جستجوی مقالات مرتبط با کلیدواژه "بالگرد" در نشریات گروه "مکانیک"

In this article, to investigate the severity of damage to the helicopter pilot under the crash impact, the numerical simulation of the actual helicopter cockpit seat has been done. To limit the complexity of the problem, a fully vertical impact was considered as a reference scenario for the assembly consisting of a collapsible helicopter seat, an energy absorption section, and a humanoid dummy. For this purpose, the three-dimensional model of the chair in the laboratory was studied in two states with and without the addition of the energy absorption mechanism. A honeycomb structure was used in the seat cushion section. The results of the research showed that the use of UPVC damper to test the crash impact with a certain mass based on biomechanical criteria, an average 80 % decrease in serious injuries to the skull and spine has been achieved. Also, based on the results obtained in this research, although the aluminum honeycomb structure meets the criterion of damage to the head and is within the permissible range, it has rejected the criteria of damage to the spine and permissible acceleration range. However, compared to the case without honeycomb, it has performed much better and has been able to absorb the energy of the crash impact.

Helicopters can be a source of loud noise. The high production noise of helicopters makes them unsuitable for densely populated areas, especially in low-flying conditions. This study examines methods and offers solutions to reduce or eliminate the noise produced by helicopters. Several methods have been considered to reduce the noise produced. Solutions such as muffler for motors, use of modulated blade spacing, X-force control, reduced tip speed, blade tip modification, airfoil tailoring, Increasing the number of main rotor blades, active blade control and variable diameter rotor in The rotor and the use of the strut in the gearbox were introduced. According to the studies conducted in the present study, combined methods haveas the best noise reduction. although Independent methods reduce noise, depending on the amount of reduction required in the targeting, combining the methods can be achieved the appropriate answer.

Considering the complexity of analyzing the phenomena affecting the aerodynamic performance of the main rotor helicopter and how to simulate the dynamic movements of the blade relative to the center of rotation, Using methods such as blade element theory together with computational fluid dynamics can be a simpler and less expensive solution than the physical simulation of a helicopter rotor. The geometric characteristics of the rotor of the Bell UH-1 helicopter have been investigated as a virtual disc in two modes of the rotor alone and with the body in static and forward flight conditions. To simulate the flow, unsteady compressible equations with turbulence components are used, and for their discretization, upwind second-order accuracy is used, and the functional effects of the rotor in the form of a spring component are included in these equations.

An investigation has been conducted to determine the optimum blade planform required to minimize the rotor power, maximize the lift-to-drag ratio, and maximize roll attitude quickness of the helicopter using numerical optimization techniques. The optimization process is based on response surface method, I-optimal design expriment, and helicopter inverse simulation program (HISP), developing mathematical model of performance, and Turning a multi-objective optimization problem into a one-objective problem using Desirability approach that the optimal numerical solution will eventually be calculated. The effects of helicopter weight and blade planform parameters (i.e., root chord, taper ratio, the taper starting point on the blade, and blade twist) on the performance and handling quality of the helicopter are therefore investigated. Responses of helicopter were obtained through a HISP developed for rotors with quasi-steady aerodynamic formulations. The resulting system provides a systematic evaluation to examine the rotor blade design variables and their interactions, thus reducing the time and cost of designing rotor blades. The results also confirm that the optimum tapered blade lowers the power required by about 7% and enhances the lift-to-drag ratio and roll attitude quickness up to 10% and 36% with a satisfactory improvement relative to the helicopter with rectangular planform a NACA 0012 cross-section in slalom maneuver, which is a good improvement for rotor blade design.

The effect of ground proximity on the some performance parameters of tandem rotors was measured using a multifunctional test rig in this study. Trust, produced power and induced power measurements of the rotors were performed in three different overlap values ​​to investigate the effects of ground proximity on these values ​​in hover flight. The results showed that the positive effect of ground proximity on the produced trust of tandem rotors is more than single rotors. In the ground effect, as the amount of overlap of the tandem rotors increased and the effect of the fountain flow recirculated from the ground increased, the amount of thrust increased . The results of power measurements showed that with decreasing the height of the rotors in the ground effect, the amount of induced power as well as the negative effect of aerodynamic interference due to their overlap decreased, These findings lead to a new approach to evaluating the performance of this type of helicopters.

Several research efforts have been directed towards better understanding the causes of accidents. While some studies provide useful insights into accidents, they do not provide an accurate understanding of accidents if viewed from an event-based perspective. Air accidents in Iran, especially in the last two decades, do not show a significant decrease in the number of accidents or casualties; In this study, we deal with the most important causes of helicopter aviation accidents in Iran. To better understand the causes of aviation accidents, this study offers a state-based approach to examining existing logical gaps or neglected cases. For this purpose, first, using statistica software, situations and factors that are possibly related to fatal and non-fatal accidents are identified; In this software, accident states, signs and accident information codes are automatically detected in a database and the information is automatically classified. We apply the model to 6200 helicopter accidents that occurred between 1982 and 2020. To better understand the causes of accidents, a state-based approach is proposed to examine existing logical gaps or omissions and examines records that are potentially full of errors. Also, the method of air accident ontology and model-based modeling with machine learning tools, which is a new method in this field, has been used to achieve more desirable results.

One of the major challenges in the use of predictive control systems, particularly in the fast system is computational burden. To accelerate the process and reduce the amount of computation and optimization of functions, we use the Laguerre functions. The purpose of this paper is to provide a linear predictive control method using Laguerre functions with constraints on signal and the rate control signal for a helicopter flight control system design in the status of hover maneuver. By tuning parameters of predictive control in nonlinear model, the performance of the proposed method evaluate by two index entries, maneuverability and coupling effect based on standards for design a helicopter flight control system. Multiplicative uncertainty in state-space model has been described due to uncertainty on system modeling to study the robustness of the proposed method. The simulation results of this method have been compared with the results of generalized predictive control method. Simulation results show that in addition of public benefits in generalized predictive control, Laguerre predictive control has the advantage of reducing the time and burden of computation and it is clear to see that the control law we have obtained for the hovering flight condition achieve the top level performance in two categories under examination.

Variable pitch propeller (VPP) are used in advanced helicopters, in order to achieve greater efficiency, better stability and achieve higher altitudes. This study is going to assess the behavior of VPP propeller with coupled non-linear displacement in three degrees of freedom. Accordingly, the behavior of this type of propeller with Changes of elastic axis distance, Length, mass, speed, polar radius of gyration, Stiffness in three degrees of freedom, and pitch have been investigated. In this paper, Gallerkin method is used to extract natural frequencies and the results were evaluated with the results reported by other researchers. The results show convergence and accuracy of the used method. In this study, it was found that parameters of mass, length and rotational speed of the propeller have effect on the natural frequencies, and all modes of vibration. However, other parameters except for the pitch angle effect on the odd or even number of frequency modes. It was also found that the pitch angle in the static mode does not effect on natural frequencies but in the case of rotation of propeller, affect on natural frequency of vibration modes as sine or cosine form.