Aerodynamic performance optimization for the rotor design of a hovering agricultural unmanned helicopter

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The importance of using Agriculture unmanned helicopters (AUHs), especially for spraying pesticides and fertilizers on any terrain type to ensure crop yields, has been recently acknowledged. Apart from flying these helicopters at a super-low altitude and low speed, using an efficient and optimum rotor blade ensures a uniform and deep penetration of pesticide and fertilizers over a specified area. Accordingly, this work attempts to optimize the rotor blade of an AUH by using coupling statistics and several numerical techniques, including design of experiments, response surface method, and computational fluid dynamics. The experiments are designed using the central composite design method and by selecting the geometric variables that affect the aerodynamic performance of the rotor blade, including the root chord, tip chord, and angle of attack. The angle at the root and tip is optimized in order for the resulting twist to produce a uniform blade loading, achieve maximum lift, and minimize the required hover power. The required aerodynamic forces and limited availability of engine power are identified as constraints. The blade is optimized only when the helicopter is hovering at a persistent rotational speed, and the hover efficiency of the rotor blade with an optimal twist distribution is significantly higher than the baseline.