This paper analyzes the ground effect in multirotors, that is, the change in the thrust generated by the rotors when flying close to the ground due to the interaction of the rotor airflow with the ground surface. This effect is well known in single-rotor helicopters but has been assumed erroneously to be similar for multirotors in many cases in the literature. In this paper, the ground effect for multirotors is characterized with experimental tests in several cases and the partial ground effect , a situation in which one or some of the rotors of the multirotor (but not all) are under the ground effect, is also characterized. The influence of the different cases of ground effect in multirotor control is then studied with several control approaches in simulation and validated with experiments in a test bench and with outdoor flights.
Sanchez-Cuevas, P., Heredia, G., & Ollero, A. (2017). Characterization of the Aerodynamic Ground Effect and Its Influence in Multirotor Control. International Journal of Aerospace Engineering, 2017, 1–17. https://doi.org/10.1155/2017/1823056