Tour - how engines work

Thrust to propel an aircraft forward is based on the English mathematician and physicist Isaac Newton's third law of motion, which states that for every action, there is an equal and opposite reaction. For example, if you blow up a balloon, point it upwards and let it go, the high pressure air inside rushes down out of the open neck (action). In response to the volume of air thrusting down, the balloon is pushed up (reaction) until all the air is gone. When all the air has escaped (power has stopped) the balloon returns to the ground.

Two basic means are used to provide the thrust for an airplane in flight - propeller or jet propulsion. In a propeller driven airplane either a piston or a jet turboprop engine is used to drive a propeller round to push air backwards. The performance of a propeller reaches such a low level of efficiency that jet engines are used exclusively on aircraft that operate above 800 km/hr (about 500 mph).

The combustion chamber consists of a cylinder that is closed at one end and in which a close-fitting piston slides. The piston is attached to a crankshaft by a connecting rod. The crankshaft transforms the reciprocating (up and down) motion of the piston into rotary (round and round) motion. An engine may have from 1 to as many as 28 cylinders.

The fuel supply for a piston engine consists of a tank, a fuel pump, and a device for vaporizing or atomizing the liquid fuel which can either be a carburetor or, more recently, a fuel-injection system. The fuel enters the cylinder(s) where it vaporizes and is ignited by a spark. The resulting explosion forces the piston down which turns the crankshaft and the propeller which is fixed to it.

Car engines are normally started by means of an electric motor which turns the crankshaft until the engine "starts". Some aircraft use an explosive "starter", which uses the explosion of a blank cartridge to drive a turbine wheel that is coupled to the engine.

Nonreciprocating aircraft engines, all of which operate on the principle of jet propulsion, include the turbojet, the turboprop, the ramjet, and the rocket engine. The turboprop, turbojet, and turbofan engines, which are modifications of the turbojet engine, are gas turbine engines, in which the air that enters the intake of the engine (INDUCTION (suck)) is first compressed (COMPRESSION (squeeze)) in a compressor. Fuel is then added to burn the oxygen in the air (IGNITION (pop)), increasing the gas temperature and its volume. The high pressure gases are then partially expanded through a turbine which drives the compressor (and the propeller in a turboprop engine). The residual gas that is now at intermediate pressure is accelerated by expansion through a rear-facing nozzle (EXHAUST (blow)), to produce a high leaving velocity and, with it, the desired thrust. Turboprop engines are efficient for medium-sized planes at speeds up to about 480 to 640 km/hr (about 300 to 400 mph). At higher speeds, turbojet or turbofan engines perform better. The performance of a propeller reaches such a low level of efficiency that jet engines are used exclusively on aircraft that operate above 800 km/hr (about 500 mph).