A Methodology For Linearization Of Highly Coupled Rotor-Body Dynamics For Side-By-Side Helicopters

Abstract

This paper presents a 38-state space linear flight dynamics representation of a side-by-side helicopter. The aim of the paper is to propose an original linearization and trim methodology to deal with highly complex numerical mathematical models involving coupled flap and lead-lag rotor dynamics. The trim and stability features of the helicopter are computed by using this method and the effects of blade's flexibility on body flight dynamics are discussed. Rotorcraft's stability is governed by two unstable oscillatory modes, identified as typical phugoid and dutch-roll, and four real, stable, dynamics of different frequencies. The results show also that while the rotor lead-lag is beneficial for the overall stability, the lateral/longitudinal inflow modes destabilize the motion. The presented methodology allows furthermore to evaluate the impact of the rotor- body - couplings on vehicle characteristics and can be extended to investigate the stability of any vertical take-off and landing (VTOL) configuration.