Aerodynamic Aspects of Unmanned Aerial Vehicle Aerial Refueling

The feasibility of refueling a high-endurance unmanned aerial vehicle was investigated numerically, focusing on the aerodynamic effects. For this study, a single-aisle transport aircraft-based tanker was proposed (the Airbus A320) and, for the much smaller unmanned aerial vehicle, the MQ-9 Reaper was selected (and the weight ratio between these two airplanes was less than 6%). This refueling scenario was different from most previous studies where the tanker and the refueling airplanes were of similar weight. Computed results showed that the aerodynamic coefficients changed significantly with lateral and vertical separation between the two airplanes, and they changed only marginally when changing the following distance. In spite of the size and performance differences, it was found that, when the refueling plane approached from reasonably below and behind the tanker airplane, the induced rolling moments were within the unmanned aerial vehicle aileron control limit and a refueling maneuver was possible.