Hybrid heavy lift airship (HHLA) is a proposed candidate vehicle aimed at providing heavy lift capability at low cost. This vehicle consists of a buoyant envelope attached to a supporting structure to which four rotor systems are attached. Nonlinear equations of motion capable of modeling the dynamics of this coupled multirotor/support-frame vehicle system have been developed. Using these equations, an aeromechanical stability analysis was performed in order to identify potential instabilities for this type of vehicle. The coupling between various blade, supporting structure, and rigid body modes is identified. Furthermore, the effects of changes in buoyancy ratio (buoyant lift/total weight) on the dynamic characteristics of the vehicle were studied. © 1985 American Institute of Aeronautics and Astronautics, Inc., All rights reserved.