Originally published by Guy Norris for Aviation Week on November 1st 2016
Rolls-Royce has begun tests of a powerful gearbox and inaugurated a research site focused on high-temperature composite materials, both key steps toward its future vision of developing an all-new family of advanced very-high-bypass-ratio turbofans for the mid-2020s.
The two events, which occurred within days of each other last week, mark major milestones on the company’s strategic road map to developing a next-generation product family based on leaps in propulsive and thermodynamic efficiency. The plan will culminate in the UltraFan, an engine aimed at future airliners for 2025 onward and the first Rolls-Royce large commercial turbofan to incorporate a gear-driven fan.
Aimed at medium- and high-power applications up to the 100,000-lb.-thrust range, the UltraFan will have a very large, 15:1 bypass ratio and overall pressure ratio of 70:1. For the higher-thrust family variants, this is expected to provide a fuel burn improvement at least 25% over the. The gains in propulsive efficiency will come largely from development of a large, gear-driven lightweight fan, while thermodynamic gains in the core will depend on a higher compression core incorporating advanced heat-tolerant ceramic matrix composites (CMC) and other new materials.
The gear system, developed by Rolls and made by joint venture partner Liebherr-Aerospace, was produced in Friedrichshafen, Germany, and tested at the engine-maker’s purpose-built power gearbox (PGB) evaluation facility in Dahlewitz, near Berlin. The first run took place on the site’s Attitude Rig, which runs the gearbox at various angles simulating climbing, banking and descending. Rolls says the initial run confirmed rig dynamics and oil system functionality at low pressures and speeds.
The company, which cites earlier heritage gear drive system experience with turboprops such as theand T56 and the lift fan for the Joint Strike Fighter, says gear tests will eventually reach up to 100,000 hp. “More advanced testing will take place during the rest of the year to provide additional data on low-power high-speed combinations at various pitch and roll angles and at different simulated altitudes. High-power testing will take place next year on the PGB Power Rig where the gearbox will reach full power,” it adds.
Research and development of CMCs for hot-section components in the UltraFan is meanwhile stepping up in California, where the company officially dedicated a newly developed high-temperature composites research facility on Oct. 27. Based in Cypress, south of Los Angeles, the 62,000-ft.2 facility is already producing initial silicon carbide fiber-reinforced silicon carbide (Sic/SiC) matrix CMC test panels that will form the basis for next-generation components to be tested in future Rolls-Royce technology demonstrators. The unit, which employs just over 50 staff, is expected to grow to about 100 as work increases.
The core of the employees came from Hyper-Therm High-Temperature Composites Inc., a specialist engineering company based in nearby Huntington Beach that Rolls acquired in 2013. Rolls developed the facility in Cypress for planned expansion and began phasing over to the new site this April. The transition is due to be completed in November when the old site will make its final batch of CMC products.
CMC components from the original Huntington Beach facility are running in the Advance3, an engine demonstrator that will pave the way for the Advance turbofan—a follow-on engine family to the current Trent that Rolls is targeting for development at the turn of the decade. Together with the PGB rig, the Advance3 demonstrator forms fundamental building blocks of the new family plan architecture. While the Advance core forms the foundation for the follow-on Trent engine, it will also be ultimately married with the gear system to form the UltraFan.
Steve Richards, president and general manager of Rolls-Royce High Temperature Composites (HTC) and head of CMC programs at Rolls, says the facility will pave the way for methods of large-scale Sic/SiC CMC manufacturing. “The facility we came out of is 18,000 ft.2, and this is three times as large. We have only filled out two-thirds of the space, so there is expansion capability here. There are a number of components we are going to progressively march through, and the idea is we will standardize a method of manufacture so we can productionize that.”
Richards says the Rolls-Royce CMC development “road map takes us through a lot of hot parts, starting with static structures. These will be the simpler structures first, then more complex parts, but the goal is all the way through the rotating parts. We have not committed exactly when we will get there for some of the products to get to first application.”
Whereas initial CMC elements tested in Advance3 “went along for the ride,” Richards says the true thermodynamic benefits of the material will be fully explored in follow-on demonstrators such as the High Temperature Turbine Technology (HT3) program. The HT3 will be based on a-97 donor engine from the -1000 certification and test effort and follows on from the -based EFE (Environmentally Friendly Engine) demonstrator program. Initial CMC applications envisaged by Rolls include shroud segments and vanes, with progressively more complex applications as testing proceeds.
“We are making test panels here to build up and characterize the materials. The CMC in the Advance3 will not be the same one that goes into the next demonstrator,” says Allan Jamieson, manufacturing engineering manager at Rolls-Royce HTC. “We are used to working in metals, but the manufacturing challenge here is that it is not written down, there is no guidebook, no reference. The control of the process will really make or break CMCs. You can have the best design and the best materials, but if you can’t make it in the volumes for something like a Trent XWB, then it will limit the success of CMCs. So manufacturing is the key,” he adds.
Tas Singh Purewal, Rolls-Royce chief of capability acquisition, says “this facility represents our ability to take something that is innovative and new, and not just go through the challenges of designing those new materials but also use the latest state-of-the-art manufacturing technology. We have now demonstrated that we can take a technology in its infancy and mature it through facilities like this in terms of preproduction.”