An Investigation of a Lifting 10-percent-thick Symmetrical Double-wedge Airfoil at Mach Number up to 1

Abstract : Pressure measurements on the surface of a two-dimensional symmetrical double-wedge airfoil have been obtained from tests in the Langley 4- by 19-inch semiopen tunnel at lifting conditions and at Mach numbers up to 1. The object of this investigation was to obtain normal-force, pressure-drag, and pitching-moment data and to compare them with available experimental and theoretical results. The nonlifting results are in good agreement with potential-flow theory at a Mach number of about 0.5 and in fair agreement with the theoretical results of Guderley and Yoshihara at a Mach number of 1 and with the transonic small-disturbance theories of other investigators for Mach numbers from 0.85 to 1.0. Below a reduced Mach number Xio of approximately -1.0, the pressure-drag coefficient computed on the basis of the transonic theories and the drag coefficient measured in the present investigation are of opposite sign. The present experimental data and the theoretical incompressible results extended to high-subsonic speeds both indicate a thrust for the forebody. The application of transonic approximations, therefore, appears unjustified for similarity parameters less than approximately -1.0 in the subsonic portion of the transonic range. At lifting conditions, for Mach numbers up to about 0.6, the present results are in good agreement with the closed-tunnel data of Bartlett and Peterson and with low-speed theoretical data extended to a Mach number of 0.6.