Optimal Control of an Aerial Tail Sitter in Transition Flight Phases

摘要

The main purpose of this study is to generate optimal transition trajectories for an aerial tail sitter that uses cross-coupled thrust-vectoring control. A transition maneuver is most challenging for such configurations due to coupling of the forces and moments with instability in the most critical low-speed flight phases. Based on the classical Cauchy method, an improved gradient-based algorithm is developed in a collaborative process in order to find transition trajectories and increase the convergence rate. The cost function is defined in terms of minimum time in transition from hover to cruise and minimum altitude variations from cruise to hover. In addition, physical constraints are modeled via extended penalty functions. The results, including an optimal solution for states and controls, guarantee that the estimated trajectories are feasible, taking into account all imposed constraints. It is shown that the initial cruise speed in the landing phase will greatly affect the altitude variation and transition time when meeting the mission requirements. A sensitivity analysis shows that increasing the thrust-to-weight ratio would increase the efficiency of the transition maneuver in terms of final altitude and transition time. However, increasing this value is not recommended in the aspects of design and development.