Aircraft Subsystems Modelling Using Different MBS Formalisms

Abstract

The paper presents three case studies of dynamic analysis of aircraft during landing manoeuvre using two basic formalisms encountered in rigid and flexible multibody system (MBS) modelling. In the first case a formulation in natural coordinates has been used to analyze the dynamics of a medium size aircraft. Equations of motion have been formulated and solved using velocity transformation method. The aircraft has been modelled as consisting of rigid bodies connected by universal joints with springs. Aerodynamic forces have been taken into account by applying the Vortex Lattice Method (VLM) to the calculations performed. The effect of ground proximity on the results (ground effect) has been analyzed. In the second case, a dynamic analysis of a glider during the landing manoeuvre has been carried out from the point of view of stress recovery by means of various methods. Body positions and orientations have been written in absolute coordinates with floating frame approach for flexible bodies. Finite element method (FEM) and component mode synthesis has been used to model the flexibility of the bodies. A comparison of stress results obtained for different computation methods has been carried out. In the third analysis a MBS model of the Su-22 military airplane main landing gear has been presented. The absolute coordinates and the differential algebraic equations (DAE) formulations were used in all calculations. The whole landing gear model includes individual models of hydraulic actuators, shock absorber, flexible tire and contacts between some landing gear parts. Several types of simulations like landing gear extension and selected ground manoeuvres were performed. On that basis values of the forces which will allow to assess fatigue and durability of landing gear in future experiments were obtained. The received results were compared to the experimental measurements which were carried out on a real military airplane. The key issues of that comparison and general remarks were formulated. In the final part of the paper general conclusions regarding application of various computation MBS methods to dynamical analyses of aircrafts have been presented.