نشریه مهندسی هوانوردی
سال بیستم شماره 2 (پاییز و زمستان 1397)

The aircraft stabilizer stabilizes the aircraft utilizing non-fixed and controllable aerodynamic surfaces. This paper presents a model-based predictive control for F-8 fighter aircraft stabilization. In the proposed control method, meanwhile the real-time optimization, the cost-function is minimized by means of the linearized model of F-8 fighter and the output is predicted in future interval times based on the receding horizon strategy. The cost-function is defined as the aggregate of terminal cost and summation of stage costs, that the quadratic form of cost-function is utilized in control algorithm, eventually. The costfunction minimization is giving rise to stable control input. The extracted stable control input stabilized the states of the nonlinear F-8 fighter system under the various initial conditions. The considerations are taken into account in the controller designing steps, to reduce the computational load. Mathematical proof investigates that the closed-loop system with the proposed control has asymptotic stability. The simulation results well demonstrate the favorable efficiency of the proposed controller in F-8 fighter aircraft stabilization.

One of the fastest ways to repair a damaged airfield, is using the matting plates. These plates are manufactured with various size and materials. If there is no way to continuously manufacture the plates, one can produce two separately parts of them and weld to each other. In this paper, the strength of a matting plate namely AM-2 welded by TIG welding process has been analyzed. For determination of the landing loads, Hercules C-130 aircraft has been considered. Various values of subgrade CBR have been studied. The joining plan of plates has been considered in such a way that the strength in the weld region be greater than before. The results showed that by using the matting plate welded by TIG welding process, the value of the subgrade CBR should be at least 15. Simulating test with crane has been carried out in this paper and good agreement was found in the results obtained by experimental tests and that evaluated by numerical analyses.

Friction stir spot welding has been considered as one of the superior manufacturing processes with various applications which nowadays draw the attention of aerospace industries. The main goal of the current study is to compare the shear tensile-shear strength of dissimilar aluminum alloy sheets of 7075-T6 and 2024-T3 in the friction stir spot welding process with the riveting process commonly used in the wing and body structures of the aircraft. In addition, the influence of various parameters such as the influence of tool penetration speed, tool rotational speed, and the arrangement of aluminum alloy sheets on the tensile-shear strength of the joining zone have been investigated and compared with that of rivet joining process. By properly choosing these parameters, the optimum tensile-shear strength of the joint can be attainable. Results obtained during the current research can be considered to replace the riveting process with the stir spot welding process in the aerospace industries, and in particular for some portions of the wing and body of the aircraft in order to achieve higher strength for the desired joints. As a result, the damage related to the joints used in aircraft structures could be efficiently reduced.

Electromechanical Gyroscopes are based on vibrational systems. To control the driving mode of such small vibrational system is of pivotal importance for researchers. A sliding-mode control system is proposed for MEMS gyroscopes. At first, for decreasing the uncertainties existed in dynamical equations, utilizing the Inverse Dynamics method known dynamics of the gyroscope system are eliminated. To make the controller robust against the remaining uncertainties, sliding-mode control is applied. Sliding mode control will add undesired chattering on the control input, which result in a reduction in driving mode actuator's lifetime. In order to preclude the chattering problem in the control input, two approaches are presented. In the first approach, an adaptive fuzzy approximator is used to estimate the uncertainty bound in dynamical equations. The application of proposed adaptive fuzzy sliding mode control in reducing the undesirable chattering in the control input is impressive. In the second approach, by adjusting the Adaptive fuzzy sliding mode control designing process, a new variable is presented, which finally leads to designing the control input derivative. The mathematical proof shows that the proposed control method will cause the sliding surface to converge to zero asymptotically in the presence of uncertainties. Since it is imperative for implementation purposes to take integral from the control input, the chattering phenomenon will disappear completely in practice. To demonstrate the function of the proposed controllers, four simulation steps have been implemented on MEMS gyroscopes. Simulation results indicate desired operation of adaptive fuzzy sliding mode control with the asymptotical sliding surface.

Because of refraction of the incoming wave in the radar-guided interceptors, the radome can cause large miss distance and even having a destabilizing effect on the guidance system. On the other hand, the radome imposes an unwanted feedback that is not similar to the conventional feedback loops, in which output must follow a desired control signal. In this paper, the destructive effect of radome in guidance loop stability and performance is analyzed at first. Then, proposing a virtual integrator operator, the problem is transformed to a conventional tracking control problem so that the performance indexes can be defined in control aspect. Regarding the parametric uncertainty of the radome slope, µ-synthesis approach is used to design a robust compensator. Simulation results and stability analysis show that the designed compensator improves the guidance system performance in the presence of the radome, while the stability is guaranteed.

Reliability and uncertainty effect on aeroelasticity problems have been less respected by researchers. Reliability defines the ability of an item to perform the desired function during a specified time. In this paper, the flutter threshold for a panel has been studied; uncertainty in some parameters such as the elastic model, Poisson's ratio, density, thickness, and plane length is investigated. The plane is an Isotropic material considered in supersonic flow regime with three boundary conditions (SS, CS, CC). The structural model is considered based on the classical plate theory; also to determine the supersonic aerodynamic loads on the plate the first order piston theory is applied. The Generalized Differential Quadrature Method (GDQM) is used to discrete and analysis the aeroelastic equations of the panel. Then the equations are analyzed and eigenvalues are calculated. Then the threshold of the panel flutter is determined. Finally, to calculate the threshold of panel flutter reliability based on the first order reliability method, the Monte Carlo (MC) simulation is used.