Lift Airfoils Close to the Airfoils in a Flow with the Maximum “Critical” Mach Numbers

Abstract

The lift airfoils close to the airfoils optimal with respect to the critical Mach numbers М* of two-dimensional bodies optimal with respect to М* are constructed using the direct method. Their almost zero wave drag coefficients сх remain the same not only at the free-stream Mach numbers М0 which are lower than М* but also at М0 perceptibly higher than М*. These new lift airfoils differ from the supercritical lift airfoils whose сх grow extremely rapidly when М0 becomes higher than the designed values. At identical thicknesses and М0 = М* the supercritical lift airfoils implement the greater lift coefficients су. However, due to the difference in the behavior of сх at М0 which are higher than the designed ones, the lift-drag ratio of the supercritical airfoils can become lower for the ratio of су not to сх, but even to the coefficient of total drag.