An aerofoil (40) comprises a leading edge (41) and a trailing edge (42) which define a mean chord length (C), and the aerofoil (40) having an inner or root end adapted for attachment to an aircraft, and an outer end which includes a tip (43) which is adapted in use to divide the airflow into two generally equal vortices (V1, V2) one (V1) being an inner vortex and the other (V2) being an outer vortex the inner vortex (V1) being arranged to trail from an outer edge (46a) of a forward region (44) of the tip (43) and pass over a rear region (45) of the tip (43).
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