An air vehicle selectively operable in a fixed-wing mode and a rotary-wing mode, the air vehicle comprising: a main body; a pair of opposing wing members (14a, 14b) extending laterally from the main body, a first one of the pair of wing members being rotatable relative to a second one of the pair of wing members such that a leading edge of the first one of the pair of wing members can be arranged to face an incident airflow in the fixed-wing mode and the rotary-wing mode in response to a control signal, the first one of the pair of wing members comprising: a core section substantially symmetrical about its longitudinal axis; and an upper surface comprising an upper apparatus, and a lower surface comprising a lower apparatus, each of the upper apparatus and the lower apparatus being for selectively altering the cross-sectional shape of the wing member, the upper apparatus and lower apparatus being movable from a rest position whereby the respective apparatus lies substantially flat against the core section to a deployed position whereby the respective apparatus protrudes outwardly away from the core section to define a curved aerofoil cross section; and a pair of propulsion devices (16a, 16b), a first one of which is mounted to the leading edge of the first one of the pair of wing members and a second one of which is mounted to the leading edge of the second one of the pair of wing members, wherein in the fixed-wing mode the pair of propulsion devices provide thrust in the same direction as each other, and in the rotary-wing mode the pair of propulsion devices provide thrust in opposite directions to each other; wherein in the fixed-wing mode the upper apparatus is controlled to be in the deployed position while the lower apparatus is controlled to be in the rest position, such that a longer airflow path is defined by the upper surface of the wing member than the lower surface, and wherein in the rotary-wing mode the first one of the pair of wing members is rotated through 180 degrees relative to the second one of the pair wing members such that its leading edge faces the incident airflow, and wherein the upper apparatus is controlled to be in the rest position and the lower apparatus is controlled to be in the deployed position, such that the airflow path defined by the lower surface of the first one of the pair of wing members is longer than that defined by the upper surface. a main body; a pair of opposing wing members (14a, 14b) extending laterally from the main body, a first one of the pair of wing members being rotatable relative to a second one of the pair of wing members such that a leading edge of the first one of the pair of wing members can be arranged to face an incident airflow in the fixed-wing mode and the rotary-wing mode in response to a control signal, the first one of the pair of wing members comprising: a core section substantially symmetrical about its longitudinal axis; and an upper surface comprising an upper apparatus, and a lower surface comprising a lower apparatus, each of the upper apparatus and the lower apparatus being for selectively altering the cross-sectional shape of the wing member, the upper apparatus and lower apparatus being movable from a rest position whereby the respective apparatus lies substantially flat against the core section to a deployed position whereby the respective apparatus protrudes outwardly away from the core section to define a curved aerofoil cross section; and a core section substantially symmetrical about its longitudinal axis; and an upper surface comprising an upper apparatus, and a lower surface comprising a lower apparatus, each of the upper apparatus and the lower apparatus being for selectively altering the cross-sectional shape of the wing member, the upper apparatus and lower apparatus being movable from a rest position whereby the respective apparatus lies substantially flat against the core section to a deployed position whereby the respective apparatus protrudes outwardly away from the core section to define a curved aerofoil cross section; and a pair of propulsion devices (16a, 16b), a first one of which is mounted to the leading edge of the first one of the pair of wing members and a second one of which is mounted to the leading edge of the second one of the pair of wing members, wherein in the fixed-wing mode the pair of propulsion devices provide thrust in the same direction as each other, and in the rotary-wing mode the pair of propulsion devices provide thrust in opposite directions to each other; wherein in the fixed-wing mode the upper apparatus is controlled to be in the deployed position while the lower apparatus is controlled to be in the rest position, such that a longer airflow path is defined by the upper surface of the wing member than the lower surface, and wherein in the rotary-wing mode the first one of the pair of wing members is rotated through 180 degrees relative to the second one of the pair wing members such that its leading edge faces the incident airflow, and wherein the upper apparatus is controlled to be in the rest position and the lower apparatus is controlled to be in the deployed position, such that the airflow path defined by the lower surface of the first one of the pair of wing members is longer than that defined by the upper surface.