Influence of Different Take-Off Weights on the Longitudinal Dynamic Stability of Flapping-Wing MAVs

Abstract

Due to different requirements of flight tasks, take-off weights vary according to different payloads, which will definitely influence the trim characteristics and flight dynamics of vehicles. When the mass ratio between the flapping wing and body increases to a certain value, it is necessary to regard flapping-wing microair vehicles (FWMAVs) as a multibody system, and the rigid-body model is no longer appropriate to be used as dynamic modeling. The flight dynamic stability analysis considering the oscillation of body, wing flexibility, and variation of take-off weight in forward flight is worthwhile to be studied. In this study, based on a method coupling three-dimensional computational fluid dynamics (CFD), computational structural dynamics (CSD), and multibody dynamic equations for FWMAVs, the dynamic and trim characteristics of systems with different take-off weights have been studied and compared. In addition, the dynamic stability has been analyzed and compared by three different methods including the averaged method, Floquet method, and direct time integration. Results show that with the increase of take-off weight, the FWMAV in forward flight changes from unstable (wing to body mass ratio is 8.5%) to stable (wing to body mass ratio is 6% and 7%). The transformation of stability mainly results from two contributions: the change of trim conditions and body oscillation. Furthermore, a direct time integration method has been used to address the impact of nonlinear effects. The results show that a nonlinear term does not change the qualitative results of stability but will change the specific evolution of state variables compared with a linear model. The quantitative results can give insight into the design of FWMAVs with different wing to body mass ratios.