This work represents a new paradigm for the dynamics and control of maneuvering flexible aircraft. Using the system concept, the theory integrates seamlessly all the necessary material from the areas of analytical dynamics, structural dynamics, aerodynamics, and controls. It includes automatically all six rigid-body degrees of freedom and elastic deformations, as well as the gravity, propulsion, aerodynamic, and control forces, in addition to forces of an external nature, such as gusts. The seamless integration is achieved by using the same reference frame and the same variables to describe the aircraft motions and the forces acting on it, including the aerodynamic forces. The formulation is modular in nature, in the the sense that the structural model, the aerodynamic theory, and the controls method can be replaced by any other ones to better suit different types of aircraft, provided certain criteria are satisfied. A perturbation approach permits the separation of the equations of motion into a flight dynamics problem for the maneuvering aircraft rigid-body translations and rotations and an extended perturbation problem for the elastic deformations and perturbations in the rigid-body variables, where the second problem is subject to inputs from the maneuvering aircraft. The formulation is ideally suited for unmanned aerial vehicles (UAVs), and in particular for autonomous UAVs requiring autopilots. A numerical example presents a variety of time simulations of rigid-body perturbations and elastic deformations for two cases, 1) a steady level flight and 2) a level steady turn maneuver. All the time simulations were carried out on a 1-GHz personal computer, which is particularly important for autonomous UAVs, as the required onboard computer is likely to be much closer to a personal computer than to a multiprocessor supercomputer. The unified theory is expected to stimulate new interest in aeronautics research, ultimately providing a useful tool for the analysis and design of flexible aircraft.
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