Nauka i Obrazovanie (Jan 2015)
A Study of the Mortar Firing Process Taking into Account the Propellant Gases Flow from the Tail Tube into the Space Behind the Shell
Abstract
Characteristics of inertial forces driving the arming process of fuse safety system mechanisms are determined by the parameters of shell motion in the barrel. The motion of the elements of fuse mechanisms is studied in a non-inertial coordinate system. Reasonable consideration of the reliability of unlocking the safety stages during the shot is obviously possible only when there is an adequate description of the inertia forces. The arming of inertial type safety mechanism should be completed before the moment when the level of the axial inertia force reaches a certain value rated to the maximum level (determined by the arming safety factor). Classical methods of internal ballistics do not identify the parameters of the part of the setback which is important for fuse arming.In the traditional method of calculating the process of mortar firing the pressure required to break the perforations in the tail stabilizer tube of the mortar shell performs the role of a "forcing pressure", and consequently the combustion of the main charge is supposed to begin instantaneously, i.e. it acts merely as an igniter for the additional charge. In reality (physically) there is some initial portion of the pressure rise and, correspondingly, the force of inertia (setback).An approach is proposed to the study of a shot from a mortar based on consideration of the temporal process of the propellant gases flow after breaking the stabilizer tube perforations in the space behind the mortar shell. It is assumed that the ignition of the additional charge and the movement of shell begin simultaneously. This approach allows one to identify the leading portion of the setback curve, allowing a more adequate description of fuse mechanisms functioning during arming. The periods of shot are considered consecutively in cases of absence and availability of the additional charge. Differential equations are reduced to dimensionless form simplifying the procedure of computer aided solution.A comparison of the calculation results for the 82-mm mortar shells on the basis of the proposed and conventional techniques is presented. It is shown that the integral parameters of the shot (the pressure on the muzzle and the initial velocity of the shell) are quite close to each other.
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