Projectile Fin Damage from Propellant Combustion

Thermal ablation of anodized (hard coated) aluminum fins on high-velocity , gun-launched kinetic energy penetrators is a serious problem at long ranges. It degrades flight performance by reducing stability and roll. Additionally, uneven ablation creates aerodynamic asymmetries that further increase projectile dispersion. The problem is known to begin in-bore. A fin-testing procedure is used to create in-bore heating conditions similar to those of a normal launch, without actually launching the fin. Postfired examination of the fins is then used to ascertain the fin damage mechanism for the nonlaunched fins as well as to infer the fin damage mechanism for normally launched fins. A two-phase flow interior ballistic code is also used to model the fin temperature profile for both the nonlaunch and the normal launch configuration. Qualitative comparison is made between the effects expected from modeling and those actually observed. Experimentally, the nonlaunched fins sustained mostly leading-edge damage, entailing loss of hard coat followed by the uneven downstream ablation. Modeling appears to underpredict the observed effects, but this is thought to be a consequence of neglecting, a priori, the possibility of rapid fin surface oxidation (burning). Nomenclature H = q82/l2, solution to the given heat conduction equation h = heat transfer coefficient ^con = convective film coefficient /irad = radiative film coefficient k = thermal conductivity of fin material