PT Expansion Overview

Purpose

PT Expansion is used to refine the projectile loading characteristics based on measured data such as chamber pressure, muzzle velocity and action time. In a typical design process, one of the other Interior Ballistics modules would have been used previously to predict performance of a new design. PT Expansion helps make minor adjustments to the analytically determined projectile kinematics based on measured data. The outcome will be a more accurate model of projectile acceleration useful as input to other PRODAS modules like BALANS and also useful for projectile structural and functional analysis.

Analytical Approach

PT Expansion uses a single degree of freedom model of the projectile to predict muzzle velocity and action time based on the chamber pressure vs. time data and other parameters. Resistance pressure and base pressure are calculated at each time step and then used to calculate an instantaneous acceleration value. A fourth order Runge Kutta integrator is used to determine projectile velocity and position. When projectile travel equals the length of the gun barrel the integration is stopped and muzzle velocity and action time are reported.

PT Expansion is most useful once measured chamber pressure data is available. The shape of the experimental P-T curve often varies from the analytical prediction in subtle but important ways. PT Expansion allows the user to refine the prediction of projectile kinematics for use as inputs to other PRODAS analysis modules. When complete the analysis will be based on the experimental chamber pressure data and analytical predictions of projectile base pressure and resistance pressure that have been refined to match test results for muzzle veloctiy and/or action time.