Supersonic airfoils

At supersonic conditions, aircraft drag is originated due to: • Skin-friction drag due to shearing. • The wave drag due to the thickness (or volume) or zero-lift wave drag • Drag due to lift Therefore, the Drag coefficient on a supersonic airfoil is described by the following expression: CD= CD,friction+ CD,thickness+ CD,lift Experimental data allow us to reduce this expression to: CD= CD,O + KCL2 Where CDO is the sum of C(D,friction) and C D,thickness, and k for supersonic flow is a function of the Mach number. The drag due-to lift component is calculated using lift-analysis programs. The wing design and the lift-analysis programs are separate lifting-surfaces methods that solve the direct or inverse problem of design and lift analysis. ==Supersonic wing design==

Years of research and experience with the unusual conditions of supersonic flow have led to some interesting conclusions about airfoil design. Considering a rectangular wing, the pressure at a point P with coordinates (x,y) on the wing is defined only by the pressure disturbances originated at points within the upstream Mach cone emanating from point P. Whether a shock or expansion wave is generated at different locations along an airfoil depends on the local flow speed and direction along with the geometry of the airfoil. ==Summary==

Aerodynamic efficiency for supersonic aircraft increases with thin section airfoils with sharp leading and trailing edges. Swept wings where the leading edge is subsonic have the advantage of reducing the wave drag component at supersonic speeds; however experiments show that the theoretical benefits are not always attained due to separation of the flow over the surface of the wing; however this can be corrected with design factors. Double-Wedge and Bi-convex airfoils are the most common airfoils used for supersonic aircraft. ==See also==