How does a jet engine even start?
HOW THINGS WORK
Ordinary airliners have two large jet engines – one under each wing. During flight, the engines suck air in at the front and force compressed air out at the back. However, the jet engines cannot make the plane take off from the ground without the APU engine at the back of the aircraft.
1
The compressed air from the APU is sent via long pipes in the plane body to a turbine at the front of the aircraft's 2 jet engines located beneath the wings.
2
When the pilot starts the plane, a small extra engine, the APU, located at the back of the aircraft is activated. The APU sucks in air, which is compressed in a compressor.
3
The compressed air makes the turbine rotate and suck in even more air. The sucked in air is directed through a compressor at the centre of the jet engine.
4
On the rear side of the compressor, compressed air is directed into the engine's combustion chamber, where aviation fuel is added. The gases ignite.
5
The combustion gases are forced out of the engine's rear end, providing thrust. The gas also powers the engine's front turbine, which sucks in more air.
6
As the pilot increases power, the engine is fed more fuel, until thrust builds enough to let the plane take off. The engines can be kept running without the APU.