February 12, 2013
Rolls-Royce (R-R) is getting ready to start assembly of a prototype version of the Trent XWB-97 for the Airbus A350-1000, the most powerful production turbofan it has ever developed.
The engine is expected to help prove several design features of the higher-rated variant, the first development unit of which is due to make its first run in mid-2014. The Trent XWB-97 is on track to power the first A350-1000 in mid-2016 and enter service a year later. Assembly of the demonstration engine gets under way as R-R prepares to deliver additional baseline Trent XWBs to Airbus in Toulouse for A350-900 MSN1, the first variant of the new twinjet widebody.
The engine maker shipped the first shipset of flight-compliant XWB-84s in December and completed assembly of two more. R-R Trent XWB Program Director Chris Young says three more XWB-84s are in build, and parts are “kitted” for an additional four. The baseline engine received certification from the European Aviation Safety Agency on Feb. 7. Certification covers the XWB-75 and -79 variants for the A350-800 and -84 for the A350-900, effectively encompassing the 75,000- to 84,000-lb.-thrust range required for the two versions of the A350 family.
R-R in January completed the preliminary design review (PDR) for the 97,000-lb.-thrust-rated Trent XWB-97. “This is a key milestone for us, as it takes us into detailed design and the making of individual components of engines, the pouring of castings and the creating of forgings. It also enables us to get ready to begin machining,” says Young. Although the XWB-97 is sized for considerably greater thrust, Young says a success from the PDR will be confirmation that 80% of the line-replaceable units will be common for the various engine variants. The only exceptions will be fuel pumps and fuel metering units, which have to be larger for the 97,000-lb.-thrust version.
Development of the XWB-97 follows the 2011 decision by R-R and Airbus to revise the A350-1000 thrust requirement from 93,000 lb. to the present 97,000 lb. To maximize commonality with the baseline XWB and avoid changing the outer mold line with an expensive increase in fan diameter, R-R sought to meet the higher power need by scaling up the core and boosting the flow. The fan will spin 5% faster, and the annulus at the base of the fan blades has been redesigned with an inflection to boost the flow capacity around the spinner.
“We will get more power out of the core by making it bigger and improve the turbine’s capabilities to run the engine hotter,” says Young, adding that the focus is on putting new technology into the turbine. Changes for the XWB-97 include the use of next-generation CMS-X4 single-crystal materials and anti-oxidation coatings in the high-pressure turbine, which will be shroudless for the first time on a Trent engine.
The turbine disc also will be forged from a dual microstructure disc that will provide greater stress capability toward the center of the hub, while exhibiting better creep resistance toward the tips. Other improvements include a more sophisticated adaptive bleed system, which is designed to turn cooling air bleed off during cruise when not required. The intermediate (IP) compressor features a “rising line” or inner annulus line that increases in radius, thereby boosting the tip speed of the aft stages. The high-pressure compressor is derived from the European New Aero Engine Core Concept program and is connected to the IP by a swan-neck duct.
“We will be testing one of the 84,000-lb.-thrust (XWB-84) development engines and putting a selection of ‘97K’ new turbine technology into the engine, so we can run it as close as possible to XWB conditions,” says Young. The prototype XWB-97 engine is expected to start first runs about the middle of the year, he adds.