With flight tests of the Trent XWB-powered A350-900 progressing according to plan in France, Airbus is marching on schedule with Rolls-Royce to define a higher-thrust version of the XWB set to power the larger version of the advanced twinjet in mid-2016.

Despite benefiting from a high degree of similarity to the engine now in flight test, the challenge is far from straightforward. The XWB-97 is designed not only to generate over 15% more power for the stretched A350-1000, but it must do so within the same overall nacelle size as used on the A350-800/-900. And it must accomplish this without impacting the specific fuel consumption or on-wing life of the engine. To solve this conundrum, the larger engine incorporates a higher-flow-capacity fan to pump more air, a larger core to increase flow and higher-capability turbines to extract power for the fan.

With encouraging signs emerging from the test program that indicate they have a stable platform on which to build, Rolls-Royce and Airbus completed a critical design review (CDR) for the XWB-97 engine in mid-September. Prototype demonstrations to prove key technology for these moves have meanwhile begun at INTA in Spain using a modified XWB-84, and initial data from these tests were reviewed as part of the design review meeting held at Rolls's Derby site in England.

“Some key milestones are coming,” says Chris Young, Trent XWB program director. Development activity is rapidly accelerating on the new engine as the first Trent XWB continues in flight test. “We still have a lot of people working on the 84K (XWB-84), but we have passed the crossover point where there are more people working on the XWB-97.”

Prior to the joint review with Airbus, Rolls had “just completed the CDR (at Rolls) for the 97K engine. It is a really important milestone because it is the one that says you are good to start machining and to start releasing the drawings to get into final manufacturing. After that is when parts start coming in to store at the end of the year and early next year. That clears the way for the start of assembly and first test in the middle of next year,” Young says.

Following completion of a preliminary design review for the XWB-97 in January, Young said, “there is real raw material coming together for forgings and castings.” These include the completion of rough machining of the first variable stator vanes, initial machining of the intermediate pressure (IP) compressor sixth-stage disc, and trials of the linear-friction stir-weld process on the IP compressor first-stage blisk. The cone for Stage 6 of the high-pressure (HP) compressor rear drum assembly and other core parts of the first engine are also underway.

Rolls has begun runs of XWB-97 development materials and tip clearance control systems using baseline development engine ESN20001. Tests are evaluating new shroudless HP turbine blades and seal segments. “So we are trying to prove that when the turbine runs into the ceramic seal, it will last forever, even though it has had a rub,” Young adds. A second run in early in 2014 will include tests of a “full standard of shroudless turbine with tip clearance and cooling.” The engine is scheduled to be flight tested on the A380 flying testbed at the end of 2015, and will power the A350-1000 for its maiden flight in 2016. The entry-into-service date is targeted for mid-2017.

Testing of the XWB-84 on both the A380 evaluation aircraft and the A350 has proved uneventful, says Young. “Clearly, flying was a huge moment for us and seeing the aircraft go into the air after seven years of preliminary design was a great moment. So far, flight test-wise, it has been really, really boring.” Commenting on Sept. 19, he noted that well over 200 hr. had been accumulated over almost 50 flights. “It really is routine and operational, which, to me, proves the dividends of the overall structure of the program. This was designed with a lot more resource up front in which we did more virtually before doing more physically.” Citing the extensive use of the flying testbed as an example, Young says: “The key thing for us was to find things really early, well before you found them in flight test on the A350. The engines are operating immaculately.”

The finesse of the engine design and fidelity of tests also reflect increases in computer power from which modern engine designers can benefit, he adds. “Our most powerful computer when we designed the Trent 1000 used 30 parallel processors. With the XWB, it was 3,000. Now we are starting with 10,000 parallel processors on a whole engine thermo-mechanical model. So things that previously took four to five months now take a day. That means you can get more iterations or make them more representative of the real world. The A380 flying testbed, meanwhile, was a deliberate investment decision between ourselves and Airbus,” Young says.

Production of the XWB-84 to support flight testing continues to keep pace with a planned rate of one engine per month. “We are focusing on our industrial ramp-up, but flight-compliance-wise, we have delivered the second shipset. It is on MSN3, which is now in the paint shop in Toulouse. “The next set is for MSN4, and the first of those engines is on the way to Toulouse and the second is about to be shipped,” he adds. Two spares have also been delivered, while module assembly of engines for MSN5 is underway. Core assembly of engines for MSN2, the first A350 to have an interior, has also begun. “In terms of production ramp-up we start assembly of the first production engine in the first quarter of 2014 for Qatar. It is a fairly steep ramp-up as we move out into the full assembly line. We will deliver around 40 engines in 2014 and 120 the year after,” Young says. Qatar is due to receive its first aircraft in the second half of 2014.

Twelve engines have also been involved in the certification, test and development program, which is targeting an accumulated 5,500 hr. and approximately 10,500 cycles. “We've done the tough part to get certification and we are now up to well over 10,000 cycles. We doubled the cycles this year and completed three cyclic tests on an engine at Madrid-based INTA,” he says. The parts from one such engine, ESN21005, Build 3A, have been prepared for a full layout inspection by more than 20 A350 customers who will come to scrutinize the parts in Derby on Oct. 10. “This is demonstrating a more representative type of service operation and longevity,” Young says. Engine 20002, Build 4, at Rolls's facility at NASA's Stennis, Miss., site has meanwhile completed more than 1,000 cycles and 3,000 thrust-reverser cycles.