This Engine Will Change The Future Of Flying — Forever

On August 20th, 1986, a Boeing 727 took off from the California desert with something strapped to its right side that looked like a mistake, not a normal jet engine, a set of enormous curved blades spinning, completely exposed to the open air, no casing, no cowling, nothing protecting them from the wind rushing past. It looked unfinished, it looked dangerous, and it worked better than almost anyone expected. That engine burned roughly 30% less fuel than the turbofans of its era, a number so good it still holds up four decades later. Then the industry looked at that result and buried it anyway. Today, a nearly identical engine is being tested again, and Airbus is about to bolt it onto the biggest passenger jet ever built to prove it can finally survive the second time around. To understand why an idea this good got shelved for 30 years and why it's suddenly worth billions of dollars again, you need to understand the one rule that has quietly governed every jet engine ever built. Look at the engine hanging under the wing of almost any airliner today, and from the outside, it looks like a single tube. Inside, it's really two machines working together. At the core sits a compact, screaming jet engine, burning fuel hot enough to melt the metal around it if that metal weren't carefully cooled. But most of the actual thrust doesn't come from that core. It comes from the giant fan at the front, and the core's real job is mostly just to spin that fan, which pushes an enormous volume of air backward around the outside of it. The ratio between that bypassed air and the air flowing through the core is called the bypass ratio. Here's the rule that has shaped aircraft engine design for 50 straight years. Moving a huge amount of air gently burns dramatically less fuel than moving a small amount of air violently. Every major leap in aviation fuel efficiency since the 1960s has come from pushing that bypass ratio higher. Early jets sent almost all their air screaming through the core, which is why they were deafening and drank fuel at a terrifying rate. Bigger fans, more bypass, less fuel, generation after generation. It became the single most reliable formula in aerospace engineering. The best modern expression of that formula is CFM's LEAP engine, a joint venture between General Electric in the US and Safran in France. When it entered service in 2016, it burned roughly 15% less fuel than the CFM-56 it replaced, an engine so successful that more than 30,000 units have been delivered, making it the best selling jet engine family in history. Today, the LEAP powers the A320, NEO, the 737 MAX, and China's C919. And together with its predecessor, it powers roughly three quarters of every single aisle jet in service. In 2025 alone, CFM delivered around 1,800 LEAP engines, a production record it expects to break again. This isn't a company chasing market share. It already owns the market. So why would the most dominant engine maker on earth gamble everything on something radical? Here's Jet Verdict, and if you're enjoying stories about the engineering decisions that quietly reshape entire industries, this is a good time to hit subscribe because the conventional turbofan is running straight into the exact thing that made it work in the first place, the casing. That smooth outer cowling wrapped around the fan adds real weight and creates real drag. As fans grow larger to chase higher bypass ratios and better efficiency, the casing around them has to grow too. And eventually the weight and drag of that housing start canceling out the gains from the bigger fan underneath it. The formula that carried aviation for half a century is running out of room to keep improving. CFM's engineers looked at that wall and reached a conclusion that sounds almost reckless. If the casing itself is the problem, remove the casing entirely. Let the fan spin in open air where it can grow as large as the aerodynamics actually demand. No duct, no limit. That's the open fan concept and the projected bypass ratio sits somewhere around 20 to one compared to roughly 11 to one on today's best leap engines. That's not a small step forward. It's an entirely different category of machine. But here's where the story folds back on itself because engineers reached this exact conclusion once before in the most desperate decade American aviation had ever faced. Back in the 1970s, oil shocks sent fuel prices through the roof and airlines were bleeding money on every flight. Fuel efficiency stopped being an ambition and became a matter of survival. NASA launched research programs chasing radical fuel savings and General Electric answered with the GE36, the unducted fan. GE took the core of an F404 fighter engine, the same family powering 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 project with a contract worth more than $20 million and Boeing offered one of its own 727s as a flying test bed. The results stunned the industry. The unducted fan pushed that test aircraft to Mach 0.84 at 39,000 feet right inside the cruise envelope of a conventional jet while burning dramatically less fuel. Testing by GE and NASA showed savings of roughly 30%, a figure the Smithsonian's National Air and Space Museum, which holds one of these engines today, still records as accurate. In 1987, it flew again, mounted on a McDonnell Douglas MD-80, but GE wasn't working alone either. Pratt & Whitney partnered with Allison Engine Company to build a competing open rotor, the 578DX, using a reduction gearbox between the turbine and blades, unlike GE's gearless approach. That engine first flew in March 1987 on a Gulfstream business jet and later an MD-80, too. Two of the largest engine makers on the planet were flying open rotors simultaneously. This wasn't a fringe experiment. Boeing was convinced enough to design an entire airliner around it, the 7J-7, a roughly 150-seat jet with two unducted fans mounted at the tail, launched at the 1985 Paris Air Show. McDonnell Douglas studied prop fan versions of its own jets. Major airlines took it seriously. The future genuinely seemed to be arriving on schedule. Then the future got canceled. Oil prices collapsed in the late 1980s, and the fuel savings that justified all that engineering risk stopped mattering to airline accountants. The exposed blades were loud and the industry doubted passengers would tolerate the cabin noise or that airport communities would tolerate it on the ground. Airlines hesitated to commit to an unproven configuration right as cheap fuel made the conventional turbofan good enough again. British Airways, which had shown real interest in the 7J-7, bought conventional 737s 300s instead. American Airlines chose a different aircraft entirely. Order by order, the business case evaporated. Boeing shelved the 7J-7, the test engines came off their aircraft, and one of the most successful experimental programs in aviation history went into museum storage instead of onto commercial wings. There's one more reason that 1980s program collapsed, and it's the exact same obstacle the current engine faces today, certification. Every commercial jet engine flying right now is certified under rules written for ducted fans, where the casing serves one brutal purpose. If a fan blade breaks loose during takeoff power, the casing is engineered to physically contain it, catching a piece of spinning metal or composite before it can strike the fuselage or wing. An open fan has no casing by definition, which means the engine maker has to prove a blade release event is either so improbable or so survivable that the aircraft stays safe regardless. Regulators on both sides of the Atlantic now have to judge a configuration their rule books were never written to cover. The engineers who flew the GE-36 in 1986 believed its noise levels would ultimately prove acceptable and certifiable. They never got the chance to prove it because the program ended before certification testing ever began. Their successors intend to finish what that generation started. For roughly 30 years, the unducted fan concept stayed dead. Then the world changed again. Fuel prices climbed back up, airlines committed publicly to net zero carbon targets, and the exact pressure that killed the open rotor back in 1988, cheap oil, reversed itself into the pressure that now demands its return. In June of 2021, CFM International formally announced the RISE program, short for Revolutionary Innovation for Sustainable Engines, with a headline goal of an engine burning more than 20% less fuel than today's most efficient turbofans, compatible with sustainable aviation fuel and eventually hydrogen. At the center of that program sits the open fan, the direct engineering descendant of that 1986 experiment. But this isn't simply a copy of the GE-36. CFM's engineers studied exactly why the original design failed and changed the formula accordingly. The GE-36 used two counter-rotating rows of blades, and much of its noise came from those two rows slicing through each other's wake. RISE instead uses a zingle rotating row of long, thin carbon fiber blades, paired with a stationary row of guide vanes behind it that straighten the airflow back out. The blades can change their pitch mid-flight, adjusting their bite into the air like a propeller, but CFM insists this isn't a turboprop. The design will cruise at up to Mach 0.8, the same speed as today's single-aisle jets, with a noise signature engineered to meet future regulations. And despite how dramatic it looks, the open fan blades aren't much larger than the fan blades already flying on GE's own GE-9X engine, currently hanging under Boeing's newest wide-body jet. The open fan is also only one piece of the broader RISE program. It also includes a smaller, hotter, more efficient engine core developed in partnership with NASA, since a more compact core wastes less energy just generating the power needed to drive the fan in the first place. And it includes hybrid electric technology, with ground tests of electrically-assisted engine systems planned within this decade, letting electric motors support the engine during specific phases of flight. Stack all three of those technologies together, and the 20% efficiency target stops sounding like a marketing slogan and starts looking like straightforward arithmetic. The testing campaign behind this program is one of the largest in aviation history. Engineers have logged more than 500 hours of wind tunnel testing on the open fan alone, working with European aerospace research institutions to map exactly how the exposed blades behave aerodynamically 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 on the project. The blades and guide vanes have been pushed through impact testing, ice and dust ingestion, fatigue trials, and vibration testing, essentially the same punishment certification authorities will eventually demand. In July 2026, CFM announced its key design reviews were complete and a full-scale front section of the open fan would run inside a newly built test cell at Safran's facility in Villarosa, France. Somewhere inside that test cell, the ghost of 1986 is spinning again. Then comes the moment the industry is waiting for. The open fan will fly first on GE's own 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 that aircraft while its four normal engines keep it safely in the air, letting engineers measure thrust, drag, vibration, and noise, both from the ground and inside the cabin. At Farnborough in July 2026, Airbus and CFM unveiled the test aircraft's new paint scheme and confirmed the first design review was complete with test flights planned out of Toulouse before the end of the decade. The double-decker jet the industry once dismissed as a commercial failure is quietly becoming the midwife of the next generation of flight. There's a strategic wrinkle worth knowing too. CFM isn't betting absolutely everything on one design. Industry reporting indicates the company is quietly maintaining a backup, a more conventional advanced ducted engine, in case the open fan can't meet its performance targets or its timeline. That tells you two things simultaneously. First, even the people building this engine understand the risk is genuinely real. Second, they've deliberately structured the program so the 20% efficiency target survives, even if the radical architecture itself doesn't. The open fan is the preferred future here, not the only acceptable one. So will this engine actually change the future of flying? Here's the honest picture. Airbus is leaning in hard, evaluating the open fan for whatever eventually replaces the A320 family expected sometime in the second half of the 2030s. CFM has said a RISE-based engine could realistically be ready within that window. But an engine maker can't launch an airliner alone. Boeing has publicly said it's too early to take a position on open fan technology at all, and rival Pratt & Whitney is betting the opposite direction, refining its existing geared turbo fan and positioning itself as the low-risk, proven choice at a moment when plenty of airlines are craving exactly that kind of stability. The last time the aviation industry faced this exact choice, it chose familiar over radical, and the revolutionary engine spent the next three decades sitting quietly in a museum instead of flying commercially. But the specific conditions that killed it back then are gone now. Fuel is expensive again. Climate targets are binding, not aspirational. And a 20% fuel saving applied across the thousands of single-aisle jets that will be ordered over the coming decades is worth billions upon billions of dollars to whoever gets there first. Somewhere in a test cell in France right now, blades taller than a grown adult are spinning in the open air, running essentially the same experiment aviation abandoned 40 years ago. The first time, the future arrived too early. This time, it might actually be arriving right on schedule. If you want to see exactly how Rolls-Royce is betting billions against this entire open fan concept with its own conventional Ultra Fan 30 program, that story is already on this channel. Subscribe to Jet Verdict to keep following which of these engine bets actually wins.