Analysis and experimental results of a fin stabilized subcaliber projectile with a blunt step in the external propulsion accelerator

摘要

The paper presents the resutls of the first proof of concept test of the External Propulsion Accelerator using a subcaliber fin guided projectile. The fin guided subcaliber projectile is fired in the 120 mm Ram Accelerator facility of ARL. The projectile body shape is similar to the free flight projectile body except that the fins do not span the 120 mm tube diameter. The projectile body diameter is 52 mm and the body length is selelected so that the flow over the projectile will not be affected by reflected shock waves from the tube wall. A forward-facing step of a 1 mm height is used. The projectile weight is 1.017 kg. The 120 mm RA facility of ARL was modified to accommodate the subcalliber EPA projectile test. The first tube section was filled with nitrogen at intial pressure of 2.0 MPa. The solid 6 m long accelerator tube section is followed by a clear test section. Thsi test section is a 1.8 m long plastic tube filled with the combustible mixture of CH_4+2O_2+10CO_2 also at 2.0 MPa. The projectile velocity history is measured by a doppler radar apparatus. The resutls of these measurements indicate that after the projectile is clearly separated from the orburator the projectile decelerates in the nitrogen by about 4500 +- 2500 g's. It is found that in the clear tube that is filled with the combustible mixture, the projectile picks up thrust to cancel the drag after a flight time of about 0.4 ms. The projectile then reaches an equilibrium velocity of 1905 m/s that is 1.59 tiems the detonation velocity of the mixture. The projectile stayed at about this velocity, from 1907-1905 m/s, for 0.7 ms until it exited the tube. High speed photography is used to visualize the combustion on the projectile. The photographs clearly indicate combustion on the projectile, probably initiated by the step and by the leading edges of the root chord of the fins. Calculations using a CFD code are used to verify the position of hte combustion on the projectile. The reuslts of this first test indicate that combustion was initiated and stabilized on the rear part of hte projectile. It was also shown in this first test that thrust, sufficient to balance the drag, was generated by the external combustion.