Fixed-wing UAVs in Windy Environments: A Circular Delivery System

Abstract

Abstract In some situations, when delivering packages with a fixed-wing UAV, a better accuracy is necessary than can be achieved with a fly-by drop. One alternative method is to circle close to the target point with the package suspended below the UAV with a rope. Through simulations it is shown that this circular method can deliver packages with a higher precision than can be done with the fly-by method. In steady wind conditions, it is proven possible to get a close estimation for where the package would land, were it to be released. This is done by a combination of an analytical solution to a system of differential equations in conjunction with a disturbance function based on previous simulations. In isolation, the impact of the turbulence can be minimized by releasing the package from as low a height as possible, and with a low relative velocity between the wind and the package in the horizontal plane at release. Contrary to that, when combining the estimation with the circular delivery method, the headwind releases gives a higher accuracy. For headwind drops the algorithm can land within 1m of the target approximately 94 to 95 % of the time for wind velocities up to 10m/s. This is significantly better than the fly-by algorithm, which can with 95 % certainty land only within 4m of the target for a similar wind. For even stronger winds the accuracy decreases and for 15m/s wind the circular algorithm can land within one meter with approximately 61 to 69 % probability. Compared to the fly-by, the package also has a lower velocity when it lands, when released with the circular delivery method. The 95th-percentile velocities are 9m/s and 8m/s respectively. One drawback with the circular algorithm, however, is that it takes longer time before the package is released, with an approximate time of 3 min on average compared to 10 s for the fly-by.