Clean configuration refers to the flight configuration of an airplane when its external equipment is positioned to minimize drag and thus maximize speed for a given power setting. For most airplanes, clean configuration means simply that the wing flaps and landing gear are retracted. On more complex airplanes, it also means that other devices on the wings (such as slats, spoilers, and leading edge flaps) are retracted. Clean configuration is used for normal cruising at altitude. During take-off and landing, when slower speeds are needed, an airplane will be in "dirty configuration," with landing gear, flaps, and other devices extended. This creates drag, but the trade-off is that the flaps and similar devices change the shape of the wing and produce more lift than would otherwise be generated at the lower airspeed. Fixed-wing aircraft is a term used to refer to what are more commonly known as aeroplanes in Commonwealth English (excluding Canada) or airplanes in North American English. ... Main and nosewheel undercarriage of a Qatar Airways Airbus A330 The undercarriage or landing gear is equipment which supports an aircraft when it is not flying. ...