The four jet innovations that revolutionised aviation and helped us conquer the skies

Apr 23, 2022

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Summer 1940, England. As children played in fields, their gaze would be drawn skyways by the roar of a Rolls-Royce Merlin engine. A tiny dart tearing through the sky, with the agility of a gymnast but the power of a weightlifter, the Spitfire was proving the game-changer in the Battle of Britain. The same engine was being used in the Lancaster bomber, as Allied forces hit back against the Germans with raids deep into enemy territory.

At the time, it seemed that engine technology couldn’t get much better than this sublime piston engine. It was king of the skies.

However, behind the scenes, both British and German engineers were working on something that would change aviation forever.

How jet engines work

In simple terms, there are 4 stages for a jet engine to generate thrust, colloquially known as ‘suck, squeeze, bang, blow’.

The first stage of the engine is designed to suck as much air in as possible, this is why the front fan of a modern engine is so big. It is then fed into several compression stages where it is compressed down before being forced into the combustion chamber.

Here, it mixes with the fuel where it ignites before being blown through the turbine stages at the rear of the engine, creating the thrust to drive it forwards.

Origins of the jet engine

The basis of jet propulsion began much earlier than you may imagine. No, even earlier than that. The origins story of the modern jet engine actually begins in Egypt, circa AD50 with the inventor Heron of Alexandria.

He designed a sphere into which steam was fed from a cauldron below. However, the key design point was the two outflow tubes on opposite sides of the sphere, bent at right angles. As the steam was forced out of these tubes, it caused the sphere to rotate on its bearings. This was the first time that steam had been used to create rotary motion and was called an aeolipile.

Fast forward several hundred years and Leonardo da Vinci had made his input by drawing sketches of a machine that used the power of hot rising gasses to turn disc-like fans. The structure of the modern jet engine was beginning to take shape.

However, the real game-changer came in the early years of WW2, and, unbeknownst to each other, on both sides of the English Channel.

In Britain, Frank Whittle invented the first gas-turbine engine that would power the Gloster E28 aircraft. However, over in Germany, Hans Joachim Pabst von Ohain was one step ahead of Whittle and was able to create an engine that would enable Germany to be the first country to launch a jet-powered aircraft during the war.

However, it wasn’t actually von Ohain’s engine that turned out to be the game-changer for the Luftwaffe. It was a tweak on his design, by Anselm Franz, that powered the first jet fighter to enter service. The Messerschmitt 262.

Messerschmitt Me 262

Even as early as 1938, work was underway in Germany to develop a jet-powered fighter aircraft. However, due to delays in the production of the engine, the first Me262 only took to the skies in July 1942.

Seeing the potential of the aircraft, Hitler declared that it should be further developed as a fighter bomber. However, those working close with the project realised that it would be much better evolved as a pure fighter aircraft. Hitler’s orders were bravely ignored and the fighter aircraft entered service in mid-1944.

The Me 262 (Image warbirdsnews.com)

Having held aerial superiority over the Germans for some time, Allied forces were stunned by the speed of their new foe. The Me262 massively outperformed even the fastest of the Allied aircraft, flying over 120mph faster than the American P1 Mustang and was set to pose a huge threat to the progress of the war.

However, its introduction came too late for it to make any real difference. Chronic supply shortages in Germany meant that only a handful were ever able to enter service before the war came to an end.

That said, the engine and aerodynamic technology that went into designing the aircraft would be incorporated into the next generation of post-war military and civilian aircraft,

Ghost 50 Mk1- de Havilland Comet

The post-war era saw a boom in commercial aviation fed by a supply of now redundant aircraft and technology gleaned from designs such as the Me 262. As jet engine technology improved, aircraft were able to fly faster, further and higher. The next game-changer came in the shape of the British built de Havilland Comet.

The Comet was the world’s first pressurised commercial jetliner, entering service with BOAC in 1952. The pressurised cabin meant that the aircraft could fly higher, enabling it to halve the journey time between London and Tokyo.

A big part of the Comet’s initial success was down to its engine, the Ghost Mk1.

Development of the Ghost actually began in 1943 by Frank Halford who had designated his engine the H-1. Knowing that the Comet would require more power, he changed the 16 small combustion chamber design of the H-1 for one with 10 larger combustion chambers into a new engine named the H-2.

The de Havilland Comet was the first pressurised commercial airliner (Image dailypost.co.uk/NCJ Archive)

 

Whilst this prototype engine was being built, the de Havilland company bought Halford’s company and renamed the two engines the Goblin and the Ghost respectively.

The Ghost was actually ready for use well before the Comet was. As a result, it was used in various other fighter aircraft before being used by the Comet in its maiden flight in 1949.

However, the life of the Comet was short-lived. A number of high profile crashes attributed to metal fatigue — a new phenomenon as a result of repeated cabin pressurisations — spelt the end for this revolutionary aircraft.

Rolls-Royce/Snecma Olympus 593 – Concorde

Aircraft don’t come much more iconic than Concorde. If you ever got to see her fly, you’ll never forget that long slender neck, the swept-back yet curved wing and of course, the sound. The sound the 4 Olympus engines made was staggering.

You’d normally hear Concorde before you saw her (I say ‘normally’ because it would be unlikely that you’d see her during supersonic flight where, by definition, you’d see her before you’d hear her). During take-off, the engines would create so much noise that they would set off car alarms as the aircraft roared over carparks at the end of the runway.

By the time Concorde was being designed, the jet engine was well established and well understood. So, because of this, engineers knew that they faced a problem.

Concorde was powered by 4 Rolls-Royce/Snecma Olympus engines (Photo by David Parker/BWP Media/Getty Images)

A conventional jet engine requires a continuous and steady flow of air into the core parts. If this flow is disrupted for any reason, it can cause the engine to surge. This reduces the thrust output and can cause the engine to fail completely.

The problem with supersonic flight was that when the shockwave was created by the aircraft, it disrupted the required smooth airflow into the engine. As a result, engineers needed to come up with a system that would overcome this problem.

The solution was to have a changeable inlet at the front of the engine that could change shape depending on the stage of flight.

At subsonic speeds, the inlet behaved like any other jet engine and allowed air to flow unobstructed. However, as the aircraft went supersonic, panels extended into the inlet creating ramps that created a shockwave at the inlet, slowing the flow of air.

The flow was slowed even further as the intake widened as it neared the engine (liquids/gasses will slow down when the passage they are travelling in widens).

This clever bit of design meant that by the time the air reached the front stage of the engine, it was at a speed that allowed the compressors to do their job efficiently, enabling efficient combustion and, in turn, thrust production.

The variable intake of the Olympus engine (Image en-academic.com)

 

Pratt & Whitney JT9D – Boeing 747

Whilst Concorde revolutionised air travel for the elite, the introduction of the 747 was to change air travel for the masses. Able to seat 366 passengers in 3 classes, it was 2.5 times the size of its long-haul predecessor, the Boeing 707 — as requested by Pan American Airways.

Everywhere you looked, the 747 was massive. From its height and its length to the size of its wheels and the width of its wings. It is where the phrase ‘jumbo jet’ was coined. However, in order for this mass of metal to lift into the air, it needed some serious engines to get it moving. For this, Boeing turned to Pratt & Whitney who designed the JT9D engine.

The program was launched in September 1965 and by December 1966 P&W had an engine ready to test. Just 3 years later it would power the 747 on its maiden flight.

The Pratt & Whitney JT9D (Image prattwhitney.com)

 

The JT9D was a high bypass turbofan engine meaning that the majority of air sucked in by the front stage fan didn’t actually go through the core of the engine. Instead, it was channelled around the outside of the core. This was in stark difference from the original turbojet engines where all the incoming air went through the engine core.

The reason for this is that turbojet engines are inefficient in their thrust production during subsonic flight. A way of improving this would be to make the core of the engine bigger and hotter but even though this would increase the thrust slightly, the exhaust gases leave the engine at an even faster speed, taking most of the extra energy with it.

The way around this problem was the creation of the turbofan engine, like the JT9D.

The turbofan engine uses air that bypasses the core to create thrust (Image wikipedia.com)

Simply put, the turbofan emits a large amount of air at a slower speed whereas the turbojet emits a small amount of air at a faster speed — a far less efficient way to generate the same amount of thrust.

This extra efficiency meant that the engine used much less fuel, allowing the 747 to take its place as the world’s first true long haul aircraft.

Bottom Line

The jet engine changed aviation forever. It enabled aircraft to fly faster, to fly higher and to fly further. When it used to take propellor driven aircraft days to hop across the world, the same journey can now be done non-stop in a matter of hours.

Along the way, the jet engine made the name of some of the most iconic aircraft in commercial aviation history. The sense of wonder of how it will continue to develop and the aircraft it will power is what makes the world of aviation as inspirational as it is.

Picture by Monty Rakusen / Getty Images

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