Aerodynamic performance assessment of a ducted fan UAV for VTOL applications

Abstract The aerodynamic performance of a recent developed ducted fan Unmanned Aerial Vehicle (UAV) was experimentally assessed by means of force, pressure and PIV measurements. Experiments were conducted on the UAV for both hover and forward flight configurations. Particular attention was given to the in-ground-effect which is important for the take-off and landing modes of the UAV during flight. Variations included rotational speed of the contra-rotating fan, incident angle, forward flight speed and the exit-to-ground distance were examined, allowing a comprehensive understanding of the overall aerodynamic characteristics of the ducted fan UAV. Wind tunnel measurement has successfully defined an initial operation region of the ducted fan UAV. The inlet velocity distortion at the inlet of the UAV during forward flight can significantly influence the inlet circumferential pressure distribution and therefore in principle affect the overall aerodynamic performance. The presence of the ground during take-off and landing can enhance the total lift generation with slightly sacrificing propulsive efficiency. In addition, when the UAV flies in proximity of the ground the back pressure at exit will be increased and thus alleviates the lift production by the duct lip. The outcomes can provide essential information in design and optimization of ducted fan type flight vehicles.