Dynamic stability and control of rotorcraft for suspended load transportation: an analytical approach

Abstract

In the present paper a fully–analytical framework is outlined to investigate the effects of cable–suspended loads on rotorcraft. In particular, the dynamics of an isolated multirotor is first investigated by including the complete model of the electric propulsion system. Then, system description is extended to the presence of a suspended load, thus generating non–actuated degrees of freedom. In order to provide the complete slung–load system with a closed– loop desired behavior, an auxiliary controller is proposed to restore or even improve the initial multirotor dynamics, while stabilizing load oscillations with prescribed behavior. To this end, closed–form expressions are derived to design the auxiliary controller gains, based on the knowledge of a limited set of parameters which include the position of the cable hook point. A test case is proposed relative to a commercial–off–the–shelf hexarotor whose propulsion units have been characterized by an experimental campaign performed at University of Bologna premises.