Methods for determining the stiffness properties of a helicopter main rotor blade based on computational experiments

Due to the widespread use of composite materials in the designs of helicopter main rotor blades (MRB), special attention should be paid to monitoring the obtained stiffness characteristics at all stages of their development and operation. The available experimental control methods have inherent limitations and can only be used at the late stages of blade development, as well as at the stage of mass production. This paper proposes the methods for determining the stiffness properties of a composite blade based on the results of a computational experiment, performed on the basis of the finite element method (FEM) in the MSC.Laminate Modeler submodule of the MSC.Patran/Nastran computing complex and numerical processing of the obtained deformations of the model blade suitable for use also during the design and development stages of the MRB. Numerical processing of the results is performed according to the ratios obtained as a result of the transition from the initial equations of bending and torsion of a cantilevered beam of variable cross-section, modeling the blade to their discrete matrix notation. For this purpose, the calculated sections are selected based on the blade length, the number and location of which depend on the features of its design. In this case, the values of the higher derivatives (curvature and relative twist angle) included in the specified equations are calculated by formulas representing their difference approximations. The proposed methods have been tested on the FEM MRB of the Mil-34 (NATO reporting name: Hermit) helicopter. The estimates of the quality of the coincidence of the calculated and experimental stiffness properties are obtained.