by Guy Norris, originally published in Aviation Week on May 19th 2016
Parts for Rolls-Royce’s next-generation Advance demonstrator are coming together for an initial run later this year, marking the first concrete steps away from the RB.211 architecture that has been the foundation of the company’s large fan family since the 1960s.
“We laid out a strategy in February 2014 and now we are doing it and it is coming to life,” says Alan Newby, Rolls-Royce director of Aerospace Technology and Future Programs. The demonstrator, dubbed the Advance 3, is being assembled in the company’s Bristol, England, facility and will fire up for the first time in Derby in the August-September time frame, he adds.
Advance is targeted primarily at the next step change in thermodynamic efficiency beyond the Trent XWB engine for the Airbus A350 and will be built around a new high-pressure (HP) core with a pressure ratio at or above 60:1. The new core provides both the foundation of a potential new turbofan family in its own right, as well as a stepping-stone to a follow-on engine called the UltraFan. Advance will have a bypass ratio in excess of 11:1 and a fuel burn at least 20% better than the current Trent 700 when it enters service around the end of the decade.
The UltraFan will build on the Advance core and incorporate an enhanced intermediate-pressure (IP) turbine to drive the fan via a power gearbox to boost propulsive efficiency. The engine, which would no longer require the low-pressure (LP) turbine, could be ready for service from 2025 and is targeted at a fuel-burn improvement at least 25% better than the Trent 700. The engine’s fan drive gear system will drive a variable pitch fan, and is outlined with a 15:1 bypass ratio and overall pressure ratio of 70:1.
“Advance is both a portfolio of technologies and an engine architecture; we look at it in both ways,” says Newby. “If it happens to be an engine architecture, fine, and if the technologies apply to existing engines or lay down the future of bigger engines, then that is also fine,” he adds. The development time line means the concept will be available to power potential next-generation aircraft such as the New Midsize Airplane, currently under study by Boeing. However, if new platform opportunities emerge after the middle of the 2020s, both Advance and UltraFan will be options, adds Caroline Day, Strategy and Future Programs head of marketing. “Advance doesn’t stop when UltraFan starts. We will be offering it as a solution after 2025 if it is the right answer,” she says.
The Advance demonstrator is a hybrid combining a Trent XWB-84 case and fan system and the LP turbine from a Trent 1000. “In the middle is the all-new core, both in terms of architecture as well as new technology [that] includes the two new compressors [HP and IP], a lean-burn combustor, ceramic matrix composite [CMC] seal segments and advanced cooled turbine blades. The demonstrator brings them together in a system context,” Newby says.
Compared to the current Trent family, the Advance core “changes the work split significantly,” says Newby. “We will do much more work on the HP compressor with a two-stage HP turbine driving it and a lightly loaded IP compressor. This allows us to grow the pressure ratio in a very efficient manner but also provides a core which leads us to the UltraFan.” Rolls believes the plan takes advantage of the three-shaft configuration in ways that have not been possible before. “You can have a very lightly loaded HP spool with a decent pressure ratio in the IP compressor because it runs at its optimum speed,” Newby says. This provides the launch platform for the UltraFan because “then you take the HP spool and combine that with a geared LP system, and it allows you to grow the bypass ratio as well.”
Having crafted the vision, Rolls is now focused on bringing the strategy to life through an intense series of technology demonstrations in the U.K., Germany and the U.S. “A lot is happening on Advance, with a particular focus on the lightweight LP system,” says Newby. “To get propulsion system efficiency, you need improvements such as lightweight blades and casings,” he adds. Although flight tests of the CTi (composite titanium) fan system under the Advanced Low-Pressure System program have been completed, further evaluation of the composite fan continue in 2016 with ground tests on a full Trent 1000 engine in Berlin and fan system ice work later in the year.
“The key thing is we have flown it, tested it on the ground in engines, and now we are going through the final throes of proving the design and making sure we have enough data, so that we can go through certification when required,” says Newby. “We are also testing bigger blades. The last was 112 in., which is Trent 1000 size and now we are testing blades beyond 120 in. We have thrown birds at them and are testing them in extremes of environmental conditions to make sure the material properties stay good. The final back-to-back engine test in Berlin on the new 61 bed is to validate performance with the standard titanium and new composite fan.” Verification testing has been underway since December, and in the fall tests will begin of the engine fitted with the full composite fan and casing.
A big part of the composite initiative “is to mature the production system so that we can make it at rate and cost,” says Newby. The company’s specialized preproduction site on the Isle of Wight, England, where testing of the manufacturing process has taken place, is moving to Bristol as part of an initiative to cluster expertise and experience in composites. The preproduction site will be developed alongside Rolls-Royce’s new facility for carbon-fiber electrical harness rafts, currently being constructed on the Bristol site. Both facilities will work in partnership with the National Composites Center in Bristol, as well as the Rolls-Royce University Technology Center at the University of Bristol. The U.K. government provided £7.4 million ($11 million) funding support for establishment of the preproduction facility and equipment at the Isle of Wight.
Compressor research also forms another key focus for 2016 in support of the Advance 3 demonstrator. An IP compressor made up of four stages, versus the usual Trent 8-stage design, has been tested at the Rolls-Royce AneCom facility in Wildau, Germany. The rig, which comprised advanced 3-D blading for transonic and subsonic stages, an integrated compressor-duct design and a revised flowpath design “did very well, frankly,” says Newby. “We also have an HP compressor rig made up of 10 stages, which has left Derby and is in AneCom ready to run. This rig will begin validation tests later [in May]. It is the first time we have ever done a large multistage compressor for the large engine size, though of course we have done them for small engines,” he notes.
Testing of the company’s lean-burn combustion technology also continues to reach new levels in 2016. “The main idea is to bring it into an engine and confirm its behavior at an engine level both on the ground and in flight,” says Newby. Following several years of testing in Europe and the U.S., lean-burn technology is going through the final validation stages. Altitude rig testing was successfully completed at the Institute for Aviation Compressors in Stuttgart, Germany, in December, with good high altitude and cold starting, and “then we brought this design back to Derby and made sure that sea level performance works as expected as well,” he adds.
Further tests at Rolls’s NASA Stennis site in Mississippi are planned to check the noise of the combustion system, while work at the company’s Manitoba facility will evaluate cold day starting and ice shedding. “In 2017, we will fly the lean-burn combustor on our flying testbed,” Newby says.
Higher core operating pressures mean higher temperatures, so research also continues into advanced cooled metallic components and CMCs. Technology will be validated on the HT3 (high-temperature turbine technology) program using a modified XWB-97 donor engine. “We retired EFE [the environmentally friendly engine research program], and sort of put it out to grass, so we have now moved on to the 97,000-lb.-based engine to do all our high-temperature work. So the basic message is, we have laid down the plans; now we are doing the design, and it is all coming to pass this year and the next,” says Newby.
“We are borrowing a flight-compliance engine and replacing the HP turbine with next-generation materials and manufacturing technologies to improve cooling capability,” he says. Newby adds that the focus is on testing intricately crafted blades and vanes made using the company’s cast bond process. “We want to really take down the cooling airflows in the metallic vanes and we have CMC shroud segments in there too. We will do a couple of builds, one to prove the basic integrity and system functional tests and another to run 1,000 cycles to make sure the technology behaves,” he adds.
“We have a big program ongoing in this area and we will start with static structures and probably go into blades as well. We are just about to open a preproduction facility in Huntington Beach, California, [the recently acquired Hyper-Therm High Temperature Composites], where we started with a relatively small unit and are now moving to a larger unit,” Newby says. The combined impact of cast bond, CMCs, cooling air and weight reductions with architecture changes “are quite powerful,” he notes. “If you feed these technologies into an UltraFan type engine you get some pretty significant fuel-burn savings and also can tune emissions better.”
Planning for the UltraFan remains on track, with design freeze of the demonstrator due in late 2017. “The main activity at the moment is getting the power gearbox on test and looking at the next generation of low-speed fan but also at the back end looking at next-generation titanium-aluminum for the high-speed turbine,” says Newby. The company is partnering with ITP of Spain for the turbine and GKN for the intercase through the European Clean Sky research program. Rolls has also signed a joint venture with Liebherr on the gear system. “That is up and running and delivering the first parts for testing and will begin in the third quarter of 2016,” he says.
Editor’s note: This article was updated to correct the derivation of the Advance demonstrator’s fan system and the time frame for delivery of first gear system parts for testing.