NACA-RM-A53I17

Abstract

INTRODUCTION <br>The maneuverability requirements for high-speed, high-altitude missiles have led to the need for knowledge of the aerodynamics of bodies at large angles of attack. Studies of the angle-of-attack characteristics of a number of bodies have revealed that the flow on the lee side of these bodies is characterized by a vortex system. It has been shown in reference 1 that as the angle of attack is increased the vortex system changes from a steady symmetric pair to a steady asymmetric configuration of two or more vortices and, finally, at large angles of attack, to an unsteady asymmetric arrangement. It is evident that these vortices can affect the stability of body-tail configurations if the vortex paths pass near the tail surfaces. If this vortex flow is steady, there should be no difficulty in the calculation of the induced effects on the tail surfaces, provided that the strengths and positions of the vortices are known. However, if the wake vortex flow is unsteady, then large and erratic fluctuations of the forces on the tail surfaces such as those discussed in references 2, 3, and 4 may occur, and it may be impossible to control the roll attitude of a missile subjected to this dynamic condition. <br>The emphasis of the present investigation has been placed upon a study of factors which affect the onset of unsteady wake flow since greater control difficulties are associated with the unsteady vortex wake than with either of the other wake configurations. It is realized that for full-scale vehicles in flight there exists the possibility of coupling between the shedding of the wake vortices and the movement of the aircraft. Hence, the results of a wind-tunnel investigation using a model, the movement of which is restrained by its mounting system, may not be directly applicable to full-scale vehicles. However, the effects on the wake vortex configuration of certain variables such as model geometry and Reynolds number may indicate significant trends. It has been previously shown in references 2 and 3 that both the vortex configuration in the lee of a body and the magnitude of the rolling moment accompanying an asymmetry in the vortex pattern were altered by changing the nose shape from conical to ogival. In order to investigate further the effects on the wake vortex pattern of changing the nose shape as well as the effects of other variables, such as after body shape, separation-fixing devices, and Reynolds number, the present investigation was undertaken.