ZONA Technology, Inc. (ZONA) proposes to develop an integrated flight dynamics simulation capability with nonlinear aeroelastic interactions by combining a flight dynamics model and an added-on nonlinear aeroelastic solver in a Simulink environment. This nonlinear aeroelastic solver is generated by interacting a nonlinear structural reduced order model (ROM) with a Neural-Network-based (NN-based) aerodynamic ROM, called the ROM-ROM procedure, to provide the incremental aeroelastic forces and moments to a given flight dynamics model. In this way, the flight dynamics model is kept with minimum changes so that this integrated flight dynamics simulation remains in the frame work of a 6 degrees-of-freedom simulation environment. The nonlinear structural ROM employs a so-called ELSTEP/FAT procedure that operates on a nonlinear finite element method, such as MSC.Nastrans solution 106 to construct a set of modal-based nonlinear stiffness matrices. The NN-based aerodynamic ROM is generated using a system identification technique operating on a CFD code to evaluate the weights and biases in a two-layer feed-forward neural network system. The end product is called NL-DFS which can simulate the key aeroelastic coupling mechanism between nonlinear structural dynamics and nonlinear unsteady aerodynamics with classical rigid body dynamics of a slender, flexible and sizable aircraft in nonlinear aerodynamic flight conditions.