The Engine That Will Change The Future Of Flying

There is a jet engine being tested right now that looks like someone forgot to finish building it. The fan blades, each one taller than a grown man, spin completely exposed to the open air. No cover, no casing, no protective shell around them. To most passengers it looks wrong, unfinished, maybe even dangerous. But the two companies building it, General Electric and Safran, believe this strange naked engine will cut fuel consumption by more than 20 percent. That number sounds small until you understand what it means. Fuel is one of the largest costs any airline faces, and a 20 percent reduction would be the biggest single leap in engine efficiency in a generation. Airbus is preparing to mount this engine on a massive A380 test aircraft and fly it over the south of France. The entire industry is watching. But here's the part of this story almost nobody talks about. This engine is not new. An almost identical idea flew over the American desert in 1986, strapped to the side of the Boeing 727. It worked. It delivered astonishing fuel savings, numbers so good they still look impressive four decades later. And then the industry buried it. To understand why this engine is coming back, and why it might actually change the future of flying this time, you need to understand why it died the first time. Start with the engine hanging under the wing of almost every airliner flying today. From the outside it looks like one big tube. Inside it is really two machines working together. At the core sits a compact jet engine. A screaming heart of compressors and turbines burning fuel at temperatures hot enough to melt the metal around it, if that metal were not protected by clever cooling. But most of the thrust does not come from that core. It comes from the giant fan at the front. The core's job is mainly to spin that fan, and the fan pushes an enormous mass of air backward around the outside of the core. Engineers call this the B-Y pass ratio, the amount of air flowing around the core compared to the air flowing through it. And here is the rule that has governed engine design for 50 years. Moving a huge amount of air gently burns far less fuel than moving a small amount of air violently. Every major efficiency gain in modern aviation has come from pushing that ratio higher. The early jets of the 1960s sent almost all their air screaming through the core, which is why they were deafening and drank fuel at a terrifying rate. Then came bigger fans and more bypass, and with every generation the fuel bills dropped. Bigger fans, more bypass, less fuel. It became the most reliable formula in aerospace. The best expression of that formula today is the CFM LEAP engine, built by CFM International, a 50-50 partnership between GE in the United States and Safran in France. When the LEAP entered service in 2016, it burned about 15% less fuel than the legendary CFM-56 before it, an engine so successful that more than 30,000 were delivered, making it the best-selling jet engine family in history. Today, the LEAP powers the Airbus A320neo, the Boeing 737 MAX, and China's C919. Together with the CFM-56, these engines power roughly three-quarters of all single-aisle jets in service. In 2025 alone, CFM delivered around 1,800 LEAP engines, a record-breaking production rate, and the company expects to break that record again. This company does not just compete in the single-aisle market, it owns it. So why would the most dominant engine maker on earth gamble on something radical? Because the turbofan is hitting a wall, and that wall is the very thing that made it work, the casing. That smooth cowling around the fan, the nacelle, adds thousands of pounds of weight and creates drag. As fans grow larger to chase efficiency, the casing around them grows too, until the drag and weight of the housing start canceling out the gains from the bigger fan. The formula that carried aviation for half a century is running out of room. The engineers at CFM looked at that problem and reached a conclusion that sounds almost reckless. If the casing is the problem, remove the casing. Let the fan spin in the open air, where it can grow as large as the aerodynamics demand. No duct, no limit. That is the open fan. And the projected result is a bypass ratio in the neighborhood of 60 to 1 compared to roughly 11 to 1 on today's LEAP. It is not a small step. It is an entirely different category of machine. But this is where the story folds back on itself, because engineers reached this exact conclusion once before in the most desperate decade American aviation ever faced. In the 1970s, oil shocks sent fuel prices through the roof, and airlines were bleeding money on every flight. Fuel efficiency stopped being an engineering ambition and became a matter of survival. NASA launched research programs to find radical savings, and General Electric answered with something called the GE36, the unducted fan. GE took the core of an F404 fighter jet engine, the same family of engines that powered the Navy's Hornet, and mounted two rows of curved scimitar-shaped blades on the back spinning in opposite directions, completely exposed, with no gearbox between the turbine and the blades. NASA backed the work with a contract worth over $20 million, and Boeing offered one of its 727s as a flying testbed. On August 20th, 1986, the strange machine took to the sky for the first time, mounted on the right side of that Boeing 727, replacing one of its normal engines. The results stunned the industry. The unducted fan pushed the testbed to Mach 0.84 at 39,000 feet, right in the cruise envelope of a conventional jet, while burning dramatically less fuel. Testing by GE and NASA showed fuel savings around 30% compared to the turbofans of the day. The Smithsonian's National Air and Space Museum, which holds one of these engines in its collection, records fuel consumption reductions of over 30% in flight testing. In 1987, the engine flew again, this time on a McDonnell Douglas MD-80 testbed, and GE was not alone. Pratt & Whitney, its greatest rival, teamed up with the Allison Engine Company to build a competing open rotor called the 578DX, which differed in one key way. It used a reduction gearbox between the turbine and the blades. That engine first flew in March 1987 on a Gulfstream business jet, and later on an MD-80 as well. Two of the biggest engine makers in the world were flying open rotors at the same time. This was not a fringe experiment. Boeing was so convinced it designed an entire airliner around the concept. The 7J7, a roughly 150-seat jet with two unducted fans mounted at the tail, officially launched at the 1985 Paris Air Show. McDonnell Douglas studied prop fan versions of its own jets. Major airlines took a serious look. The future, it seemed, was arriving on schedule. And then the future was cancelled. Oil prices collapsed in the late 1980s, and suddenly the fuel savings that justified all that risk stopped mattering to airline accountants. The exposed blades were loud, and the industry doubted passengers would accept the noise in the cabin, or that communities around airports would accept it on the ground. Airlines hesitated to bet on an unproven configuration when cheap fuel made the conventional turbofan good enough. British Airways, once interested in the 7J7 as a replacement for its older 737s, bought the conventional 737-300 instead. American Airlines went with a different aircraft entirely. Order by order, the business case evaporated. Boeing shelved the 7J7. The engines came off the testbeds. And one of the most successful experimental engine programs in history went into museums instead of onto wings. Before we get to why it came back, I'm curious about something, and be honest in the comments. If an airline offered you a flight tomorrow on an aircraft with open, uncovered fan blades spinning outside the window, would you board it without hesitating? And if you are enjoying this story, take one second to hit the like button and subscribe because it genuinely helps the channel keep making documentaries like this one. There is one more reason the 1980s program collapsed, and it matters because it is the same obstacle the new engine faces today. Certification. Every commercial jet engine flying today is certified under rules written for ducted fans, where the casing serves a brutal, specific purpose. If a fan blade ever breaks loose at takeoff power, the casing is designed to contain it, catching a piece of spinning metal or, in modern engines, composite material before it can strike the fuselage or the wing. An open fan has no casing by definition. That means the engine maker must prove, through testing and analysis, that a blade release is either so improbable or so survivable that the aircraft remains safe, and regulators on both sides of the Atlantic will have to judge a configuration their rulebooks were never written for. The engineers who flew the GE-36 in 1986 declared afterward that the noise levels of an unducted design would be acceptable and certifiable. They never got to prove it because the program ended before certification ever began. Their successors intend to finish the job. For 30 years, the unducted fans stayed dead. Then the world changed again, fuel prices climbed, airlines committed to net-zero carbon targets, and the pressure that killed the open rotor in 1988, cheap oil, reversed into the pressure that now demands its return. On June 14, 2021, CFM International announced the RISE program, short for Revolutionary Innovation for Sustainable Engines. The headline goal, an engine that burns more than 20% less fuel than today's most efficient turbofans, compatible with sustainable aviation fuel and even hydrogen. And at the center of the program sits the open fan, the direct descendant of that 1986 experiment. But this is not a copy of the GE-36. The engineers studied why the old design failed, and they changed the formula. The GE-36 used two rows of blades spinning in opposite directions, and much of its noise problem came from those rows slicing through each other's wake. The RISE open fan uses a single rotating row of long, thin carbon fiber composite blades, with a row of stationary guide vanes behind it that straighten the airflow. The blades can change their pitch in flight, adjusting their bite into the air like a propeller. But this is not a turboprop. CFM states the design will cruise at up to Mach 0.8, the same speed as today's single-aisle jets, with a noise signature designed to meet future regulations. And despite the dramatic look, the open fan blades are not much larger than the fan blades already flying on GE's giant GE-9X engine under the wings of the newest Boeing widebody. The open fan is also only one piece of the program. RISE includes a smaller, hotter, more efficient engine core developed with NASA, because a compact core wastes less energy generating the power that drives the fan. And it includes hybrid electric technology, with ground tests of electrically assisted systems planned in this decade, allowing electric motors to support the engine during parts of the flight. Stack those technologies together, and the 20% target stops looking like a slogan and starts looking like arithmetic. The testing campaign behind this engine is one of the largest in aviation history. Engineers have logged more than 500 hours of wind tunnel testing on the open fan concept, working with European aerospace research institutions in both low-speed and high-speed facilities to map exactly how the exposed blades behave, and how loud they really are. By mid-2026, the broader RISE program had completed roughly 500 test campaigns, and more than 3,000 endurance cycles, with over 2,000 CFM engineers working on it. Blades and guide vanes have been through impact tests, ice, dust ingestion, fatigue, and vibration trials. The same brutal punishment certification authorities will eventually demand. In July 2026, CFM announced that key design reviews were complete, and that a full-scale front section of the open fan would run in a newly built 26-foot test cell at Safran's facility in Villaroche, France. Somewhere in that test cell, the ghost of 1986 is spinning again. Then comes the moment the whole industry is waiting for. The open fan will fly, first on GE's Boeing 747 flying testbed out of Victorville, California, and then on something far more dramatic. Airbus is converting an A380, the largest passenger aircraft ever built, into a flying laboratory. The experimental engine will be mounted on the aircraft while its four regular engines keep it safely in the air, letting engineers measure exactly how the open fan performs in real flight—thrust, drag, vibration, and noise—measured from the ground and inside the cabin. At the Farnborough Air Show in July 2026, Airbus and CFM unveiled the test aircraft's new paint scheme and confirmed the first design review for the flight campaign was complete, with flights planned from Toulouse before the end of the decade. The double-decker that airlines once dismissed as a commercial failure is getting a second life—the midwife of the next generation of flight—and there is a strategic wrinkle worth knowing. CFM is not betting everything on one horse. Industry reporting indicates the company is quietly maintaining a backup—a more conventional, advanced, ducted engine design—in case the open fan cannot meet its targets or its timeline. That tells you two things at once. First, even the people building this engine know the risk is real. Second, they are structuring the program so that the 20 percent goal survives even if the architecture does not. The open fan is the preferred future, not the only one. So, will this engine actually change the future of flying? Here is the honest picture. Airbus is leaning in hard, evaluating the open fan for the successor to the A320 family—an aircraft expected sometime in the second half of the 2030s. CFM has said a RISE-based engine could be ready in that same window, but an engine maker cannot launch an airliner. Boeing has publicly said it is too early to take a position on open fan technology. And rival Pratt & Whitney is betting the opposite way, refining its geared turbofan—a conventional ducted design—and positioning itself as the low-risk choice at a moment when airlines crave stability. Which raises the question every airline executive is quietly asking, and I will ask it to you too. If you ran an airline, would you bet a fleet on the radical option or the familiar one? The last time the industry faced this exact choice, it chose familiar, and the revolutionary engine spent three decades in a museum. But the conditions that killed it are gone, fuel is expensive, climate targets are binding, and a 20% saving on the thousands of single-aisle jets that will be ordered in the coming decades is worth billions upon billions of dollars. Somewhere in a test cell in France, blades taller than a person are spinning in the open air, running the same experiment aviation abandoned 40 years ago. The first time, the future arrived too early. This time it might be arriving right on schedule.