Structural, Flight Dynamic Modeling Andun-modeled Analysis Of Very Flexible Aircraft

High altitude long endurance unmanned aerial vehicle(HALE UAV), solar-powered airplane have drawn more and more attention in recent years. The structures of the aircraft always have noticeable wings structural flexible, and may result in large elastic deformation during flight, which has a great influence on flight dynamics characteristic of the aircraft. So that, the traditional dynamics model which based on linear, small deformation assumptions is not appropriate. A multidisciplinary(structures, aerodynamic, controls, etc.) models need to be developed, which can accurately describe the nonlinear dynamic behaviors of the aircraft. In addition, the real dynamic system of very flexible aircraft(VFA) is highly complex and contains many uncertainties. This dissertation focuses on the research of VFA, including dynamic modeling, dynamic characteristics analysis, uncertainty modeling and model validation.First, the dynamic model is based on a fully geometrically-exact nonlinear flexible beam model coupling with a quasi-steady aerodynamic model. The finite element method is used for system discretization and flight dynamic equations of the high aspect ratio flexible aircraft are obtained by Lagrange's equations. Second, a method for trim analysis of VFA with large deformation has been presented in this dissertation, and the generalized ? method is used to solve the equations of motion(EOM) of VFA. The flying wing configuration is used to investigate the characteristics of dynamic stability, time-domain response, dynamic stiffening and influence of the number of finite element on dynamic characteristics of the high aspect ratio flexible aircraft. At last, the balanced realization and truncation and minimum state method is used to reduce the system size, and based on this reduced-order model, robust stability theorem is used to analysis the uncertain VFA system, and the validity of the model is tested by model validation method based on matrices interpolation theory.The results obtained indicate that the model involves the telescopic deformation and coupling with the longitudinal bending deformation, and also includes automatically all six rigid-body degrees of freedom and elastic deformation, as well which reflects comprehensive multidisciplinary interaction between nonlinear flight dynamics characteristics. External payload which under the flexible wing can improve anti deformation of wings to a certain extent, and the dynamic characteristics of the aircraft also can be influenced, but it is related to the position of external payload, the stability of multi-beam wing structure is better than single beam wing. As the payload increases, the wing bending deformation becomes larger, which increases of lift acts departs more and more from the vertical direction. What's more, the motion of flexible aircraft becomes unstable, and the structure of wings may be destroyed. In order to ensure the stability of the aircraft and avoid the wing structure being destroyed, it is necessary to design controller. Besides, the stretch/bending coupling almost has no effect on dynamic characteristics of VFA, which means the phenomenon of dynamic stiffening does not appear in this dissertation, but it does not mean that the phenomenon of dynamic stiffening does not appear in VFA system during flight. Minimum state method can better retain some important information of the full model. Base on reasonable distribution the proportion of magnitude of each uncertainty weighting, the model validation algorithm can more really reflect the ture physical system.