The Evolution of the Jet Engine, From Whittle to the Open Fan

Every jet engine hanging under a wing today is the answer to the same single question, asked and re-answered roughly every fifteen years since the 1930s: how do you push more air, more efficiently, through the same basic machine? That question has a real, surprisingly dramatic history — two rival inventors who never met, a fighter that arrived four years too late to matter, an engine programme saved from cancellation by two weeks, and a technology now being bet on again, in the open, for the decade ahead.

Two inventors, working in secret, on opposite sides of a war neither engine helped win

The jet engine has two fathers who never knew about each other until after the fact. In Britain, RAF officer Frank Whittle patented the turbojet in 1930 and spent years struggling to get anyone to take it seriously — funding was scarce, and it wasn’t until 1937 that his first test rig, the Whittle Unit, actually ran. In Germany, Hans von Ohain arrived at essentially the same underlying idea completely independently, formulating his own theory of jet propulsion in 1933 while still a doctoral student at the University of Göttingen. Neither man had any idea the other existed. What decided who got there first wasn’t the idea — it was industrial backing: von Ohain partnered with the Heinkel aircraft company, and on 27 August 1939, days before the Second World War began, the Heinkel He 178 became the first aircraft in history to fly under pure jet power. Whittle’s own aircraft, the Gloster E.28/39, didn’t fly until May 1941 — nearly two years behind, entirely because Whittle had spent the 1930s trying to convince Britain to fund something that sounded, to most people who heard the pitch, like science fiction.

The engine that actually went to war

Neither Whittle’s nor von Ohain’s original engine ever saw combat. That distinction belongs to a third, genuinely different design: the Junkers Jumo 004, an axial-flow turbojet developed by Junkers under Anselm Franz, architecturally distinct from Whittle’s centrifugal-flow layout — and it’s the axial-flow layout, not Whittle’s, that became the template nearly every jet engine since has followed. Paired to the Messerschmitt Me 262, the Jumo 004 powered the world’s first operational jet fighter into combat in 1944, roughly 100mph faster than any Allied piston fighter it met. It arrived too late and in too few numbers to change the outcome of the war — production was hammered by Allied bombing and chronic shortages of the heat-resistant alloys the engine’s turbine blades needed — but it proved, under genuine combat conditions, that the axial-flow jet engine was the design worth building on.

From wartime secret to airline seat

Commercial jet travel began in 1952, when the de Havilland Comet entered service — a genuine technological leap that cut journey times dramatically, and a programme that was then badly damaged by a string of fatal crashes traced to metal fatigue around the Comet’s square window frames, a lesson in structural engineering the entire industry absorbed. The aircraft that actually built the commercial jet age at scale was the Boeing 707, powered by Pratt & Whitney’s JT3D — not a pure turbojet like the Jumo 004 or Whittle’s engines, but an early, low-bypass turbofan: some of the incoming air was now deliberately routed around the engine core rather than through it, a small first step toward the idea that would define every engine generation after it — that bypassing more air, rather than accelerating a smaller amount harder, was the real path to a better engine.

The idea taken seriously: high bypass, and the widebody it made possible

The real break came in the late 1960s, when Pratt & Whitney committed to a high-bypass turbofan on a scale nobody had attempted commercially: the JT9D, developed specifically for an aircraft that didn’t exist yet — the Boeing 747, covered in full in this site’s own 747 story. Rather than pushing a relatively small volume of air through the core at very high speed, the JT9D pushed a much larger volume of air around the core at a comparatively gentler speed for the same thrust — quieter, and meaningfully more fuel-efficient, precisely because moving more air slower is aerodynamically cheaper than moving less air faster. The JT9D entered service on the 747 in January 1970 and went on to power the 767, Airbus A300 and A310, and the McDonnell Douglas DC-10 — the engine that proved high bypass wasn’t just theoretically better, it was the engine an entire generation of widebody aircraft would be built around. General Electric followed close behind with the CF6, first run in 1971 and derived directly from the TF39 GE had built for the military’s C-5 Galaxy transport — a rare, genuine case of military engine technology flowing straight into civil aviation rather than the more usual direction.

Two weeks from cancellation: the engine that became the most common ever built

Not every engine that mattered arrived through triumph. CFM International — a 50/50 joint venture between GE and France’s Snecma, formed in 1974 — ran its first CFM56 that same year and then spent more than five years unable to sell a single one. By March 1979, the programme was two weeks from official cancellation. What saved it wasn’t a design breakthrough; it was three airlines — Delta, United and Flying Tigers — choosing the CFM56 to re-engine their ageing Douglas DC-8 fleets, followed within weeks by a US Air Force order to re-engine its KC-135 tanker fleet with the same design. Boeing, meanwhile, had spent that same period trying and failing to sell airlines on a CFM56-re-engined 707 to meet tightening noise regulations — an irony the engine’s own history carries: the aircraft it was originally pitched to save couldn’t save it, and a completely different aircraft did. From that near-death, the CFM56 went on to become the default engine of the Boeing 737 Classic/NG and Airbus A320ceo families — two of the best-selling airliners ever built — and with more than 20,000 produced, it remains the single most common jet engine in the world by a wide margin.

The next real architectural break: letting the fan think for itself

For four decades after the JT9D, every high-bypass turbofan shared one structural limitation: the fan and the low-pressure turbine driving it were bolted to the same shaft, spinning at the same speed — forcing a compromise, since a fan wants to turn slowly for efficiency while a turbine wants to spin fast for power. Pratt & Whitney’s geared turbofan, the PW1000G family, finally broke that constraint by inserting a reduction gearbox between the two, letting each spin at its own genuine optimum speed for the first time. The payoff was real and verified, not marketing: bypass ratios above 12:1, a roughly 12–15% improvement in fuel burn, and up to 50% quieter than the direct-drive engines it replaced — the engine now flying under the wing of every Airbus A220 and most A320neo-family aircraft.

What comes after the geared turbofan

The next real break is already in flight testing, and it’s a stranger-looking machine than anything before it: CFM’s RISE programme strips away the fan cowling entirely, exposing the blades in an open-rotor configuration to push bypass ratio — and efficiency — further than a shrouded fan physically allows, aiming for entry into service around the mid-2030s. It isn’t flying passengers yet, and it won’t for years. It’s real enough, though, that GE’s own newsroom put out a piece specifically explaining why Mentour Pilot — Petter Hörnfeldt, one of the most-watched airline pilots on YouTube — has become a public partner in explaining the programme to a general audience, a genuine sign of how seriously the manufacturers are treating the communication challenge of an engine that looks, on first glance, like something has gone missing.

Sources & Further Reading

• Timeline — Sir Frank Whittle, Inventor of the Jet Engine ↗
• Pratt & Whitney JT9D — Wikipedia ↗
• CFM56 — History and Future of the Go-Anywhere Engine — Mentour Pilot ↗
• CFM International CFM56 — Wikipedia ↗
• Why the CFM RISE Program Has Mentour Pilot Telling the World — GE ↗