Technical Focus: Jet Engines

Ever wanted to know how a plane actually works and flies, but have been put off by complex jargon and tons of maths? With this occasional series, we’ll explain it all in plain language and you’ll become an expert in no time!

This month, we take a look at…

Jet Engines!

While most planes in World of Warplanes are propeller-driven, a few of the top-tier aircraft use jet engines (also called gas turbines). The first true jet fighter plane was the Messerschmitt 262, which you can fly in-game.

Of course, jet engines are still the most common source of thrust in modern airplanes of all types. The basic concept is very simple and has been tinkered with for 2,000 years. The principle is that the ejection of high pressure air causes forward thrust. Have you ever blown up a balloon and then let it go without tying a knot in the end? Perhaps in school, you even did a ‘balloon rocket’ experiment using a balloon, a drinking straw and some string?

The amazing balloon rocket!

The physics principle behind this is Newton’s Third Law of Motion. This states that forces exist in pairs – where there is an action, then there is an equal and opposite reaction. To put this slightly more accurately, when one body exerts a force on a second body, the second body simultaneously exerts a force that is equal in magnitude and opposite in direction to the first. In the case of the balloon rocket, the first body is the air and the second body is the balloon. When the air is released out of the end, it forces the balloon forwards. This force is called thrust and it is what provides the forward motion needed for flight.

A jet engine works much like the balloon, albeit in a far more technologically impressive way. It shoots air out of the nozzle at extremely high pressure and velocity, creating an equal and opposing force on the engine itself. The result is that the engine and everything attached to it (i.e., the rest of the plane) move forward. The technical name for this device is ‘gas turbine’ and the most basic form is called a ‘turbojet’. 

A typical modern aeronautical jet engine.

After the invention of powered flight, it didn’t take long for engineers around the world to start considering how to use turbojet technology to achieve greater speeds for aircraft. Even before World War II, engineers had realised that the piston-driven propellers currently in use were approaching their maximum performance level (the limit being the tips of the propeller blades reaching the speed of sound – approximately 343 m/sec depending on the air type). If planes were to have more power and attain higher speeds, then a whole new propulsion system was needed. The answer was the turbojet.

Throughout the early years of the 20^th century developments were made across Europe, but it was in 1932 that the first true patent for a working turbojet engine was awarded to Frank Whittle from the United Kingdom. At around the same time, Hans von Ohain in Germany worked on his own designs, independently from Whittle. The world’s first turbojet-powered aircraft was the He 178, which flew in 1939.

It was only a few years after World War II that jet engines began to dominate flight. Their use not only resulted in more powerful aircraft for warfare but they also made long distance international travel possible, both practically and economically. They also made it possible for larger and larger aircraft to fill the skies – take a look at the size of the double-deck Airbus A380! Jet engines also function at high altitudes that would be impossible for propellers due to the thinness of the air.

Can you imagine something like this flying with propellers?

The jet engine is an invention that truly did change the world, and one with very simple principles behind it.

The gas turbine is simply a machine for taking in air, compressing it and then blasting it out of the nozzle at the back. The whole process can be summed up in four words that describe what happens to the air as it passes through the machine – SUCK, SQUEEZE, BANG, BLOW.

Remember these four words – they tell you everything you need to know about how a gas turbine works! Take a look at the diagram above and compare it with the cut-away image below. Can you see in which part of the gas turbine each of the four stages takes place?

Cut-away of Rolls-Royce Trent 1000 Gas Turbine, as used on many large modern passenger aircraft. This is a turbofan engine.

SUCK

The intake phase is first, and refers to air being drawn into the engine by the huge fan on the front. This fan is the part you can see on any airplane engine, and when it is on the ground, it is generally fenced off to prevent people getting too close. The fan is incredibly powerful and hence can be dangerous for anything near to it! A typical engine such as the Trent draws in a ton of air per second – the equivalent of taking all the air from a squash court in less than one second. Some of the air is drawn into the main part of the engine, while the rest is pulled through bypass valves and goes straight to the ‘Blow’ stage.

SQUEEZE

Once it is inside the engine, the air is compressed through a series of progressively smaller fans, called turbines (shown in gold on the Trent 1000 image above). The turbines squash the air into a much smaller space, resulting in extremely high pressure. High pressure air holds a huge amount of energy, which among other things makes it more susceptible to detonation, leading to the next stage.

BANG

The fuel is drawn into the engine through a small tube and mixed with the high pressure air. The entire mixture is then ignited. This causes a controlled explosion, in which all the gases massively expand at a rapid rate. The shape of the engine means the full force of the blast is directed out of the rear.

BLOW

The final stage! Here the hot blasted air from inside the engine is mixed with the bypassed air from the main fan, and the whole lot is blown at high velocity out of the back of the engine, creating a huge amount of thrust. Some of the air flow is used to turn the main shaft of the engine in order to keep it going, while the rest of the thrust is used purely for motion.

A Junkers Jumo 004 at the RAF Museum, Cosford, UK.
This was the engine used on the Messerschmitt 262.

That’s it! This is the process for a simple turbofan engine, in which the thrust is provided solely by the expelled air. A pure turbojet engine, as used in the early World War II jet fighters, doesn’t have the large fan to aid intake – it runs purely on the stream of air that passes through the engine.

Another variant is the turboprop engine, which includes a propeller attached to the turbine shaft that can be used at lower altitudes for increased fuel economy.

Internal combustion engines (or ‘piston engines’) also use similar terminology as in some ways the processes are similar. How piston engines work will be the subject of a future article.

While many modern jet engines are used for flight, they also serve a wide variety of other purposes. Some are used on large marine vessels to drive the propellers. Others have been used at ground level for attempts to break the land-speed record. The current world record for the fastest land-speed was set in October 1997 in Nevada, USA, by the vehicle Thrust SSC. It managed a speed of almost 1,228 km/h, breaking the sound barrier!

The Thrust SSC, dominated by its huge jet engines.

Note: Much of this article is based on the functionality of jet engines as presented by Rolls-Royce. You can visit their page for more information and some interesting animations.

Are you an expert now? Get in your planes and fly, pilots!