On lifting surfaces supporting one or more plane shock waves

Abstract

Stream surfaces from the flow through a plane shock wave are used as compression surfaces to obtain high lift to drag ratios. The inviscid performance of these compression surfaces is known exactly, and at given values of M∞ and CL, higher values of L/D can be achieved than the two-dimensional wedge value. The improvement that can be obtained over this value depends on the similarity parameter ... and is large when this parameter is small. Two such compression surfaces can be combined into a W-Nonweiler shape, which gives in effect a central body below a swept wing. The viscous drag tends to be high, because the shapes have a large ratio of wetted area to plan area. For hypersonic speeds (M > 5) where the inviscid improvement over a two-dimensional wedge is small, the high viscous drag puts the W-wings at a disadvantage compared with fiat-bottomed configurations (though not as compared with caret wings). At high supersonic speeds (3 < M < 5) the inviscid improvement is more marked and a gain in performance, including viscosity, over that of the two-dimensional wedge, and hence over that of fiat-bottomed shapes can be shown. Such conclusions do not take into account the relative problems of converting idealised shapes into practical aircraft configurations. For best performance the trailing edge of the W-wing is swept and its pressure drag and viscous drag are approximately equal.