نشریه مهندسی هوانوردی
سال بیست و ششم شماره 2 (پاییز و زمستان 1403)

Slot waveguide array antennas are used in many of missile and radar because of their simple structure mixability feature which causes being mixed with the body of many missiles and radiates equipment. This antenna is actually a waveguide which there are some slot arrays located on its wall. The wave inside the waveguide radiates from the slots through the outer space. And the favorite beam is made. The advantages of this type antenna are usage in high power and also low costs of fabrication and also having the ability of electronic scanning and high level of mechanical durability in different conditions. According to the mentioned advantages they are used in many of proximity fuse of many guided missile. Proximity fuse is actually short radar which is located in guided missile and has to detect the targets properly. In this paper, an X band slot array antenna with 20 longitudinal slots on the broadwall of the rectangular waveguide, with a gain of about 18 dB have been designed, simulated and fabricated witch it is suitable for proximity fuse of guided missiles. Finally the results of the test are compared with the results of simulation.

Havaniroz helicopters fly in all parts of dear Iran and performing missions in different weather conditions has a great impact on the parts of these types of helicopters and sometimes they cause corrosion. In this research, to reduce the amount of wear and adhesion and enhancing corrosion resistance of helicopter skid shoes, the HVOF process is used. The HVOF process is one of the most advanced spraying systems which the most important advantages of that are the very effective and uniform heating of particles due to the intense turbulence that occurs in the combustion chamber, as well as very little surface oxidation. In this article, to reduce the wear and adhesion of helicopter brake shoes, tungsten carbide coating was done on 7075 aluminum. Coating was done by thermal spraying and with the help of tungsten carbide powder, in addition to increasing the hardness and resistance of the surface, the amount of wear was reduced to a significant extent. The metallographic structure of the part after the WC86%-Co10%-Cr4% coating had high density, no oxide particles and not melted. By creating this coating, the amount of adhesion increased to 89 MPa, which is not comparable to conventional coatings. Also, the results of the hardness tests show that the microhardness measurement of the coating had a hardness of about 1300 Vickers, which indicates that this hardness is higher than other coatings in the form of plating. By using WC86%-Co10%-Cr4% coating, the amount of wear during helicopter landing at 1000 meters reached , which shows the high hardness and high quality of the coating..

Detonation pulse engine is used in the production of propulsion power for aerospace applications. This engine works based on detonation and basically consists of a tube with a high ratio of length to internal diameter with an open end, ignition system, fuel supply system and control system. In this research, detonation pulse wave power generator has been designed and built. This generator uses compressed natural gas (CNG) with a purity of 88% methane as fuel and oxygen gas as oxidizer. In this pulse detonation generator, fuel and oxidizer are placed in two separate tanks, and for their proper combination, a suitable mixing system is placed on the way to enter the explosive tube. The performance of the engine was evaluated in the tests carried out. To investigate the effect of methane concentration on detonation combustion characteristics in the engine, the temperature and pressure of the exhaust gases of the engine have been measured. In the investigations, it was found that by increasing the equivalence ratio of fuel and oxidizer from 0.7 to 1.6, the pressure increases almost uniformly from 17 to 21 bar. Also, with the increase of the equivalence ratio to the stoichiometric equivalence ratio, the engine output temperature increases and then gradually decrease.

Rotor imbalance in helicopters can lead to a flight quality degradation and a significant reduction in the lifespan of affected components. Considering the fundamental importance of safety and helicopter control being dependent on rotors, the propagation of this issue can result in undesirable events and catastrophic failures. Therefore, early detection of mass imbalance and misalignment plays a crucial role in reducing events and costs, and researchers in this field have recognized its significance. This paper focuses on experimental studies conducted on a coaxial rotor model helicopter to detect the presence of mass imbalance, misalignment, and a combination of them. A total of 320 tests were performed for eight conditions, including healthy, misalignment in the blades, and mass imbalances at various points on the blade's tip and center, within a rotational speed range of 880 to 1050 rotations per minute. Based on the time and frequency response of the system, signal features were extracted in the form of time-domain, frequency-domain, and time-frequency (using wavelet transform) graphs. In the next step, using Principal Component Analysis (PCA) in conjunction with the Ant Colony Optimization algorithm, 15 features containing more information were selected and inputted for classification into a neural network. According to the empirical evaluation, the proposed algorithm classifies and identifies the faults with a high-efficiency ratio. Thus, it can be utilized in condition-based maintenance of the rotorcrafts.

In this article, the effect of semi-analytical alignment error on the performance of the navigation system has been investigated. Although investigating the effect of various error-causing factors on the performance of the navigation system is not a new issue, the conducted investigations show that the effect of the alignment error has not been studied in the semi-analytical working regime. To perform this analysis, after introducing the related coordinate frames, the ideal and real functional equations of the navigation system in the desired working regime were extracted and then the performance of the navigation system was analyzed by taking into account the errors of horizontalization and initial orientation. The results have been showed that although the presence of this error causes errors in the navigation parameters, this error does not increase with the passage of time and has Shuler and day and night periods. It was also shown that the initial orientation error of the stable platform does not play a role in the calculation error of horizontal velocities and longitude and latitude, and the bias that occurs in the error of determining the side angle of the stable platform is equal to the initial orientation error of the stable platform.

Attention to plasma actuators as a tool for active flow control has been rapidly growing in recent years. This device, by injecting momentum, accelerates the fluid on the surface, which can be used to control flow separation. In the current study, the control of flow separation in an axial compressor cascade by plasma actuator and boundary layer suction, both separately and simultaneously, has been investigated. To study the effects of the plasma actuator and boundary layer suction on flow control, the flow characteristics, such as the static pressure ratio and the total pressure loss coefficient, have been experimentally evaluated with and without the plasma actuator, as well as the effect of boundary layer suction at different suction rates. Experimental results show that the use of plasma actuator at low speeds reduces total pressure loss and hence improves performance. Moreover, this experimental study indicates that the performance of the compressor cascade with the plasma actuator and boundary layer suction simultaneously, at suction rates of 25, 50, 75, and 100 percent at a speed of 10 meters per second, respectively improves by 13.3, 14, 15, and 17 percent, showing better results compared to using only boundary layer suction.

Due to the proven performance of fibrous insulations in various industries, including manufacturing, energy, aerospace, and construction industries. These insulations were studied in several papers. Ceramic tiles used on the space shuttle are one of the most famous high temperature applications of these fibrous insulation. Due to high porosity of these insulations, the main method of heat transfer in these materials is radiation, especially when heat transfer occurred in more than 500 degrees of Celsius. Anomalous Diffraction Theory (ADT) is one of the theoretical methods to estimate extinction coefficient of fiber insulation. Roseland theory calculates the radiation heat transfer coefficient according to the radiation extinction coefficient. Results obtained from the developed code were validated with the results of other articles. In this article, the effect of fiber diameter on the radiative heat transfer coefficient is investigated. The results show that the radiant heat transfer coefficient of the fibers changes with the change of the diameter of the fibers and also the radiant heat transfer coefficient of silica insulation will be minimum if the fiber diameter is 6 micrometers, and with increasing or decreasing the fibers diameter, the radiant heat transfer coefficient will increase. In the case of silicon fiber insulation, the fiber diameter of 4 micrometers will have the lowest radiation heat transfer.

Airport accidents are one of the most important challenges in the aviation industry. The present research aims to identify and prioritize the factors affecting on preventing and dealing with airport accidents (case study: Shahid Sadoughi International Airport in Yazd). In this research, the method used by purpose is practical and is descriptive-survey in terms of data collection method. The statistical population of the research includes all managers and experts working at Shahid Sadoughi International Airport in Yazd. The statistical sample of this research includes 30 people, who were selected by the purposive sampling method. A researcher-made questionnaire named "Pairwise comparisons of factors affecting on preventing and dealing with airport accidents and accidents" was used to collect data. The paired comparisons questionnaire was designed using background and theoretical foundations under experts' supervision. 5 major criteria including, human factors, technical factors, managerial factors, support factors and technological factors as well as 22 indicators (minor criteria) were identified. Fuzzy analyzing hierarchical process (FAHP) has been used to weight the major criteria and indicators and to prioritize them. The results showed that among the major factors, the technical factors has the highest priority, followed by human, technological, support and managerial factors respectively. Also, among the indicators, ensuring the technical soundness, preparedness of employees against accidents and knowledge of employees have the greatest influence on preventing and dealing with airport accidents.

In this research, a new combined-cycle consisting of a turboprop engine equipped with a solid oxide fuel cell is presented. Modeling and analysis of the proposed system has been done in flight conditions with a flight height of 7500 meters and the results have been compared with the results of the analyzes performed on the real turboprop engine. In analyzes, the compressor pressure ratio is considered to be 2 to 30. The evaluation of the results shows that the integration of solid oxide fuel cells with turboprop engines will improve the efficiency of this engine. In addition to that, adding solid oxide fuel cells to the turboprop engine will increase the efficiency of the whole system from 20% in the turboprop engine to 26% in the combined cycle. The results also show that the combined cycle generates somewhat more thrust than a real turboprop engine and also provides 70 kWh of aircraft electrical energy.

One of the ways to estimate aerodynamic coefficients and derivatives is flight testing and using real flight data, which in this method distinguish real data from noise-tainted data, which has a great effect on the estimation accuracy. In this paper, a new method using time-frequency analysis of wavelet transform data is proposed to reduce noise from flight data. Robustness against flight conditions and no need for system modeling are advantages of this method compared to existing methods. The performance of the proposed method is verified by applying it to two types of data: six degrees of freedom simulation data and flight test data of an unmanned bird. The results show that the proposed method has a high capability in extracting real data against noise and external factors or non-linear behavior of the bird in turbulent weather conditions, which can be used to estimate the parameters of the bird with high accuracy. In this research, first, the algorithm was applied on the simulation data of six degrees of freedom, which were affected by noise, and it was somehow validated by comparing the original data with the cleaned data of the algorithm. Next, it was applied on the flight data of the unmanned bird and from The cleaned data have been used to extract the longitudinal and transverse transformation functions of the bird and analyze the stability and extract the frequency of its different modes.

The structure examined in this article is a sandwich structure comprising seven layers. Four of these layers are made of aluminum, designed to enhance strength and distribute the load across the structure. Two other layers are made of metallic foam, with three types of foam being analyzed in this study. The remaining layer, acting as the core, features a honeycomb cell structure with auxetic properties. Due to its lightweight and blast-resistant characteristics, this structure is extensively used in the aerospace industry. The aim of this research is to prolong the lifespan of the sandwich structure by achieving optimal strength. The structure is subjected to axial loading, leading to buckling. Therefore, this paper investigates the nonlinear buckling and post-buckling behavior of the structure. Initially, the mechanical properties of the foam and honeycomb are formulated, followed by the extraction of equations based on the Euler-Bernoulli beam theory. The Ritz method is employed to solve these equations. The innovation of this research lies in the fact that such a structure has never been subjected to buckling in previous studies. The findings reveal that increasing the honeycomb cell angle and reducing the porosity coefficient enhance the structure's strength.

Aviation Safety has always been one of the key and important topics in the aviation industry. Since the first human flight, aviation accidents and incidents worldwide have led to extensive efforts to improve flight safety. Identifying the factors contributing to these accidents and accurately analyzing them can greatly assist in reducing incidents and enhancing flight safety. In this regard, various models and theories have been developed to assess the factors influencing aviation safety. When sufficient historical data is unavailable, using fuzzy logic and fuzzy analytical hierarchy process (FAHP), in combination with expert opinions, can be an appropriate alternative for evaluating the technical factors affecting aviation safety. This study employs the fuzzy analytical hierarchy process (FAHP) to evaluate the technical components influencing aviation safety. For this purpose, the five-part classification from the International Air Transport Association (IATA), including human, technical, environmental, organizational, and incomplete information factors, was used as the main criteria, with 36 sub-criteria. Specifically, the findings show that technical and human factors hold the highest weight among the other criteria.  another significant finding of this study is the high impact of incomplete information on reducing aviation safety levels. The lack of access to complete and up-to-date data can affect decision-making processes and lead to increased risks. By employing FAHP, aviation organizations can focus on key factors and implement effective safety improvement programs through precise prioritization.