Effects of Blade-to-blade Dissimilarities on Rotor-body Lead-lag Dynamics
Small blade-to-blade property differences are investigated to determine their effects on the behavior of a simple rotor-body system. An analytical approach is used which emphasizes the significance of these effects from the experimental point of view. It is found that the primary effect of blade-to-blade dissimiliarities is the appearance of additional peaks in the frequency spectrum which are separated from the conventional response modes by multiples of the rotor speed. These additional responses are potential experimental problems because when they occur near a model of interest they act as contaminant frequencies which can make damping measurements difficult. The effects of increased rotor-body coupling and a rotor shaft degree of freedom act to improve the situation by altering the frequency separation of the modes. Keywords: Rotor dynamics; Floquet theorem; Mismatched blades; Helicopter rotor blades; Equations of motion.
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1/rev response 1000 ROTOR SPEED Aeroflightdynamics Directorate Ames Research Center blade properties blade-to-blade dissimilarities BLADES O REGRESSING body degree body initial condition collective mode damper constant degree of freedom Dissimilarities on Rotor-Body EFFECTS OF BLADE-TO-BLADE eigenvalues equations of motion fc coordinate figure 17 Fixed system frequencies Floquet eigenanalysis Floquet theory Floquet's theorem frequency separation function of mismatch function of rpm isolated blade frequency Lead-Lag Dynamics Michael lower rotor speeds mass center matched blade results McNulty mismatched blades mode of interest mode plus 2/rev Moffett Field multiblade coordinates multiblade cosine coordinate multivalued frequencies N-m-sec N-sec/m cy N/m ky natural frequencies nonisotropic body numerical integration periodic mode shapes PROGRESSING A COLLECTIVE progressing excitation qN+3 regressing lead-lag mode regressing mode frequency rotor shaft degree Rotor-Body Lead-Lag Dynamics rpm Fig shaft freedom shaft properties shown in figure simple rotor-body system soft body configuration spring constant stiff body configuration U.S. Army