Fuel-efficient open fan engines have been tried before, but noise issues proved to be a barrier to adoption. Now, with the help of the world’s most powerful supercomputers, such drawbacks are a thing of the past.
In an interview with LARA, GE Aerospace’s Arjan Hegeman outlines the intrinsic benefits of the concept, the status of work so far, and how the technological challenges were overcome. Gerrard Cowan reports.
This article was published in the February/March 2025 edition of LARA. To receive more articles like these, apply for your complimentary subscription to LARA.
Arjan Hegeman is VP Commercial Engines Future of Flight Engineering at GE Aerospace, which partners with Safran Aerospace on CFM, the manufacturer of engine families such as LEAP and CFM56.
CFM is pursuing a range of technological innovations through its Revolutionary Innovation for Sustainable Engines (RISE) programme, with the aim of achieving 20 per cent better fuel efficiency.
The systems are capable of operating with hydrogen, sustainable aviation fuels (SAF), hybrid-electric and existing Jet-A fuel.
The technologies produced through RISE could form the foundation of a next-generation CFM engine, according to the company, with such a product potentially available by the mid-2030s. As of December 2024, RISE has conducted more than 250 tests.
Open fan architectures – How next-generation engines are transforming fuel efficiency
Spot the difference: Open fan engine architectures are unducted. Image: CFM
Open fan architectures are at the core of these ambitions. The benefits come from the “unducted” nature of the system. The duct that sits around a fan represents a significant amount of surface area, creating drag and resistance to forward movement.
Removing the duct makes the system more aerodynamic. It also enables larger fans, thus improving propulsive efficiency.
“That’s where the double-digit propulsive benefit comes from,” says Hegeman. “It allows the fan to be larger, but [still] fitting on the same type of aircraft.”
He adds that the engine core is also smaller, so it uses less fuel while driving a larger fan. Hegeman places the RISE research into the wider context of CFM’s work in engine technology, with one existing engine being replaced by a new design. For instance, CFM56 was eventually replaced with LEAP.
When CFM works on such new programmes, it draws on the “latest and greatest technologies that we have proven”, he says, in terms of their ability to deliver on commitments around weight, fuel efficiency, safety, durability and beyond.
“Since we refreshed all our products, we pretty much depleted all the technologies that we had ready to go,” Hegeman explains. “So now we are in a cycle of maturing the next generation of technologies for next-generation engine offerings, ready for when airframers start asking for new engines.”
RISE was developed to lay the groundwork for the company’s future engine technologies. It is a demonstrator programme, developing a prototype engine. This will involve multiple demonstrations, both on the ground and in-flight, on GE Aerospace’s Boeing 747 and Airbus A380 testbed aircraft.
“That will generate the data and the confidence as to which [technologies] are working and ready for product introduction in the future and which ones need more work,” says Hegeman.
Open fan is a central element because “we see a world where there is going to be a continually increasing cost associated with energy,” he says, with a need to progress towards a “net zero” aviation industry.
Hegeman says open fan represents “two generational updates in a single step”.
He accepts there are challenges associated with the concept. The aircraft will have a different appearance to ducted versions, so there will be a need to build public acceptance, according to Hegeman.
But he says: “I do think that with forecasts of future energy costs, the time is right – there will be a demand and willingness to take this concept and put it into certification and then production, simply because the fuel efficiency is tremendously better than anything else.”
Addresing the noise issues – Supercomputers tackling open fan engine challenges
Open fan engines are not a new concept, with the technology having first been demonstrated in the 1980s. In the past, noise has been a challenge, but Hegeman indicates this problem has now been overcome.
“It’s very quiet,” he says. “It delivers the performance. It has turned into a much simpler engine design – it’s very durable – so we think the time is right to demonstrate it.”
The key to addressing the noise challenge has been an improved ability to model and analyse air flow, according to Hegeman.
This is achieved using GPU cluster supercomputers. This work includes the largest supercomputer in the world – the Frontier supercomputer at the US Department of Energy’s Oak Ridge National Laboratory (ORNL).
“We also have our in-house GPU cluster that we are using. We have very powerful hardware, and on that very powerful hardware we are running a very advanced code that solves the airflow [challenge].”
This has enabled the company to optimise the airfoil shapes of the engine.
“Not just the fans that you see, but everything inside the engine as well,” says Hegeman. “That has allowed us to optimise it to get the best performance while creating the lowest noise signature possible.”
This computer model is designed to reduce turbulence, creating a calm and efficient movement of air, without producing the energy for noise.
Hegeman says: “This tool and this capability has optimised the airfoils to prevent that from happening, which has unlocked a very quiet and simple engine design.”
He adds that there are a large number of tests running at any point in time between GE Aerospace and Safran. This is part of a long process, which begins with the design of the engine and its components, then moves on to testing components in simulated conditions, then on to modules.
“We are building our way up to the whole engine, running the whole engine on the ground, before eventually we start flying it.”
“It’s very quiet. It delivers the performance. It has turned into a much simpler engine design – it’s very durable – so we think the time is right to demonstrate it.”
Arjan Hegeman, VP Commercial Engines Future of Flight Engineering, GE Aerospace
A range of technologies – Advanced materials & 3D manufacturing in open fan engines
RISE is built on a range of technologies, as well as open fan. This includes an advanced compact core that will increase thermal efficiency and decrease fuel consumption, according to CFM; hybrid-electric systems; advanced metal alloys and ceramic matrix composites, also designed to improve thermal efficiency; and carbon fibre composite blades, manufactured using a 3D weaving process to enable the larger fan diameter.
CFM is now on the fifth generation of its composite fan blades, with over 200 million flight hours on the technology as of December 2024.
Similarly, it has long utilised non-metallic materials such as ceramic matrix composites in the core, first introduced in the LEAP engines.
Hegeman says the company plans to continue building on these types of material technologies, but he cannot disclose precise plans due to business confidentiality.
The plan for RISE in the immediate future is to continue developing and maturing technologies on the demonstrator, says Hegeman, which can then be drawn on for any purpose as projects progress.
“It could be whole new engine designs, or it could be a smaller programme where we take one of the technologies and insert it into an existing engine.
“The exact timing as to whole new products is really a question for the airframers – when do they do a new aircraft that needs new propulsion systems?”
If successful, the reduction in fuel use and boost in efficiency promised through open fan technology will have clear benefits for the low-cost and regional markets, though Hegeman notes that “We are all ultimately driven by similar economics.”
CFM is pursuing an extensive range of technological innovations through its RISE programme. Image: GE Aerospace
More than a paper vision – Engineers powering the future of sustainable aviation
The key takeaway, Hegeman stresses,“is that this thing is real and it is going to work”.
He notes that CFM has more than 2,000 engineers working on RISE across GE Aerospace and Safran.
“This isn’t just a paper vision – we are making progress every day with the tests we are executing.”
There has been significant progress over the course of 2024, he adds.
“As I reflect on the year and where we started versus where we are today, it is a phenomenal journey to be part of and to see so many skilled engineers working to the same purpose of creating a propulsion system that is truly much, much better than anything ducted.”
The bottom line is the importance of the technology in getting to a net zero aviation industry.
“There is no silver bullet here,” says Hegeman. “You need all the solutions leveraged to get there: aviation fuels, optimised operations, etc. Our part as GE Aerospace and CFM is to provide the propulsion systems that are the most fuel efficient to make sure that the scarce resources of sustainable energy are getting used properly.”
We hope you enjoyed this article. You may find these news stories interesting:
GE Aerospace wins US government supercomputing time for Open Fan engine project
GE Aerospace partners with UAMCO to provide CFM LEAP MRO
