An Integrated Modelling Approach for Flight Dynamics, Manoeuvre- and Gust-Loads Analysis

Abstract

An integrated modelling approach, suitable for flight loads analysis and flight dynamics investigations is presented. These scenarios need fast loop capable simulation models. Typically, they are evaluated many times in the entire flight envelope, for varying mass cases and for changing parameters during the aircraft design process. Further, the simulations models have very different requirements depending on their application. Flight dynamics models must account for large nonlinear rigid Body motions and aerodynamic nonlinearities, manoeuvre loads analysis, additionally need to take flexible deformations into account, and hence require distributed aerodynamics, and for gust loads Analysis unsteady aerodynamic effects are essential. The proposed integrated model is based on nonlinear equations of motion using mean axes constraints. Potential flow based aerodynamics with low computational cost are the method of choice for most aeroelastic applications. Presented in this paper are some important aspects regarding the aerodynamic modelling, which are handled differently compared to other implementations. Instead of the Doublet Lattice Method (DLM), the 3D panel method NEWPAN is used, which is able to capture previously neglected flight mechanical effects such as roll-yaw coupling and induced drag. Since, the Aerodynamic Influence Coefficient (AIC) matrices obtained from NEWPAN are nonlinearly dependent on the flight state, a Reduced Order Model (ROM) based on Proper Orthogonal Decomposition (POD) is setup and subsequently interpolated. The proposed ROM interpolates directly AIC matrices (AIC-ROM) instead of pressures. The advantages of a ROM based on AIC matrices over similar approaches based on pressure coefficients are explained. Similarly to the Doublet Lattice Method, the 3D panel code is able to compute frequency based unsteady Aerodynamic Influence Coefficient (AIC) matrices, which are approximated by a "physical" Rational Functions (RFA) to make them amenable for time domain simulations. Unlike other approaches, the physical RFA allows a clear separation of quasi-steady, added mass and unsteady lag terms. Several application examples are presented and their particular needs are addressed. The proposed modelling approach supports flight dynamics by including previously neglected aerodynamic roll yaw coupling and nonlinear angle of attack dependencies, manoeuvre loads, including aeroelastic deformations, and gust loads analyses, including unsteady aerodynamics in one integrated model and is suitable for for investigations regarding active gust and manoeuvre load alleviation, primary flight control design, or performance improvement through lift redistribution.