Helicopter Tailrotor Dynamics Characterization and Stability by Multibody/Multidisciplinary Analysis

The multibody approach allows to use modular models to build complete de- tailed systems. The size of the resulting model may become soon very large; its complexity is dictated by the complexity of the problem and by the advantages of a generic approach. The capability to obtain a dynamic charaterization and to analyze the local stability of pe- riodic orbits is of paramount importance, especially in industrial applications. This paper presents all the hurdles which may be encountered while trying to extract eigensolutions for a multibody model based on a redundant coordinates set index three DAE system for- mulation. This paper applies an ee ctive method to overcome these limitations, based on Proper Orthogonal Decomposition (POD), to the analysis of a helicopter tailrotor. Data analysis using POD is conducted to extract a set of basis functions, called Proper Or- thogonal Modes (POM) from numerical simulations, for subsequent use in a Galerkin projection that yields low-dimensional dynamical models. The POMs are a minimal set of output signals that can be used to identify the dominant eigenvalues of the transition matrix. Finally the same methodology is applied to the periodic stability investigation re- curring to the construction of stroboscopic Poincar e maps.