Predicted flight performance of base-bleed projectiles

Abstract

Current Army programs are applying a base-bleed concept to achieve increased range for projectiles. Base bleed is a technique in which low-speed mass is injected into the base region to reduce base drag and extend range. The U.S. Army Ballistic Research Laboratory is developing an engineering computational model capable of predicting the flight performance. The model analyzes three problem elements: a solid propellant gas generator, the effect of injection on the aerodynamic drag, and trajectory computations. Because each element is time dependent, all three must be solved simultaneously. The analysis is based on experimental and numerical data generated for the M864 base-bleed projectile. Navier-Stokes computations for the near wake region have been performed on the Army's Cray X-MP/48 supercomputer. The results were used to correlate base pressure change with injection rate, gas temperature, and Mach number. These results provide critical data for the analysis. The mass generation analysis is combined with the effect of mass injection on base pressure to obtain the projectile base drag at each step of a two-dimensional, point-mass trajectory computation. Computed results are in reasonable agreement with the flight data. Ranges are predicted within 4.2%.