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International Journal of Energetic Materials and Chemical Propulsion
ESCI SJR: 0.28 SNIP: 0.421 CiteScore™: 0.9

ISSN Druckformat: 2150-766X
ISSN Online: 2150-7678

International Journal of Energetic Materials and Chemical Propulsion

DOI: 10.1615/IntJEnergeticMaterialsChemProp.v1.i1-6.100
pages 125-142

A Model of the Axial Drag Coefficient for Base Bleed Projectiles

Nils Bartelson
Furusundsgatan 12, S-11 537 Stockholm, Sweden
Sven Linde
Studsvik AB, Studsvik Data S- 61182 Nyköping, Sweden

ABSTRAKT

The axial drag on a projectile is usually expressed in terms of the axial drag coefficient CD. For a conventional projectile CD 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 CD. 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 CD'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.


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