Development of a Payload Control System for a Single-airplane Tethered Lifting System

Vertical lifting methods using circling airplanes tethered to a centralized payload have been studied since the 1940s. These methods combine the high efficiency of fixed-wing airplanes with the vertical lifting ability of helicopters. However, such lifting systems must tackle the challenge of accurately controlling the position of the centralized payload in order to be viable. Typically, a kilometer-long tether configuration, subject to aerodynamic damping, is studied to achieve a small orbit radius for the payload, resulting in nearly stationary movement. This article presents the development of a payload control system (PCS) for a circling single-airplane tethered lifting system. A PCS mounted onto the payload compensates for flight path deviations of the airplane and allows the use of a shorter tether because it removes the dependency on aerodynamic forces to position the payload. This article presents the mechanical architecture and the control strategy of the PCS, along with experimental flights done under a DJI Matrice 600 drone to mimic the trajectory of a circling single-airplane. The DJI drone followed a circular path of 16 m in diameter with a period of 14 s during which a payload, including the PCS, was linked to the drone with a 31 m (102 ft) tether. During the experiments, the PCS maintained payloads ranging from 1.6 kg (3.5 lb) to 4.8 kg (10.6 lb) at ∼10 cm (∼4 in) of the target position, regardless of the trajectory deviations of the DJI drone. The PCS is a key feature of this novel vertical lifting method which has the potential to provide an alternative to rotorcraft and multi-rotor drones for cargo delivery