Military aircraft typically carry under-wing stores such as bombs or external fuel tanks. During a mission, one or more stores may be ejected with the aid of a jettison force that pushes them away from the aircraft into a safe trajectory. Store release changes the load balance on the aircraft, causing both static and dynamic structural response of the flexible wings, as well as a rigid body motion of the whole aircraft. The large ejection forces might result in excessive structural dynamic loads that must be accounted for in the structural design process. The problem of ejection loads is becoming more severe for modern, flexible aircraft configurations (typically, unmanned aircraft vehicles), in which small stores are ejected with large jettison forces. Additionally, stores are sometimes released in ripple, namely shortly one after another, before the dynamic response from the previous ejection has decayed completely.
The study presents a frequency-domain method for computing the structural dynamic response of an elastic aircraft to store ejection, accounting for the jettison, the inertial, and the unsteady aerodynamic forces. A novel solution method is proposed, that accounts for the time-variation of structural properties of the configuration (following each store release) in the frequency domain. The study examines the physical factors that affect the aircraft response to store ejection. The study also presents cases of ripple ejection and shows how the time-interval between ejections could be optimized to reduce the loads. The methodology is demonstrated on a test case of a subsonic elastic generic unmanned aircraft vehicle carrying up to six stores on each wing.
