An airplane is a heavier-than-air machine that is kept aloft by the forces on its wings. It is thrust forward by a propeller or other means of propulsion, such as a jet or rocket. Common types of airplanes are airliners, large planes usually used to transport passengers; military planes; and general-aviation aircraft, which cover all airplanes that are not airliners or military aircraft. They generally are smaller than airliners and can transport people or cargo or perform a wide variety of specialized functions such as crop-dusting, flight training, and recreational flying.
[ larger image]