نشریه مهندسی هوانوردی
سال پانزدهم شماره 2 (پاییز و زمستان 1392)

The first step in this paper is to simulate the dynamics of a projectile، carrying a gun-launched UAV، from launching to the time that the wings open. The changes that the UAV undergo such as coming out of the shell، opening the parachute and then the wings، all have been accounted in the simulation process. The second step in this study involves defining a multidisciplinary optimization problem. In the end، in order to maximize the range of the projectile، the optimization problem is analyzed. Through this analysis، considering stability constraints، optimal values for parameters such as the geometry of the projectile، diameter of the parachute، launch angle and separation altitude are achieved and regarding each one، some arguments are raised.

Deposition of ice on external surfaces of flying airplanes is one of the major meteorological aviation hazards. Icing is an atmospheric phenomenon, which is not easily predicted. In this study, a number of reported icing cases by pilots were investigated. Moreover meteorological reports, weather charts corresponding to ground surface and¬¬ 500 & 850 Millie-Bar Pressure levels plus upper air sounding data were studied. Analysis of weather charts and synoptic patterns effective on icing, verification of icing intensity using liquid water content of clouds, determination of freezing level height based on surface temperature and applying -8D method for occurrence of icing and also the instability indices were studied. The results indicate that the maximum number of icing events occurred in April, while the most intensive icing events occurred in January and April. In most cases, the dynamical low-pressure levels, synoptic patterns, trough and cold frontal regions are the most probable patterns for icing to occur over the country. Intensive icings are associated with deep cumulonimbus (CB) clouds with high extension. Moreover the -8D method is an acceptable procedure in determination of severe icing possibility in Jan & Apr, while in other cases the method does not seem to indicate good results in determining icing possibility in the corresponding surfaces reported by pilots.

The purpose of this paper is the three-dimensional guidance tracking of an unmanned aerial vehicle using robust nonlinear control strategy. For this purpose, the model of the reference tracking error is produced first, and using Lyapunov stability guidance commands are then provided. Terms of the Lyapunov equation is exponentially stable, partly by adding a set of disturbance variables to the input error state variables and Developing a virtual dynamic system, the stabilization and disturbance rejection is provided using nonlinear H∞ strategy. In order to apply this strategy and avoid the complexity of the problem, the inverse optimality approach is used to derive the controller. Finally, the stabilizer control added to guidance commands, and the Lyapunov stability of the whole system from optimality perspective due to the minimization of a cost function is provided. The simulation results indicate that by using this algorithm, the UAV follows the flight trajectory as well.

Aviation accidents due to the icing of aircraft wings in recent years raised the need for investigation of this phenomenon. In this paper, icing on NACA 23012 airfoil, due to the frequent usage in general aviation and also severe impact of the icing on this airfoil, has been studied. To study the effects of icing phenomenon, the experiments were carried out over a range of angles of attack from -8° to 22° at Reynolds number of 600000 on the clean airfoils, horn ice and spanwise ridge ice shape, and thereafter, the corresponding results were compared. According to the results, the icing phenomenon strongly affects the flow field around the iced airfoils, and it also has negative influence on the behavior of aerodynamic coefficients of the airfoil. Generally, it can be said that these two types of icing formation on the airfoil cause the formation of flow separation bubble on the upper surface at the downstream of the leading edge. In addition, it is found that the spanwise ridge ice has more negative effects on the aerodynamic parameters of the airfoil in comparison with the horn ice. In the case of spanwise ridge ice, ∝ stall and CL max decrease 8° and 50%, respectively, whereas, for the case of horn ice, these values reduce about 4° and 21%.

The unexpected nature of chaotic dynamics behavior can result in many operational problems in the engineering systems. The rotating machinery such as jet engines and cooling turbine in the aircraft environmental control systems, suspected to undergo chaotic vibration in the engineering systems. In the chaotic region, the vibration responses have unpredicted amplitude. Since the aerial rotating systems operate in high speeds, the cyclic stresses could emerge and therefore, the operational life of the system would decrease. Thus, investigation and detection of the chaotic regions in the nonlinear systems is of great importance. In this paper, the nonlinear behavior analysis applied to the Duffing and modified Duffing equations. The analytical techniques such as bifurcation diagram, phase plane, Poincare map, power spectrum and Lyapunov exponents have been applied to investigate the system’s behavior. After detecting the chaotic region, the excitation frequency was used to control the chaos and return the motion state to a periodic one. The results verify the effectiveness of this strategy.

In this paper, miss distance analysis of a modified proportional navigation with lateral acceleration feedback is presented using normalized equations of adjoint method in the presence of radome effect and seeker noise. In this analysis, linear model is utilized. Also, radome error slope is assumed to be constant. Approximate formulas of miss distance are presented for second-order control system with two real distinct poles, using obtained nondimensional miss distance curves. These curves and formulas are useful for guidance system analysis and preliminary design. Moreover, using the approximate formulas, the guidance gain and time constant can be designed as variables to enhance the stability and performance of the guidance and control system in low and high altitudes.

TCAS has been designed to avoid the collision of aircraft on flying. Basically, one of the most important pillars of aviation industry in ensuring proper operation of systems and devices is specialized testers of each segment. In this research, the design and construction of the corresponding tester of TCAS Display Unit (TDU) is studied. Since TDU is an interface between pilot, flight computer and TCAS antenna, it is used by the pilot to be aware of intruder aircrafts and chances of collision, so he will be able to choose and take the appropriate maneuver to avoid collision. So, it is apparent that TDU has a very important role in avoiding aerial accidents. The purpose of this research was to obtain technical knowledge of design and construction of TDU tester which would help to minimize the occurrence of aerial incidents.