Projectile AFT-Body Drag Reduction by Combined Boat-Tailing AND Base Blowing.

An experimental study is made at a Mach number of 3 toward reducing the aft-body drag of a slender projectile configuration by means of boat-tailing and base blowing. Nine aft-body configurations were tested, including boat-tail angles of 0, 3, 6, 9, and 12 degrees, three boat-tail lengths, and three base blowing orifice diameters. Both air and helium at room temperature were used as injection gases, Results show that the largest blowing orifice yields the greatest drag reduction, that considerably smaller mass injection rates are required for helium than for air, and that helium injection gives a greater drag reduction than air. These findings confirm those of other investigations. Maximum aft-body drag reduction was obtained with the 6 degree boat-tail 1-caliber in length. Boat-tailing alone reduced the aft-body drag by as much as 23 percent and base injection alone, by as much as 50 percent. Combination of the two showed possible gains of 60 percent. The aerodynamic flow field of the projectile configuration is fully described. Author