Notes on the transonic movement of wing aerodynamic centre

Abstract

These notes aim at providing a framework to display what is known of the backward movement of the aerodynamic centre of wing shapes likely to be used for transonic operation, as the flow progresses from incompressible through subsonic to supersonic, the shock-wave regime being ignored. A new geometrical parameter (see Figs. 1, 2) is taken as the main variable because (a) it gives a neat classification of the various wing shapes, (b) it expresses the results of supersonic theory in a simple form, (c) it simplifies the subsonic analysis by making direct use of the similarity law for three-dimensional compressible flow, and so (d) it is possible to display on one diagram most of the theoretical and experimental data at present available. On the supersonic side, where very little experimental data is known in this country, the analysis is based on the conical solution by Puckett and Stewart for pointed tips; this has been extended on a simple but questionable assumption to cover blunt tips. On the subsonic side the laborious approximate theoretical methods have not yet yielded much data that is both systematic and reliable, and though model data is accumulating it inevitably lacks cohesion except in the case of delta wings. The work of R. T. Jones on the aerodynamic centre of shapes so slender that it is independent of Mach number is linked up, so far as it goes, with the supersonic data, and should be extended. When the existing fragments of the subject are assembled within this framework as in Table 1 and Fig. 13, the problem begins to get into focus and certain general trends are broadly discernible, but no very definite conclusions can be drawn except for pointed tips in general and delta wings in particular. These summaries do however show what will be the most profitable lines of research to illuminate quickly the whole subject, and recommendations are made to this end (see conclusions, section 9).