Electromagnetic and aeromechanical analysis of sabot discard for railgun projectiles

Experimental and engineering modeling techniques were applied to examine th e role that electromagnetics plays during the sabot discard process in a so lid-armature railgun. Current and magnetic field diffusion in the conductin g armature and sabot produce residual forces that tend to clamp:the sabot p etals during in-bore acceleration and after launch. The effect of this forc e on sabot discard was investigated. The experimental portion of this work used the measured downrange magnetic fields to quantity the effect on subpr ojectile performance. The time rate of change of launcher and switch curren ts and launcher voltages Were measured. In addition, the time rate of chang e of the armature magnetic field was measured downrange from the launcher. Electrical parameters that characterize the magnetic fields were used to ca lculate the residual current flowing in the armature after exit, An enginee ring model that includes both aeromechanical and electromagnetic forces was developed to predict the sabot discard process. The model for the magnetic clamping force used the inferred current from the magnetic fields measured downrange, The results from the sabot discard analysis are in good agreeme nt with the measured sabot trajectory data, particularly when the sabot pet als are in dose proximity. The analysis shows that the aerodynamic moment a cting on the sabot is relatively small following launch, and small magnetic clamping forces could delay sabot separation.