[custom_adv] An aircraft is a machine that is able to fly by gaining support from the air. It counters the force of gravity by using either static lift or by using the dynamic lift of an airfoil, or in a few cases the downward thrust from jet engines. Common examples of aircraft include airplanes, helicopters, airships (including blimps), gliders, and hot air balloons. [custom_adv] Common examples of aircraft include airplanes, helicopters, airships (including blimps), gliders, and hot air balloons. [custom_adv] The human activity that surrounds aircraft is called aviation. The science of aviation, including designing and building aircraft, is called aeronautics. [custom_adv] Crewed aircraft are flown by an onboard pilot, but unmanned aerial vehicles may be remotely controlled or self-controlled by onboard computers. [custom_adv] Aircraft may be classified by different criteria, such as lift type, aircraft propulsion, usage and others. Flying model craft and stories of manned flight go back many centuries, however the first manned ascent – and safe descent – in modern times took place by larger hot-air balloons developed in the 18th century. [custom_adv] Aerostats use buoyancy to float in the air in much the same way that ships float on the water. They are characterized by one or more large gasbags or canopies, filled with a relatively low-density gas such as helium, hydrogen, or hot air, which is less dense than the surrounding air. [custom_adv] When the weight of this is added to the weight of the aircraft structure, it adds up to the same weight as the air that the craft displaces. [custom_adv] Small hot-air balloons called sky lanterns were first invented in ancient China prior to the 3rd century BC and used primarily in cultural celebrations, and were only the second type of aircraft to fly, the first being kites which were first invented in ancient China over two thousand years ago (see Han Dynasty).
