Browse Topic: Cables
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.
ABSTRACT
The National Research Council of Canada and Université de Sherbrooke performed flight testing of an Actively Stabilized Slung Load on the NRC Bell 206 Research Aircraft. Hover, Attitude Capture, NRC designed Lateral Precision Hover, and Frequency Sweep mission tasks were performed for bare airframe and slung load aircraft configurations. The load mass ratio was 0.12 while the slung load pendulum mode was 1.3 rad/sec at a damping ratio of 0.2 for the 40-pound per active tether saturation load system setting. Time domain response indicated that the load remained controllable with damped and underdamped behaviors. Frequency domain analyses confirmed pilot comments indicating HQR 4 handling qualities ratings for bare airframe and stable slung load behavior. This rating degraded to HQR 5 for task execution with slung load oscillation. Pilot workload was due to lateral cycle input requirements of 2 to 3 inch amplitudes at 1 to 2 Hz frequency. Operationally, the coincidence of pilot inputs with active tether induced airframe and short period modes led to high compensation requirements for lateral axis tasks under study. The complexity of active tether management, an actuator failure, and telemetry faults represented system deficiencies. Comparable bare airframe and slung load configuration task execution results indicate the magneto-rheological actuation system’s potential to improve slung load mission task performance.
2016, to form their 34th Student Design Competition around designing an aircraft capable of hovering for a duration of 24 hours with a 176 lb (80 kg) payload. This paper presents the preliminary design of the Swarm, a configuration of the Electric Powered Reconfigurable Rotor (EPR2 ) concept, drafted by the joint Universite de Sherbrooke and Georgia Tech team. The Swarm, comprised of a central fuselage tethered to three electrically propelled unmanned fixed-wing aircraft flying in a circular trajectory, achieves its goal through rotor reconfiguration. Throughout the flight, the fixed-wing aircraft modify their trajectory and airspeed to optimize performance and minimize fuel burn rate. A hybrid-electric powerplant in the fuselage supplies power via conductive tethers to the fixed-wing aircraft. The design and reconfiguration were optimized using a 2-step time-marching optimization. The designed system greatly exceeds the competition requirements by accomplishing 31 hours of hover flight using readily available technologies and COTS components. The Swarm, weighing a maximum of 2,700 lb (1,224 kg), requires only between 62 and 120 hp (46-89 kW) to perform hover out of ground effect. Safety, reliability and maintenance analyses were also conducted, in addition to estimating production and operational costs of the system.
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