is reduced in thickness to 1 mm from 1.5 mm. Together with improved nozzle guide vane sealing, as well as build improvements and the introduction of three-dimensional stators in the intermediate- and high-pressure compressors, Rolls estimates the EP2 will generate typical specific fuel consumption reductions of 1%.

The upgrade work is seen as a valuable investment in what has become a successful engine-airframe franchise for Rolls. Since first entering service with Cathay Pacific in 1995, the Trent 700-powered A330 is now in service with 58 operators with approximately 533 aircraft in service. Earlier this year, this became the largest in-service fleet for Rolls, finally overtaking the RB211-535-powered 757.

In other EP developments, Rolls says the first upgraded Trent 800 with refitted elliptical leading-edge blades has been completed for an undisclosed customer. The 800EP should provide between 0.5-0.7% fuel-burn benefit, worth around $200,000 per aircraft per year. However, the concrete determination of how much benefit has accrued is yet to be determined. “We need to build and test at least 20 engines before we're sure, but so far everything indicates it is going well,” says Johnston.