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Published: 2000

Total Pages: 0

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The 120-mm M831A1 projectile is a low-cost training projectile used by U.S. armor troops. For the last several years, program managers have received feedback from the users that in some cases, M831A1 impact performance did not appear consistent with the current M831A1 computer correction factor. Based on this information, a low-scale but in-depth experimental analysis of the projectile was conducted to assess its aero-ballistic qualities and hopefully identify any potential issues that could affect accuracy performance. The work was conducted by the U.S. Army Research Laboratory at the Transonic Experimental Facility. Although the projectile has undergone fairly extensive target impact dispersion (TID), radar, and wind tunnel testing, this study presents the first spark range data and detailed free-flight aero-ballistic analysis for the M831A1. Roll data were measured via roll pins for the computation of roll-related coefficients. All rounds exhibited very little roll over the measured trajectory, mostly because of a very small roll moment. Yaw magnitudes displayed variability, and several shots had at least moderate levels. The source of the yaw levels imparted to the projectiles was the launch dynamics, and a detailed study of in-bore dynamics is in progress. Most shots exhibited a 'stepping', motion in plots of total yaw versus range. This phenomenon is the result of trim, which is believed to be caused by an aerodynamic asymmetry. A source of the trim has not been isolated. Accurate free-flight drag and pitching moment coefficients were computed on the basis of the measured trajectories. Pitch-damping characteristics were marginal. Although the M831A1 currently performs within acceptable TID standards, further experimental work is recommended, as well as a study of possible stabilizer design modifications.