Theoretical Underpinnings of Spin-Balance Machines for Measuring Mass Imbalance of Projectiles and Determining Its Effect on the Trajectory Deflection
Technical Report,01 Jun 2017,31 Dec 2019
CCDC Army Research Laboratory Aberdeen Proving Ground United States
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Spin balancing is used to determine the mass imbalance of rotating machinery parts. Recently, the US Army Combat Capabilities Development Command Army Research Laboratory commissioned the development and construction of a spin-balance machine for measuring the mass imbalance of projectiles. Mass imbalance is one source of error that contributes to increased target impact dispersion and reduced hit probability. Such a machine would be useful in assessing and quantifying the mass imbalance of as-manufactured projectiles or recovered postlaunch projectiles. The current report presents the theory behind the operation of these machines and how they are used to measure the static and dynamic imbalance of projectiles. The report also provides analysis that links the measured static and dynamic imbalance to the trajectory deflection produced by the mass imbalance. Results of measured imbalance of a set of calibration pins are presented to benchmark the measurement capability. The methodology is also used to predict the trajectory deflection of a 20-mm projectile with a mass asymmetry, and the predictions are validated with previously published results.