Effect Of Hub Impedance On The Inplane Oscillatory Blade Loads Of A Two-Bladed Rotor System

Dynamic reaction between the rotor and support system for two-bladed rotors has a first-order influence on rotor behavior under normal operating conditions. Many earlier papers treat the stability characteristics of the rotor/pylon system, but little literature has been devoted to the discussion of the effects of support system parameters on rotor stress response. This paper discusses the effect of hub impedance (support system parameters) on the inplane oscillatory loads of a two-bladed rotor with two- and multi-degree-of-freedom supports. Analytical results are presented which show that the rotor one-per-rev response (inplane blade root bending moment) can vary from zero (rigid body) to resonance loads depending on the rotor's hub impedance. The paper shows how the inplane response of a two-bladed rotor can be qualitatively evaluated using only the system coupled and uncoupled rotating natural frequencies. Analytical and test results are compared for a small-scale dynamic model, and data is presented from a larger-scale model tunnel test with more realistic aerodynamics.