نشریه مهندسی هوانوردی
سال نوزدهم شماره 2 (پاییز و زمستان 1396)

Nowadays, aging of aircraft is one of the most important problems in evaluation of their airworthiness. In structural area, it is very important to assess the rate of degradation of the material properties of aircraft after their long time service. Therefore, this subject is practiced in this article. In order to evaluate the effect of aging of aircraft on deterioration of the mechanical properties, some specimens are prepared from the structural units of a few aged aircraft in Air Force to do the tensile and fracture tests. Also in order to evaluate the results, similar tests are accomplished on unused ingot materials. In this manner, source values are obtained from reference books too. The tensile tests are accomplished on some parts of upper and lower skin of trailing edge flap torque box and also unused sheets of similar materials either in rolled direction and the opposite direction. The fracture toughness tests are accomplished on some parts of lower skin of center wing and upper skin of middle area of two wings in several directions. The results show that because of precipitation hardening of being tested alloys, the yield and ultimate strength are increased but, decrease of fracture toughness make it leads to brittle fracture.

Mathematical Modeling of the main rotor dynamics is very important in modeling of unmanned helicopters, and its quality and performance will play an effective role in ability of the model to behave the same as a real helicopter. There are different methods for modeling rotor dynamics which are different from each other in simplifying assumptions and relations complexity. In most investigations, the complete unmanned helicopter dynamic modeling is performed, applied and evaluated which decreases the concentration on main rotor modeling and its quality. In this paper, main rotor dynamics have been modeled independently using 2 different methods (theoretical method based on blade element theory and approximate method using 1st order dynamics for flapping). Considering complexities arisen in theoretical modeling method, using similarly behaving approximate model will make the final model more applicable. To do this, using system identification technique, the probability of using approximate model instead of theoretical one (which is a closer model to real rotor dynamics) has been investigated. After that, a robust control system is designed based on approximate model and its successful implementation in controlling the theoretical model, shows that it is possible to control the theoretical model using much simpler approximate one.

This paper deals with numerical simulation of store separation from aircraft wing. In this study the effects of 4 variables, wing aspect ratio, store aspect ratio, forward and backward ejector force have been studied and analyzed. Unstructured tetrahedral grid was used for flow field discretization. Flow governing equations are Euler equations which are solved simultaneously with six degrees of freedom code for rigid body motion to obtain the trajectory of store. The results of numerical solution method were compared with experimental data provided by Arnold engineering development center and a good match was observed. To determine the number of numerical solutions needed to evaluate the effects of parameters, Box-Behnken method, which is one of the conventional methods of experimental design, was used. By these results, the model of fall amount proposed. It was found that the most important determinant of the fall is store aspect ratio and wing aspect ratio has the least impact.

In this paper, a model-based fault detection problem for air-launched systems is considered. Firstly, the position, velocity and attitudes of the system are estimated using Kalman filter, then the sensor fault is detected by defining a suitable threshold. The fault detection is done using stochastic forward variables. In this algorithm, the covariance of data is used to model the faulty mode of sensor. The Monte-Carlo simulations was used to adjust the parameters of the algorithm in static mode. Numerical experiments on an unmanned aerial vehicle show when the system states are observable the fault detection algorithm is capable to detect the sensor fault. When the system lost its observability condition, the algorithm just can detects the instantaneous faults but, the method cannot detects in the static mode.

Following the construction of new airports in the country and the development of aeronautical industry and sensitivity to the desirability of serving the passengers as a competitive advantage in the country's tourism industry, evaluating performance and estimating the efficiency of airports in the country and aviation companies an important issue has changed. However, there is very little research on the analysis of airport systems with the network view of Data Envelopment Analysis and discussion of finding the causes of inefficiency of subunits that are effective in performance. To assess airport performance, an independent view has been used in data envelopment analysis. In this view, there are always problems due to the nature of the mean values. In this paper, for the first time, the evaluation of the performance of 30 airports in Iran in 1394, is used from the Cooperative approach of view of the subunits, and in addition, ineffective factors are considered in the priority Cooperative in subunits. Our initiative in this article presents a new methodology in which the efficiency of the airport and the efficiency of the aviation subunit are of more importance, the causes of the inefficiency of the complications and the airports to be evaluated.

Despite low weight and high strength of composite materials, early failure and their weakness in vibrational environments are the main obstacles in using them in presence of dynamic loading. Detection of inter-laminar delamination as one of the most common failures in laminated composites is important for future life of structure. In this study, the effect of a small size delamination on the modal behavior and frequency response functions (FRFs) of a composite cylinder is experimentally investigated. Among usual damage mechanisms, the effect of impact mostly considered as delamination, is increased in four stages. In each state, modal analysis is implemented and results are compared with those of other states. Experimental modal analysis shows that small damage doesn’t change natural frequencies. However, raw data of frequency response functions may leads to damage identification due to the variation of its features with respect to damage size. To localize damage, the curvature of FRFs are calculated and compared with those of the healthy cylinder by choosing optimum frequency range.