Aerodynamic Modeling of Fully-Actuated Multirotor UAVs with Nonparallel Actuators

The beneficial aspects of fully-actuated multirotor UAVs, provided by nonparallel rotor configuration, are increasingly being recognized and utilized to great benefit in high-precision applications. Full six-degree-of-freedom force control, higher control bandwidth and improved disturbance rejection prove valuable. However, the cant angle will cause great multirotor dihedral effect and significantly affects blade flapping, which decreases the flight performance of nonparallel actuated UAVs. Therefore, this paper presents a novel aerodynamic model for fully-actuated hexrotor UAVs while considering the aerodynamic effects caused due to tilt angled propeller configurations. In the proposed aerodynamic model, the significance of multirotor dihedral effect, defined as an aerodynamic coefficient proportional to the relative linear velocity of the UAV, is modeled for nonparallel actuators. Additionally, the modeling for blade flapping effect for cant angled propellers is provided to accurately model the aerodynamics. Wind tunnel experiments were conducted to characterize the aerodynamic constants for multirotor dihedral effect, blade flapping effect and air friction. Experimental results are presented to validate the proposed aerodynamic model on a fully-actuated hexrotor UAV (Purdue’s Dexterous Hexrotor). Lastly, the multirotor dihedral effect and blade flapping effect at different cant angles and at different wind speeds are analyzed.