Dynamics Modeling and Autonomous Landing for Flexible Parafoil-Vehicle Multibody System

In this paper, the autonomous landing of the parafoil used for aerial vehicles is investigated through the numerical approach. The coupled parafoil-vehicle dynamics model is developed based on the multibody method. The transition process from aircraft flight to parafoil glide is designed in a global system framework. To deal with large flexible deformations during the deployment process, the parafoil canopy is approximated as interacting symmetric subparts using the geometric division method. The pseudo-spectral method is employed to generate a reference trajectory for the landing target. As the system dynamics are introduced into constraint conditions, the generated trajectory is beneficial to improve landing precision. In addition, other optimization objectives, including minimal energy consumption and obstacle avoidance, are considered in trajectory planning. The enhanced proportional integral control is designed to follow the reference trajectory. The neural network inversion model is used to reduce the coupling effect between the longitudinal and the directional control channels. There is a coupling effect that the two controls both are implemented through left and right trailing-edge deflections. An adaptive output allocation method is proposed to ensure that the directional control always is effective in particular when one side reaches saturation. Finally, simulations for autonomous landing under different conditions are carried out to validate the integrated system.