Optimization of deep stall landing trajectory for morphing aided UAV

In order to recover small unmanned aerial vehicles (UAVs) at a confined area, deep stall landing is investigated for UAV aided by morphing wing. Inspired by perching maneuver of birds, morphing wing is adopted to gain extra controllability during deep stall landing. Constraints like terminal velocity, sink rate, terminal attitude, down range of approach, input saturation, etc are considered. Then, deep-stall landing problem of small UAV aided by morphing wing in longitudinal plane has been formulated as an optimal control problem. The optimal trajectory and nominal reference control is solved numerically based on Gauss pseudo spectral method. Numerical results verify the effectiveness of proposed optimization method, and characteristics and mechanisms of optimized deep-stall landing trajectory for morphing aided UAV are discussed under various flight conditions and limits.

1 Introduction

It is difficult for an unmanned aerial vehicle (UAV) with fixed wing to land at confined area that surrounded by trees or buildings. The horizontal speed needs to be decreased to nearly zero and the deep descent path angle must be maintained to make sure the UAVs being recovered safely. Solutions like parachute landing, vertical take off and landing (VTOL) and deep stall landing are feasible. Parachute landing can be easily implemented but the landing point is hard to be predicted because of wind disturbance. Based on VTOL technique, UAV can land at target area with small space. However, its payloads and endurance are limited. Furthermore, its tilting structure is complicated. Deep stall landing aided by morphing wing, which is studied in this paper, is a novel method to make UAV maintain deep descent path angle and land with short distance runaway. Utili zing large aerodynamic drag at deep stall state, the horizontal speed can be reduced effectively and the deep path angle is kept. Before the UAV coming in to land, suitable attitude and sink rate is adjusted by control system aided by morphing wing to ensure the impact force is small enough when the UAV touches down.