Effect of Uncertainty on Hub Vibration Response of Composite Helicopter Rotor Blades

In this study, an assessment is made to quantify the influence of random material properties and fabrication/manufacturing uncertainties on the aeroelastic response and hub vibratory loads of composite rotor blades. The random variables include lamina stiffness properties, ply thicknesses and fiber orientation angles of the laminate structures,and the elastic-axis offset from the aerodynamic center in the section of the blade. The stochastic behavior of the random variables obtained from previous experimental or analytical studies are used to evaluate the stochastic behavior of the cross-sectional stiffnesses of the blades. The uncertainties in the stiffness properties result in the dissimilarity of the rotor system, which brings extra non-N(b)/rev vibrations. It is observed that the probability histograms of N(b)/rev hub vibratory loads exhibit a normal distribution, whereas those of non-N(b)/rev hub loads show non-Gaussian-type distributions. Numerical results showing the effects of material and geometric uncertainties on the aeroelastic response and hub vibration behavior of composite rotor blades are illustrated and important conclusions are drawn based on the observations.