Modelling Framework for Handling Qualities Analysis of Flexible Aircraft

Abstract

Accurate prediction of interactions between aeroelasticty effects, flight control and flight dynamics are critical for the evaluation of handling qualities for future aircraft concepts. A simulation framework for such analyses, known as CA2LM, is presented in this paper together with the modelling techniques and methods used to develop the framework. Aerodynamic surfaces were modelled using the Modified Strip Theory (MST) approach and a state-space representation of the Leishmann-Beddoes unsteady aerodynamics model. A modal approach allows the analysis of structural flexibility and each mode’s influence on structural deflections. The derivation of equations of motion that provide a new approach to modelling flexible aircraft is presented. This takes into account the variations in mass and inertia properties due to structural deformations. The AX-1 generic large transport aircraft model is analysed as an example of the CA2LM framework capabilities. Results show that according to the Gibson Dropback Criterion longitudinal handling qualities of the AX-1 with no flight control system are unsatisfactory. The analysis of the structural stiffness influence shows that increasing flexibility of an aircraft structure deteriorates the longitudinal handling qualities. The short-period damping ratio is within Level 2 acceptability requirements. In contrast, the short-period frequency and acceleration sensitivity graph shows that the AX-1 model handling qualities are within Level 1 acceptability requirements. Finally, steps towards the future development of the CA2LM framework are listed.