Resumen
Variable diameter rotor can improve the flight performance of the aircraft both in hovering and forward flying and a duct can improve the rotor performance further both in force and efficiency. In previous studies, those two parts are always studied in the one-factor-at-a-time method, and the duct is lack diameter change so that it cannot cooperate with the variable diameter rotor. In this paper, the Chinese utility helicopter Z9 is taken as the prototype, and the structural parameters of the variable diameter ducted fan (VDDF) are selected by an orthogonal experiment method. Based on the momentum-element theory, the aerodynamic theoretical model of the disk is established, and the structural parameters that can achieve the best efficiency in hover/propulsion and the best lift/thrust force ratio under different modes are obtained in the orthogonal range by computational fluid dynamics method. The structural parameters of the VDDF under the set working conditions are obtained by a technique for order of preference by similarity to ideal solution (TOPSIS) evaluation and the flight performance of the aircraft equipped with the VDDF is superior to the prototype: The max takeoff weight raises 25%; the hover ceiling raises 90%; the cruise altitude raises 11%; the cruise speed raises 23% and the max speed raises further. However, a better engine may be needed to provide greater power.