Numerical Aerodynamic Characteristics Analysis of the Close Formation Flight

Abstract

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.

The formation of unmanned aerial vehicle swarm

“…The Echelon Formation could be quite usual in practical use, with the trailing aircraft assigned at the side rear of the leading one on the same side. As is shown in figure 9, the lift-todrag ratio is significantly high for UAV C at the cost of more power consumption of UAV A and B, for the reason that drone C can take advantage of the tip vortex of both A and B in echelon formation [32]. However, the advantage of upwash flow has not been fully taken in that formation pattern, so echelon formation may not suit movements of long distance, but it is specified in saving UAV C's power, especially suitable for missions such as relay [32].…”

Aerodynamic Interactions in Formation Flight for Wake Vortex Surfing

“…As trailing aircraft is the beneficiary, its position in the formation must be determined and maintained during the vortex surfing phase to maximize the gains. Other than the flight test, several numerical simulations research [25][26][27][28] have been conducted over the last few decades to investigate the trailing aircraft position and its aerodynamics implications on vortex surfing. With the available data from SAVE program, Halaas et al [25] used Reynolds-Averaged Navier Stokes (RANS) for the C-17 formation simulation, with consideration on the trim condition of following aircraft.…”

“…The authors found that both the Vortex Lattice Method (VLM) and RANS turbulence models predict the same location of minimum drag and maximum lift, but RANS is more accurate in the lift and drag calculation, with a smaller deviation from the experimental results. Whereas Zhang et al [27] used RANS to determine the optimal lateral spacing, vertical distance and the optimum formation of simplified tailless delta wing UAVs in the close formation flight. Vechtel et al [28] used Large Eddy Simulation (LES) to generate vortex flow fields with small perturbations of the vortex lines, which is a more representative flow field for real flight conditions.…”