Generally speaking, if an aircraft requires a landing strip it is considered to be a fixed wing airplane. The wings are permanently attached to the fuselage of the plane and do not provide power for thrust. Fixed wing aircraft can range in size from the smallest experimental stunt plane to the largest commercial jet or military bomber. The one thing all of these planes have in common is a wing and rudder assembly combined with a separate power source such as a jet engine or propeller. Aircraft such as helicopters and hovercraft are not considered fixed wing, because they use the power of rotors to achieve both thrust and lift.
To fully understand fixed wing aircraft, it may help to travel back to the earliest days of powered aviation. The Wright brothers created the first plane which utilized the fixed wing design. A standard plane wing has a curved upper surface and a flat lower surface. When the propeller or jet engine pushes the entire airplane forward, the air strikes the front edge of the wing with substantial pressure. The wing is fixed in place very securely, so the air current can only go in two directions, above or below. As the air flows over the curved top of the wing, it moves faster than the air flowing under the bottom of the wing. The result is a phenomenon called lift. The plane can be angled to take advantage of this lift, making powered flight possible.
The main difficulty with fixed wing technology lies with the engineering of the wings. In order to provide maximum lift for larger payloads, the wingspan of a plane must be increased exponentially. Supporting the sheer weight and length of these larger wings means using advanced welding techniques and internal support structures. Fixed wing aircraft also suffer from a lack of mobility, unless they are configured for stunt flying. This is one reason the government assigned fixed wing aircraft responsibility to the Air Force and helicopters to the Army. Fighter jets and bombers use fixed wing technology to the fullest, but helicopters provide greater mobility.