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CONTENTS
Volume 6, Number 5, September 2019
 

Abstract
In the design of flight control systems there are issues that deserve special consideration and attention such as external perturbations or systems failures. A Simple Adaptive Controller (SAC) that does not require a-priori knowledge of the faults is proposed in this paper with the aim of realizing a fault tolerant flight control system capable of leading the pitch motion of an aircraft. The main condition for obtaining a stable adaptive controller is the passivity of the plant; however, since real systems generally do not satisfy such requirement, a properly defined Parallel Feedforward Compensator (PFC) is used to let the augmented system meet the passivity condition. The design approach used in this paper to synthesize the PFC and to tune the invariant gains of the SAC is the Population Decline Swarm Optimization (PDSO). It is a modification of the Particle Swarm Optimization (PSO) technique that takes into account a decline demographic model to speed up the optimization procedure. Tuning and flight mechanics results are presented to show both the effectiveness of the proposed PDSO and the fault tolerant capability of the proposed scheme to control the aircraft pitch motion even in presence of elevator failures.

Key Words
simple adaptive control; population decline swarm optimizer; parallel feedforward compensator; fault tolerant control

Address
Andrea Alaimoa, Antonio Espositob and Calogero Orlando: Faculty of Engineering and Architecture, Kore University of Enna, Cittadella Universitaria, 94100, Enna, Italy

Abstract
The implementation of a robust H_infinity Control, which is numerically efficient for uncertain nonlinear dynamics, on longitudinal and lateral autopilots is realised for a quarter scale Piper J3-Cub model accepted as an unmanned aerial vehicle (UAV) under the condition of sensor noise and disturbance effects. The stability and control coefficients of the UAV are evaluated through XFLR5 software, which utilises a vortex lattice method at a pre-defined flight condition. After that, the longitudinal trim point is computed, and the linearization process is performed at this trim point. The \"u-Synthesis\"-based robust H_infinity control algorithm for roll, pitch and yaw displacement autopilots are developed for both longitudinal and lateral linearised nonlinear dynamics. Controller performances, closed-loop frequency responses, nominal and perturbed system responses are obtained under the conditions of disturbance and sensor noise. The simulation results indicate that the proposed control scheme achieves robust performance and guarantees stability under exogenous disturbance and measurement noise effects and model uncertainty.

Key Words
aerodynamic; aeroplane equation of motion; flight control; nonlinear control; robust H_infinty control; multi-input multi-output control surface; u-synthesis; unmanned aerial vehicles

Address
Caglar Uyulan:Department of Mechatronics Engineering, Bulent Ecevit University, Turkey

Mustafa Tolga Yavuz: Department of Aeronautics and Astronautics, Istanbul Technical University, Turkey

Abstract
Flight trajectory optimization has become an important factor not only to reduce the operational costs (e.g., fuel and time related costs) of the airliners but also to reduce the environmental impact (e.g., emissions, contrails and noise etc.) caused by the airliners. So far, these factors have been dealt with in the context of 2D and 3D trajectory optimization, which are no longer efficient. Presently, the 4D trajectory optimization is required in order to cope with the current air traffic management (ATM). This study deals with a cubic spline approximation method for solving 4D trajectory optimization problem (TOP). The state vector, its time derivative and control vector are parameterized using cubic spline interpolation (CSI). Consequently, the objective function and constraints are expressed as functions of the value of state and control at the temporal nodes, this representation transforms the TOP into nonlinear programming problem (NLP). The proposed method is successfully applied to the generation of a minimum length optimal trajectories along 4D waypoints, where the method generated smooth 4D optimal trajectories with very accurate results.

Key Words
trajectory optimization; 4D waypoint navigation; spline parameterization; Nonlinear programming

Address
Kawser Ahmed, Kouamana Bousson and Milca de Freitas Coelho:LAETA/UBI - AeroG, Laboratory of Avionics and Control, Department of Aerospace Sciences,
University of Beira Interior, Covilhã, Portugal


Abstract
The aim of the present work is to study the nonlinear behavior of the laminated composite plates under transverse sinusoidal loading using a new inverse trigonometric shear deformation theory, where geometric nonlinearity in the Von-Karman sense is taken into account. In the present theory, in-plane displacements use an inverse trigonometric shape function to account the effect of transverse shear deformation. The theory satisfies the traction free boundary conditions and violates the need of shear correction factor. The governing equations of equilibrium and boundary conditions associated with present theory are obtained by using the principle of minimum potential energy. These governing equations are solved by eight nodded serendipity element having five degree of freedom per node. A square laminated composite plate is considered for the geometrically linear and nonlinear formulation. The numerical results are obtained for central deflections, in-plane stresses and transverse shear stresses. Finite element Codes are developed using MATLAB. The present results are compared with previously published results. It is concluded that the geometrically linear and nonlinear response of laminated composite plates predicted by using the present inverse trigonometric shape function is in excellent agreement with previously published results.

Key Words
laminated composite plates; geometrically nonlinear; finite element method; new trigonometric shear deformation theoryc

Address
Dhiraj P. Bhaskar and Ajaykumar G. Thakur: Department of Mechanical Engineering, SRES\'s Sanjivani College of Engineering, Savitribai Phule Pune University, Kopargaon-423601, Maharashtra, India

Abstract
Small satellites represent an emerging opportunity to realize a wide range of space missions at lower cost and faster delivery, compared to traditional spacecraft. However, small platforms, such as CubeSats, shall increase their actual capabilities. Miniaturized electric propulsion systems can provide the satellite with the key capability of moving in space. The level of readiness of miniaturized electric propulsion systems is low although many concepts have been developed. The present research intends to build a flexible test platform for the assessment of selected small propulsion systems in relevant environment at laboratory level. Main goal of the research is to analyze the mechanical, electrical, magnetic, and chemical interactions of propulsion systems with the modern CubeSat-technology and to assess the performance of the integrated platform. The test platform is a 6U CubeSat hosting electric propulsion systems, providing mechanical, electrical and data interfaces, able to handle a variety of electric propulsion systems, thanks to the ability to regulate and distribute electric power, to exchange data according to several protocols, and to provide different mechanical layouts. The test platform is ready to start the first verification campaign. The paper describes the detailed design of the platform and the main results of the AIV activities.

Key Words
CubeSat test platform; miniaturized electric propulsion system; verification of small satellites

Address
Sabrina Corpino, Fabrizio Stesina and Daniele Calvi: Department of Mechanical and Aerospace Engineering (DIMEAS) Politecnico di Torino,Corso Duca degli Abruzzi 24, 10129Torino, Italy

Giorgio Saccoccia: European Space Agency (ESA), Kepleerlan 1, Noordwijk, The Netherlands


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