Aircraft

An aircraft is any machine capable of atmospheric flight.

Categories and sorting
Aircraft fall into two broad categories:

Heavier than air
Heavier than air aerodynes, including autogiros, helicopters and variants, and conventional fixed-wing aircraft. Fixed-wing aircraft generally use an internal-combustion engine in the form of a piston engine or a turbine engine, to supply thrust that moves the craft forward through the air. The movement of air over the airfoil produces lift that causes the aircraft to fly. Exceptions are gliders which have no engines and gain their thrust, initially, from winches or tugs and then from gravity and thermal currents. For a glider to maintain its forward speed it must descend in relation to the air. Helicopters and autogiros use a rotating rotor to provide lift; helicopters also use the rotor to provide thrust. The short form of VTOL is applied to aircraft other than helicopters that can take off or land vertically. STOL is Short Take Off and Landing.

Lighter than air

A hot air balloon takes off from Royal Victoria Park, Bath, EnglandLighter than air aerostats: hot air balloons and airships. Aerostats use resilience to float in the air in much the same manner as ships float on the water. In particular, these aircraft use a comparatively low density gas such as helium, hydrogen or heated air, to displace the air around the craft. The distinction between a balloon and an airship is that an airship has some means of controlling both its forward motion and steering itself, while balloons are carried along with the air stream.