Rolls

Sep 06, 2023

All tests of the UltraFan demonstrator in Rolls-Royce's specially built Testbed 80 will run on 100% sustainable aviation fuel.

Rolls-Royce has run the UltraFan demonstrator for the first time, marking the start of an extensive test program for the world's largest geared turbofan and—the engine-maker hopes—the birth of a new generation of more efficient propulsion systems.

The demonstrator was started quietly and without fanfare on April 24 in the company's specially built Derby, England, Testbed 80 facility in the first run of an all-new-centerline big-fan engine at Rolls since the Trent XWB-84 in 2010. It occurred a little more than nine years after the company revealed plans to pursue a geared architecture for its next-generation product line.

Since then, despite uncertainties in the widebody market and two years of delays caused by the financial fallout of the pandemic and the costly recovery from Trent 1000 reliability issues, the embattled company has continued to gamble on the UltraFan concept as the best bet for boosting the prospects of its future engines. Rolls’ determination to stick with the program also comes amid an extensive restructuring under recently appointed CEO Tufan Erginbilgic.

Erginbilgic describes the demonstrator as "a game changer." "The technologies we are testing as part of this program have the capability to improve the engines of today as well as the engines of tomorrow," he says "That is why this announcement is so important. We are witnessing history in the making—a step change in engine efficiency improvement."

While no immediate application is in the offing, Rolls expects the scalable design—covering the 25,000-110,000- lb.-thrust range—will make it a low-fuel-burn contender for future single- and twin-aisle concepts as well as for potential reengining opportunities. The company also intends to use the UltraFan as a wellspring of technology for upgrading its current engines.

The demonstrator will be used to evaluate a raft of advanced features at an engine system level ranging from a high-power gear-driven architecture to lightweight, high-temperature materials and an all-new high-pressure core. The company says the focus is on maximizing lessons from tests of the new engine which, with its power gearbox and Advance3-based core, represents a radical shift away from the traditional three-shaft designs that have been the hallmark of Rolls-Royce's large engine configurations since the 1960s.

UltraFan testing got off to a good start, says Alan Newby, director of aerospace technology and future programs at Rolls Royce. "It was uneventful, which is exactly what you want," he says. "It's taken a while, but that's because it's a new engine on a new testbed, and there are lots of instrumentation parameters. So we’ve just been making sure everything is talking to each other on the testbed and the new monitoring system." The instrumentation installed in Testbed 80 is capable of measuring 10,000 parameters at a rate of up to 200,000 samples per second.

Although the large gear system represents a first, Rolls-Royce engineers started the UltraFan cautiously for its initial run using a time-honored process. "You do the dry cranks first just to make sure everything turns, and then you do the wet crank where you put the fuel through," Newby says. "Then eventually during the wet cranks, you put the ignition on and light it off. We did that and it started. It's a great moment for us."

However, the company has entered unknown territory. Following a run-up to idle, the engine was quickly shut back down. "That's mostly because the things that you take for granted—like the way you schedule the fuel, the control laws, all those things—all have to be evaluated at the start of the program," Newby says. "It feels slow, but we’ve deliberately not rushed it because it's the first time, and it's an extremely important asset. So we just want to make sure we get it right and have resisted pressure to get it done by a certain date."

"We’re going through a staged commissioning process of the different components, understanding them subsystem by subsystem to see how they’re behaving and whether they are matching what we’re expecting," Ultra-Fan Chief Engineer Pete Young says. "With the UltraFan, it's a very different world. If we were to commission a Trent as a new engine, we’d spend a handful of days doing this, whereas for us it's been a week-by-week process since December when we installed it. We’ve been doing commissioning testing of the engine with the facility. How does that work? What interactions have we got? Does it work in the way we would like it to?"

The test buildup has included "one-shot checks," Young says. "This is firing signals from the engine location up through the pylon and down through the testbed and into the control room. We’ve been doing that meticulously for every one of the 2,800 parameters we are measuring and checking that they all work."

To ensure the testing is done steadily and carefully, Rolls has developed a three-stage "defense in depth" approach to evaluating the UltraFan, he adds. "We’ve got a control room, which is where the person who's running the engine sits, and we’ve then got near-term engine safety, which is the first step to the defense in depth. Then there's the dynamics teams who are monitoring the high-frequency instrumentation and measurement system. Then we’ve got a monitoring room, which has a glass divide between it and the rest. In there is a miked-up room director who's talking directly with the control room and giving instructions.

"We want to be on the front foot," Young continues. "So as part of that monitoring arrangement, we’ve got an automated model, or ‘tramlines,’ as to what we expect the engine to be doing. As the data comes off the engine, we’re comparing it to the model and seeing if it's within the tramlines which have been defined as to what we think our tolerance or error bands might be. If it's outside of that, we hold the test and evaluate. That's why we do the NASA-type control room where we literally go around the room. So we have the air system, engine performance, oil system, engine temperatures, oil, fuel and the power gearbox teams all monitoring and providing feedback."

One advantage of not being tied to an airframe development schedule is that Rolls can focus on maximizing the technology demonstration aspects of the program. "We are still continuing to work with all the airframe manufacturers to understand what its first application will be and whether or not it's going to be a widebody or narrowbody," Newby says. "As we have emphasized many times, this is a scalable architecture. We chose to do the large size because we think it's more challenging, but who knows where it will be first applied."

Configured with a 140-in.-dia. fan—some 6 in. wider than the fan on General Electric's GE9X, the largest turbofan currently flying—the engine's 50-megawatt power gearbox will be a focus for close monitoring after its initial test and development at Rolls-Royce's facility in Dahlewitz, Germany. The planetary-style gear is the largest ever developed for an aerospace application. Approximately 2.6 ft. (80 cm) in diameter, the gear system consists of a ring gear on the outside and five planet gears inside rotating around a central sun gear. The fan is driven by a centrally mounted planet carrier.

"Part of the testing we’ve been doing in Dahlewitz on the power gearbox rig is making sure that we’ve cleared the full suite of temperatures we would experience on ground tests here, and all the rest of the durability issues as well," Newby notes. "It's been a great program, and the knowledge that we’ve gained in terms of thermomechanical modeling is world-leading. It's been a key part of getting to this point."

Testing also will proceed with caution because of the wide range of new manufacturing and materials technology in the UltraFan, Newby says. "We’re focused on the whole engine integration, but there's a lot of stuff that we’ve been developing over the years," he adds, referring to new features including the composite fan system, hybrid ceramic bearings, ceramic matrix composites (CMC), high-torque-density shafts, advanced cast bond turbine blades and second-generation nickel disk superalloys.

The CMC components, primarily used for turbine seal segments, are lighter and more tolerant of high temperatures. Made from a continuous silicon carbide fiber reinforcement with a fiber-matrix interface coating surrounded by a ceramic matrix primarily of silicon carbide, the CMCs and other high-temperature features were evaluated in the HT3 (High-Temperature Turbine Technology) demonstrator based on a Trent XWB-97.

"So yes, the UltraFan is a new architecture, but it brings together a lot of the technology programs that we’ve been doing for a while—some of which can be applied to other engines potentially as well," Newby says. "For example, we’ve developed a new way of rapidly developing software which we’re going to use on the Pearl 10X [business jet engine]. Some of the high-temperature materials also may find applications in the Trent fleet."

Along with the gear, one of the key changes to the conventional Trent architecture with the UltraFan is the new core, which redistributes the workload between the intermediate- and high-pressure shafts. Tested in the Advance3 core, the increased compression work on the high-pressure spool produced an overall pressure ratio (OPR) of more than 60:1. The UltraFan will push the Advance3 core OPR to more than 70:1 for a typical large engine application, Rolls-Royce says. The engine-maker also configured the new powerplant with a multi-stage intermediate-pressure turbine system. The Advance3 core was used to evaluate the Alecsys (Advanced Low-Emission Combustion System) low-nitrous-oxide combustor as well.

Although Rolls originally planned to run four engines in the initial test program, delays and cost pressures have reduced this to just one, with spares for assembly of a second if required. "We are going to take it gently," Newby says. "It's an asset we want to preserve, put it that way, so we will be treating it with respect. We will do some running, analyze the data, then keep on testing through this summer.

"The beauty of this is most of the individual systems have been proven on other assets," he continues. "This is the key." The tests will evaluate how well "they work well together, rather than in isolation," he notes. "We shall be looking at what we call emergent behaviors. We know the gear works and the low-pressure turbine, but how does it all work when you put it together? That's what we are trying to find out here."

Beyond the current test effort, the UltraFan architecture also is the focus of more advanced studies under Europe's Clean Aviation aeronautics research program. Led by Rolls-Royce, Heaven (Hydrogen Engine Architecture Virtually Engineered Novelly) is a €35.6 million ($38.6 million) project aimed at evolving the UltraFan by scaling the engine down to the short-/medium-range market and integrating both hybrid-electric technology and direct hydrogen combustion.

The Heaven team includes academic, research and industrial partners across France, Germany, the Netherlands, Spain and the UK and will study an UltraFan H2 version with the goal of achieving a 20% fuel-burn reduction over current engines. "It will also provide a platform for hydrogen technology and hybrid-electric technology to be suitably incorporated into our civil aerospace portfolio," Rolls-Royce says. "It does not involve any full engine build or testing."

Heaven will be supported by Cavendish, another Clean Aviation program led by Rolls-Royce. Under the €29.2 million project, a design team is planning to integrate lean-burn hydrogen combustion into a Pearl 15 donor engine for ground testing on liquid hydrogen starting in late 2024. "This will prove the hydrogen technology by integrating a liquid-hydrogen system into a ground-test engine and define requirements toward flight demonstration," Newby says.

Guy is a Senior Editor for Aviation Week, covering technology and propulsion. He is based in Colorado Springs.