Technology – How a Jet Engine works

“There are only two things required to fly a modern airliner – a pilot and a dog.

It’s the pilot’s job to feed the dog.

It’s the dog’s job to bite the pilot if he touches anything in the cockpit.”

Anon

The vast majority of commercial airliners today use jet engines to power them. There are still aircraft using propellers but they are usually found on smaller planes flying shorter routes. Most short-haul and certainly long-haul operations use jet engines.

    The jet engine was invented in Britain by Sir Frank Whittle in 1937. However, the first aircraft to fly using such an engine was a single-seat seat German aircraft, the Heinkel 178. Britain again took the lead when it produced the first jet-powered airliner, the Comet 4. It featured four jet engines integral with the wing and grouped two on each side next to the fuselage. And it was in 1958 that regular jet flights took place across the Atlantic Ocean.

    Okay, so since they are so important to air travel today, let’s take a look at how a jet engine works. In essence, it’s quite a simple design. If you look at the front of a typical jet engine you will see lots of blades splaying out from a central hub. This is why another name for this type of engine is a fan jet.

Fan Blades at the front of an engine

    The whole of the engine itself is covered by an engine cowl which makes it difficult to see how it works. But stand to the side of such an engine and you will see that it tapers in from the front to the exhaust at the rear. What happens is that air is taken in via the spinning fan blades at the front and compressed by use of a compressor. This compressed-air then enters the combustion chamber where it is mixed with burning fuel. This fuel/air mixture now expands very quickly and the gases then power a turbine which helps to drive the compressor. The gases are then exhausted out of the rear of the engine at great speed.

Schematic of a Jet Engine

    So the gases are vented out with great power. If we now consider Newton’s Third Law of Motion which states that “to every action, there is an equal and opposite reaction,” we can see that this opposite reaction is going to “push” the aircraft forwards. In essence, that is how a jet engine powers an aircraft.

    As I said before, this is a simple example to illustrate the principle involved. Modern jet engines are more complex and use design features that make them much more efficient. For example, bypass engines may only use 25% of the air to mix with the burning fuel. The remaining 75% is directed around the engine and vented straight out through the exhaust tubes. This results in a saving of fuel and less polluting gases.

    In addition, modern jet engines will have up to three compressors which are known as N1, N2 and N3. The first one at the front is the N1 and is a low-pressure compressor. N2 and N3 are high-pressure compressors. The fuel used in these engines is kerosene and is known as Jet A-1. It has the advantage of not so much igniting but burning continually. This is a feature of our fuel we want in our engine.

    It is common sense that jet engines can be dangerous when operating. Ground engineers are very careful not to stand either in front or behind one when it is operating. The N1 fan at the front could suck you in even when operating on idle power. And if you’re standing behind an engine winding up to full power you could easily be blown back over fifty metres.

    But as passengers, you will be safely seated inside the aircraft knowing that you are being powered by one of the most efficient engines ever developed. But watch this space. The first all-electric aircraft have already flown and the designers are now looking towards developing electric engines to power airliners. It will take a number of years but they will come.

    Happy Flying.

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