PROPULSION SYSTEMS

In aerospace, thrusters are used to generate a thrust or traction force required to move aircraft. Both thrust and traction can be achieved by projecting a fluid mass in the direction of motion, but in the opposite direction.
The term 'jet engine', therefore, could rightly refer not only to jet engines, but also to propeller engines.
Aero engines are subdivided into 'exoreactors' and 'endoreactors'.
While exoreactors use outside air as an oxidiser, endoreactors bring both fuel and oxidiser into the combustion process.
The following propellers belong to the group of exoreactors:
- Motor propeller: propeller driven by a piston engine.
- Turbojet: "gas turbine" essentially consisting of the compressor, combustion chamber and turbine. A diffuser and exhaust nozzle are also usually associated with these elements. This type of engine is also known as a 'turbojet' and can also be 'dual-flow'.
- Turbo propeller: propeller driven by gas turbine.
- Turbofan: 'fan' driven by gas turbine and mostly known as a 'fan'. A variant of the turbofan propeller is the 'Propfan' propeller, whose fan is located on the outside of the engine 'nacelle'.
- Turbo-shaft: helicopter propeller driven by a gas turbine.
- Propeller: consisting of the diffuser, combustion chamber and exhaust nozzle. This type of propeller is also known as a 'statorjet' or 'ramjet' and is used to reach high supersonic speeds, but, since the air is 'self-compressed' due to the speed of the vehicle itself, this type of propeller is not only unable to operate 'at a fixed point' (i.e. stationary with respect to air speed) but also performs poorly at low speeds. For this reason, the autoreactor must first be brought to supersonic speed by some other type of thruster.
Variants of the autoreactor are:
- the Scramjet (supersonic combustion ramjet), inside which the air flow always remains at supersonic speed, enabling this type of propeller to operate efficiently at extremely high supersonic speeds;
- the Autoturboreactor or Turbojet, combines the characteristics of the statorjet with those of the turbojet. This type of thruster was in fact designed to overcome the impossibility of fixed-point start-up.
- Pulsoreactor: also known as "pulsjet", this is a propeller in which combustion takes place intermittently, providing the thrust in pulses. Unlike the autoreactor, it is capable of providing thrust from a standstill.
Endoreactors are also known as 'rockets' and may be liquid, solid or mixed propellant. Sometimes such thrusters make use of 'cryotechnical' technologies, because they can use propellants with very low temperatures.