Aerodynamic characteristics of rectangular wings of small aspect ratio

Abstract

The results of a programme of low-speed wind-tunnel measurements of the lift, drag and pitching moment on a number of model wings, each fitted with a full-span plain flap, and of a much more limited programme of hinge-moment measurements are presented. The wings differed from one another in profile but all were of rectangular plan-form and of aspect ratio 1.25. The flap chord was varied between 0.125 and 0.500 of the overall chord. Three of the profiles investigated were conventional in having zero trailing-edge thickness but the other three had large trailing-edge thickness, a feature thought to be of interest in connection with the design of torpedo fins. Theoretical values of the lift slopes, hinge moments and positions of the centre of pressure were calculated from Lawrence's theory for thin rectangular wings of various aspect ratios in inviscid flow and the results are presented in tabular and graphical form. Predicted values, combining aspect-ratio effects with largely empirical allowances for thickness and boundary-layer effects, are checked against the measured values of the required aerodynamic characteristics of the 'conventional' profiles and the agreement is fairly satisfactory. Although the aspect ratio was small, the induced drag associated with incidence and flap deflection was found to be well represented for all profiles by the usual expression derived from consideration of the elliptically loaded lifting line. A limited number of measurements suggested that the size of the gap between the control surface and the main part of the wing exercises little: influence on the lift slopes, drag and c.p. positions if the gap width is less than 0.5 per cent of the overall chord.