Aircraft are vehicles that fly in the air, often powered by mechanical power. They may be manned by human pilots or unmanned. Some aircraft are small, such as toys and recreational items, while others are large, such as the Boeing 747.
The basic principle behind an aircraft is to use the lift of air to counter the force of gravity, either by static or dynamic lift or in a few cases, the downward thrust from jet engines. In the latter case, a wing may have to be extended from its base in order to create enough room for an engine.
Lighter-than-air types include aerodyne (airplanes), balloons, dirigibles, and aerostats such as airships. These all have wings, although the distinction between an aerodyne and an aerostat depends on how the wings are supported.
Aerodynetypes have one or more fixed wings, typically a biplane or monoplane. They also have a fuselage, and often a tail for stability and control. They have a central engine or rotary engines, although in some designs they use a rotor system.
Blimps
Non-rigid dirigibles, such as blimps, are characterized by a moderately aerodynamic gasbag with stabilizing fins at the back. They were used to carry cargo and passengers, particularly during World War II.
Heavier-than-airtypes, such as planes, helicopters, and autogyros, have one or more fixed wings. They have a fuselage, and often rotorcraft and autogyros may have a central engine or rotary engines.
Poweredtypes have an onboard source of mechanical power, typically a jet engine or some other type of power plant, but rubber and manpower have also been used. They have propellers, which are mounted in tractor configuration in front of the power source in most designs, and in pusher or contra-rotating configuration for some designs.
The main power source on a powered aircraft is the engine, which typically consists of lightweight reciprocating engines or gas turbines, though some aircraft have other sources of mechanical energy, such as hydrogen. These power sources are stored in tanks, often in the wings.
Lift, the force of airflow that opposes the force of gravity, is created by the pressure difference between the top and bottom parts of an aircraft’s wing. The air atop the wing moves faster than that beneath it due to what is called equal transit time, where two parcels of air, separated at the leading edge of each wing, must join up simultaneously at the trailing edge.
This can explain why a flying wing reaches a higher velocity than a non-flying wing, but there are many other explanations. The most common one is that the air atop the wing has to travel farther than that beneath it in a given amount of time.
Other explanations are that airfoils must be shaped in such a way that they cause the oncoming air to be forced up and away from them, or that they must be curved so as to bend the airflow around them. These ideas are largely theoretical, but some of them do exist in reality.
