The very first aircraft used engine-driven propellers to drive them through the air and, of course, many planes still use propellers today. However, if you want to achieve serious speed in the air then you’re going to need an awful lot of thrust, and for that you need a jet engine.
To demonstrate how a jet works, hold a high-pressure hosepipe up to the palm of your hand – the pressure of the water squirting out the end will try to push your hand back. In fact, the engine on a jet ski works by firing water out of a nozzle to drive the vessel forward.
The simplest form of jet is the firework rocket, which dates back to the 13th Century. An explosive is ignited and the resultant gasses are propelled out of a nozzle which creates thrust to push the rocket forwards. Rocket engines in spacecraft work in the same way; they’re simple but use a huge amount of fuel in a short time, and aren’t practical for everyday use. Most so-called jet planes actually have turbofan gas-turbine engines. Near the front of the engine is a compressor, which is essentially a larger number of vanes that suck air in, compress it, and then force it at high-pressure into a combustion chamber. At this point the air is moving at hundreds of miles an hour.
Fuel is injected into the combustion chamber, where it mixes with the fast-moving compressed air and is ignited. The hot gasses then pass back where they drive a turbine which, in turn, provides propulsion for the aforementioned compressor. The remaining energy is expelled from a nozzle at the back of the engine to create forward thrust.
At the very front of a turbofan engine is a large fan that also sucks air in. Some of this air is picked up by the compressor but the rest bypasses the main turbine and is led around to the back of the engine where it supplies additional thrust.
Because a turbofan relies on the rotating turbine to drive the compressor and fan, and the turbine can’t turn without air from the compressor, it needs help to get started. This is done with compressed air that spins the compressor and fan at such a speed that, when the fuel is ignited, there is enough airflow to ensure the hot gasses are thrust backwards and don’t explode.
Compared to the internal combustion engines used in cars and propeller-driven aircraft, a turbofan is reassuringly free of complex parts and so is extremely reliable. Which in the case of an aeroplane is reassuringly good news!
Who was Sir Frank Whittle?
Sir Frank Whittle is credited with inventing the modern jet engine, along with German Hans von Ohain, who independently came up with a similar idea at the same time.
Born in Coventry in 1907, Whittle trained as an RAF officer and wrote a thesis on future aircraft which considered the idea of using a piston engine to create compressed air for thrust. He abandoned that plan but later thought of using a turbine in place of a conventional engine. He passed his idea to the Air Ministry but was told that it would never work.
Undeterred, Whittle raised finance to set up his own company, Power Jets Limited. He struggled to keep it going until, with the Second World War looming, the Air Ministry finally realised the project’s potential and began to fund it.
Finally, in 1939, the Air Ministry commissioned the Gloster Whittle – the first British jet plane, soon after the Germans trialed their Heinkel He 178 – the world’s very first jet aircraft.
Whittle later moved to the United States, where he died in 1996 but is still remembered for changing the face of aviation forever.