A fluid flow control device for an aerofoil comprises an aerofoil-tip body of aerofoil shape, coupling apparatus adapted to couple one end of the body to an aerofoil, and a passive tip blowing assembly. The passive tip blowing assembly is provided at the other end of the aerofoil-tip and comprises a housing defining a fluid chamber and a vane of aerofoil shape. The fluid chamber extends along part of the chord-length of the body and has a fluid inlet and a fluid outlet. The vane is arranged along the chord of the aerofoil-tip, with its leading edge at the inlet and its trailing edge at the outlet. The aerofoil section of the aerofoil-tip has a higher camber than that of the aerofoil, which turns fluid flow across the low pressure side of the aerofoil towards the aerofoil-tip, so that the fluid flow mirrors the fluid flow across the high pressure side of the aerofoil.