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Nowadays, optimization is becoming one of the most important techniques in engineering and industry to provide competing products in design and manufacturing. Therefore, it is a necessity to search for optimum designs with productibility. In aerospace industry reducing weight and improving reliability of the products are major concerns. As regards the gearbox is one of the most important parts in the helicopter propulsion system, these objects should be more considered. However, most of the existing designs consider only one object, hence, it is vital to implement optimization techniques to include different objectives to improve the existing designs and provide optimum products. In this paper, optimum design parameters including module and face width of gears for the main gearbox of Sikorsky ASH-3D helicopter have been determined (modified) using single and multi-objective mixed discrete- continuous optimization method to minimize weight of the gearbox, increase the safety factor and reduce the difference between safety factors of different gears. The results show that the weight of the gears can be reduced by 27.24% comparing with the existing gearbox. The results of the multiobjective optimization have also been presented as Pareto front diagram wich can be used by the manufacturers to satisfy the prefered requiments.

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Traffic issue is an international challenge in the sophisticated countries in which over population is considered as an important factor in creating this problem. Studies show that the accidents’ report during the minimum time is the best way to control the traffics. For this purpose, this paper has been done in such a way that after modeling the flying robot using Newton-Euler equations, a three-dimensional constrained optimal trajectory has been generated through Direct Collocation Approach. In other words, the proposed problem in this paper is first formulated as an optimal control problem. Afterwards, the optimal control problem is discretized through Direct Collocation Technique, which is one of the numerical solving methods of the optimal control problems, and it is transformed into a Nonlinear Programing Problem (NLP). Eventually, the aforementioned nonlinear programming problem is solved via SNOPT which works based on the gradient algorithm like SQP. It should be noted that since the main objective of motion planning in this paper is controlling the urban traffic, the urban constrains are utilized during the trajectory optimization. In other words, all of the high-rise buildings located during the course are modeled by the various cylinders. The efficacy of the aforementioned method is demonstrated by extensive simulations, and in particular it is verified that this method is capable of producing a suitable solution for three-dimensional constrained optimal motion planning for a six-degree-of-freedom quadrotor helicopter for urban traffic purposes.

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Variable pitch propeller (VPP) are used in advanced helicopters, in order to achieve greater efficiency, better stability and achieve higher altitudes. This study is going to assess the behavior of VPP propeller with coupled non-linear displacement in three degrees of freedom. Accordingly, the behavior of this type of propeller with Changes of elastic axis distance, Length, mass, speed, polar radius of gyration, Stiffness in three degrees of freedom, and pitch have been investigated. In this paper, Gallerkin method is used to extract natural frequencies and the results were evaluated with the results reported by other researchers. The results show convergence and accuracy of the used method. In this study, it was found that parameters of mass, length and rotational speed of the propeller have effect on the natural frequencies, and all modes of vibration. However, other parameters except for the pitch angle effect on the odd or even number of frequency modes. It was also found that the pitch angle in the static mode does not effect on natural frequencies but in the case of rotation of propeller, affect on natural frequency of vibration modes as sine or cosine form.

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In this paper, the adaptive second order sliding mode (SOSM) controller is designed for two input - two output (TITO) uncertain nonlinear systems and the robustness properties are ensured in the presence of uncertainties and bounded external disturbances. The objective is to design a controller that ensure stability and path tracking despite the effects of coupling. To this end, the system model is divided into two subsystems, and the coupling effects between such subsystems are considered as uncertainties. The sliding mode approach with PI sliding surface is used to remove the offset and converge the steady state error to zero. To avoid chattering phenomenon, Second order sliding mode method is proposed. Using adaptive switching gain, a new method is presented which unlike other methods, does not require the upper bound of the system uncertainties in the design procedure. Robustness properties against system uncertainties and external disturbances is shown by the Lyapunov stability theorem. Finally, the proposed method is used to control azimuth and elevation angle of as a laboratory helicopter with two degrees of freedom. Simulation results show performance of the algorithm in the presence of perturbations.

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In this article, the effects of helicopter main rotor blade tip geometric shapes on the aerodynamic of hover flight are analyzed. Aerodynamic coefficients, vortical flows and vortex wakes are discussed. Fluent software with implicit finite volume method has been used for numerical simulation process. The grids are structured. Experimental results of the Caradonna and Tung have been used for aerodynamic validations. In this investigation, the flow has been considered turbulent, compressible, and viscous. The results of several RANS models for a specific rotor have been compared together and finally the standard k-ε turbulent model has been selected. The Roe method with second order scheme was selected. Thirteen different geometrical shapes on the tip of the blades have been presented and the results of the models have been compared together. These studies show that the blades of BERP IV, Blue edge, Actual, Bell-214 and BERP III produce maximum thrust and MIL-17, Sikorsky RH-53D, Tapered, Bell-412, Sikorsky SH-3D and Comanche RAH-66 produce minimum torque and also the blades of BERP III and IV, Ogee and Bell-214 produce maximum torque.

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The helicopter rotor blade flapping results in a helicopter rotor symmetry lift and has a significant impact on stability and control. In this paper, the modeling of helicopter flapping in the presence of aerodynamic forces and moments and the effect of offset, blade torque, hinge resistant spring, blade geometry, natural frequency effect, and forward ratio to achieve reliable relief from flapping was investigated. In the simulation, the effects of small and large flapping angles and the role of offset on the momentum entered on the blade, as well as the role of the forward ratio in moments were investigated. Different models of flapping dynamics and equations for the flight of a hover and are fully presented and all of the important issues are examined for a numerical example. Also, the effect of non-uniform flow in the flapping equations of the blade is the effect of the natural frequency of the flapping motion with the blade offset. This leads to increasing the accuracy in modeling the phenomenon of on a helicopter. Simulation results show the importance and impact of offsets, moments and forces imposed on the blade in the motion of the flapping, which leads to an increase of accuracy in modeling.