A tip structure may be arranged for example on a rotor blade (12) of a HAWT (10). The tip structure comprises a pressure side structure (50) arranged on a pressure side (43) of the blade, and a suction side structure (60) arranged on a suction side (44) of the blade (12). The pressure side and suction side structures (50, 60) have different pitch angles (αP, αS) so that the chord (CP2) of the pressure side structure (50) extends forwardly in the direction of motion (D) and relatively more radially outwardly away from the blade root, or less radially inwardly towards the blade root, than the chord (CS2) of the suction side structure (60), defining a relative twist angle (αT) between the two structures (50, 60).