Multibody Dynamics Modeling of Flexible Aircraft Flight Dynamics

Abstract

Because of the focus on weight minimization, aircraft are becoming more and more flexible. Therefore, the frequency separation between flight mechanics motion and structural vibration decreases. This calls for a flight mechanics model that includes aeroelasticity. The development of such a model was the subject of the current research. This model can be used for gust and maneuver load prediction in the preliminary design phase. With accurate load prediction, structural integrity can be ensured and unstable flight conditions can be avoided. Moreover, the model may be used to design active load alleviation systems to increase passenger comfort, reduce fatigue, and decrease loads on the wing structure. A modal structural model and a quasi-steady aerodynamics model are integrated in a partitioned manner to form an aeroelastic wing model. This aeroelastic wing model is implemented in a multibody dynamics environment, in order to model flight dynamics and the effect of aeroelasticity thereon. An A320-like aircraft was analyzed in the current research. The effect of aeroelasticity on flight mechanics was investigated. Inclusion of flexibility substantially affected the trim control variables, but had an almost negligible effect on the flight mechanics modes and stability derivatives. When flexibility increases, these parameters are affected. Aeroelasticity has a non-negligible effect on the (peak) wing loads after maneuvers or disturbances. Especially for maneuvers or disturbances that increase lift, and therefore wing deformation, the peak loads are affected. Moreover, wing loads are particularly affected by disturbances that have a direct effect on the wing, such as aileron deflection. The objective of the current research was to improve on an existing aeroelastic flight mechanics model, based on the lumped-parameter approach. The modal model created in the current research proved to have a computational effort that is several times lower than the lumped-parameter model. In addition, the accuracy of the modal model can be increased beyond that of the lumped-parameter model at only a small additional computational cost. Because of the reduced computational cost, and the potentially increased accuracy, the modal model performs better than the lumped-parameter model. Due to the qualitative nature of these conclusions, it is probable that they can be extended to other conventional, low aspect-ratio aircraft in the subsonic flight regime. Definitive, quantitative conclusions could not be formulated, because of the absence of complete validation data.