Modeling, Analysis, and Control of Close Formation Flight

Close formation flight is extensively investigated from the perspectives of dynamic modeling, aerodynamic analysis, and control design. A lifting-line based aerodynamic model is presented to describe the aerodynamic coupling between two aircraft in close formation. The introduced aerodynamic model is validated via the comparison with a single horseshoe vortex-based model, a vortex lattice method-based model, and experimental results. Comprehensive analysis is thereafter conducted to investigate the drag reduction variations with respect to different relative positions, angles of attack, sideslip angles, and leader-to-follower wing span ratios. The analysis indicates that the drag reduction performance of close formation flight is sensitive to the formation position accuracy. Additionally, basic requirements are formulated for close formation flight control. In terms of the proposed aerodynamic model, a linear robust adaptive formation controller is developed specifically for close formation at level and straight flight. The proposed robust adaptive controller shows dramatic increase in both transient performance and robustness against model uncertainties and disturbances. The nonlinear robust close formation control problem is thereafter studied under a leader-following architecture. Nonlinear robust close formation controllers with different considerations are proposed based on a command filtered backstepping method and an uncertainty and disturbance estimation technique. The proposed nonlinear robust formation controllers could accommodate more complex flight scenarios, for instance, different flight maneuvers and close formation of more than three aircraft. With the increase of the number of aircraft in close formation, a leader-following formation controller might become less and less efficient. Regarding the efficiency degradation issue of leader-following formation controllers, two cooperative control algorithms are introduced, which exhibit better tracking performance for close formation of a large number of aircraft. Extensive simulations are carried out to validate the effectiveness of all proposed close formation control algorithms.Ph.D