ESDU TM 4:1972

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.