In order for a plane to fly it needs thrust, this is attained by the heart of the aircraft that is the gas turbine jet engine. a small plane can be powered by a normal gasoline or diesel 4 stroke engine as described in my engine article but a large aircraft is generally powered by a jet engine. Depending on the make or intended use of the plane, a jet engine is design so therefore there are four types of jet engine as shown below :-
- turbo jet – It is composed of an inlet, a compressor, a combustion chamber, a turbine and a nozzle. They are generally of two types axial and centrifugal turbojets. The compressor compresses the air and sends it at high speed to combustion chamber. fuel is than injected and ignited. Expanding gas then drives a turbine which is connected to the front compressor hence keeping the engine moving while exhaust gases provide thrust to the aircraft.
- Turbo fan – in this case the inlet air is divided into two streams i.e one stream into the engine core and the other by-passing the engine core. this air is responsible for increased thrust and cooling the engine.the term by-pass ratio is the ratio of mass air flow passing through the fan to the mass airflow passing through the engine. the engine part works similar to the turbo jet. the low pressure compressor and the low pressure turbine combine to form the low spool while the high pressure compressor and high pressure turbine form the high spool. This low and high spool are driven by a two shafts one inside the other hence enhancing more thrust.
- turbo prop – This is an engine that drives a propeller via a reduction gear. Just like in turbo jet exhaust gases drive a turbine connected to a shaft that drives all the way front to the gearbox. this gearbox enables better fuel consumption and better performance at low speeds mostly in take off and landing. The rest of the engine works similar to turbo jet.
- Turbo shaft – in this the energy created by expanding gases is used to drive a power turbine which creates rotary motion that drives for example a rotor blade i.e in a helicopter. They are also used as A.P.U i.e auxiliary power units in huge aircraft. The rest of the engine works similar to turbo jets.
in jets rear heat is added at a chamber past the turbine where fuel is added for a second combustion. This increases thrust. incase one wants to reduce speed thrust reversers, airbrakes & spoilers are used. as shown in my other article