6-DOF Flight Dynamics Model Identification of a Hybrid-Lift Multicopter in Hover

This paper presents the identification and verification of a six degrees-of-freedom (6-DOF) flight dynamics model of a hybrid-lift (buoyancy and propulsive lift) multicopter unmanned aerial vehicle using the frequency-domain system identification technique. The hybrid-lift flight vehicle of interest was a dynamically representative (by z-axis CB vs CG location and Buoyancy Ratio) 29% hub-to-hub scale prototype of a full-scale vehicle designed for multi-use operations with a maximum payload of 250 lbs. From the system identification process, it was concluded that stable roll and pitch dynamics can be expected from a hybrid-lift multicopter configuration designed with high Buoyancy Ratio (BR) and a stabilizing buoyant restoring moment. This dynamic behavior is uniquely different from standard multicopters, which exhibit extremely unstable dynamics in those axes. Additionally, from the heavily attenuated yawaxis dynamic control response, it was concluded that a vertical tail or other yaw effector is needed for the control of similarly configured hybrid-lift vehicles.