The wings of a fixed wing aircraft provide the necessary lift for take-off and cruise flight. Wing geometry affects every aspect of an aircraft’s flight. The wing area will usually be dictated by aircraft performance requirements (e.g. field length) but the shape of the planform and other geometry may be influenced by wing layout factors.[29] The wing can be mounted to the fuselage in high, low and middle positions. The wing design depends on many parameters such as selection of aspect ratio, taper ratio, sweepback angle, thickness ratio, section profile, washout and dihedral.[30] The cross-sectional shape of the wing is its airfoil.[31] The construction of the wing starts with the rib which defines the airfoil shape. Ribs can be made of wood, metal, plastic or even composites.[32]