An Investigation of the Structural dynamics of Helicopter Rotors.

摘要

An analysis and computational procedure has been developed for predicting the natural vibration modes and frequencies of rotor blade and hub systems. This method is capable of treating configuration variables which are normally neglected. An experimental apparatus and a testing technique have been developed which are capable of determining the natural vibration modes and frequencies of two-bladed rotor systems of general configuration in the absence of aerodynamic loads. An initial test program was conducted to determine the adequacy of the equipment. The tests revealed a problem with extrinsic excitation of the test rotor at frequencies other than the shaking frequency. Recommendations are made for modifications to the system and the techniques in order to reduce the levels of these extraneous excitations and to minimize their effects. Spanwise moment distributions and the corresponding natural frequencies are presented for six natural vibration modes at several rotational speeds. The theoretical and experimental results are compared and their differences are discussed. (Author)