要約

The axial drag on a projectile is usually expressed in terms of the axial drag coefficient C_D. For a conventional projectile C_D is often regarded as a function of the Mach number only. For base bleed projectiles, in their bleed phase, ballistic range data indicate that some factor beside the Mach number has a significant influence on C_D. It is reasonable to expect that the ambient atmospheric pressure is one such factor.
We attempt to relate, in an empirical way, the drag of a base bleed projectile to the geometry of its trajectory and the state of the atmosphere. The relations are not derived from physical principles - our approach is descriptive and statistical. The purpose is to summarize observations of flight performance in a way that permits us to predict a trajectory from its initial conditions and from a picture of the atmosphere.
We propose a functional relation between the Mach number, the ambient atmospheric pressure and the drag coefficient. Its parameters are determined by a regression procedure based on time-of-flight recordings from a Doppler radar instrument. The model proves capable of reproducing observed C_D's along trajectories of widely differing shapes. As a side effect some light is thrown upon the extinction of the bleed charge. It turns out to be a more drawn-out process than is often assumed. We report on a verification of the model and also touch upon the problems of modelling the transition from active to inert base bleed.