The Influence Of Dynamic Inflow And Torsional Flexibility On Rotor Damping In Forward Flight From Symbolically Generated Equations

The combined effects of blade torsion and dynamic inflow on the aeroelastic stability of an elastic rotor blade in forward flight are studied. The governing sets of equations of motion (fully nonlinear, linearized, and multiblade equations) used in this study are derived symbolically using a program written in FORTRAN. Stability results are presented for different structural models with and without dynamic inflow. The study shows that symbolic and numerical programs written in FORTRAN can be conveniently used in a complicated helicopter-rotor aeroelastic modeling and analytical process. It is observed that for a large number of degrees of freedom and for fully nonlinear models, the amount of data needed for the symbolic program increases exponentially, making it inconvenient to consider the multiblade equations explicitly. However, a combination of symbolic and numerical programs at the proper stage in the derivation process makes the obtainment of final stability results an efficient and straightforward procedure. The symbolically generated equations are subsequently used to investigate the influence of elastic torsion modes and dynamic inflow on isolated rotor inplane stability in forward flight. Results are presented for both singlerotor- blade models and multiblade rotor systems. For both soft inplane and stiff inplane hingeless rotors, the elastic torsion mode significantly affects the predicted inplane damping. Dynamic inflow does change the magnitude of the predicted damping, but the influence on damping trends is generally small with varying advance ratio or elastic coupling parameter.