نشریه دانش و فناوری هوافضا
سال پنجم شماره 2 (پاییز و زمستان 1395)

In this paper a mini turbofan engine which would be used in a UAV with 25 hours mission time in each flight, is considered to be in the early and reverse design phase and reliability and maintainability analysis have been performed. To overcome the lack of data in design phase, it is used generic data or expert judgments.Then simulation process utilizing reliability block diagrams is performed. The results involve reliability evaluation of system, reliability importance and availability. The engine has less than 98 percent reliability in 126 flight hours. A reliability allocation method has been utilized to improve the reliability measure to 98 percent in 250 flight hours. An availability analysis utilizing Monte Carlo simulation has been done and 0.753 percent as mean availability has been estimated during 3 years usage and maintenance policies have been proposed for 3 years usage of the engine. Results reveal that the oil and fuel filters, pumps and the disks and blades of the rotating subsystems are the most critical parts of the engine.

Several methods for perturbation estimation can be found in the literatures. The dynamic Inversion technique is a well-known technique to estimate perturbation in the noisy environment. The main idea in the dynamic inversion techniques is replacing the measurement output by state variables in the dynamic equation. The problem with implementing the dynamic inversion method is that it might be difficult to construct the derivative output from noisy measurement. In this paper, a second order sliding mode differentiator and super twisting algorithm is applied for obtaining the derivative of noisy measurement signal. For this purpose, after the measurement noise has been approaches to sliding surface, the measurement output has been decoupled from noisy environment and it is possible to extract derivatives of measurement signal in a noise-free environment. The proposed method is evaluated to estimate the space perturbation in the presence of measurement noise. The advantages of the proposed method in comparison with other methods are illustrated through simulations.

Quadrotor is a flying robot with six degrees of freedom which can do vertical flight and complex maneuvers. Since the robot has nonlinear and coupled dynamic model, designing a controller with desired performance involves a large number of interdependent design parameters. The application of meta-heuristic algorithms for PID controller design and adjusting the gain values of the controller is presented in the paper. Therefor three meta-heuristic algorithms have been used for optimal tuning of PID parameters. Genetic Algorithm (GA), Particle Swarm Optimization (PSO) and Harmony Search (HS) are compared in minimizing the performance criteria formula that can result a better performance for controlling of quadrotor. Finally the PSO algorithm could reduce the cost function more than other evolutionary algorithms and provides suitable answers. To study the performance of PID controller on attitude control of the system, a quadrotor is installed to the designed stand. The system consists of accelerometer and gyroscope sensors and a microcontroller which is used to design PID attitude controller for the quadrotor. Considering that the experimental data has lots of errors and noises, Kalman filter is used to reduce the noises. Finally using the Kalman filter leads to better estimation of the quadrotor angle position and the PID controller performs the desired motions successfully.

High pressure gas flow at the outlet of the nozzle jet and rocket engines and gas engines in the combustion chamber is one of the factors affecting driving force, fuel consumption, emissions and engine efficiency. Hence its study is very important. High pressure gas from the nozzle exit and the process of mixing with ambient air, depending on the flow properties of compressibility and density barrel shaped like waves, creating shock waves and the stopper. The purpose of this article is the numerical study of these properties. The Mach disk contours, speed and pressure profile that is the effective parameters in the gas flow exit from the nozzles are presented in this paper. Gas jet flow simulation results showed that high pressure ratio of 81.4: 1, the formation of the gas jet boundary due to the high amount of kinetic energy is independent of viscosity or turbulent flow in the gas jet. Also the results showed that if the pressure ratio is higher than 18.6: 1 the characteristics of the local Mach number and the dimensionless pressure P/Pn is independent of the pressure ratio between the nozzle and the environment, which it depends only on dimensionless distance x/d.

By arrangement of flexure-load cell columns in the six-component test stands, the thrust vector components of force and moment of a propulsion system can be measured. In this research, the main considerations in the flexure design process of a six component test stand is introduced. Also, a Flexure with new geometric structure to take account of these considerations is proposed. Then, by using computational constrained multi-dimensional optimization of direct methods, geometrical dimensions of the flexure are calculated. In the next step, finite element analysis is carried out on designed flexure and its results are compared with results of the analytical solution. To validate the results of the theoretical solution, natural frequencies of the flexure and buckling critical loads are measured experimentally. Based on the acceptable correlation of the theoretical and experimental results, it can be said that the proposed flexure is a good choice for using in a propulsion system six - component test stand.