GB605765A - Improvements in or relating to aerofoil sections for low reynolds numbers - Google Patents

Abstract

605,765. Aerofoils. WALKER, N. K., and ANNENBERG, R. H. W. Jan. 4, 1946, No. 365. [Classes 4 and 114] [Also in Group XXVI] The upper surface of an aerofoil for use at low Reynold's Numbers is so shaped that the maximum ordinate is located between the midchord point and the trailing edge, and the profile does not substantially change in direction from the leading edge to the maximum ordinate and thus defines with respect to the chord-line a protuberance or hump in the rear section, merging gradually into the aerofoil section forward of, and merging sharply into the section aft of, the point of maximum depth, leaving the trailing edge sharp. Fig. 2 shows an R.A.F.32 aerofoil modified by the addition of a hump 7 in the rear portion between 60 and 90 per cent of the chord, giving maximum thickness and ordinate at about 50 and 60 per cent respectively of the chord. This form of section with a shallow cavity 13 towards the trailing edge is intended for the wings and control surfaces of light aircraft, sailplanes, gliders and rotating wing aircraft, but for fan and slow speed propeller blades the undersurface is made flat. The leading edge 15 preferably has a radius equal to 2 per cent of the chord, but in the case of very thin sections with a thickness/chord ratio of less than 6 per cent a radius of at least 4 per cent of the chord may be used to camber the portion immediately aft of the leading edge. Such sections may be used for the blades of axial flow compressors or turbines. In the case of hydrofoils and steering surfaces the section is symmetrical.