Orders from Singapore Airlines covering up to 50 additional Rolls-Royce (R-R) Trent XWB-engined A350-900s boosted Airbus as it made final preparations late last month [May] for the new airliner’s first flight. The Asian carrier has booked 30 examples and taken options on 20 more (convertible to larger A350-1000s), boosting the total number of A350-900s it has ordered to 70.
The Trent XWB, the only engine powering the A350-900 and the exclusive propulsion unit for the larger A350-1000, is the fastest selling of the six Trent-family models with more than 1,300 sold to 35 customers, said Rolls. The series comprises six variants: Trent Model 500 (powering the Airbus A340-500), Model 700 (A330), Model 800 (Boeing 777), Model 900 (A380, Model 1000 (Boeing 787) and the new Model XWB (A350 XWB).
Having logged about 20 hours’ running before delivery, two very early Trent XWB preproduction engines (serial numbers 21002 and 21003) were fitted to the first A350 and were expected to be run for another “couple of hours” before the maiden flight, according to Trent XWB program manager Chris Young. Following manufacture of 12 development units, R-R had built at least six (of up to 18) preproduction Trent XWBs, with four more in manufacture, by the beginning of June.
Last month, the engine-maker was preparing to test a more-powerful 97,000-pound-thrust XWB-97 variant in a technology-demonstration program set to continue through 2013, ahead of an initial formal run in about 12 months. R-R has achieved about 106,000 pounds thrust with a basic core and the XWB-97 is “on track” to enter service powering the A350-1000 in mid-2017, following initial A380 flying-testbed (FTB) work a year earlier.
Trent XWBs will power the 8,500-nm-range, 270-seat A350 Series 800; 8,100-nm-range, 310-seat Series 900; the Srs 900F cargo variant; and the planned longer-haul Series 900R, with some 1,200 R-R engineers engaged on the XWB program. The engine’s 118-inch-diameter fan is the largest so far introduced by the manufacturer, which received European Aviation Safety Agency certification for the 75,000-pound-thrust Trent XWB-75, 79,000-pound-thrust -79 and -79B (A350-800), and 84,000-pound-thrust -84 (A350-900) models four months ago.
The engine sports a two-stage intermediate-pressure turbine with “advanced” blade-tip clearance control, and “very encouraging” results from FTB and ground trials mean that it is “on track” to achieve targeted fuel-consumption (fuel/pound of delivered thrust), according to R-R. The company is accelerating engine testing in efforts to establish maturity and production.
Civil large engines strategy and future-programs executive vice president Simon Carlisle said R-R has achieved a 16-percent efficiency gain during over 50 million flying hours (FH), demonstrating continuous performance improvements since the original 1970s’ RB211 three-shaft powerplant designed for the Lockheed TriStar. Following 18 years of operation, Trent engines are powering 50 percent of next-generation widebody aircraft and recording about eight million flying hours a year.
In developing the Trent XWB-97, R-R has been encouraged by simulated altitude-chamber work with the XWB-84 that provided very-high-flow fan conditions, allowed the manufacturer to understand the requirements of the larger powerplant for the A350-1000. Since baseline Trent XWB tests showed better-than-expected fuel burn with greater efficiency and surge margin, R-R has traded that leeway for fuel consumption on the larger XWB-97.
Originally planned at 93,000 pounds, the additional power has been obtained via a 6-percent increase in fan flow, combined with a slight change in bypass ratio and aerodynamic improvements in the larger core that increases flow. The XWB-97’s fan runs faster than those of smaller XWB units, but can be accommodated in a common nacelle with unchanged aerodynamics.
R-R says the XWB-97 turbine benefits from its use of advanced coatings and cooling technology, blade tip-clearance control (reducing “leakage”) and improved materials. An enhanced combustor is claimed to provide a 20-percent margin over CAEP 6 nitrous-oxide standards, with noise levels put at QC1 arrivals and QC2departure limits. Depending on Airbus development of the A350, the XWB-97 could be improved through “technology insertion,” according to R-R.
The company claims that a preliminary design review in early 2013 showed that the XWB-97 could use 80 percent of Trent XWB-84 line-replaceable units–effectively most items of equipment except fuel-metering units and more powerful pumps. All ground-support equipment and tooling is common as are “externals and consumables.”
Earlier this year, R-R started part-manufacturing trials and had made the shroud-less high-pressure (HP) turbine module Trent XWB-97 demonstrator engine and was readying fabrication of the intermediate-compressor stator section and HP compressor rear drum.
Although RR has been “investing in the technology for years,” its use of composites for Trent XWB fan blades (rather than titanium, as on the Trent 700) is an evolution, according to Carlisle. Such material provides “significant” weight savings–“700 pounds per blade set”– and allows broader design architecture for the rear fan case (the front case is titanium).
The company also has made composite blades for a fan to run in its advanced low-pressure system demonstrator project that has supported R-R’s environmentally friendly engine, which is derived from the Trent 1000. “We’ve always said we’d only use composites when [the material] was better than the best,” asserted Carlisle.