JOURNAL OF AERONAUTICAL ENGINEERING (JOAE)
Year:2011 | Volume:13 | Issue:2|Papers Count:9

In this research, effects of vortex generator on flow pattern over the upper surface of an airplane wing model and its aerodynamic coefficients have been investigated both experimentally and numerically. Wing section airfoil is NACA 65-210. Yawing angle of the vortex generators respect to the flow direction are 0- and 15-degrees. Flow visualization is performed using Taft over the upper surface if the wing and the lift and drag coefficients are measured. The numerical analyses are performed using the Fluent software and the Reynolds stress modeling. Investigations are carried out at free stream velocity of 30 m/sec, corresponding to the Reynolds number of 265,000 and different angle of attacks ranging from -2 to 20 degree. The experimental and numerical results showed that applying the vortex generators increases the maximum lift coefficient and the stall angle of attack and reduces the drag force. In addition, the vortex generators having the yawing angle of 15-degree results maximum lift and minimum drag forces. In low angle of attacks (before the stall angle), the numerical results have a good agreement with the experimental data and in high angle of attacks (after the stall angle and flow separation), due to the complexity of the separation, the Fluent software accurate diminishes.

In this study, the idea of "Soft recovery using un-stabilizing" technique applied to a supersonic rocket. The tail of rocket is separated and the tumbling ogive-cylinder body decelerates very soon and then recovers with a two stage parachute mechanism. Aerodynamics of tumbling ogive-cylinder was solved numerically by a finite volume method using a pressure based implicit upwind scheme. Further, second order upstream interpolation and Spalart-Almaras turbulence model were employed. Governing flight dynamics equations of tumbling body were solved numerically using fourth order Runge-Kutta integration method. Numerical results were verified using available velocity-time curve of tumbling fore-body, which recorded experimentally by Doppler radar. Finally, comparing with commercial soft-recovery methods the un-stabilizing technique was proposed.

Purpose of this paper is the study of primary holes geometry effectiveness on film cooling efficiency and thrust of combustion chamber. In this paper numerical solution method is used for scrutiny of temperature contour and combustion products, the achieved results are compared with the experimental results and demonstrate acceptable accordance. In this paper, flow is a three-dimensional, steady, incompressible, viscous and turbulent flow, also it is with radiation. Combustion is a Non-premixed combustion. In this study, circle, square, rectangular, triangular and ellipse geometrics are used. Results indicated that geometric form of the primary holes, effects on the film cooling efficiency and thrust of combustion chamber. The film cooling efficiency and thrust of combustion chamber increase with increasing ratio of length to width. Geometric shapes without picked corner (ellipse or circle shape) are suggested for cooling primary holes.

This paper presents an approach for life estimation of helicopter main rotor shaft based on the standard Federation aviation administration (FAA) spectrum. According to Federation aviation regulation (FAR), the safe life approach has been employed in order to estimate the shaft life. Since the loading of the shaft is non-proportional and the material ductility is low, Findley's critical plane criterion has been applied. In order to apply Findley's criterion, an individual code was developed using ANSYS Parametric Design Language facilities. The code uses the minimum circumscribed circle approach to calculate the amplitude of shear stress and finds the critical plane. The lives of the shaft for the most severe maneuvers and for the standard FAA spectrum were found to be 76 and 1090 flight hours respectively. The fatigue sensitivity chart has been plotted and the effect of replacing another material with the shaft material on the life of shaft has been studied. To validate the result, the life of the shaft in the critical node has been calculated according to federal administration aviation AC 27-1B. Good agreement with these two results was observed.

shimmy vibration is one of the main important problems encounters in the design of aircraft landing gear and maybe occur in the ground maneuver, take-off and landing operations. The elasticity of landing gear mechanism and the tire's flexibility are the principal source of this phenomenon. In this paper, the shimmy vibration of landing gear is investigated within the framework of linear and nonlinear model. The landing gear is considered with non-zero rake angle which is incorporated into the effective caster length and the classical stretched string theory is used for the simulation of tire mechanical behavior. Then, the governing equation of motion is derived and the linear and nonlinear dynamical behavior is studied. The linear stability analysis is performed and the nonlinear behavior of the system is accomplished thorough time history response and compared with linear results. It is demonstrated that the nonlinear analysis anticipate the limit cycle of the landing gear which is known as shimmy vibration.

As the importance of aviation-aeronautical safety, identifying and understanding the effective factors on emerging of aviation and accident is one of the main goals of aviation industry. In exciting models the human aspects were emphasized more than other aspects. Despite all these efforts the number of accidents has not been decreased so far. These findings reinforced the idea that there should be other factors. Hence, this article by studying literature review in aviation-aeronautic safety field deals with identifying the effective factors pattern in aviation accidents. The population of the research consists of aviation accident experts in aviation industry. Purposive non probability sampling method is used to determine the sample of this research. Data collection is done by in-person questionnaire and archival data. The method research is field- descriptive. Concluding results indicate that there are factors that are presented in so-called "Semnan" model. Finally, concerning research findings and implementing aforementioned model, some suggestions were presented.

In this paper a robust autopilot is designed for a low altitude and short range interceptor. Operating point is selected with v-gap metric tool and robust static H¥ loop shaping controller is designed for the linearized model. Propose method does not use gain scheduling approach and guarantees stability of the interceptor's nonlinear dynamics in the whole flight envelope. Also an algorithm is proposed in order to reduce complexity synthesis of the weights in the loop shaping controller. In this algorithm the weights are optimized in order to maximize the robust stability margin. It is shown that robust stability margin which achieved by the controller can guarantee the stability of interceptor in the whole flight envelope.