NEXT-GENERATION SINGLE-AISLE ENGINE? CFM OPEN-FAN CONCEPT
GE AEROSPACE in conjunction with SAFRAN AIRCRAFT ENGINES, a consortium called CFM INTERNATIONAL, published the below article heralding the incredible prospects for their OPEN FAN ENGINE. They intend to develop a compact and durable HP (core (compressor, combustor, and turbine) as part of the CFM RISE program. The development program was announced in 2021. GE AND SAFRAN EACH SPEND BILLIONS PER YEAR on R&D. The Open Fan is described as “one of the most ambitious demonstrator programs in the history of our {CFM} company,” which strongly implies multi‑billion‑dollar cumulative investment, but no precise public figure is given.
The endeavor includes U.S. and European public agencies/research programs that support sustainable propulsion, hybrid‑electric, and advanced materials/aeroacoustics are involved. Universities, national labs, and aeroacoustic/wind‑tunnel facilities contribute to blade, OGV, and noise testing, plus supercomputing
centers used for aero‑acoustic optimization.
Since 2021 CFM has directed -500 test campaigns. CFM’s has endurance tested HP turbine airfoil technologies, in which simulations of high-thrust takeoffs and climbs were conducted. More than 3,000 cycles of endurance tests validated the durability, reliability, and fuel efficiency of the HPT system.
In 2022, CFM and Airbus jointly launched a flight test demonstrator program that would facilitate testing of the advanced open fan onboard an A380 test platform. The flight test campaign will also focus on the engine’s acoustic performance as well as its compatibility with 100% Sustainable Aviation Fuels (SAF).
Each fan blade is over 5.25 feet in length and designed with advanced 3D Resin Transfer Molding (RTM) through Safran Composites’ innovation platform. The composite technology has been used the molding in CFM LEAP fan blades, allows significant weight reduction and improved fuel efficiency. The engine is designed to cut FUEL CONSUMPTION AND CARBON EMISSIONS BY 20% COMPARED WITH TODAY’S
ENGINES, with entry into service targeted for the mid-2030s.The open fan architecture is designed to fly at speeds similar to existing commercial aircraft, with greater operational efficiency and lower carbon and noise footprint. As technologies continue to mature, the CFM RISE program will leverage synergies with aviation partners to begin full-scale open fan tests.
The Open Fan engine is being designed for future single‑aisle aircraft typical short‑ to medium‑haul stage lengths. The approximately 20% lower fuel burn and CO₂
emissions vs today’s most advanced single‑aisle engines (e.g., LEAP) are further selling points. Further, the marketing materials will also highlight the Bypass ratio >5× greater than tomorrow’s advanced ducted engines, thanks to the single‑stage open fan. Search found no public list price yet; modern narrow‑body engines typically list in the $10–15M per shipset range before discounts.
Industry analysts and trade press have commented that the Open Fan as being economically promising if noise, safety, and integration hurdles are solved—because a 20% fuel burn cut is hard to ignore in a world of volatile fuel prices and tightening climate policy. Some commenters note that the public perception of exposed blades, bird‑strike and blade‑off containment, and airport noise footprints.
VERY PROMISING DEVELOPMENT and all will be watching the progress.
Open Fan engine technology aims for epic efficiency. It also has major durability potential
By GE Aerospace | Paid content
The Open Fan engine, the distinctive architecture that could power the next generation of single-aisle aircraft, targets a SIGNIFICANT STEP CHANGE IN EFFICIENCY for the aerospace industry. A quick primer: Shedding the ducts that traditionally enclose the engine allows for a much larger fan and greater bypass ratio with less drag, yielding improved propulsive output. THE PROJECTED RESULT IS 20% BETTER FUEL EFFICIENCY FOR CUSTOMERS THAN TRADITIONAL TURBOFAN ENGINES.
Efficiency isn’t the only advantage of the Open Fan engine architecture, which is part of the RISE* technology demonstration program of CFM International, a 50/50 joint company between GE Aerospace and Safran Aircraft Engines. It is also being designed for enhanced durability, with its unique fan blade system, aerodynamic design,
and adaptive cycle engine capability, which could significantly reduce the engine’s DUST INGESTION — a boon for hot and harsh environments.
Engineers are now pushing the Open Fan technology even further. They’ve already completed more than 500 tests and 3,000 endurance cycles of components for the engine’s core. This includes the earliest-ever dust ingestion testing for any CFM program, following the “test early, test often” philosophy. Along with the intense testing regime, they’re also applying various program updates that bolster the durability of the next-generation engine’s architecture. The various measures will boost the Open Fan engine’s reliability and time on wing, further advancing the future of narrowbody flight.
Durability built in
The UNIQUE AERODYNAMIC DESIGN OF THE OPEN FAN ENGINE is a win-win-win for the engine’s propulsive and thermal efficiency, as well as its durability. The engine’s large fan blades harness more air than the blades on next generation ducted engines. They also allow a greater proportion of that air to flow around, or “bypass,” the engine’s core, where combustion and high-pressure processing occur. The goal? LESS DRAG, A COOLER CORE, AND REDUCED DUST INGESTION.
“CFM’s objective is to actually get hot and harsh operators to experience the same durability levels that today’s operators in more neutral environments enjoy,” said Arjan Hegeman, vice president of future of flight engineering at GE Aerospace, in a recent webinar discussing the RISE program.
The Open Fan architecture’s ADAPTIVE CYCLE ENGINE[1] capability also boosts its durability. Also known as variable bypass architecture, the adaptive technology optimizes
engine performance at every stage of a flight, such as allowing more thrust during a takeoff or climb, and more bypass air in a cruise-type environment. Those cycles create additional airstreams for dust to exit the engine, leading to less part erosion and deposit buildup in the engine’s combustor and high-pressure turbine. Working with the US Air Force through the Adaptive Engine Transition Program (AETP), GE Aerospace has completed testing on the XA100, the world’s first flight-weight, three-stream adaptive cycle engine.
“The value proposition of the RISE program’s Open Fan is that you GET DOUBLE-DIGIT FUEL EFFICIENCY COMING OUT OF THE PROPULSIVE SYSTEM,” Hegeman added. “Which means you don’t need to stress and tax the hot part of the engine as much to get to that 20% [efficiency] number.”
PIERRE COTTENCEAU, vice president of engineering, research and technology at Safran Aircraft Engines, concurs. “MATERIALS play a key role in keeping the engine light and making it durable despite the harsh conditions that it has to operate in. There has been a lot of work on the CFM side, [and with] both partners, to develop new materials and apply them to this engine architecture.”
Airframers see the potential too. “Evaluating a radical architecture like the Open Fan requires a completely integrated approach between airframer and engine designers,” said FRANK HASELBACH, senior vice president of propulsion engineering at Airbus, in the same webinar. “The technological potential of the Open Fan is huge, and this demonstrator allows us to jointly mature the architecture and see how it behaves in flight.”
Test, rinse, repeat
Relentless testing is enhancing the engine’s durability credentials. The RISE program places safety and reliability at the center of each innovation cycle, and its engineers are now testing every aspect of Open Fan architecture, from materials selection to cycle design. They’re leveraging decades of engine development learnings. “With the RISE technology demonstration program, we’re pursuing durability and efficiency improvements with equal focus,” said Hegeman.
“We probably have 30 to 50 tests running continuously,” he noted. “We started with component tests, and we’re now looking at modules and more system-level-type testing, including the durability testing. And that then eventually matures to full engine ground and flight testing.”
Hegeman explained the exact science of dust ingestion tests. “We spent a lot of time getting the right dust, the right operating conditions, the right simulation in a test environment that we can exactly replicate all the learnings that we have in our current suite,” he said. “This [rigorous testing] incorporates lessons from the flying fleet today to inform our future engine products.”
Durability: always front of mind
CFM continues advancing RISE technology. It is collaborating with Airbus on an Open Fan flight demonstration, which is planned for later this decade, and actively working with the airframe manufacturer to optimize the engine-to-aircraft integration. Flight tests are important to advance understanding of engine performance, safety, noise, and aerodynamics in real operating scenarios — a key step before launching an engine product. “We have already achieved more than 400 hours of Open Fan blade testing in a wind tunnel at ONERA,” the French National Aerospace Research Center, noted Cottenceau. “That gives us a lot of test evidence that we can achieve the future levels of noise emission targets.”
In collaboration with NASA, RISE program engineers recently announced completion of ground tests of a narrowbody hybrid electric engine system,
demonstrating on a test stand the integration and controls of electric motors in a high-bypass commercial turbofan to supplement power during different phases of operation. A hybrid electric engine with integrated electric motor/generators can optimize engine performance by creating a system that can work with or without energy storage, like batteries. Then ground tests pave the way for flight testing and could help accelerate the introduction of hybrid electric technologies for commercial aviation prior to large-scale energy storage solutions being fully matured.
Haselbach remains optimistic about Open Fan’s future, noting the industry will need roughly 40,000 new commercial aircraft over the next 20 years, with single-aisle jets making up about 75% of that demand. “They’re the backbone of the industry,” he said. The Airbus executive is also upbeat about CFM’s capacity to define the future of narrowbody flight. “You have several thousand engineers working today on RISE, and we’re all committed to this program, making the investments in the tools to make it happen and do it faster,” he added. “We know how important it is to deliver on safety, fuel efficiency, and durability.
* Revolutionary Innovation for Sustainable Engines (RISE) is a technology demonstration program of CFM International, a 50-50 joint company between GE Aerospace and Safran Aircraft Engines. It is not a product offered for commercial sale.
[1] Adaptive bypass ratio — The engine can shift between high‑bypass (efficient cruise) and low‑bypass (high‑thrust) modes by adjusting internal valves and ducts.; Variable cycle operation — It uses movable components to redirect airflow between the fan and core, effectively “adapting” to mission needs — similar to how military adaptive engines like GE’s XA100 work.; Thermal management — The adaptive cycle allows better heat control for hybrid‑electric integration and sustainable fuels.; Efficiency and emissions — By optimizing airflow and pressure ratios, the system can reduce fuel burn by up to 20% compared to current LEAP engines.
