A Nonlinear Response Analysis and Solution Method for Rotorcraft Vibration

The governing equations for a fully coupled, rotor‐fuselage vibration model are derived. There are three sets of equations involved. First are the equations of motion far a uniform, elastic blade that can undergo flap and lead‐lag bending deflections. The second set of equations comprises the hub‐load equations. For both the blade and hub‐load equations, the aerodynamic forces are derived from quasi‐steady strip theory. In modeling the fuselage, beam finite‐elements and generalized isolator elements are used to generate the third set of equations, the fuselage equations of motion. The blade and fuselage responses, as well as the hub loads, are computed by an iterative, combined harmonic‐balance, impedance‐matching method. In addition, the uncoupled blade and fuselage modes and frequencies, which are by‐products of the blade and fuselage analyses, and the coupled system natural frequencies may be obtained.