Edward M. Schmidt

Wind-Tunnel Measurements of Sabot-Discard Aerodynamics

Abstract : This report addresses the flow field around a fin stabilized, hypervelocity projectile during the sabot discard process. The mutual interference of the flows around the flight body and three sabot components is examined through wind tunnel tests conducted at a free stream Mach number of 4. 5. Since it was not practical to attempt the actuation of all three sabot components, the flow field was simulated by using splitter plates to develop reflection surfaces along planes of symmetry. The data show the effects of multiple shock interactions, shock-boundary layer interactions, and the variation in aerodynamic loadings as the sabot discard proceeds.

Disturbance to the Launch of Fin-Stabilized Projectiles

The sabot discard from a gun launched, fin-stabilized projectile is examined from the time of shot ejection until the round enters undisturbed flight. Trajectory perturbations due to muzzle blast, fin shadowing, mechanical contact, and aerodynamic interaction are evaluated and a relative ranking is determined. Analysis shows that muzzle blast and fin shadowing result in negligible changes to the launch angular momentum of the projectile; however, mechanical contact with sabot components markedly alters both the projectile momentum and the subsequent trajectory of the sabot sections. The resultant geometric asymmetry in the pattern of these discarding sections is shown to cause strong aerodynamic interaction between the sabot flowfields and the projectile. For the case investigated, aerodynamic interaction was determined to be the major source of postseparation trajectory perturbation.

Aerodynamics of Asymmetric Sabot Discard

Abstract : Experimental results are presented which examine the pressure distributions upon projectiles during the portion of the launch cycle which involves strong aerodynamic interference between the flight body and sabot components. Particular attention is given to the simulation of asymmetric sabot discard geometries since these configurations result in transverse loadings upon the projectile. The pressure distribution in a given section of the projectile surface is shown to be strongly influenced only by the flow field associated with the sabot component facing that section. The basic features of the flow are similar in both the symmetric and asymmetric cases. The experiment is compared with existing analytical models and recommendations for improvements are made.

Influence of Muzzle Brakes Upon the Trajectory of Fin-Stabilized Projectiles.

Abstract : The dispersion of groups of fin-stabilized projectiles fired from high velocity cannon was measured for cases with and without a muzzle brake in place. The data clearly show degradation in precision due to the presence of the device. Diagnostic experiments and analyses were performed which indicate that the difficulties arise mainly due to gasdynamic loads within the muzzle device influencing both the projectile motion and sabot discard. Muzzle device design modifications are suggested to solve the problems. (Author)