Stable Control in Climbing and Descending Flight under Upper Walls Using Ceiling Effect Model Based on Aerodynamics

Abstract

Stable flight control under ceilings is difficult for multi-rotor Unmanned Aerial Vehicles (UAVs). The wake interaction between rotors and the upper walls, called the "ceiling effect", causes an increase of rotor thrust. By the thrust increase, multi-rotors are drawn upward abruptly and collide with ceilings. In previous work, several thrust models in the ceiling effect have been proposed for stable flight under ceilings, assuming that the airflow around the rotor is in steady states. However, the airflow around rotors in vertical flight is not in steady states and each model is skillfully determined based on large amounts of experimental data. In this paper, we introduce an aerodynamics based thrust model and a stable control method under ceilings. The model is derived from the momentum theory and relationship between a vertical climbing/descending rate of a rotor and an induced velocity. To confirm the proposed model, we collect thrust data at various vertical rates in flight. Here, we use only onboard sensors to estimate self-state, for structural inspections. Consequently, we demonstrate that the proposed model is in agreement with the experimental results. Based on aerodynamics, we need not collect huge precise experimental data to construct the model. Furthermore, the vertical flight under ceilings demonstrate that the proposed unsteady-state model based controller outperforms the conventional steady-state ones.