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Rolls-Royce Lines Up Greener Future With UltraFan

 - June 20, 2019, 1:56 AM
Testbed 80

Rolls-Royce (Chalet 93) reports "great progress" with the UltraFan engine that it plans to run in a testbed in 2021. With lean-burn/low-emission combustion, an advanced core with ceramic-matrix composites and super nickel alloys, as well as a power gearbox (PGB) to reduce fan speed, program building blocks are falling into place, according to Rolls-Royce civil aerospace future programs chief engineer Phil Curnock.

Other characteristics include carbon/titanium (CTi) fan blades and composite engine casing to reduce weight. The manufacturer aims to complete design and analysis this year, ahead of manufacture and assembly in 2020.

UltraFan is a scalable design planned to be 25 percent more fuel-efficient than R-R's first-generation Trent engine and suitable for new single- or twin-aisle aircraft entering service from the mid-2020s. It represents the company's most-significant step in engine architecture since the RB211 three-shaft powerplant pioneered around a half-century ago.

The consistent drive for improved fuel-burn has driven gas-turbine development for at least 40 years, according to UltraFan chief engineer and head of program Andy Geer. "After five evolutions of the Trent [itself derived from RB211-524 technology], Rolls-Royce has identified the need for a step change to meet the demands of the next decade on civil large engines."

Rolls-Royce aims to cover three "closely inter-connected" pillars of product innovation: continue to optimize the gas turbine, increase airframe/engine integration, and electrification.

Regarding integration, Curnock said that aerospace philosophy is no longer to marry the very best airframe and engine to obtain the optimum end-product. Now, manufacturers must address engine/wing close-coupling, short-inlet, pylon-mount, and engine heat-load challenges.


He detailed several such integration challenges. Powerplant/wing coupling has implications for structural concepts and novel pylon technologies, while short engine inlets might require "translating cascades, novel surface treatments, [and] electrical nacelle anti-icing." Meanwhile, pylon mounting includes consideration of engine stiffness, but management of higher engine-heat loads must not compromise powerplant-system integration.

To improve environmental performance of its engines, R-R is committed to driving down emissions. Hence, UltraFan and its related Advance core sibling represent a "big step forward"—an enhanced intermediate-pressure turbine (IPT) drives the fan via a gearbox, allowing deletion of the low-pressure (LP) turbine.

Compared with late-20th century engine performance, R-R aims for UltraFan to demonstrate by 2025 respective reductions 25 percent, 60 percent, and up to 15 percent in CO2, NOx, and noise (dB) emissions. Longer term, Advisory Council for Aviation Research and Innovation in Europe (ACARE) Flight Path 2050 targets of 75 percent, 90 percent, and 65 percent, respectively.

Six Technology Programs

As R-R continues optimizing propulsive efficiency by increasing engine-bypass and -pressure ratios, UltraFan is one of six full-scale architecture and design-technology programs underpinning company strategy. These include an advanced core, lean-burn/low-emissions combustion, and small-engine core and fan development alongside manufacturing, materials, and "intelligent" systems work.

Further, the very-high bypass-ratio design is one of 12 full-scale demonstrator programs also covering advanced LP systems, high-temperature turbine-blades, and electric-aircraft research.

High-power testing of the PGB, which involves more than 500 lines of instrumentation, has been under way since May 2017 on attitude ("tipping and turning") and power rigs at R-R's Dahlewitz plant in Germany. Running started in 2016 and now has begun on the fifth—of a planned seven or eight—test articles, with a sixth one "on build." Some 250 hours' testing had been completed by late last month as endurance and reliability running continues.

The PGB involves an outside ring gear, five internal "planet" wheels running around a central "sun" gear. In 2017, the company demonstrated a maximum power output of 70,000 to 80,000 pounds of thrust, although the gearbox is thought to be good for up to around 120,000 pounds of thrust—"whatever airframe manufacturers may require," said Curnock.

Beyond the PGB, another new element on UltraFan is the high-speed IPT, which drives the fan and IP compressor and on which full aerodynamic testing has been completed. An aerodynamically representative IPT prototype was run at very high speeds and temperatures.

Since, in Curnock's words, "big engines need big testbeds," R-R is building a new facility, Testbed 80, which will be commissioned in Derby next year. Testbed 80 will be used initially to run a Trent engine before UltraFan testing. 

Under an April 2018 agreement, Rolls-Royce is collaborating with Airbus for integration flight-testing of UltraFan. The arrangement, which is co-funded by the Clean Sky 2 European Union emission-reduction technology research program, will see the European airframe manufacturer providing both nacelle- and engine/aircraft-integration architecture and technology "enablers."