Analysis of Ground Effect for Small-Scale UAVs in Forward Flight

Abstract

The letter investigates how the behavior of small-scale unmanned aerial vehicles (UAVs) is influenced by the system's close proximity to the ground/rigid surfaces both at hover and in forward flight. We perform an extensive experimental study where a quadrotor is tasked with flying in forward velocities in the range of 0–8 m/s and at altitudes that range between 0.05–0.5 m. Experimental data are used to evaluate four existing ground effect models. Results suggest that existing models for helicopters and in-hover multi-rotors cannot fully describe the forward motion of a quadrotor when it operates close to ground. We introduce two new data-driven models for rotorcraft operating in ground effect both at hover and in forward flight, and evaluate the proposed models with another quadrotor of different size. The proposed models simultaneously consider several operating conditions, which are parameterized by the vehicle's forward velocity and altitude. The models link the thrust produced when operating in ground effect and hovering out of ground effect as forward velocities vary. This information can be incorporated into flight controllers for robust and adaptive UAV flights, and can benefit motion planners for safe and energy efficient near-ground trajectory planning.