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.