An axial fan adapted to be rotatably mounted in a cylindrical duct ring (3) has a plurality of fan blades (2) with peripheral blade tips (4) describing, in operation, a circular path adjacent the duct ring (3) The blade tips each have a leading edge (6) in the axial direction, a trailing edge (9) and a tip outer surface, at least one of the edges and/or the outer surface having a non-uniform profile for influencing the flow of air over the said tip outer surface.
