Assessment of Added Masses Effects on Airship Dynamics and Stability

Airships have recently emerged as attractive candidates for several aerospace applications, leading to an increasing interest in the modeling of the dynamic behavior of these vehicles for flight mechanics analyses and mission simulation purposes. One of the peculiarities of the airship model is the need for the inclusion of the dynamic effects due to the mutual interaction between the moving vehicle and the fluid in which it flies. This phenomenon is usually represented by introducing fictitious added masses. This paper presents a method to rigorously manage the added masses, including them in the flight dynamics equations without considering any simplifying assumptions concerning airship shape or centers of added mass. The paper also defines a method for the computation of the added mass matrix and centers of added mass position in any reference frame, which is required for the accurate writing of the airship equations of motion. The effectiveness of the proposed approach is validated numerically by solving a potential flow problem through the boundary element method. Finally, the effects of added masses are assessed with reference to a high-altitude airship by evaluating its dynamic stability properties with and without the inclusion of the added masses.