Store Separation Trajectory Deviations due to Unsteady Weapons Bay Aerodynamics

Abstract

The combined trends toward internal carriage of weapons in modern aircraft and the design of new weapons to be neutrally stable for in creased performance have increased the probability that unsteady aerodynamics will effect store separation trajectories. Reports from time accurate computational fluid dynamics trajectory simulations have shown trajectory sensitivity to time of weapon release. Typical wind tunnel data collected to support store separation analysis cannot detect thi s effect since the data collected consists of time averaged store loads. Flight testing to inves tigate effects of bay unsteadiness has not been done since it is expensive and typically there are insufficient funds to conduct repeated store drops at identical flight conditions. Carefu lly designed and conducted small scale drop testing in wind tunnels provides a means to identif y the effect of unsteady weapons bay aerodynamics on store separation trajectories. Time accurate computational fluid dynamics trajectory analysis results on the Small Smart Bomb separating from an F-111 aircraft and a GBU-12 separation from the B-52 aircraft are reviewed. Small scale drop test data from a generic 10% scale rectangular cavity in a flatplate and from a 6% scale B-1B are introduced to provide experimental evidence of the effect of u nsteady flow on the store separation trajectory.