Generalized dynamic wake model applied to rigid blade equations for helicopter rotor in hover

Abstract

The aeroelastic stability of helicopter rotors in hover is examined through a generalized dynamic inflow model coupled to elastic restraint rigid blade equations. The blade configuration contains a root spring to model pitch-link flexibility, and a set of hub and blade torsional springs to restrain flap and lead-lag motions. The state-space treatment of the inflow allows a standard eigen analysis for the time dependent equations established after perturbations are taken about blade equilibrium and steady-state inflow. Static and dynamic analysis results for a two-bladed rotor show how the finite-state unsteady aerodynamics performs in the presence of a simple rigid blade model. Steady-state results capture three-dimensional tip relief effects and show good agreement with their elastic blade counterparts. Damping results for configurations including precone and droop fail to correlate well because the structural model does not account for elastic flap-lag-torsion couplings.