Sideslip effects on fin-fin interference in supersonic missile aerodynamics

Abstract

The supersonic missile fin-fin interference factor K0 is a measure of the normal force change on a fin, in the presence of a body and other fins, caused by changes in sideslip angle. A finite-difference Euler code, SWINT, is used to numerically determine the fin forces for different sideslip angles for two-, three-, four-, and six-fin missile configurations at small angles of attack. The fin forces are used to evaluate K^ at Mach numbers from 2.5-3.5, positive arid negative sideslip angles, and various fin aspect ratios. The K+ values from SWINT for two-fin configurations have similar magnitudes to those from previously published slender body theory analytical solutions; however, the SWINT predictions for four-fin configurations show that K+ breaks away sharply from the slender body theory values as the fin span increases. The fin span at which the breakaway occurs is shown to be directly related to the position of shock waves and expansion fans originating from neighboring fins. The breakaway fin span is also shown to be a strong function of the number of fins, Mach number, and sideslip angle. Values of K^ for use in preliminary design are presented.