Development of a Novel System Identification Modelling Technique: Nonlinear Dynamic Inversion Stitching Applied to Rotorcraft

Abstract

High-fidelity modelling and simulation are essential for informed decision-making in rotorcraft design and development. They play a critical role in evaluating performance, handling qualities, control law development, aircraft dynamic load analysis, and the creation of realistic simulation environments. The model stitching technique, commonly used in full-flight envelope helicopter simulations, has shown success but offers limited physical insight. This paper introduces a novel approach: Nonlinear Dynamic Inversion (NDI) Model stitching. This method works backwards from identified linear models to the isolated linearised rotor model. It improves physical insight by isolating the derivatives of rotor forces and flapping angles, offering a deeper understanding of their contribution to the helicopter dynamics. In this exploratory study, the novel NDI method was applied to an 8-DoF nonlinear BO105 simulator and the EC135 HeliWorkX nonlinear simulator provided by the German Aerospace Centre (DLR). The new methodology provided a promising error reduction of up to 70% compared to the state-of-the-art stitching methodology on selected manoeuvres.