Inside the race to build the next generation of jet engines
Radical ‘open-fan’ design part of proposals to help meet Boeing and Airbus demands for lower fuel consumption
Engineers at GE Aerospace, one of the world’s biggest aircraft engine makers, have become among the heaviest users of two of the world’s fastest supercomputers over the past three years. Access to the machines at the US Department of Energy has helped them model the behaviour of a new kind of engine concept they believe could be a future mainstay of commercial air travel.
GE and its partner Safran, the French engine maker, are working on technologies for a revolutionary design called the “open fan” — an engine whose fan blades spin uncovered, rather than housed in a casing.
The pair’s joint venture, CFM International, thinks the open fan is the key to powering the next generation of narrow-body aircraft — the workhorses of the world’s airline fleets used for short- and medium-length flights. Both Airbus and Boeing are exploring plans for successors to their best-selling A320 and 737 Max jet families.
The stakes for the industry are high: climate change poses a serious threat to commercial aviation and the next generation of aircraft will need to consume significantly less fuel if the industry is to meet its target of net zero emissions by 2050 while continuing to expand.
Airbus and Boeing are not expected to bring new aircraft into service until the end of the 2030s but given the long development times needed, engine makers are battling to find ways to deliver significant improvement in fuel efficiency. Executives from GE and Safran believe the open-fan design offers the greatest potential reduction in fuel consumption with a 20 per cent improvement.
“The industry and the world requires a step change in the performance of the engine,” said Arjan Hegeman, GE’s future of flight vice-president. “You can choose to pursue that while evolving current [engine] architectures, but it’s very limited in what it can achieve.”
Open-fan engines lack the conventional nacelles, or casing, that surround the fans of traditional turbofans, meaning less weight and drag — allowing for larger fans that help to improve fuel efficiency.
They are not new, with GE itself testing designs in the 1980s, but technical challenges including noise, hampered progress. Access to supercomputing had helped GE to optimise the design of the fan blades to reduce noise, said Hegeman.
“The physics are very clear: an open fan brings significant fuel burn reduction over any conventional ducted architecture,” said Olivier Andriès, chief executive of Safran, during a visit to London in December.
CFM is working with Airbus on a prototype of its open-fan engine, with the world’s largest planemaker preparing to run test flights on a modified A380 superjumbo towards the end of this decade. The flights will inform an eventual decision on how best to power the next generation of aircraft.
Executives at Airbus insist that the group has yet to make a final decision on what kind of engine to choose. It is also talking to other engine manufacturers Rolls-Royce and RTX’s Pratt & Whitney about their proposals, which are focused on more conventional enclosed-fan designs.
Rolls-Royce, which only builds engines used on larger wide-body aircraft, hopes to begin ground testing of a scaled-down prototype of its new UltraFan engine in 2028. The company said it was in talks with “all players” and was “seeking to form strong partnerships to deliver this once in a lifetime opportunity”.
Alan Newby, director of research and technology at the FTSE 100 group, said it was “very familiar with open rotor engines” but had concluded it was not the right technology for the next generation of aircraft.
Despite the efficiency promised by open fan, “when you consider the additional safety requirements needed for aircraft fitted with [these] engines, it negates much of that advantage”, he added.
Pratt & Whitney, meanwhile, is working on a second generation of its ducted geared turbofan engine for the next narrow-body planes. Rick Deurloo, president of commercial engines, said P&W had concluded that the “installation, integration, noise and industrial challenges associated with an open rotor architecture would increase the overall executional risk and reduce the potential fuel burn benefit”.
Aviation experts said the industry needed to incorporate the lessons learned from today’s engines, which have been dogged by durability issues, leading to higher maintenance costs for airlines. Airbus said this week that it expected engine supplies to remain constrained this year after suffering acute shortages over the past two years.
“For the next generation of engines, the airlines are saying: we want you to keep maintenance costs in check and offer 15 per cent better fuel consumption,” said Bjorn Fehrm, aeronautical and economic analyst at Leeham News and Analysis.
GE’s Hegeman said the company was already incorporating such lessons with early trials for durability including dust ingestion tests.
For the open fan, CFM will need to address specific challenges around the design, including safety, given the absence of the engine casing. Shielding is likely to be added to an aircraft’s fuselage to reinforce areas that could be susceptible to any damage from a fan blade breaking off.
If Airbus does partner with CFM this will influence the design of the plane itself, with complexities around the positioning of the engines. Airbus is studying different installations of the open-fan engine, including a traditional wing-mounted configuration and a rear fuselage-mounted option.
Simply hanging the open-fan engines under the wing of a “conventional tube and wing” aircraft would be “difficult to make work from a certification point of view and from an efficiency point of view”, said Nick Cunningham, analyst at Agency Partners.
He believes one solution will be a design with more of a “blended wing body”, where the wings merge into the fuselage, and mounting the engines at the rear. That would address noise and safety concerns.
Both GE and Safran stress that they are focused on refining the technologies for a possible open-fan engine rather than being ready to start development.
“Most of the technologies we are developing for open fan could apply for a ducted fan as well,” said Safran’s Andriès. Any decision, however, would be up to Airbus and Boeing, he added, as neither can afford to lag significantly in terms of fuel consumption.
Hegeman believes the industry and passengers will accept open-fan engines once manufacturers can demonstrate their safety and efficiency: “Yes, it looks different . . . but I think it looks different for a reason. It’s a different product. It doesn’t compare. We want this to become the new industry standard.”