How do jet engines work?

A fully laden Boeing 777-300 can weigh over 300 tons as it takes off and just one of its engines alone is capable of lifting it safely into the air. 

So how do they work? (Check out the video above courtesy of CFM International)

Well it helps to start by explaining how the first type of jet engines operated. These would have been on some of the first jet liners such as Boeing 707’s, 727’s and older 737 models and are called turbojets. In simple terms, turbojet engines work in 4 stages.

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  1. Air is sucked in through the front of the engine.

  2. That air is then compressed through a series of compressor sections. 

  3. Fuel is added and then ignited. 

  4.  It blows out the back at a much greater force thereby providing thrust.

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(The not so scientific term for this is known as Suck, Squeeze, Bang, Blow)

Modern jet engines work in a similar way but with an extra element added. They still have a turbojet core which does essentially the same as described above but the hot compressed air after stage 3 then drives a set of turbine blades at the back of the core which in turn drive (via a shaft) the large turbine blades at the front (the ones you can see). These produce a huge amount of cold air flow which flows around the outside of the core and out the back bypassing the core itself (for this reason these kind of engines are called high-bypass or turbofan engines). 

Turbofan engines are far more efficient than the older type of turbojet engines. Also the cold air flowing around the jet core of the engine has the added benefit of insulating the noise produced which makes engines today a lot quieter than those on older aircraft. 

In addition to providing the thrust to carry planes into the air, modern jet engines also provide generator power for the electrics on-board and also the air to pressurise and condition the cabin. 

What about turboprop engines?

Turboprop engines, as you would find on smaller commuter aircraft aren’t too dissimilar to modern turbofan engines. They have an open propellor instead of a contained set of fan blades but this propellor is driven also by a turbine at the rear of the engine in the same way. 

So that’s it in a nutshell without trying to bore you too much. Any questions, drop us a line at hello@askthepilots.com

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