Flutter Analysis of Aircraft with External Stores Using Modal Coupling

Abstract

A new modal coupling technique for efficient flutter and aeroservoelastic analyses of aircraft with multiple external-store configurations is presented. The aircraft is represented by a set of free-free normal modes obtained with large fictitious masses loading the interface coordinates to yield high-accuracy subsequent coupling results. Each store is represented by its own vibration modes obtained with a subset of statically determined interface coordinates clamped to the ground, and the remaining coordinates (if any) are loaded with large fictitious masses. The technique is formulated in a way that facilitates its application using standard options of common commercially available software packages. A finite element code is used to construct the aircraft and stores modal databases. A linear unsteady aerodynamics code is used to read the modal information, calculate the aerodynamic databases, construct and solve the aircraft-store coupling equations, and perform frequency-domain and state-space flutter analyses with or without control system effects