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Emerald Article: Aircraft terrain following flights based on fuzzy logic Mohammad Rahim, Seyed Móhammad-Bagher Malaek Article information: To cite this document: Mohammad Rahim, Seyed Móhammad-Bagher Malaek, (2011),"Aircraft terrain following flights based on fuzzy logic", Aircraft Engineering and Aerospace Technology, Vol. 83 Iss: 2 pp. 94 -104 Permanent link to this document: http://dx.

Purpose -The purpose of this paper is to present a novel approach in aeroservoelastic analysis and robust control of a wing section with two control surfaces in leading-edge and trailing-edge. The method demonstrates how the number of model uncertainties can affect the flutter margin. Design/methodology/approach -The proposed method effectively incorporates the structural model of a wing section with two degrees of freedom of pitch and plunge with two control surfaces on trailing and leading edges. A quasi-steady aerodynamics assumption is made for the aerodynamic modeling. Basically, perturbations are considered for the dynamic pressure models and uncertainty parameters are associated with structural stiffness and structural damping and are accounted for in the model by a Linear Fractional Transformation (LFT) model. The control commands are applied to a first and second order electro-mechanical actuator. Findings -Dynamic performance of aeroelastic/aeroservoelastic system including time responses, system modal specifications, critical flutter speeds, and stability margins are extracted and compared with each other. Simulation results are validated through experiments and are compared to other existing methods available to the authors. Results of simulations with four structural uncertainties and first order controllers have a good agreement with experimental test results. Furthermore, it is shown that by using a high gain second order controller, the aeroservoelastic (ASE) system does not have any coupling nature in frequency response. Originality/value -In this study, modeling, simulation, and robust control of a wing section have been investigated utilizing the m-Analysis method and the wing flutter phenomenon is predicted in the presence of multiple uncertainties. The proposed approach is an advanced method compared to conventional flutter analysis methods (such as V-g or p-k) for calculating stability margin of aeroelastic/aeroservoelastic systems. Nomenclature a ¼ non-dimensional distance from the mid-chord to the elastic axis b ¼ semi-chord of the wing (m) c a ¼ viscous damping coefficient of EMA (Ns/m) c h ¼ structural damping coefficients in plunge (Ns/m) c a ¼ structural damping coefficients in pitch (Ns/m) c la ¼ lift coefficient due to angle of attack ›c l2 c/4 /›a c mb ¼ lift coefficient due to trailing edge flap deflection ›c l2 c/4 /›b c mg ¼ lift coefficient due to leading edge flap deflection ›c l2 c/4 /›g c ma ¼ moment coefficient due to angle of attack ›c m2 c/4 /›a c mb ¼ moment coefficient due to trailing edge flap deflection ›c m2 c/4 /›b c mg ¼ moment coefficient due to leading edge flap deflection ›c m2 c/4 /›g d b ¼ input noise to trailing edge d g ¼ input noise to leading edge e ¼ weighting modeling errors h ¼ plunge displacement (m) k ¼ controller gain k a ¼ stiffness of EMA (N/m) k h ¼ spring constant in plunge (N/m) k a ¼ spring constant in pitch (Nm/rad) m ¼ mass of the wing (Kg) m a ¼ mass of moving parts of EMA (Kg) m T ¼ total mass of the pitch and plunge system (Kg) m w ¼ total ...

In this paper, the problem of two dimensional Terrain Following / Terrain Avoidance trajectory optimization has been considered for an Unmanned Aerial Vehicle (UAV) in vertical flight plane. This problem is formulated as an optimal control problem, and then Direct Collocation method is employed as a solver tool for generating flyable path. Chebyshev polynomial has been used to model the geographical data of the terrain in a given route. The results indicate that the method is suitable for the terrain following problem especially in the case of producing more reliable flyable path based on the system dynamics, physical limitations and also the mission requirements.

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