نشریه مهندسی هوانوردی
سال بیستم شماره 1 (بهار و تابستان 1397)

Unmanned aerial vehicles (UAVs) are well-suited to a wide range of mission scenarios, such as search and rescue, border patrol, and military surveillance. The complex and distributed nature of these missions often requires teams of UAVs to work together. Despite the complexity of the environment and patrol procedures, thepersistent surveillance is a one of an important problem in aerial patrol which can be simplified with basic patterns. The main object is minimizing the maximum revisit time in specified path. In this article, the single and multi-agent aerial search and patrol patterns are described and revisit time equation is driven for known UAV with real model and several situations. The impact of changing speed and the number of agents on the efficiency of persistent surveillance has been evaluated and compared with another patrolling pattern. As results of this paper, the basic search methods are distributed to an arbitrary number of the agent in several patterns. The revisit time function as a dependent parameter can be calculated from agent’s number as an independent parameter also in fixed value of revisit time, the optimal number of UAVs can be obtained due to specified search area. The results show that in the high-speed situation, increase the number of UAVs in the particular area, little performance improvement occurs in minimizing of maximum revisit time. A velocity and UAV number domain can be determined whereas the maximum revisit time always is minimal.

n this paper, an alignment algorithm is proposed based on using the outputs of inertial measurement unit (IMU). Accurate initialization of attitude angles containing the azimuth angle is an important step to increase the accuracy of inertial navigation system output of a moving vehicle. Two step alignment algorithm including course and fine calculation is proposed in this paper which derives the Euler attitude angles including azimuth of vehicle with accuracy of a few arc minutes. First a course alignment is performed based on the components of gravity acceleration and angular velocity of the earth in body coordinate which are measured by inertial measurement unit sensors. Then the fine alignment is performed by constructing an error model of navigation system and estimation of the attitude angles error using a Kalman filter. The observations which are feed to the Kalman filter are the velocity components of vehicle in navigation frame and the eastern angular velocity component of the earth which are zero. To evaluate the accuracy of the proposed alignment algorithm, the IMU is mounted on a 3DOF table which can be aligned with 5 arc second precision as reference attitude. Then the alignment algorithm is executed in several azimuths. The results show the acceptable accuracy of azimuth angle.

In this paper, a functional model, which is identified based on flight test data sets, is used to improve the performance of guidance loop of a commercial quadrotor equipped with a low-cost autopilot and navigation system. For this purpose, relationships between horizontal velocities and the quadrotor attitudes around the horizontal axes and relationships between three quadrotor attitudes with the correspondent commands sent to the autopilot are identified independently. The first model describes the relation between rotation around the axes of the quadrotor with declared commands in the autopilot system and the other describes the relation between horizontal velocities with the angle around the longitudinal and latitudinal axes of the quadrotor. According to the experimental test results, a first order transfer function has enough accuracy to describe the rotation around the vertical axis with related commands. Also, the description of the relation between the horizontal velocities and the autopilot commands has suitable accuracy using two consequent first order transfer functions; one model between the applied commands and changes of roll and pitch angles, and the other between roll and pitch angles and the horizontal velocities. Due to the linear time invariant characteristics of the system, the least square estimator is used to estimate unknown parameters of the models. To evaluate the identified models, the performance of the path tracking using a PID controller as the outer controller is investigated. The results of the indoor tests show significant improvements in path tracking that confirms enough accuracy of the identified models.

The purpose of this study was to identify the factors affecting the competency of pilot’sinstructors of atShahid Sattari Air University. For this purpose, after reviewing the background, the theoretical framework of the research was formulated and then modified by interviewing key experts.The researcher then designed a questionnaire whose validity and reliability were confirmed by statistical techniques and methodology. Then, the questionnaire was distributed among pilot instructors of Shahid Sattari Air University and 68 questionnaires were returned. 61 of them had the necessary requirements for entering the software and formed the basis of research analyses. First-order factor analysis showed that all observed variables had a good load factor on their variable and, according to PLS indices, these observed variables can measure their corresponding latent variables. Also, the results of second-order factor analysis showed that all of the first latent variables had an appropriate factor load and had a significant effect on their second latent variables. In other words, all the components have enough load factorsto predict their own variables and can predict the competency of pilot’sinstructors at Shahid Sattari Air University and are considered as its underlying factors

In this research, behavior of a cylindrical sandwich panel with the flexible core in different boundary conditions, under the influence of follower force are studied. For this purpose, using the theory of the first-order shear deformation, and the principle of Hamilton, the governing equations have been extracted and by using generalized differential quadrature method (GDQM)are solved. The obtained results indicate that by considering simplicity of present method compared to the other methods in the analysis of stability problems of the cylindrical sandwich panel, the present results have the acceptable accuracy.Also, the results review show that the flutter phenomenon occurs in the free and clamp boundary conditions and for other boundary conditions only the divergence phenomenon or static buckling occurs.Another significant result is that increasing the number of composite layers, makes the flutter phenomenon in the cylindrical sandwich panel with the flexible core occurs later

Aviation risk assessment and analysis is one of the contributing factors in reducing accident and human and unhuman expenses. Todays, most organizations have recognized but despite this problem in the aviation Training university, there is no specific study in this field. On the other hand, proper training to pilot training student, improving safety and reliability of the aircraft, increasing awareness of pilot professors and other factors in reducing damage can be very effective. Every year, a number of students register in university and aeronautical organizations to learn pilot skills that should be some safety acts to preserve their lives during education. In this paper, identification, documentation and rating of all kinds of risks in pilot training have been made to this end;it is possible to prevent any kind of risk during training by providing a suitable approach. This study uses the Job Safety Analysis to identify and assess the existing or potential risks in pilot training and uses the questionnaire technique to rank the identified risks. The analysis of the risk assessment model showed that each student and Professors have weaknesses that need to be addressed which, in the end, will provide solutions to address these risks and reduce them so thatorganizations associated with The implementation of this method reduces the risk, incidents and risks of existing ones.