Aerodynamics of Self-Docking UAS on Tether

In the past several years, the interest in the use of autonomous unmanned aircraft systems (UAS) has exponentially increased. However, battery capacity technology has not kept pace for the longer flight times required for many applications. Therefore, many UAS operators are turning to power by tether systems. The use of tethering is a concern for operators as the introduction of a free-swinging pendulum below a UAS during cross-winds raises concern for stability control of the vessel. The following experiments investigate the ability of a UAS to dampen the oscillation of the tether as a result of the downwash flow from the UAS’ propellers while landing. Experiments are conducted using a large octocopter UAS in both indoor and outdoor environments to record frequency and amplitude data of an oscillating tether in a variety of cross-wind velocities. That data will then be compared to data gathered at similar mean air velocities, however, with the addition of propeller downwash equivalent to what is expected from a UAS during landing/docking.  Qualitative and quantitative data from these experiments will be useful in determining the optimal approach and tethering mechanism for a self-docking tethered UAS.