High ram acceleration using open-base projectile

High-acceleration operation has been realized in a 25-mm-bore ram accelerator by employing an open-base projectile. The projectile comprises a centerbody and four fins like. a conventional ram accelerator projectile, but is manufactured as a single piece. The base of the centerbody is perforated so that pressures inside and outside are almost balanced, thereby reducing the required thickness of the centerbody wall and the total mass. Reliable ram acceleration could be started only when the entrance velocity was increased by 0.1 km/s from that set for the conventional projectile. Although the propellant fill pressure was as modest as 3.5 MPa, an average acceleration of 4.4 x 10(4) g and a velocity increment of 1.0 km/s have been achieved through a 4.1-m-long, three-stage ram acceleration section.