Modeling and natural mode analysis of tethered multi-aircraft systems

Abstract

Two complementary simulators aimed at the dynamic analysis of airborne wind energy systems based on multi-aircraft configurations are presented. The first model considers a train of stacked aircraft linked among them by two inelastic and massless tethers with no aerodynamic drag. The architecture of the mechanical system in the second simulator is configurable, as long as the system is made of a set of aircraft linked by an arbitrary number of elastic tethers. In both cases, the aircraft are modeled as rigid bodies and the controller is incorporated in the aerodynamic torque through the deflections of control surfaces. An analysis of the symmetric equilibrium state and the corresponding natural modes of a train (stacked configuration) of aircraft was carried out. It revealed that the higher the position of the aircraft in the train, the more they participate in the modes. Tether inertial and aerodynamic drag effects increase the equilibrium angles of attack of the aircraft and the tether tension at the attachment points. The potential applications and computational performance of the two codes are discussed.