GEnx-1Bs Burn Two Percent Less Fuel Than Rivals In Early 787 Operations, Claims GE
Operators of Boeing 787s powered by the latest-standard GEnx-1Bs are promised real fuel savings over similar aircraft with competing engines, according to engine maker General Electric. The powerplants also will be more durable and remain “on wing” longer if equipped with two performance improvement packages: PIPs I and II.
The latter is scheduled for certification at the end of this year, with PIP I–which was primarily driven by a requirement to improve fuel consumption–having received U.S. Federal Aviation Administration airworthiness approval last month. The two-stage enhancement aims to ensure that the engines meet Boeing’s original fuel-burn specification, while also offering higher thrust that will support growth in aircraft weights, perhaps including the 787-10X being mulled by Boeing.
The latest PIP II development adds various fan, booster, compressor and combustor changes to the low-pressure turbine (LPT) improvement covered by PIP I, which represents the current build standard. Together, the two packages could provide customers with a claimed “two-percent fuel advantage over our competitor,” said GE Aviation GEnx program general manager Chuck Nugent. The U.S. manufacturer believes there will be “an additional one-percent advantage from [better] performance retention” than its British rival. “That is our big news,” GE told AIN.
By mid-June the eight GEnx-1Bs flying with Japan Airlines had accrued 4,500 hours in about 1,000 flights since services began on April 22. Overall, the engines, including -2Bs powering Boeing 747-8s, have logged about 115,000 hours during 25,000 flights, representing a rate of use about three times that of the GE90-115 when it entered service on the Boeing 777, according to Nugent.
He said the production ramp-up is two to three times that of GE’s previous engines for widebody airliners, reflecting the company’s investment in capacity. The U.S.-based manufacturer has suppliers in 15 countries and in 16 U.S. states.
As the GEnx fleet begins to grow, Nugent said preparations for series production had gone well, meeting or exceeding requirements. This year GE expects to deliver at least 150 examples, 50 percent more than in 2011, and more than 200 next year. Production is likely to reach around 300 units per year in 2014 and 2015 and to stabilize at that rate as the manufacturer addresses orders from 45 customers currently covering some 1,300 engines.
In addition, there are about 250 more 787s for which engine selection remains to be announced. Nugent did not expect to see any “significant” orders announced here at the show this week, but predicts “a lot more” in the coming year. As the production ramp-up continues, GE expects to be very busy in the coming six months as it prepares for the delivery of GEnx-powered 787s to Air India, China Southern, Ethiopian Airlines, Qatar Airways and United Airlines.
In a six-year development program, GE has tested more than 50 GEnx engines, logging 38,000 ground and flight cycles and accumulating 43,000 hours engine-running experience. Another 26,000 cycles will form part of an aggressive maturation program by the end of 2014 to anticipate issues or repair requirements before customers suffer them.
Nugent maintained that there is nothing unusual or untoward about the introduction of two performance packages within a year of GEnx entering service, saying that additional improvements often appear only after an original configuration has been established. “You always learn from tests and the entry-into-service process, and [because of the extended 787 development period] we had a larger ‘window’ in which to identify [changes],” he explained.
A major contribution to the improved GEnx-1B fuel performance arising from implementation of PIP I, introduced on the first 787-8 in late March, has come from LPT changes, which have increased the number of titanium-aluminum blades in the seven-stage turbine.
“The original engine design had about 30 percent fewer LPT blades than the GE90 engine, but we discovered during testing that we were not getting the desired performance,” said Nugent. “So [we put] about 20 percent of the blades back in, which helped performance.”
Three-dimensional changes to the blades also have improved efficiency. Other factors include optimization of the engine’s turbine blade-tip clearance-control system, achieved through a software adjustment to ensure clearances can be controlled throughout the flight operation, and improvements to the hot-section turbine nozzle durability. A further gain from this package has been the prospect of increased on-wing time, a key element of GE’s “value proposition.”
Following introduction of PIP I, the GEnx-1B was certified at 75,000 pounds thrust, which permits operators to fly from hot and/or high airports or from shorter runways. “It was very important that we be able to offer that,” said Nugent.
The manufacturer’s PIP II package includes the PIP I elements, plus a half-inch increase in fan diameter, optimized outlet guide vanes, a high-flow booster (for increased thrust), improved high-pressure compressor (HPC) aerodynamics, as well as better combustor and high-pressure turbine durability, said the program manager.
The PIP II-enhanced engine has been approved for operation at 78,000 pounds thrust, allowing GE (Hall 4 Stand B7) to maximize its engineering capability for future requirements. According to Nugent, a significant part of the PIP II gains has arisen from the better HPC aerodynamics, which follows an airfoil re-design based on all the test data GE has accrued.
By mid-June some 70 percent of PIP II testing had been completed and initial results had been “positive.” There had been 37 flights on GE’s 747 testbed and recent trials had included large-bird ingestion. A core engine test to validate aeromechanical changes was completed in May. Further use of the flying testbed covers performance optimization of the GEnx-1B PIP II package and, separately, aerial trials next year of the -2B PIP changes.
GE has been “very active” in building engines for endurance block tests or flight trials, and it was expecting to complete PIP II emissions testing by the end of June.
In mid-June, the GEnx-2B had recorded 110,000 engine hours in the air during some 23,000 flights. There were 80 engines in service on 16 B747-8 Freighters–flown by Atlas Air, Cargolux, Cathay Pacific, Korean Air and Volga Dnepr–the single Lufthansa passenger variant and three corporate models, which were in completion centers being fitted out.
The PIP for the GEnx-2B powering the 747-8 has followed a similar pattern to the -1B packages, with improvements to fan and turbine aerodynamics and the engine core, which is similar to that of the -1B. The two engines enjoy 80-percent line-replaceable unit and 90-percent tooling commonality. Specifically different PIP elements on the -2B have been optimization of core “turbo machinery” arising from the engine’s smaller, 105-inch diameter fan (employing different blade-tip clearances) and of flow patterns through low-pressure systems.
Again, such considerations had meant “very subtle” changes resulting in claimed “significant improvements.” Nugent declined to comment on reports that Boeing has seen 747-8 fuel burn one percent better than expected at this point in the program, results it had not expected for another two years.