Impact of Airfoil Profile on the Supersonic Aerodynamics of Delta Wings

A theoretical study of the effect of airfoil profile on the aerodynamics of delta wings at supersonic speeds has been conducted using a full-potential solution method. Analysis was performed for wings of aspect ratio A of 0.5 to 3.0 over a range of values of the leading-edge sweep-parameter Afi from 0.5 to 4.0 for diamond, circular arc, and NACA modified 4-digit airfoils. The primary intent of the study was to establish the "real flow" aerodynamics of delta wings for various airfoil shapes. A set of zero-lift wave drag curves for delta wings, which can be used to account for nonlinear aerodynamics in the preliminary design process, has been defined. The predicted zero-lift wave drag differed substantially from the linear theory predictions for all airfoils. The analysis of the modified 4-digit airfoil series showed that the zero-lift wave drag is independent of airfoil leadingedge radius. The linear theory dependence parameter (CDfW varies with thickness 7* and aspect ratio A} was verified for thin wings. A detailed study of the surface pressures revealed that for all airfoil geometries analyzed, 90% of the wave drag was produced at the wing apex and trailing edge. The lifting characteristics were also evaluated for the various airfoil profiles, and the results indicated that for ft cotA values greater than 0.6, the liftcurve slope is less than that predicted by linear theory. Nonlinear analysis also showed that increasing the airfoil bluntness increased the wing's lift-curve slope and decreased its drag-due-to-lift characteristics. For blunt leading-edge airfoils, increasing the airfoil thickness and wing aspect ratio and decreasing the maximum airfoil thickness position reduced the drag-due-to-lift parameter. The drag-due-to-lift characteristics were also found to be sensitive to Mach number and lift coefficient in addition to the known dependence upon aspect ratio and the leading-edge-sweep parameter that is predicted by linear theory. b c