JOURNAL OF AERONAUTICAL ENGINEERING (JOAE)
Year:2022 | Volume:23 | Issue:2|Papers Count:12

Space engines are used for missions such as altitude change, position control, position maintenance, landing, and orbit change. In recent decades, the use of plasma thrusters as a space propulsion system has been considered, one of which is the pulsed plasma thrusters. In this paper, a quasi-experimental electromechanical model for rectangular flat plate electrodes has been developed using two different approaches: slug and snowplow. By equating the whole physical process as a one-dimensional electrical circuit and in the next step, coupling it with the force equation as well as using some experimental parameters, the electromechanical model is obtained. The results of this semi-empirical model are compared and evaluated with the basic experimental parameters for pulsed plasma thrusters used in two satellites. According to the positive results of the evaluations, using this semi-empirical model, the basic parameters of a pulsed plasma thruster such as impulse bit and plasma exhaust velocity can be calculated and some geometric parameters and capacitor parameters of a thruster can be optimized and controlled. The two approaches of slug and snowplow in this model are also compared with experimental results.

The main objective of the engineers and flight control system designers is to achieve the best performance and behavior of a controllable aeronautical vehicle. Trajectory optimization of a flying vehicle may improve performance, reduce costs, enhance the vehicle capabilities and lead to other favorable results. Trajectory Optimization is a knowledge that presents the ways of achieving optimum dynamic processes. Using the optimal control is one way to find the optimal trend of state variables. Since long range and endurance missions require some forms of fuel management, there is ongoing research in the area of minimizing the fuel consumption. In the current article, the problem of minimum fuel consumption for an unmanned aerial vehicle, during a circular maneuver in a predetermined area, is presented. UAV equations of motion are developed based on a point mass model. Optimality conditions of Pontryagen Minimum Principle (PMP) are found using the Hamiltonian function. Fuel consumption is the optimum performance index and multiple shooting method is chosen as numerical method for solving the problem at hand. Naturally, wind energy is expected to affect the flight path, so numerical simulations have been performed considering the effect of wind speed and direction on the optimal turn maneuver problem. Current research results show that in order to acquire a minimum fuel consumption loitering flight, in a circular trajectory, periodic climbing and descending maneuvers are needed.

In this research, the aerodynamic behavior and the time lag of supercritical airfoil SC-0410 undergoing a classic maneuver were investigated. This maneuver consists of pitch-up motion, pause and then pitch-down motion. In this research, the effect of reduced frequency and stop duration were investigated. The experiments were conducted in a subsonic close return wind tunnel with test section dimensions of 0. 8 m×0. 8 m. A pitching motion was produced by oscillation system about the quarter cord axis at reduced frequency of 0. 01 to 0. 12. In this study, both the mean angle of attack and oscillation domain were constant. The stop occurs between the upstroke motions. The stop angle of 5 degrees, was smaller than the static stall angle. Immediately after upstroke motion, suddenly stop and down stroke motion, the flow field is not achieved the static condition and the time lasts that the changes of 3 stages pass the flow field about airfoil and gain to initial steady state condition. The results show that reduced frequency was major parameter on the time lag. While the measured time lag was not sensitive to the pause duration. By increasing the reduced frequency, the time lag decreases because of large amount of energy dissipation at high frequencies. It was worth to point that the aerodynamic coefficient diagram verses angle of attack forms the hysteresis loop at unsteady stream. The hysteresis loop is the result of phase difference between the motion and the flow field.

Optimization of the height and length distribution of roughness elements as an effective passive flow control tool was investigated in the current study. The purpose of this paper was to investigate the roughness element's effect and its location on upstream of the laminar separation bubble from phase portrait point of view. Consequently, the effect of the roughness element features on the bubble's behavior is considered on the vortices behind the NASA-LS0417 cross-section at the pre-stall angles. The consequences express that the distribution of roughness in the appropriate dimensions and location could contribute to increasing the performance of the aerofoil and the interaction of vortices produced by roughness elements with shear layers on the suction side. It is worth noting that due to the small size and low velocity of the flight of MAVs, the formation of the well-known phenomenon of laminar separation bubble is almost imminent. Since this phenomenon greatly affects the aerodynamic performance and patterns of the Phase portrait circuit, its recognition, investigation, and control can be a key parameter. In the meantime, the results show the emergence of nested loops from the Phase portrait circuit due to flow arrangement changes. Also, the distribution of roughness in the appropriate dimensions and location can be recognized as a factor that helps to increase the performance of the aerofoil, and can be the basis of the work of MAV designers.

In this practical investigation that has been led to manufacturing a coaxial one-maned electric helicopter, the method of electric power supply has replaced fuel systems. In order to make a fundamental change in the power supply system or propulsion energy of helicopters, this project is introduced. First, by designing the basic specifications of the system, a preliminary design is obtained. Then, with the floating design of the parameters, the system is designed and built in such a way that, if necessary, and with the effect of uncertainties in the design, an appropriate response can be obtained from it. In this paper, the analysis, construction and testing of a one-manned helicopter with a special structure, with electric propulsion energy and integrated gearbox has been performed. Achieving technical knowledge of cost-effective production method of blades without mold (taper shape, aerodynamic twist, and asymmetric geometry), design and construction of a planetary gearbox with 16 inputs and two coaxial outputs with the ability to reduce the number of inputs, the remote-control system of two sets of blades, and many others, practically paves the way for the construction of high-performance prototypes. Using mathematical and software analyzes, a suitable operating range for the system was obtained. The proper performance of the system was proved by designing, manufacturing and installing vibration absorbers. In the test stand that was designed and built for this purpose, while examining the vibrational behavior of the system, the ability of the system to lift was also successfully tested.

Anti-tank missiles have been one of the most important tactical weapons on the battlefield in the past decades. Guiding, navigating, and hitting the target are one of the most important issues in anti-tank missiles. The Tau missile can be named as one of the most powerful short-range anti-tank missiles used in the world, which can also be fired from a helicopter and it plays a significant role in the military forces of the Islamic Republic of Iran. Tau missile is a three-point strategic guidance type (missile, target and tracker), in which type of guidance, if the communication wire connected to the missile is cut or the conduction laser channel is cut in the new generation Tau missiles, the missile guidance will be lost. Also, in wired or laser guidance, the helicopter from which the missile is fired must guide the missile to the end of the path until the missile hits the target (approximately 20 seconds), which is considered a very dangerous operation in terms of safety on the battlefield. Therefore, having an anti-tank guided missile with FIRE & FORGET capability in required times is necessary. Thus, in this research, the pre-set guidance and navigation requirements for the Tau missile are investigated and it is shown that by equipping the helicopter with a laser rangefinder to determine the target position and using a sensor with low bias error in the guidance and navigation system of the Tau missile, we can use FIRE & FORGET guidance with an acceptable accuracy for the Tau missile.

The purpose of this study is to experimentally evaluate the performance of two models of new type of contact pneumatic grippers. One of them is two-dimensional and the other one is axisymmetric, which uses a dual throat ejector to handle limp and porous materials. In two-dimensional device, slotted plates with different slot width were used to investigate the effect of slot width and total pressure of inlet flow on the performance of the gripper. In the axisymmetric gripper, perforated rings with different hole diameters were used to evaluate their effect and the effect of high-pressure inlet flow on the performance of the device. Results show that in both grippers, by increasing inlet pressure, the induced pressure and suction force to hold limp materials increases. Also, regardless of the gripper mass flow rate consumption, the axisymmetric gripper with higher mass flow consumption creates more force and suction pressure, but the performance of the two-dimensional gripper in producing suction force is much better by considering the mass flow rate consumption.

Polymer nanocomposites have high strength, low weight, thermal stability, electrical conductivity, and high chemical resistance. In this paper, graphene oxide nanoparticles are synthesized using the modified Hammers method and then to improve the thermal properties of the epoxy coating, prevent the accumulation of nanoparticles, and their proper distribution on the epoxy surface by triethoxysilane (3-aminopropyl) (APTES) have become functional. The innovation of this paper is the synthesis of graphene oxide nanoparticles in an epoxy resin substrate which, in addition to investigating the microwave absorption properties, can also increase the thermal resistance. The results of the thermal analysis also show that the residual materials at 500 ° C for graphene oxide, GO and epoxy are 3. 7, 62. 4, and 8. 21 percent, respectively. Due to the fact that the thickness of the sample has increased, when graphene oxide nanoparticles with 10% by weight are used, the losses at the frequency of 9. 5 GHz reach their maximum value-57 dB. Accordingly, because the number of casualties in this analysis was high, it is a good option to put the cover on a drone. The results of UAV modeling show that coatings containing graphene oxide nanoparticles at the highest wattage (10 wt%) can reduce the radar cross-section from-15 to-25 dB.

In this paper, a satellite attitude control with observer-based modified proportional-integral-derivative (PID) controller is studied in the presence of disturbance and uncertainty. First-order dynamic has been used to model the reaction wheel as control actuator with considering the practical limit of the maximum output torque. In observer method, saturation and windup are feedbacks to control algorithm to modify control signal. Control gains have been obtained by optimization method based on genetic evolutionary algorithm with penalty method and for the performance criterion of the absolute mean of the pointing error. To evaluate the performance, a comparison study has been done between modified controller and classic controller versus control parameters, phase plane diagram, limit cycle, uncertainties, amplitude and frequency of external disturbance. To fair comparison, all conditions in optimization and initial values are selected identical for two controllers. Comparing results show better performance in the modified controller, anti-windup, and avoid saturation. In the face of perturbations and limit cycle diagrams, the performance of the modified controller is clearly comparable to that of a classical controller. In addition, the performance of the two controllers is studied versus moment of inertia, actuator model, disturbance frequency, disturbance amplitude, and maximum momentum uncertainties. The behavior of modified controller is generally more appropriate and pointing accuracy is better. For example, control accuracy in modified PID is about 15% better than classical algorithm under moment of inertia uncertainty.

During the liquid fuel spray, there are various phenomena that considering or not taking them into the numerical simulation has a great impact on the cost and accuracy of calculations. The purpose of this paper is to investigate whether or not to take into account phenomena such as radiation heat transfer, secondary breakup, gravity, and type of turbulence model. In this work, the spray of liquid fuel droplets in hot air is modeled by the Eulerian-Lagrangian approach. The radiation heat transfer and secondary breakup are simulated employing the discrete ordinates model and the TAB model, respectively. The flow governing equations are implicitly linearized and discretized of the second order. The results show that in evaporative spray flow, gravity and radiation heat transfer have a little effect on the behavior and the diameter distribution of fuel droplets in the evaporative chamber and considering them will only increase the cost of calculations. In addition, droplet breakup can be ignored. The results show that the obtained axial velocity distribution and the diameter distribution of the droplets from simulation have an acceptable agreement with the experimental data. Where the droplets are in the recirculation zone and being a higher relative velocity between the hot air and the droplets, more droplets evaporate.

The main idea of this paper is to Adopt the optimal design of the general aviation aircraft wing to reach the optimal range and weight. For this purpose, the non-dominated sorting genetic algorithm II; has been used as an optimization tool for reducing three significant elements of aircraft design, including decisions that require a trade-off, time, and cost. The cost function of the optimization was the minimization of wing weight and maximization of aircraft range which was constrained by Four penalty functions and limiting decisions variables. The first function constraint was lift coefficient which should be equal to the lift coefficient required for supporting aircraft weight at cruise flight. The second and the third functions were Taper-Ratio, and tip to root maximum thickness ratio must be between one and zero. The fourth function was to constrain the sum of the absolute value of twist with incidence angle that must be greater or equal to the absolute value of wing zero lift. The fifth penalty function does not allow the lift-to-drag ratio to exceed the maximum limit of the lift-to-drag ratio. Design parameters were root chord, tip chord, wingspan, incidence angle, twist angle, airfoil zero-lift angle of attack, maximum thickness to chord ratio tip, and chord. In the end, the optimal wing shape design was proposed and validated with the target aircraft. The results show that compared to the most efficient target aircraft, 6. 84% improvement in range but 2. 87% increased weight has been achieved in the optimal response to the problem.

In this study, the effect of rectangular finlets on the trailing edge noise of a flat plate in an incompressible turbulent boundary layer with Mach number 0. 06 has been studied numerically. The finlets are modeled upstream of the trailing edge of the flat plate with two spanwise spacing of 1. 5 and 0. 9 mm. Large-eddy simulation (LES) approach with Lund inflow generation model in open-source code of OpenFOAM has been used to simulate the turbulent boundary layer flow. Probe utility has been used for pressure and velocity data acquisitions. The finlets have increased the PSD of pressure fluctuations in the low to mid frequencies and decreased it at high frequencies between and downstream of the finlets. Also, the spanwise length scale of the pressure fluctuations increases, but the eddy convection velocity is reduced and their effects have been intensified by the reduction of the spanwise spacing. The mean velocity decreases, but the turbulence intensity increases downstream of the finlets. The reduction of the spanwise spacing of the finlets results in the formation of a stronger shear layer and the extension of the shear sheltering area downstream of the finlets. According to the results of the far-field noise prediction with Curle analogy, finlets with the spacing of 1. 5 mm have slightly reduced the noise about 0. 3 dB but the finlets with the spacing of 0. 9 mm have increased the trailing edge noise of the flat plate about 1. 0 dB.