A wing member (14b) for an air vehicle (10), said wing member comprising a core section (20) defining its longitudinal axis and having upper and lower surfaces, at least one of said surfaces comprising apparatus (22) selectively configurable between at least two positions, wherein in a fully extended position, at least portions of said apparatus extend outwardly from said respective surface so as to increase the effective cross-sectional area of said wing member and define an effective aerofoil in respect thereof.