The CFM RISE Program, the Open Fan Architecture That GE Aerospace and Safran Are Betting Will Replace the Turbofan, and the Fuel Burn Promise That Could Rewrite the Narrowbody Market by the Mid-Thirties

CFM International’s RISE program - Revolutionary Innovation for Sustainable Engines - represents the most significant departure from commercial jet engine architecture in more than half a century. The joint effort between GE Aerospace and Safran Aircraft Engines, developed through their CFM International partnership, targets more than 20% better fuel burn than the LEAP engine powering today’s narrowbody fleet. Commercial service is targeted for the mid-2030s.

This is not an incremental improvement to the turbofan. It is a proposed replacement for it.

What Is an Open Fan Engine?

RISE is an open fan design - no nacelle, no cowling around the blades. Two counter-rotating rows of fan blades, long, slender, and shaped from advanced composites, sit fully exposed in the airstream. They look far more like advanced propeller blades than anything inside a current turbofan.

The absence of a nacelle is the key to the efficiency claim. Turbofan efficiency scales with bypass ratio - the ratio of air flowing around the core to air flowing through it. Higher bypass ratios move more air per unit of fuel burned, and moving more air by a smaller amount is thermodynamically more efficient than accelerating a smaller air mass harder. Current high-bypass turbofans, including the LEAP variants, operate at bypass ratios of roughly 9 to 12 to one. An open fan, unconstrained by a nacelle wall, can reach bypass ratios well beyond what any ducted design can achieve.

The physics are straightforward. The engineering to certify that physics in a commercial aircraft is not.

Why 20% Fuel Burn Matters at Industry Scale

Twenty percent might sound modest. In commercial aviation it is transformative. The global aviation industry burns somewhere in the range of 90 to 100 billion gallons of jet fuel per year. Fuel costs represent 25 to 30% of airline operating costs in a normal pricing environment. A structural 20% reduction does not improve the economics of flying - it restructures the entire cost base of the narrowbody market, where most seat-miles are flown.

This is why CFM - the organization that built the CFM56 engine powering hundreds of millions of commercial flights across decades, and the LEAP engine that is the backbone of the current narrowbody fleet - is pursuing a fundamental architectural departure rather than another increment on a proven design.

This Concept Was Proven in the 1980s - Then Abandoned

Open fan propulsion is not a new idea. The engineering community proved it worked forty years ago.

During the oil crisis of the late 1970s and early 1980s, fuel prices tripled and airline margins collapsed. The efficiency case for open fan propulsion became impossible to ignore. NASA and industry developed the concept under names like propfan and unducted fan. GE built a demonstrator called the GE36 that flew on a Boeing 727 testbed in the late 1980s. Pratt & Whitney and Allison built their own open rotor demonstrator that flew on a McDonnell Douglas jetliner testbed around the same period. Both programs confirmed the efficiency projections in actual flight data.

Then oil prices collapsed. The economic pressure evaporated, airlines lost appetite for an unfamiliar architecture, and the programs were cancelled. The turbofan continued its dominance for another four decades.

Why the Conditions That Killed Open Fan Programs Have Reversed

Every factor that ended open fan development in the mid-1980s now points the other direction.

Oil is expensive and volatile. Airlines across Europe, North America, and Asia-Pacific are operating under sustainability commitments - many of them regulatory, not voluntary. The European Union has binding sustainable aviation fuel blending requirements with enforcement mechanisms. Carbon pricing systems are expanding into aviation across multiple jurisdictions. Every ton of fuel burned carries costs beyond the purchase price of the fuel itself.

The economic logic that killed open fan programs now drives their revival.

How Modern CFD Solved the Noise Problem

The earlier programs faced two genuine technical barriers: noise and design iteration speed. Two counter-rotating blade rows produce acoustic interactions - tones and harmonics - that the design tools of the 1980s could not adequately manage. Computational fluid dynamics in that era meant running coarse models over days or weeks on the largest available computers. The blade geometries capable of suppressing those acoustic signatures simply could not be iterated into a practical design in time.

Forty years of advances in computational fluid dynamics have changed this entirely. CFM’s engineers can now model the acoustic and aerodynamic behavior of millions of blade geometry variations before a single piece of hardware is machined. The RISE blade designs are swept and shaped in three dimensions with acoustic suppression as a primary design objective from the start - not a retrofit after aerodynamics are locked. Advanced composite manufacturing, which matured significantly over the same period, allows those complex geometries to be built with the structural integrity commercial service demands.

GE Aerospace has been running open fan hardware at its ground test facility in Peebles, Ohio. The company has been deliberate about releasing specific acoustic measurements before flight test data is available in certified-representative conditions - appropriate discipline when the applicable standards are still being developed in parallel. GE has stated publicly that test results are tracking with analytical predictions, and those predictions were designed to meet current commercial noise certification limits. The definitive acoustic story will come from flight test, which remains ahead.

Blade Containment and the Certification Challenge

A turbofan nacelle does more than shape airflow. It is a structural containment system. If a fan blade releases from the rotor, the nacelle is engineered to retain it. Certification standards require demonstrated containment under failure conditions.

An open fan has no nacelle. A blade release behaves fundamentally differently, and the FAA and EASA are developing the certification requirements for this scenario in parallel with the RISE technical program. That regulatory framework does not yet exist in codified form.

This is not a reason to dismiss the program. It is the primary reason the mid-2030s entry into service target is what it is. Developing novel certification standards, validating an architecture through flight test, and integrating an engine into an airframe designed around it - all of that work runs in parallel, and all of it must converge before revenue passengers board a RISE-powered aircraft.

Airframe Integration: There Is No Retrofit Path

An open fan cannot be mounted under the wing of any aircraft currently in service. The blade sweep diameter is substantially larger than a comparable turbofan nacelle, and conventional narrowbody fuselage heights do not provide adequate ground clearance at standard engine mounting positions. An A320 fuselage does not accommodate a RISE-sized open fan where the LEAP engine hangs today.

The aircraft carrying this engine must be designed around it from the first line of the design. There is no retrofit path.

Airbus has been the most consistent public voice on RISE as the propulsion candidate for their next-generation narrowbody - broadly referred to as the A320 successor, though Airbus has not assigned an official designation. The development timelines Airbus has discussed point toward service entry in the early to mid-2030s, aligned with CFM’s target. The two programs are being developed with awareness of each other’s requirements.

Boeing’s position is more complicated. The 737 MAX certification work, subsequent manufacturing challenges, and financial constraints have limited Boeing’s capacity to launch major new development programs. The competitive pressure will arrive when an Airbus product enters service with 20% better fuel burn economics.

Variable Pitch and What It Means for Flight Deck Operations

The RISE fan blades change pitch angle during flight and on the ground - analogous to a variable-pitch propeller. This capability allows the engine to generate reverse thrust by transitioning to negative pitch on landing rollout, eliminating conventional thrust reverser actuators, buckets, and cascade structures that add weight, complexity, and maintenance burden to turbofan installations.

For pilots flying RISE-powered aircraft, lever positions and power cues will look familiar from the flight deck. The mechanical reality behind those inputs - variable pitch actuation systems, different hydraulic or electric requirements, different failure modes - will be fundamentally unlike anything in current commercial service.

The Hydrogen Pathway

The RISE core is being developed with hydrogen combustion as a future option alongside conventional jet fuel and sustainable aviation fuel. Hydrogen burns differently than kerosene - different energy density, different combustion temperatures, different combustor design requirements. Building that pathway into the architecture from the beginning is a different engineering posture than attempting to adapt an existing turbofan after the fact.

This does not mean hydrogen-powered commercial aviation is near term. The infrastructure challenges for liquid hydrogen at airports are enormous and will require decades of investment even under aggressive scenarios. But designing the option in rather than foreclosing it is the correct engineering decision at this stage of the program.

Where RISE Fits Among the Transformative Options

Battery-electric propulsion at commercial airline scale runs into fundamental energy density limits that current chemistry cannot overcome in the foreseeable future. Hydrogen faces infrastructure and storage timelines measured in decades. Sustainable aviation fuels are real and being built out, but they are a fuel source, not a propulsion architecture change.

The open fan is the approach that is closest to proven, that addresses the largest share of commercial aviation’s fuel burn at the narrowbody scale, and that can operate on the sustainable aviation fuel infrastructure already under development. Among genuinely transformative options, it carries the least speculative risk.

Hardware is running. Certification frameworks are in development. The airframe partnership is in place. Whether RISE delivers exactly on its 20% fuel burn promise, hits a mid-2030s service entry, and navigates acoustic certification without compromise - those remain open questions. But the conditions that killed the first generation of open fan programs in the 1980s have reversed completely.

Why This Matters for Pilots

The next generation of narrowbody aircraft entering service - or the generation after - may carry an engine that looks nothing like what today’s pilots trained on. Understanding the architecture, the problem it solves, and how it behaves differently from a turbofan gives pilots a better read on where the industry is heading before those aircraft reach the simulator.

The variable pitch system alone creates a meaningfully different set of normal and abnormal procedures compared to conventional thrust reversers. Pilots entering the workforce today may well spend a significant portion of their careers flying RISE-powered aircraft. The fundamentals are worth understanding now.

Key Takeaways

• The CFM RISE program targets more than 20% better fuel burn than the LEAP engine through an open fan architecture with no nacelle - the most significant commercial engine design departure in roughly 50 years.
• Open fan efficiency has been proven in flight test since the late 1980s; the concept was abandoned when oil prices collapsed, not because the technology failed.
• Modern computational fluid dynamics and advanced composite manufacturing have resolved the noise and blade design challenges that made the 1980s architecture impractical.
• Blade containment certification for an unducted design is genuinely new regulatory territory; the FAA and EASA are developing standards in parallel with the technical program, which is a primary driver of the mid-2030s service entry timeline.
• A RISE-powered aircraft must be designed from the ground up for this engine - there is no retrofit path for existing narrowbody airframes, making the Airbus next-generation narrowbody program the most likely launch vehicle.