Airbus chief executive Guillaume Faury has made clear he expects the European airframer’s next narrowbody jet will be 25% more efficient than today’s models – and he is banking on CFM International’s in-development open-rotor engine to get there.
“We’re targeting 25% fuel burn,” Faury said on 10 September in Washington, DC. “Obviously, the RISE engine will… contribute to it.”
RISE – the Revolutionary Innovation for Sustainable Engines programme – is CFM’s effort to develop an open-rotor powerplant for the next generation of narrowbody jets, which Airbus and Boeing are expected to bring to market in the mid-2030s.
CFM, jointly owned by GE Aerospace and Safran Aircraft Engines, has said the powerplant will be 20% more efficient than the Leaps that power today’s A320neo-family jets and the 737 Max.
Airbus has been assisting with the project. CFM plans in the second half of this decade to begin flight testing an open-rotor demonstrator using an A380.
“We are working with CFM to test the RISE engine, to make sure noise, vibration, performance, installation losses, certification items – everything – can work good enough so we can select the engine,” Faury says.
His 25% efficiency target aligns with other industry expectations.
Boeing’s former CEO David Calhoun said numerous times in recent years that the US company’s next narrowbody jet must be 20-30% more efficient than the 737 Max.
NASA, meanwhile, has several programmes underway to development technologies the agency says could make future narrowbody jets 25% more efficient. Those programmes involve developing hotter-burning turbofans and hybrid-electric systems, and testing a truss-braced-wing aircraft with Boeing.
The two aircraft manufacturers are expected to launch development of their next narrowbody jets this decade, but neither have disclosed details. They have shied from committing to powerplant architectures, as engine makers settle on their own development strategies and progress with testing.
CFM insists its open-rotor engine is the way of the future, saying the design can achieve an efficiency step change. Because open rotors lack nacelles and other surrounding structures, they tend to weigh less than traditional “ducted” turbofans and allow for increased bypass ratios, translating into improved fuel efficiency.
But open rotors are a fairly radical break from today’s turbofans, and therefore pose new risks and challenges.
The designs will necessitate “a lot of changes, because [it has] a much bigger fan, and there are more interferences,” Faury says. “It’s more difficult to integrate the engine on the plane, so it requires a lot of additional work and study.”
Notably, unlike ducted fans, open rotors lack containment rings, which are designed to prevent blades and other components from damaging aircraft structures in cases of uncontained engine failures.
Engineers must therefore find news ways to ensure uncontained failures of open rotors do not cause broader structural damage. One solution could involve adding shielding material to aircraft structures, though doing so would add weight, eroding efficiency gains.
Faury insists designers could use other means to prevent blade-out risks, without being specific. “There are many ways of dealing with a problem like this one,” he says. “That’s what we need to work on.”
He also says pinpointing the open rotor’s exact efficiency benefit when fully integrated onto an aircraft is not yet possible due to the early state of development.
“There’s no easy answer,” Faury says. “RISE is not completely defined, and depending on how we want to optimise between the engine, the aircraft, the engine installation – the answer… can be different.”
Despite clear interest in RISE, Faury has encouraged other engine makers to explore alternative open-rotor concepts.
“We would prefer to be able to have open-[fan] offers… from at least one other engine manufacturer, if not more,” he told FlightGlobal earlier this year.
Two other leading engine makers, however – Pratt & Whitney (P&W) and Rolls-Royce – are seemingly leaning toward developing updated versions of ducted powerplants. P&W, for instance, has suggested that improvements to its geared turbofan, including a potential hybrid-electric variant, could achieve a 25% efficiency boost.
Additional reporting by Dominic Perry
