The cooling fan has a rotary base plate (10) with spaced fan blades (15) attached to its outer periphery via fixing bolts (21), the angle of each blade controlled by a setting mechanism (20). The fan blades rotate about the fixing bolts in dependence on the centrifugal force, so that the rate of increase in the quantity of air delivered by the fan decreases with increasing fan revs, within a higher rev range. Outside the high velocity rev range, the fan blades are rotated about the fixing bolts via the setting mechanisms.
