Experiments at M = 1.41 on elliptic cones with supersonic leading edges

Abstract

Tests have been made at a Mach number of 1.41 on six elliptic cones forming two families of models. In the first, the vertex angle in the plane of the major axes of the elliptic cross-sections was maintained constant at 60 deg and the ratio between the minor and major axes varied; in the second family, the minor axis was constant and the vertex angle had values of 30 deg, 60 deg and 90 deg. Two cones from the first family were pressure-plotted at incidences up to 15 deg, the resulting pressure distributions being integrated to give the lift and pressure drag arising from the curved surfaces of the cones. Except for one of the pressure-plotting models, lift, drag and centre-of-pressure position were measured for all models on a strain-gauge balance. For the one cone on which a comparison was possible, good agreement was obtained for the lift and drag derived from the two methods. The distribution of pressure on the two pressure-plotting cones was found to be approximately conical in form (i.e., constant along the cone generators) and at 0 deg, good agreement with theory was obtained. At incidence, the agreement was worse and deteriorated when, at the higher incidences, transonic-type shock waves appeared on the upper surfaces of the cones. The'se shock waves which lay along a cone generator moved inboard with increase in incidence, and vortices, formed from flow separating from near the leading edges, also appeared, with a consequent modification of the upper-surface pressure distribution. These transonic-type shock waves were observed by using optical systems of schlieren or shadowgraph type, but with the light beam passing obliquely through the tunnel so that it was approximately parallel to the shock front; the separation vortices were detected by observing the motion of an oil film on the surface of the models. Good agreement was obtained between linear (flat-plate) theory and experiment for the lift of the family of cones having a 60 deg vertex angle; there is only a small effect on the lift-curve slope due to increasing the cone thickness (i.e., the minor axis of this family). The surface shock waves and separation vortices were responsible for a change in the rate at which the drag of the cone family increased with the lift. The comparatively slender cone of the other family had a lift curve which was markedly non-linear at the higher incidences and this effect was attributed to the presence of separation vortices. The inclination of the cone-likeshock originating at the vertices of the models and also the distribution of pressure over the bases of the cones were measured.