Modified under-actuated quadrotor model for forwarding flight in the presence of ground effect

In ground effect conditions, the wake of Quad-copier rotors interacting with the ground causes significant perturbation to the flow near the rotor blades, as well as to the body. These interactions have serious effects on the handling qualities and cause instability in flight. Most studies in the ground effect are focused on hover and landing capabilities of rotorcraft. In this paper, a comprehensive non-linear model of quadrotor is provided in the state-space, which is suitable for all flight types near the ground. First of all, it is tried to add a ground surface quality coefficient in modified ground effect relation by experimental investigations. The experiments have been done in outdoor during calm days with no wind. In the next step, a robust non-linear control strategy is designed based on the modified model. The effects of ground effect and the increase of the advance ratio are then investigated on controller performance. The simulation results show that this model is closer to the actual flight conditions and the stability and the trajectory tracking are significantly improved by implementation of this control strategy. So, this strategy provides an appropriate platform to run other methods without the need for iterative learning techniques and high battery energy consumption. (C) 2019 Elsevier Masson SAS. All rights reserved.