Identification of Structural Parameters from Helicopter Dynamic Test Data

A method is presented for obtaining the mass, stiffness, and damping parameters of a linear mathematical model, having fewer degrees of freedom than the structure it represents, directly from dynamic response measurements on the actual helicopter without a prior knowledge of the physical characteristics of the fuselage. The only input information required in the formulation is the approximate natural frequency of each mode and mobility data measured proximate to these frequencies with sinusoidal force excitation applied at only one point on the vehicle. This dynamic response information acquired from impedance testing of the actual structure over the frequency range of interest yields the second order structurally damped linear equations of motion. The practicality and numerical soundness of the theoretical development was demonstrated through a computer simulation of an experimental program. It was shown, through approximately 400 computer experiments, that accurate system identificatioin can be achieved with presently available measurement techniques and equipment.