Have you ever wondered how they work, and what is inside those big "barrels" hanging under the wings of your plane? How can they move such a massive beast at such high speeds?
Aviation engines use the physical principle of "action and reaction" (hence the name "jet propulsion" or "reaction engine"): they push a mass of air backward to achieve forward motion—exactly like when you inflate a balloon and then let it go.
How it works:
At the front, outside air is drawn into a set of rotating blades called the compressor, which squeezes the air and increases its pressure.
From there, the air passes into containers called combustion chambers, where it is mixed with atomized fuel and ignited. This process provides a massive amount of energy to the glowing-hot mixture. Since the only way out is through the back of the engine, it blasts out at high speed.
As it exits, this mass of air gives up some of its energy to spin another set of rotating blades called the turbine (much like a windmill), which in turn is connected to the compressor (remember? The one at the front!). At this point, we have a jet of air shooting out the back; this would already be enough to push our plane, and it is indeed what happens in many small jets or military fighters.
The "Fan" Secret
The problem is that a "jet" that small would need to be accelerated to incredibly high speeds to move a large airliner. This isn't practical and is very energy-intensive. To put it simply: to double the speed of the exhaust air, you would need four times the fuel!
So, we use a clever trick: instead of increasing the speed of the air, we accelerate a larger quantity of it. In this case, the increase in fuel consumption stays in line with the increase in air mass, making this method much more efficient.
To do this, almost all the energy from the ignited air in the combustion chamber is transferred to the turbine. The turbine then powers the compressor and a set of much larger blades called the fan. This is the "giant fan" you see when looking at the engine from the front. Like a massive household fan, it pushes a huge volume of air backward.
You might think that the bigger the fan, the more efficient the engine; in reality, an oversized engine would create too much drag (resistance) at high speeds. Engineers study the perfect compromise based on the plane's characteristics.
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| A "fan" seen from behind |
Variations and Reliability
The turbine engine is very common in aviation. Even modern propeller planes use "turboprops" (see this post); the difference is that the energy collected by the turbine is sent to a propeller instead of a fan. The advantage is better efficiency at lower speeds, but the disadvantage is a lower top speed.
Finally, even the auxiliary generator (called the APU, or Auxiliary Power Unit, which provides electricity and air when the main engines are off) is a small turbine engine (see this post).
Now that you know how an engine works, it’s easy to understand the reason behind its characteristic roar! (see this post)
How reliable is an aircraft engine? Extremely. Airliner engines undergo incredibly strict testing during design, and in normal operation, they always run well below their maximum capacity. Throughout their operational life, they are subject to regular, thorough inspections.
Even if an engine were to fail, airliners always have at least one other, and the plane is designed to fly perfectly well with one engine out!
If you want to dive a bit deeper into how a jet engine works—still in a simple way—I’ve found this very interesting and well-made video for you. You can find many other aviation explanations on their YouTube channel.
DontWorryFlyHappy!