Characteristics of Ground Effects of an Unmanned Aerial Vehicle with High-aspect-ratio Flying Wings during Take-Off
In view of the take-off process of an unmanned aerial vehicle (UAV) with high-aspect-ratio flying wing configurations, the influences of ground effects on longitudinal aerodynamic characteristics of the UAV were investigated. By using a numerical simulation method, the effects of different angles of attack, heights from the ground, and take-off velocity on the UAV were studied. Moreover, based on comparisons with test data in previous literature, the numerical calculation method was verified to be accurate. The height from the ground is the primary factor influencing longitudinal aerodynamic characteristics of the UAV. With the increase in height from the ground, the lift and drag coefficients of the UAV, and its pitching stability, increased. When the angle of attack was small, a large suction area was generated on the lower surface of wings with a large suction amplitude therewith. This results in a large range of downwash. As the angle of attack increased, the lower surface of the trailing edge for wings presents weakening downwash. As the take-off velocity rose, the suction area on the lower surface of the UAV, and its amplitude, gradually decreased, and the negative pressure on the upper surface also decreased to a certain extent. The research results can provide a certain theoretical basis for the safe design of take-off operations for high-aspect-ratio UAVs.