How does a jet engine work?
That powerful sound rising at takeoff is the result of one simple job: taking in air and pushing it back fast.
Four steps
- Intake: the big fan at the front draws air in.
- Compression: some of the air is squeezed by rows of spinning blades.
- Combustion: fuel is added to the compressed air and burns; the gases expand.
- Exhaust: the expanding gases spin the turbine and leave out the back. The turbine in turn spins the fan at the front.
Most thrust comes from the fan
In the turbofan engines on today's airliners, most of the air the fan draws in flows around the engine's core and is pushed straight back. Most of the thrust comes from this air. The design makes engines both quieter and more efficient.
The sounds you hear
- Engine start: a rising whistle. Engines are usually started one after the other.
- Takeoff power: a strong roar as you speed down the runway.
- Power reduction: a few minutes after takeoff the sound drops; pilots switch to climb power.
- Reverse thrust: a short roar right after landing as the aircraft slows.
Two engines
Most of today's airliners have two engines. Aircraft and pilots are designed and trained to continue the flight on one engine; pilots practise this regularly in the simulator.
