Elastic-Blade Whirl Flutter Stability Analysis of Two-Bladed Proprotor/Pylon Systems

摘要

In axial flight, rotors with three or more blades result in constant coefficient equations of motion, but the polar asymmetry of a two-bladed rotor leads to equations of motion with periodic coefficients. Although numerous studies on whirl flutter of three-bladed rotors are available in the literature, only a few of these address the issue of two-bladed rotors. The aeroelastic stability of two-bladed proprotor/pylon/wing combinations is examined using an elastic-blade analysis. Several parametric studies have been conducted by varying the natural frequencies of the system. Results of these studies have been compared with the results of a simple rigid-blade analysis developed previously. It is shown that the rigid-blade analysis captures the important interactions between the various rotor and wing modes. However, significant differences are observed in the behavior of the whirl flutter speeds, as obtained from the two analyses, when the natural frequencies of the rotor are varied. The parametric studies show that blade elasticity affects the wing chord mode damping at flight speeds close to the flutter speed, leading to differences in the critical flight speed of the wing chord mode as compared to the rigid-blade analysis. Also, the wing beam mode, which is always stable as per the rigid-blade analysis, is found to become unstable if the wing torsional stiffness is reduced from its baseline value.