CALCULATED RESEARCH OF INFLUENCE OF HELICOPTER MAIN ROTORS GEOMETRY ON THE EFFICIENCY IN HOVER MODE BASED ON THE NONLINEAR VORTEX MODEL

Abstract

The efficiency of the helicopter main rotor in the hover mode is very important, because this mode essentially determines the performance characteristics of the helicopter. A feature of the helicopter rotor aerodynamics is a significant inductive blade influence that highly defines its aerodynamic characteristics. The problem of the influence of the blade twist and spatial geometric layout of the main rotor on its aerodynamic characteristics in the hover mode for a fixed value of the rotor solidity has been considered in this article. As a criterion of efficiency of the rotor in the hover mode relative efficiency (FoM – Figure of Merit) is used. The results are obtained by numerical simulation based on the nonlinear vortex blade model of the rotor, developed at the Helicopter Design Chair of the MAI. The model allows taking into account a complicated spatial shape of the free vortex path of the rotor blades that determines their inductive interaction. As the example of a four-blade main rotor with rectangular blades in plan, the influence of the value of the blades twist on the efficiency in the hover mode is studied. For different values of the rotor thrust, the values and ranges of the blade twist angles are determined, providing the maximum positive effect of the efficiency increase in hovering. For a fixed value of the blade twist, the rotor solidity, and the same operating conditions, the effect of various schemes and configurations of rotor on its efficiency in hover mode is studied. A single rotor with a different number of blades (from 2 to 6), an X-shaped rotor, coaxial rotor and rotor with crossed blades type "synchropter" are considered. The values of the efficiency increase in hovering depending on the rotor layout in comparison with the two-blade rotor are obtained. The comparative analysis of inductive velocities and streamlines for the "synchropter" rotor scheme, coaxial rotor scheme and its equivalent single rotor scheme is presented. The obtained results can be useful at the stage of preliminary design of vertically taking-off aircraft when selecting the parameters of their main rotor system.