RR Trent XWB

Trent XWB prepares for flight

Rolls-Royce has been increasing the momentum of testing in its Trent XWB programme, ahead of the start of flight trials later this year, writes Ian Goold.

Rolls-Royce (R-R) confirmed at June's Paris air show that research programmes already underway to develop higher-temperature and higher-thrust engine technology would be applied to the powerplant for the Airbus A350 XWB.

The UK-based engine manufacturer's Trent XWB is the exclusive powerplant for Airbus’s new widebody twinjet, while the Trent 1000 competes against the General Electric GEnx-1B to power the Boeing 787.

With an accelerating work programme and early test results described by the company as "positive", R-R believes the Trent XWB can be delivered as a mature powerplant, ready to enter full production by the end of 2014. Before the Paris show in June, the A350 XWB (standing for "extra wide body") had attracted orders from almost 40 customers for more than 570 aircraft (an increase of over 60 in the preceding 12 months).

Later this year, R-R should have optimised its final manufacturing methods for the Trent XWB, having applied experience gained from the assembly of eight initial development engines (see box). The manufacturer is confident that its efforts will lead to the company’s "fastest-ever" large-fan production ramp-up. What the company calls "proper production" will begin in the latter part of 2012, while the highest rate – 315 a year, or almost one engine a day – will be reached by about the turn of 2017-18.

Largest fan

The Trent XWB's 118-inch-diameter fan is the largest R-R has ever made. Adoption of a narrower rotor hub than on the Airbus A380's Trent 900 engine has contributed to a lower "hub-to-tip" ratio, with the larger fan blades ("as much as 50 percent" more surface area, R-R says) offering greater air flow and a lower drag-to-weight ratio, according to Trent XWB Chief Engineer Chris Young.

R-R has achieved a higher load differential between the various bearings in the three-shaft powerplant by combining the large fan with a smaller engine core. The "optimised bearing-load management system" results in greater loads being carried further forward in the engine. That permits better mechanical loading in the bearings, which in turn improves fuel efficiency, although Young also concedes that the "more capable" arrangement is also heavier.

"Considerable" innovation is claimed for the Trent XWB's "rising-line" compressor, in which the blades rotate at higher speeds toward the rear of the engine's intermediate-pressure (IP) stage. Performance retention, specifically fuel burn, will be enhanced through the use of increased overall pressure ratios in the two-stage IP turbine (IPT). Specific fuel consumption has been "excellent, better than expected", says Cholerton.

The Trent 900 has provided the source for the Trent XWB's low-pressure turbine (LPT), a nine-inches-shorter scaled version of that on the A380 engine. The reduced weight of the LPT serves to offset that the heavier IPT.

R-R has introduced composites material for the rear fan case, which is supplied by new partner ATK and for which development has gone well, according to Young. To make moving finished engines easier, the manufacturer has also produced a "transportation stand", which permits a simpler separation of the core from the fan case before the powerplant is shipped by air to Toulouse.

Maturity goal

The engine company has been preoccupied with efforts to deliver engine maturity at – or in advance of – the production ramp-up, says Trent XWB Programme Director Chris Cholerton. R-R has "matured" in-house design processes, analysing any disruptive events that have taken place in the Trent engine fleet and applying the lessons from previous failure modes to ensure reliability.

"Failure-mode effects and critical analysis (FMECA)" and the Pareto principle – the tendency for, say, 20 percent of causal events to generate perhaps 80 percent of resultant effects – have been applied to 400 parts and led to 1,200 "mitigation plans".

In an effort to reproduce in-service operating conditions, the manufacturer has made significant investments in computing capacity to support component and systems testing, Cholerton says. Important contributions have come from R-R's environment-friendly, high-temperature E3E (efficiency, environment, economy) two-shaft technology demonstrator engines.

By July, R-R expected to have completed four more Trent XWBs to complement its initial four units. The company has been increasing the momentum of testing ahead of flight trials of one engine on an Airbus A340 flying-testbed (FTB) later this year. Cholerton says early testing has gone "very, very well". Compared with the initial 84,000lb thrust required in service, much higher thrust levels of over 100,000lb have been demonstrated on the first unit.

R-R has invested increased resources into early development stages of the Trent XWB, including proof-of-concept work. All the design modules are said to have been validated by the "highly instrumented" engines, on which the company measures more than 1,500 parameters (including, for example, overall gas flow). The XWB has yielded the "best-ever Trent performance" results, according to Young.

Ahead of the Paris show, more than 60 rig-test programmes had been completed as R-R worked to establish reliability. Much of the testing is said to have been pushed to "extreme limits" – the company having increased diagnostic capacity and begun investigating mechanical behaviour early in the development process.

R-R had also completed a large proportion of emissions-control reliability testing before June. In anticipation of final humidity inspection and checks, it had completed inspections and product-assessment tests of humidity, thermal, and vibration performance.

Young says functional operation has been "excellent", while the IP compressor (on which one of the four rows of guide vanes has been fixed) has demonstrated a "very good" surge margin. A key step in progress toward the Trent XWB's first flight will be final nozzle optimisation to balance specific fuel consumption with operability.

X-ray analysis

A "real-time" digital X-ray facility that R-R has introduced for Trent XWB development in the Derby factory in England is said to the most powerful such equipment in western Europe. Young says that the manufacturer is able to compare actual working of all engine parts with intended operation, with the equipment saving "weeks" of time over previous film-technology methods.

X-ray results obtained by the end of May are contributing to further performance improvements and engine optimisation. The official cites the first two low-pressure turbine stages, where R-R has recognised blade-tip movement relative to the blade seal, as an example; the introduction of tighter tip clearances should enable performance to be maintained for longer.

On-wing tooling has been validated during early maintainability tasks as R-R prepares to install the engine on the FTB, which will provide a fourth "parallel stream" of testing. This began in 2010 with rig work, ahead of initial performance-envelope expansion. Subsequently, the manufacturer has begun maturity testing, followed by function and performance testing before engine-certification activity.

The A340 testbed will be fitted with a brand-new pylon, with a new engine mounting that suspends the Trent XWB from the fan and rear-engine cases instead of the previous attachments to the core, which is no longer loaded. R-R has "felt for some time that this was the preferable mounting and have worked with Airbus" to develop it, concludes Young.


Trent XWB engine testing

Eight Rolls-Royce (R-R) Trent XWBs are being used in the powerplant test programme, which involves engine serial numbers 20990 and 20001 to 2007 – although engines are not being test-run chronologically.

Trent XWB 20990 – R-R planned to complete engine "pass-off" tests with this unit, its most highly instrumented flight-test engine ever, by June. The tests will precede in-flight trials aboard the Airbus A340 flying test bed.

20001 – This engine will be equipped with strain-gauged fan blades for bird-ingestion tests that will begin with a "medium" bird in trials that were expected to continue in July with a "large" specimen. The powerplant has been used for earlier performance-envelope expansion, operability trials, and compressor-functional operations.

20002 – R-R is using Trent XWB 20001 on Derby's Test Bed 58 for integration of aircraft-interface systems. Low-pressure turbine testing in May was to be followed by thermal and emissions trials, integration of buyer-furnished equipment, and water-ingestion trials by late June.

20003 – Engine cyclic tests are scheduled to be conducted with this unit.

20004 – Endurance testing began with Trent XWB 20004 in June. The work was said to involve "lots of hours" at high speed and high thrust to confirm the design's maturity.

20005 – UK and US tests on this engine have included flutter and cross-wind operations. It also was part of thermal-survey work at Derby, which has provided positive results in the shape of lower-than-predicted disc-cavity temperatures. US trials have involved fan strain-gauging, noise, and thrust-reversal.

20006 – This unit was being reconfigured in anticipation of altitude testing scheduled to start in the US in August. The engine was used earlier for the validation of low-, intermediate-, and high-pressure bearing loads, oil-system optimisation, sea-level performance, and variable-frequency generators.

20007 – Intermediate-pressure turbine strain-gauge and thermal testing will be performed on the final test specimen

By the beginning of June, the first 84,000-pound-thrust Rolls-Royce Trent XWB engine had flown for more than 40 hours aboard the Airbus A380 flying testbed (FTB) as Airbus moves toward a first A350 flight “probably around mid-2013,” according to engine program director Chris Young. Trent XWB Serial Number 20990 had logged 43 hours and was scheduled to make two more flights before replacement by S/N21000, dubbed FTB2 (see box). Tests with the latter, which has updated parts and is said to have demonstrated the “lowest Trent XWB specific fuel consumption so far,” will be conducted using a revised instrumentation suite.


The Trent XWB-84 is fitted to a dedicated pylon in the inboard right wing (No. 3) position using a new mounting that suspends the powerplant from the fan and rear engine cases, rather than, as previously, from the now-unloaded core. Tests are being conducted jointly by Airbus and Rolls-Royce, giving both partners access to the raw data for the first time. Airbus pilots flew the initial air test and, subsequently, some Rolls-Royce pilots have taken part.

The 175-hour Trent XWB flight test campaign includes 16 flights with S/N20990 and the balance with the modified second unit, which was delivered to Airbus on May 23 and will be used for post-Phase 2 flights from about the end of this month.

Flight-test highlights are an early confirmation of specific fuel consumption, with Rolls-Royce confident the engine will meet specifications, as well as low oil consumption. Full “takeoff and go-around” power was held for 10 minutes and a full-power rejected takeoff with reverse thrust has been demonstrated, as have engine relight and wind milling.

The A380 FTB has performed high- and low-speed calibration curves and maximum angle of attack, as well as reaching FL430 and Mach 0.90. Rolls-Royce describes pilot feedback as “very positive,” while noise and rumble characteristics also are “good.”

Last month, Rolls-Royce was preparing to finish certification testing with cold-water ingestion and blade-off trials with the latest standard fan, which, at 118-inch diameter, is the biggest Trent fan the UK-based engine maker has produced. The overall test program involves 10 engines that will run for some 2,000 hours.

Apart from the two flight engines and two others earmarked for mechanical tests, the remaining six units will be dedicated trials covering airframe integration, cyclic operation, endurance, low-pressure system tests, performance and robustness, said Young. Rolls-Royce said about 75 people–drawn equally from research, production and maintenance teams–are currently working to produce the first 16 production Trent XWBs.

Because baseline Trent XWB tests demonstrated better-than-expected specific fuel consumption with greater efficiency and surge margins, Rolls-Royce has been able to trade that margin for fuel burn in developing the more powerful engine for the A350-1000 to deliver 97,000-pounds thrust from service entry.

The extra power, which had initially been planned at 93,000 pounds of thrust, comes from a 6-percent increase in fan flow (enabled by use of an inflected annulus), coupled with aerodynamic improvements to the enlarged core that also increases flow. The fan is driven at a higher speed than on the baseline engine, but because it retains the latter’s optimum-size 118-inch diameter, Rolls-Royce is able to use a common nacelle without any aerodynamic compromise.

The manufacturer said the Trent XWB-97’s turbines have increased capability arising from use of tip-clearance control, upgraded materials and advanced coatings and cooling technology. An improved combustor retains a 20-percent nitrous oxide margin to CAEP 6 limits, while noise levels are said to remain at QC1 for arrivals and QC2 on departure.

Rolls-Royce needs to agree with Airbus about flight-testing of an initial modified Trent XWB-84 engine providing the higher thrust, but has disclosed that it might need to invest in a new FTB to prove the powerplant’s capability. Young said that it might be possible to conduct the tests on an A350 airframe, although four-engine machines were traditionally used. The manufacturer expects to demonstrate a 97,000-pound thrust prototype engine early next year, ahead of a formal first engine run in mid-2014.

Jon Ostrower
‏@jonostrower





Rolls-Royce did the Trent XWB blade-out test over
the weekend. "Early indications have been positive," says RBC analyst
note.