The CFM RISE open fan engine and the radical redesign that could power every narrowbody in the twenty thirties

CFM International’s RISE engine — short for Revolutionary Innovation for Sustainable Engines — is an open fan design that eliminates the traditional engine nacelle entirely. If the program hits its targets, it will deliver a 20% reduction in fuel consumption compared to the current LEAP engine, compatible with 100% sustainable aviation fuel, and could enter service in the mid-2030s on a yet-to-be-designed narrowbody aircraft.

What Makes the RISE Engine Different From Every Jet Engine Flying Today?

Every turbofan on a modern airliner works on the same principle refined since the 1960s: a core generates hot gas, and a front-mounted fan pushes a larger mass of cooler bypass air around it. Higher bypass ratios mean better fuel efficiency. The LEAP engine achieves about 11:1, and the Pratt & Whitney geared turbofan pushes to roughly 12:1.

The problem is physical. Higher bypass ratios demand bigger fans, bigger fans need bigger nacelles, and bigger nacelles create more aerodynamic drag. At a certain point, the drag penalty cancels out the efficiency gain. Current engines are at or near that wall.

The RISE engine breaks through it by removing the nacelle entirely. The result is an open fan — a set of carbon fiber composite blades roughly 13 feet in diameter, spinning in open air with no cowling or duct. Think of it as a propeller, but one engineered with technology that didn’t exist a generation ago.

Why Did Open Fan Engines Fail Before?

This concept isn’t new. GE built and tested the GE36 open rotor engine in the 1980s. It was fuel efficient, but airlines rejected it. The blades were loud, vibration was significant, and passenger comfort was unacceptable. The program was shelved.

Three technologies matured in the intervening four decades to make the design viable now:

Blade aerodynamics. RISE fan blades are three-dimensional sculpted shapes designed with computational fluid dynamics that didn’t exist in 1986. Each blade features variable pitch, adjusting its angle in flight for different speeds and altitudes. The blade geometry manages shockwaves that created the GE36’s notorious buzz-saw noise.

Materials. The blades use woven carbon fiber composite, manufactured with the same resin transfer molding process CFM developed for the LEAP fan blade. They’re lighter and stronger than metal, can be shaped into aerodynamically optimal forms impossible to machine from titanium, and are individually inspectable and replaceable.

The gearbox. A speed reduction gearbox between the low-pressure turbine and the fan lets each component spin at its optimal speed. Pratt & Whitney proved this principle in the geared turbofan. CFM is applying it to an open architecture. This gearbox is the single hardest engineering challenge in the program — it must transmit 40,000 to 50,000 horsepower reliably for tens of thousands of flight hours.

How Much Fuel Will the RISE Engine Save?

CFM is targeting a 20% fuel burn reduction compared to the LEAP, which was itself 15% better than the CFM56 it replaced. Stacked together, an A320neo-class aircraft powered by RISE engines would burn roughly 35% less fuel per seat mile than today’s fleet.

That’s not incremental. That’s transformational.

The fuel story is also the emissions story. Twenty percent less fuel means 20% less CO2. Combined with the engine’s ground-up design for 100% sustainable aviation fuel compatibility, lifecycle carbon reductions approach 50% compared to today’s fleet. That matters directly to ICAO’s net-zero 2050 target, which the math doesn’t support without a new engine architecture.

Who Is Behind the RISE Program?

CFM International is the joint venture between GE Aerospace and Safran. They produce the LEAP engine powering the Airbus A320neo and Boeing 737 MAX, and previously the CFM56. Between those two engine families, CFM has delivered more than 45,000 engines — the most successful commercial engine partnership in aviation history.

What Are the Biggest Engineering Challenges?

Noise remains the primary concern. CFM has conducted extensive ground testing, including a full-scale open fan demonstrator at their facility in Villaroche, France, starting in 2024, with blade sets also tested at Peebles, Ohio. Initial data suggests noise levels comparable to current turbofans — a remarkable result if it holds. But the interaction between an open fan’s wake and the airframe creates noise sources that cannot be replicated on a test stand. Until the engine flies on an actual aircraft, the noise question carries an asterisk.

Aircraft integration is the second challenge. A 13-foot-diameter open fan cannot fit on an airplane designed for a 6-foot-diameter turbofan. Most engineers expect RISE will require a completely new aircraft design, not a retrofit. Airbus has studied a rear-mounted configuration with engines on fuselage pylons, similar to the DC-9 or MD-80 layout. Boeing has been less public about their plans, but the same physics apply. This ties the RISE timeline directly to a new narrowbody aircraft decision that neither Airbus nor Boeing has officially made.

Gearbox durability is the third challenge. A planetary gear system at this power level is extraordinary machinery. Pratt & Whitney’s geared turbofan experience has proven the concept works — but also revealed unexpected wear patterns causing in-service problems. The current PW1100G inspection crisis, which has grounded hundreds of A320neos, is partly gearbox-adjacent. CFM is designing with different materials and cooling strategies, but the lesson is clear: gearboxes at this power level demand humility.

What Is the Timeline for the RISE Engine?

CFM announced the RISE program in 2021, targeting mid-2030s entry into service. Ground testing of the open fan demonstrator began in 2023–2024. Flight testing is planned for the late 2020s, likely on a modified A380 that Airbus is providing as a flying testbed — one of the few aircraft with enough wing clearance and structural margin to carry a 13-foot engine without a complete redesign.

If flight tests succeed, a production engine decision would come around 2029 or 2030, with service entry no earlier than 2034 or 2035. For context, the LEAP program took roughly 15 years from announcement to service entry. Certification requirements for an engine that must run 20,000 cycles without a safety-critical failure are intentionally demanding.

How Does RISE Compare to Competing Next-Generation Engines?

CFM is not alone in chasing next-generation propulsion:

Rolls-Royce UltraFan — a geared turbofan with very high bypass ratio but still fully ducted. The demonstrator first ran in 2023 and hit full power targets. Lower risk because it keeps a conventional nacelle, but likely cannot match RISE’s 20% improvement.
Pratt & Whitney (RTX) hybrid-electric concept — uses an electric motor to augment a conventional turbofan. Adds complexity but offers operational flexibility.
CFM RISE — the most radical approach with the biggest potential payoff, but also the most integration risk.

Why This Matters Beyond the Airlines

The gap between a successful demonstrator and a certified production engine on a new aircraft is enormous. It requires CFM to execute and either Airbus or Boeing to commit to a new narrowbody program. Both airframers are currently consumed with production challenges — Airbus ramping A320neo output toward 75 aircraft per month, Boeing stabilizing the 737 MAX line and working through the 777X program. Neither is positioned to launch a clean-sheet narrowbody today.

For general aviation, the downstream effects merit attention. If open fan technology proves itself on airliners, it could eventually reach turboprop-class aircraft — a regional airplane with jet-like cabin comfort and turboprop-like fuel burn, because the open fan delivers propeller-like efficiency at jet-like speeds.

Key Takeaways

CFM’s RISE engine removes the nacelle entirely, using an open fan design with 13-foot carbon fiber composite blades to break through the efficiency wall facing current turbofans.
The target is a 20% fuel burn reduction over the LEAP engine, with 100% SAF compatibility — approaching 50% lifecycle carbon reduction compared to today’s fleet.
Three matured technologies — advanced blade aerodynamics, composite materials, and a power gearbox — make viable now what failed in the 1980s.
Entry into service is targeted for 2034–2035, but depends on a new narrowbody aircraft commitment from Airbus or Boeing that neither has made.
Noise, airframe integration, and gearbox durability remain the critical engineering risks between the demonstrator and a production engine.