Four years after the surprise launch of the Airbus A350XWB airliner, engine maker Rolls-Royce is still faced with two pleasant surprises from what might have seemed an ill-timed program given the impending global recession. First, it remains the sole powerplant provider for the new widebody airliner. Second, two years into an air transport downturn of historic proportions, its main challenge is ensuring that its Trent XWB engine enters service three years from now with sufficient engineering security to meet the expectations of more than 30 prospective operators who hold firm orders for more than 1,000 of the new turbofans.

Rolls-Royce achieved the first ground test run of the new Trent engine just over a month ago, on June 17. In doing so it met the commitments made to Airbus and to A350XWB launch customers at a time when keeping aerospace programs on time appears to have gone out of fashion.

The challenge now for the UK engine maker is that in the remaining 36 months or so of the Trent XWB development program it ensures that the new turbofan enters service meeting the exacting performance standards that airlines now have come to expect from day one.

The push for overnight in-service maturity has been under way for some time in the Rolls-Royce engineering department at Derby and it is about to be stepped up a gear or two as ground-testing paves the way for a first flying test bed sortie in the middle of next year, followed by a first A350 takeoff in the middle of 2012.

The -900 version of the A350XWB is due to enter service powered by the Trent XWB-84 engine in mid-2013, followed about 12 months later by the -800 (Trent XWB-75) and by the -1000 (Trent XWB-93) toward the end of 2015. For the A350-800, Rolls-Royce is also developing -79 and -79B versions of the powerplant to take into account some operators’ needs for greater hot and high performance and more range with higher takeoff weights.

Maturity an Issue
“Maturity is a big issue and to meet this challenge we have invested a lot more [in engineering development work] at a much earlier stage,” said Trent XWB program director Chris Cholerton. This extra investment by the UK engine maker has resulted in it committing about 700,000 more design hours on the XWB engines than it has done for previous Trent programs, as well as the addition of about seven times the computing capacity and the fact that it will have seven engines ready for testing by early next year. Previous programs have had access to only between one and five test engines.

Three of the seven engines will be dedicated to maturity testing, with the other four dedicated to certification work. “In the past, we have tended to do certification first and then maturity work later,” explained Cholerton. “This meant that there was less time to react to issues before entry into service.”

Part of the extra investment to fast-track the Trent XWB on the road to maturity is the new 58 test bed that Rolls-Royce has built in Derby, and where the first of the complete engines is now being run on a daily basis. The XWB turbofan is Rolls-Royce’s biggest engine to date and its 118-inch diameter fan (through which the fuselage of a Concorde would fit) cuts an imposing figure on the test bed. There are no fewer than 18,000 core parts in the engine.

Last year, the manufacturer also sought to reduce engineering risks with the program by conducting intensive rig testing of all the key Trent XWB components before the first complete engines were assembled. The second and third engines are now close to completion, number four has just entered the build stage and number five is in the final stages of being kitted out with its parts.

Rolls-Royce will also be using the new Glacier facility in Manitoba, Canada, to perform icing tests in natural conditions, as well as the existing outdoor test facility at Stennis, Mississippi. The engine maker has another mechanical test facility near Berlin, Germany, and an experimental logistics center in Derby. The Trent XWB development program will also include about 175 hours on a flying test bed.

10,700 Features Assessed
Some 400 engine parts have been assessed for in-service reliability risks identified from previous Trent engines and some 1,200 mitigation plans are being developed to deal with any problems that emerge. The Rolls-Royce engineering team also has made extensive use of advanced three-dimensional computational fluid dynamics and aero thermal analysis.

Looking ahead to the manufacturing phase, Rolls-Royce has assessed more than 10,700 features of the XWB engine and none of these is cleared for production until it has been fully tested to avoid unforeseen glitches. It also has conducted around 130 assessments of the engine’s maintainability to anticipate possible headaches at this stage.

“Zero in-flight shutdowns almost needs to be a given these days,” said Trent XWB chief engineer Chris Young. The main focus for his team is to meet or even exceed customers’ expectations in terms of cost of ownership through factors such as eliminating as many possible causes for even 15-minute departure delays in service. Since 2005, Rolls-Royce’s “project zero” campaign to boost reliability of its large airliner engines has resulted in a 10- to 12-percent reduction in service disruption levels each year.

The Trent XWB is the first engine that Rolls-Royce has developed for Airbus featuring a fan case mount system, although it has taken this approach for various Boeing programs. The new turbofan also features an optimized bearing load management system for better fuel burn, advanced aerodynamic compressors, a single skin combustion casing, a modulating air system, a two-stage intermediate-pressure turbine (IPT) and a short, light low-pressure turbine (LPT).

“We are on target to meet our SFC [specific fuel consumption] specification, noise and emission levels are on track, and so is weight,” concluded Cholerton. Rolls-Royce is also confident that it is on target to achieve its ambitious engine maturity projections and in-service attributes for the newest member of the prolific Trent family.

The projected SFC for the Trent XWB should be 9.5 percent better than that of the Trent 500, which entered service in 2002, delivering, potentially, a $250 per engine saving for each flight hour (depending on fuel prices).

Mindful that XWB production rates will double output rates for the Trent engine family over the next five years, Rolls-Royce is also investing in production capacity, including a new single-crystal turbine blade facility and advanced disc making facility at Derby. The fact that production rates for the Trent XWB are set to reach almost one per day was a big driver for the second assembly facility that the company is building in Singapore.    

Partners Share the Trent XWB Development Load

The Trent XWB engine program has the highest proportion of participation by risk and revenue sharing partners (RRSPs) of any member of the Trent family. Last year, Rolls-Royce concluded agreements with all 12 RRSPs, which account for about 40 percent of the value of the XWB powerplant.

There are six first-time Trent RRSPs on the XWB engine. Parker Aerospace is making the oil pump and engine build-up (EBU) hydraulics. ATK is providing the composite rear fan case, with this being the first time that composite has been used for this section of a Rolls-Royce engine. The other new Trent partners are as follows: Forgital (fan case forgings), Eaton (EBU flexes and ducting), Hispano-Suiza (accessory gear box, step-aside gear box, radial drives and oil tank) and Sumitomo Precision Products (heat management system).

The six Trent XWB RRSPs that have contributed to previous Trent programs are: Hamilton Sundstrand (air starter), Esterline (sensors), ITP (LPT module), Volvo Aero (inter-case), Kawasaki Heavy Industries (IP compressor and front bearing housing), and Mitsubishi Heavy Industries (combustor, LPT blades and IPT1 disc).

In addition to the 12 RRSPs, the Trent XWB engine will be made by no fewer than 88 different suppliers and 16 separate Rolls-Royce facilities. The engine maker concluded its RRSP agreements last year and had already been working with Volvo to study options for lightweight fabrication. There are still production contracts to be awarded that will account for about a third of the value of the engine.