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An Investigation of the Structural Dynamics of Helicopter Rotors
Final rept. Jun 1967-Oct 1969
CORNELL AERONAUTICAL LAB INC BUFFALO NY
Pagination or Media Count:
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 rotor systems which are of a general configuration and of including configuration variables which are normally neglected. An experimental apparatus and a testing technique have been developed for obtaining the experimental data necessary to verify the analytical procedure. This apparatus and the technique are capable of determining the natural vibration modes and frequencies of two-bladed rotor systems of a very general configuration while operating in the absence of aerodynamic loads. An initial test program with the apparatus was conducted to determine the adequacy of the equipment. The tests not only demonstrated the capability of the equipment and test procedure but also 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. The computed and measured spanwise moment distributions and the corresponding natural frequencies are presented for six of the natural vibration modes of the test rotor at several rotational speeds. The theoretical and experimental results are compared and their differences are discussed.
APPROVED FOR PUBLIC RELEASE