Numerical Aerodynamic Characteristics Analysis of the Close Formation Flight

The aerodynamic characteristics of the close formation flight are numerically analyzed to facilitate a greater understanding of the vortex effects between UAVs and technically support the application of close formation flight for UAVs. The aerodynamic characteristics of a single UAV are calculated, the results of which are used as the reference to the variation of aerodynamic values in the comparison with close formation flight. The vortex effects of the leading UAV on the aerodynamic characteristics of the trailing UAV in the two UAV close formation flight are analyzed. The position where the trailing UAV obtains the maximum lift-to-drag ratio is defined as the optimal position. Based on the optimal position, three different types of three UAV formations are designed to explore the preliminary application of the aerodynamic benefits in the close formation flight for multiple UAVs. It is observed that the incremental aerodynamic forces and moments of the trailing UAV vary with the lateral and vertical spacing between the two UAVs, and the trailing UAV can obtain significant aerodynamic improvement if positioned at optimal position behind the leading UAV while in close formation flight. It is also proved that the aerodynamic characteristics of the close formation for three UAVs can be improved when the formation is designed based on the optimal position, and this will increase the range and endurance of the UAVs in operational application.