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Performance assessment of a variable-span morphing wing small uav for high altitude surveillance missions

Abstract:

Morphing wings are of great interest to the unmanned aircraft community because they enable to modify the wing geometry during flight to adapt the performance of the UAV according to the flight conditions. Particularly, variable-span wings could enhance the aerodynamic efficiency of the UAV because of the increase in the wingspan and aspect ratio. However, the addition of actuators and mechanisms to produce the enlargement of the wingspan causes the increase of the total UAV weight (WTO), which can diminish the pbkp_redicted aerodynamic benefits. Considering the above, this research work presents the assessment of the mission performance of several variable-span morphing wing configurations implemented in a small electric UAV. The aerodynamic and mission performance of the variable-span configurations have been compared with their corresponding fixed-wing counterparts. For the aerodynamic assessment, a 3D-Panel method has been used for the calculation of the lift, induced and viscous drag coefficients. The lift-to-drag ratio and the lift distribution along the wingspan have been also determined. In what respect to the UAV mission performance, the endurance and the coverage area have been calculated using an enhanced parametric methodology for performance estimation of battery-powered small UAVs. The flight conditions have been defined according to typical photogrammetry and search missions carried out at high altitudes (4200 [masl]). Results indicate that an increase of 50% in the wingspan can enhance the aerodynamic efficiency of the UAV up to 15% and reduce the drag coefficient up to 6% compared with the baseline rectangular wing. However, the local lift coefficient along the span is significantly higher for the variable-span wings, contrasted with their fixed-wing analog designs, which could affect the structural reliability of the variable-span wings. In what respect to the UAV performance, the enhancement of the aerodynamic efficiency is not sufficient to increase the UAV endurance and coverage area because the total UAV weight gets also increased due to the addition of extra components for the morphing wing mechanism and the addition of more material for the wing-box structure. In summary, variable-span wings are not a feasible approach to enhance the endurance of small electric UAVs mainly because of the addition of extra weight, which withdraws the pbkp_redicted aerodynamic benefits.