Optimal hierarchical trimming method for multi-lift system with helicopters considering aerodynamic interference

It is difficult to accurately trim the multi-lift system with helicopters due to complex aerodynamic interference and troublesome manipulation redundancy. To solve this problem, a mid-fidelity method is utilized to simulate the aerodynamic interference of the system. Particularly, the lifting surface method is applied to calculate the unsteady air loads of the rotors, and the viscous vortex particle method is used to model the wake. Moreover, an optimal cable-force allocation strategy based on the equilibrium optimizer is proposed to deal with the manipulation redundancy. On the basis, the load-leading optimal hierarchical trimming method for the multi-lift system is obtained by introducing the improved delta trimming algorithm and the hierarchical theory simultaneously. The trimming results for the multi-lift system at different forward speeds verify the effectiveness of the trimming method and indicate that: the optimal force allocation strategy is beneficial to reduce coupling and there are different characteristics of helicopters in the multi-lift system. (c) 2022 Elsevier Masson SAS. All rights reserved.