INTRODUCTION

In Reference 10 the Lighthill nominally-exact method for incompressible inviscid flow has been used to design a family of low-speed aerofoils having low-drag characteristics by virtue of the attainment of a roof-top pressure distribution on the upper and lower surfaces at the extremes of a specified incidence range. The method provides for independent modification of the leading-edge radius and trailing-edge shape. An appendix to the report contains details of the geometric and aerodynamic characteristics of 240 symmetrical and 720 cambered aerofoils derived by the method.

In view of the availability of such a large variety of aerofoils (see Tables III and IV) and their associated aerodynamic characteristics in incompressible inviscid flow it seemed pertinent to attempt to correlate the data with a view a) to check and extend existing correlations in the ESDU Aerodynamics Sub-series of Data Items and b) to develop correlations for parameters not previously covered. The particular aerodynamic parameters chosen for study were lift-curve slope, zero-lift incidence, zero-lift pitching moment coefficient and chordwise position of the aerodynamic centre.

Since the aerofoils derived in Reference 10 were all, members of a single family there was a danger that correlations using these as a basis would be inapplicable to aerofoils not in that family. This was felt to be of particular significance with regard to those correlations which were camber-dependent, since there are only two basic camber-line shapes for the whole range of aerofoils in Reference 10. These are the simple-arc and reflex types and they are illustrated in Section 2.4. With these points in mind, data for a number of additional aerofoils (see Tables I and II) obtained from other sources3 ,11 Were used in ,the correlations. The- data from Reference  all relate to symmetrical aerofoils and were obtained using either exact or accurate approximate methods. The data referred to as Reference 11 were derived, using the nominally-exact method of Reference 9, for a range of aerofoils, both symmetrical and cambered; among these were members of the NACA 6 and 6A series5 and the RAE 100 to 104 and 2800 series12 The camber-line shapes for these additional aerofoils were mainly of the simple-arc type but included examples of the reflex and "double-hump"^* types.

* See sketch on Figure 4a.