Frost control

Apparatus for the frost control of agricultural and horticultural crops, said apparatus comprising a tower supporting at its upper end a radial flow fan, means to drive said fan to rotate about a vertical axis to draw air axially into the fan from above the inversion layer and discharge this air radially over the crop, said fan including a plurality of peripheral aerofoil shaped vertical blades mounted on an annular ring at the periphery of the fan, each blade being curved with a convex surface thereof facing in the direction of rotation and having a leading edge and a trailing edge, said convex surface including a straight portion adjacent the leading edge, a curved central portion and a straight portion adjacent the trailing edge, the cord line of the said blades being between 15.degree. and 25.degree. from a radial line of the fan, the point of highest position from the cord line being toward the leading edge of the blade, the leading edge being innermost and the trailing edge being at the periphery of the fan whereby on rotation the air flows axially into the fan interior intermediate said blades and then curves to have a generally radial component before being encountered by the blades.