Improved Dispersion of a Fin-Stabilized Projectile Using a Passive Movable Nose

Abstract

A key and often quoted metric associated with gun systems is impact point accuracy. Impact dispersion is a complex function of a battery of parameters including gun geometry and tolerances, the fire control system, projectile manufacturing tolerances, etc. The work reported here investigates potential impact point accuracy improvement for a penetrator type projectile realized by replacing the rigid nose cone wind screen with a passive gimballed nose. Toward this end, a gimballed nose projectile dynamic model is derived which consists of the standard six degrees of freedom similar to a rigid projectile plus three additional degrees of freedom associated with rotation of the nose with respect to the main projectile body. By comparing impact point dispersion of a rigid projectile with a similar gimballed nose projectile, it is shown that impact point accuracy can be significantly improved. For the example penetrator projectile considered, impact point dispersion is reduced by more than 50%. The investigation also considers the effect of several design parameters on impact point dispersion including mass ratio of the nose to the total projectile, gimbal joint friction, and the normal force coefficient of the nose cone. Within practical boundaries, the mass ratio of the nose and body does not alter the target dispersion characteristics. However, friction in the gimbal joint does significantly effect the impact point dispersion. As the viscous damper friction coefficient increases, the impact point dispersion slightly increases until a critical value is reached. Beyond the critical value of viscous damping friction coefficient, the nose cone rotational dynamics are unstable and the tip of the nose oscillates about the limit nose cone rotation angle. Also, a steady decrease in impact point accuracy is noted as the normal forces coefficient of the nose is reduced.