Open Fan Engines: CFM RISE vs. LEAP and the Future of Airbus–Boeing Narrowbodies

A new era of jet propulsion is emerging as CFM International—the joint venture between GE Aerospace and Safran—advances its open fan RISE (Revolutionary Innovation for Sustainable Engines) demonstrator. The concept reimagines the turbofan with a single-stage unducted composite fan, a compact hot core, and full compatibility with sustainable aviation fuel (SAF) and future hybrid-electric systems. With a target of more than 20% lower fuel burn and CO₂ emissions compared to today’s most efficient turbofans, the RISE engine could fundamentally reshape the narrowbody market if integration, acoustics, and certification stay on track.

Unlike the abandoned propfan projects of the 1980s, RISE leverages breakthroughs in supercomputing-driven blade aerodynamics, advanced composites, and lessons from GE90, GEnx, LEAP, and GE9X engines to overcome two major hurdles of earlier open rotor designs: noise and structural complexity. Testing has already logged hundreds of hours in ONERA and DNW wind tunnels, with Airbus and CFM planning A380 flight trials by the end of the decade. If milestones hold, entry into service could arrive around 2035, setting up a pivotal moment as Airbus and Boeing weigh propulsion options for their next-generation single-aisle aircraft.

Let’s compare RISE vs. LEAP and explore how Airbus and Boeing are preparing to adopt—or compete with—open fan technology.

LEAP vs. RISE at a Glance

Attribute	LEAP (today)	RISE Open Fan (demo)	What it means
Architecture	Ducted, high-bypass turbofan	Unducted, single-stage open fan	Fundamental change in propulsor shape
Efficiency vs. prior gen	~15% better than CFM56	>20% better than today’s most efficient engines (target)	Another big step in fuel burn reduction
Key tech	CMCs, 3D-woven composite fan, higher OPR	Open fan aero, compact core, hybrid-electric compatibility	Multiple levers beyond just bigger fans
Noise	Certified, airport-proven	Extensive aero-acoustic work under way	Meeting community noise regs is central
Timeline	In service (A320neo, 737 MAX, C919)	Ground/wind-tunnel now; A380 flight tests; ~2035 EIS target	Integration path set before productization

Old vs. New: From GE36/Propfan to Open Fan 2.0

1980s propfan lessons. Early unducted engines (e.g., GE36; PW–Allison 578-DX) proved striking fuel-burn gains but were hampered by noise, structural complexity (often counter-rotating), and integration challenges. The idea prefigured ultra-high-bypass concepts but preceded today’s CFD, composites, and acoustic modeling.

RISE’s single-stage approach. CFM’s open fan ditches the counter-rotating complexity for a simpler, single-stage design using carbon-fiber composite blades and a compact, hotter core. Supercomputing-enabled aero work shifted blade shapes to cut tonal noise while preserving propulsive efficiency—an evolution that closes the gap with ducted turbofan expectations for speed, safety, and cabin/community noise.

Variable pitch heritage. Open fan/propfan concepts rely on variable-pitch blades for thrust control and efficiency across the envelope—an essential feature for unducted propulsors that underpins RISE-era control strategies.

The “7J7 and others” thread. Boeing’s 7J7 explored propfan-powered narrowbodies in the 1980s but never entered service; RISE revisits that promise with 21st‑century tools, materials, and certification learning.

How RISE Compares to LEAP (And Why >20% Matters)

Today’s baseline. LEAP improved fuel burn roughly 15% over the CFM56 through higher bypass ratios, CMCs in the hot section, and 3D-woven composite fans—cementing its place on A320neo, 737 MAX, and C919.
Next S-curve. To move beyond incremental gains, CFM/GE argue the nacelle itself becomes a drag wall as fans grow. Open fan removes the duct, chasing bypass ratios an order higher (GE cites ambitions from ~11:1 toward ~60:1 in concepts), enabling >20% fuel-burn cuts versus top turbofans—subject to installation and mission specifics.
System view. RISE also co-develops a compact core (NASA HyTEC) for thermal efficiency and compatibility with hybrid-electric assistance and 100% SAF, stacking multiple avenues of performance beyond the propulsor alone.

Noise and Safety: The Twin Gatekeepers

Acoustics and noise remain key challenges to resolve. Open fan engines radiate sound differently without a nacelle, prompting Airbus, CFM, ONERA, and DNW to conduct more than 500 hours of wind-tunnel testing across low- and high-speed regimes, including high-lift interactions. In parallel, Safran and ONERA are advancing tone-noise modeling and CFD/FWH acoustic strategies to ensure compliance with certification noise footprints. Addressing acoustics is the central technical campaign for RISE throughout the 2020s.

Blade containment remains a major concern. Without a duct, industry scrutiny focuses heavily on blade-off risk. GE highlights decades of safe composite-blade operation on the GE90, GEnx, LEAP, and GE9X—with no recorded composite blade throw events—while emphasizing new blade designs and certification pathways tailored for the open fan. Safety validation will remain one of the central pillars of certification.

Airbus vs. Boeing: Who’s Driving What

Airbus and CFM have laid out an integrated testing roadmap. Airbus is co-running wind-tunnel campaigns with ONERA and DNW and plans to flight-test the open fan on an A380 by decade’s end to de-risk aerodynamic, structural, and noise integration at full scale. The effort is supported by European public programs, including Clean Aviation, DGAC, and CORAC.

Boeing, meanwhile, is prioritizing hybrid-electric and core engine technologies with NASA and GE. While not leading an open-fan flight demo today, Boeing is a partner on NASA’s Electrified Powertrain Flight Demonstration and related core-efficiency projects—technologies that could later integrate with an open fan or an ultra-high-bypass ducted solution for a next-generation single-aisle aircraft.

Outlook: What “20%+” Could Unlock

The next milestone comes with Airbus’s A380 flight-test campaign, following extensive ground and wind-tunnel trials. If results align, a new single-aisle aircraft with open fan propulsion could target entry into service by the mid-2030s. CFM currently guides toward a ~2035 EIS, dependent on airframer adoption, integration, and certification progress.

If achieved, a verified fuel-burn reduction of more than 20% compared to today’s best turbofans would reshape airline economics, emissions trajectories, and airport noise strategies. The next decade’s single-aisle competition may ultimately split between an open fan solution and an ultra-high-bypass ducted rival. Airbus is publicly leaning into full evaluation, while Boeing signals a broader propulsion trade study—with RISE firmly on the shortlist.

Sources: AirGuide Business airguide.info, bing.com, geaerospace.com, cfmaeroengines.com, airbus.com, geaerospace.com, boeing.com