Impact of the Wind on the Hovering Performance of Stabilized Payload Lifting with a Single Tethered Fixed-Wing Aircraft

Over the last 90 years, many concepts of lifting payload with a single tethered fixed-wing aircraft have been proposed. In this concept, an airplane flies along a quasi-circular flight path and the payload should remain at the center of this circle. The main challenge encountered has been payload stability in hover (i.e., when the payload is fixed in space and the aircraft flies along a quasi-circular path above). In calm conditions, lengthening the tether to reach two or three kilometers (1.5 mile) has been proven to stabilize the payload in an orbit with a radius of the order of 1 meter (3 ft). However, the presence of wind has shown a drastic reduction in payload stability. At the end of the 1990s, a patent proposed to add a thruster-based stabilization device onto the payload but no further studies explored such a concept. This study proposes a new concept inspired by the former. The main difference lies in the addition of a reel-in mechanism to control and stabilize the payload in the vertical direction. This work analyzes the impact of the wind on this new concept in hover. The results have shown a maximum power requirement of 37 kW (60 hp) for the aircraft and 15 kW (20 hp) for the stabilization device to lift a 300 kg (660 lbm) payload fixed in the inertial frame with a 400 m (1,300 ft) long tether. This work has highlighted the high impact of the tether force on the towing airplane and therefore a means to reduce this impact is required.