Robust trim procedure for rotorcraft configurations

This paper presents a highly robust trim procedure for a generic rotorcraft configuration. The procedure acts externally on time marching models to produce a trim solution and is applicable over a wide range of rotorcraft configurations, including conventional helicopters, coaxial rotor systems, tandem, and side-by-side configurations. Examples for each of these configurations are provided. It successfully determines a trim solution regardless of model non-linearities, number of modeling states involved, model contents, numerical methodology, or the stability characteristics of the configuration under discussion, without exploiting any additional stabilization mechanism. The method is shown to be highly robust and insensitive to the initial guess for the trim variables, which substantially simplifies the trim process although at a certain expense in computational time.