The CFM RISE Open Fan, the Uncowled Engine GE and Safran Are Betting Will Power the Next Narrowbody, and Why an Idea the 1980s Abandoned Is Back on the Test Stand

GE Aerospace and Safran, through their joint venture CFM International, are developing an uncowled “open fan” engine called RISE that aims to burn 20% less fuel and emit 20% less carbon dioxide than today’s best narrowbody engines. The design revives an idea first flight-tested in 1986 and abandoned when oil prices collapsed. If it works, it would power the next generation of single-aisle jets - the successors to the Boeing 737 and Airbus A320 - with entry into service targeted for around 2035.

What Is the CFM RISE Open Fan Engine?

The RISE open fan is a jet engine with no cowling around its main fan. Instead of the smooth nacelle you see on every airliner today, two rows of large, curved blades spin in the open air at the front of the engine.

RISE stands for Revolutionary Innovation for Sustainable Engines. CFM announced the program in 2021, setting a target of 20% lower fuel burn and 20% lower CO2 emissions compared to its current LEAP engine, which powers the Boeing 737 MAX and Airbus A320neo families.

That 20% figure matters more than it sounds. A typical new engine generation delivers 10 to 15% improvement, and airlines spend billions re-engining entire fleets to capture it, because fuel is the single largest cost they carry. A 20% gain can be the difference between a profitable route and a cancelled one.

Why an Uncowled Engine Design Is Back After 40 Years

The concept isn’t new. On a test stand in Ohio in 1986, engineers ran an “unducted fan” with its blades exposed to the open air. It flew on a Boeing 727 and later on an MD-80, and it burned roughly one-third less fuel than the conventional engines beside it.

Then oil prices collapsed, the airline industry had no reason to prioritize carbon, and the idea sat unused for nearly four decades.

What changed is the world around the engine, not the engine itself. Sustained fuel costs, carbon regulations that aren’t going away, and modern composite materials and computing power have turned the old obstacles into merely difficult engineering problems. The technology waited for a reason to exist.

How the Open Fan Achieves 20% Fuel Savings

The key is a single number: bypass ratio.

A modern jet engine is really two engines wrapped together. A hot core burns fuel to spin a large fan, but most of the air the engine moves goes around the core rather than through it. The bypass ratio measures how much air bypasses the core versus how much passes through it.

Efficiency lives in that bypass air. Moving a large volume of air slowly is far more efficient than moving a small volume violently fast - the same reason a big helicopter rotor lifts more per horsepower than a small ducted fan.

For 50 years, engine design has marched toward bigger fans and higher bypass ratios. A 1960s Boeing 737 engine had a bypass ratio near 1:1. Today’s LEAP runs around 11:1. Each step up meant a bigger fan, a heavier cowling, and more drag - and airframes are running out of room. On the 737 MAX, the fan grew so large that engineers had to flatten the inlet into an oval and raise the nose gear just to keep it off the pavement.

The open fan removes the constraint entirely. Take off the cowling, and the fan can grow as large as you like. CFM is targeting a bypass ratio of 60 or more - a huge leap up the ladder in one step. That bigger fan, not any exotic fuel or material, is where the 20% comes from.

The Real Engineering Problems With Open Fan Engines

The cowling was doing several jobs you don’t notice until it’s gone.

Noise. The inside of a nacelle is packed with acoustic lining that absorbs fan noise before it reaches the ground. Without it, the fan sings directly at the surrounding neighborhood. Loud isn’t just an annoyance - it means airport curfews, failed noise certification, and routes an airline can’t fly at night. CFM says modern blade design lets them run much quieter than the 1986 version, and that’s likely true, but it remains a test-stand claim until it flies over a real community and is measured against FAA and international noise rules.

Containment. When a fan blade fails inside a conventional engine - from bird strikes or fatigue - the cowling is an armored case whose entire job is to catch that blade before it becomes a projectile aimed at the fuselage. Proving containment is one of the most demanding certification tests an engine faces. An open fan has no case. CFM’s answer is to build a blade from woven carbon fiber composite that essentially cannot fail, and to position the engine so a departing blade would miss anything critical. Safran has genuine experience with composite fan blades, but the safety argument shifts from “we caught it when it broke” to “it won’t break” - and regulators will make them prove that, slowly.

Installation. The engine is physically huge across the front with blades exposed. Slung under the wing, it creates ground-clearance problems and puts the wing directly in the fan’s airflow. Some concepts mount it on the tail instead, which solves some issues and creates new ones around balance and structure. Either way, the airframe has to be designed around the engine from a blank sheet - a far bigger and slower commitment than bolting a new engine onto an existing jet.

Who Is Building It and When Will It Fly?

The developers are CFM International - the 50/50 joint venture between GE Aerospace in the United States and Safran Aircraft Engines in France, partners since the 1970s and collectively the most prolific engine builders in the world.

They’ve committed to ground-testing the technology and, tellingly, have signed up Airbus to flight-test an open fan on a flying testbed. The plan is to mount the engine on one side of an Airbus A380 - the four-engine double-decker - and gather in-flight data impossible to collect on the ground. GE has also discussed using one of its own testbeds.

Entry into service is targeted for the middle of the 2030s - around 2035, give or take. Clean-sheet engine and airframe programs almost always slip, so a realistic expectation is that a student pilot soloing today will likely be a working airline pilot before this engine carries a paying passenger.

Why This Matters for Pilots

(Current as of August 3, 2026.) This isn’t a science project - it’s a serious, decade-long, multi-billion-dollar bet by two rivals with a flagship jet lent for flight testing. If it succeeds, it reshapes the narrowbody fleet most airline pilots will spend their careers flying, and it likely means new airframe configurations, possibly tail-mounted engines, and different handling and ground-clearance considerations than anything flying today. The timeline is measured in the length of a career, not the length of a lease - but the direction of travel is set.

Key Takeaways

• The CFM RISE open fan removes the engine cowling to allow a far larger fan, targeting 20% lower fuel burn and CO2 emissions versus the current LEAP engine.
• The design revives a concept flight-tested in 1986 that was shelved when oil prices fell; changed economics and modern materials brought it back.
• Its bypass ratio target of 60+ dwarfs the LEAP’s ~11:1, and that bigger fan is the main source of the efficiency gain.
• The hardest challenges are noise, blade containment without a case, and fitting the huge engine to a clean-sheet airframe.
• Developed by GE Aerospace and Safran (CFM International), with Airbus A380 flight testing planned and entry into service targeted around 2035.