نشریه فناوری در مهندسی هوافضا
سال سوم شماره 3 (پیاپی 10، پاییز 1398)

Composite solid propellants have found wide spread applications in missile industries, such as high density, high specific impulse, and possibility of producing large scale grains. These solid propellants consist of three main chemical ingredients, including oxidizer, fuel, and binder. Recently ,Hydroxyethyl Terminal Poly-Butadiene (HTPB) has been used abundantly for these propellants due to its good mechanical properties and ability to high solid loading (88 to 90% of solid loading, including Al and AP). The mechanical properties of solid rocket propellants are crucial for proper functioning of rocket engines. In this study, the effect of T313 (chain extender) and MAPO (bonding agent) on mechanical properties of propellant is investigated. In addition tothe necessity of these substances in the propellant, the formulation and the reasons for utilizing MAPO and T313 are discussed. Different compositions havebeen prepared by incorporating different percents of MAPO and T313 for evaluation. Also, their effects on pot life, mechanical properties, and density are studied. Based on the results, the amount of MAPO and T313 should be used in optimum amount and these compounds have great influence on the rheological and mechanical properties.

Increasing the orbital height and mass of the satellites' cargo, in addition to multi-staging the satellites, requires use of stronger propulsion systems. One of the commonly used methods to provide the required thrust in each stage is proper arrangement of several engines in conjunction with each other, in order to provide the amount of propulsion needed to carry out the mission. The overall purpose of this paper is to present the results of a statistical study of massive energy and system parameters of satellites and missiles in countries that use clustered or multi-compartment engines in their propulsion system. Extracting thrusts, trust weights, specific impulse, chamber pressure of these engines, and examining the type of pressurizing system, vector control system, etc. It is possible to compare the mass-energy parameters and system characteristics of propulsion systems. The results show that the C* efficiency of the liquid-gas injection system for both components of the crosene and liquid hydrogen injector is higher than that of the liquid-liquid injection systems, indicating the superiority of the propellants in comparison to refractory propellants. On the other hand, the pressure of the open-cycle engine compartment with a storable propellant is more than that of engines with cryogenic propellant.

In this research, a dynamic simulator software has been designed to calculate the time varying load factor acting on an aircraft wing and on a horizontal tail relation to elevator deflection angle. The related loading equations were extracted and solved by MATLAB software and were presented as a GUI software. By introducing time varying angles of the elevator deflection in each flight maneuver and the necessary derivatives, the dynamic load factor on the wing and on horizontal tail were calculated with respect to time. In derivation of equations, the moment due to elevator camber, the effect of time lag in downwash, and the change in tail angle due to rotation were also considered. Comparing the results with the analytical ones confirms the reliability of the software. This software provides a rational approach in aircraft loading calculations that is applicable for structural design of the wing and the horizontal tail, as well as for conformity with the requirements of aviation regulations for loading, to obtain an airworthiness certificates.

In this paper, Extreme Learning Machine method is used to model the rate of material transfer as an effective parameter in process speed and surface quality. Using neural network model of Extreme Learning Machine, the mean squared error (MSE) for the material transfer rate in the learning data is 0.000,387 and in the test data is 0.001,7. While, the mean error squared for the average reset layer thickness, calculated in the learning data, was 0.000,214 and in the test data was 0.001,7. The proposed algorithm of Extreme Learning Machine with experimental results has high accuracy in predicting a process output parameters.

Reflected-type shock tube, equipped with laser absorption spectroscopy, is one of the most applicable facilities for experimental investigations in combustion kinetics. Ignition delay time of a specific fuel, as well as the products of combustion can be studied with a reflected-type shock tube. However, a minimum test time of 10 ms for test gas in designed pressure and temperature is required to investigate the combustion kinetics. A shock tube at “tailored condition” should be designed to produce a minimum test time of 10 ms with steady temperature and pressure. In this study, after a short review of the basic principles of a reflected shock tube, its design procedure is presented with the deigned stagnation temperature of 950K. Finally, the steady-state test time is measured to assure that the designed facility can provide the desired pseudo-steady thermodynamic conditions for combustion kinetic studies.

This paper reports a review and comparison of the methods used for calculating convective heat transfer coefficient in combustion chambers and in diverging-converging nozzles. Therefore, a history of applying different methods for calculating the convective heat transfer coefficient is explained first. Then, the nozzle flow is numerically solved, using the explicit McCormack method. In a Bates nozzle, The methods of Bartz, Stanton, Preiskorn, and Adami were selected among the proposed methods and were compared with CFD. Convective heat transfer coefficient of a solid fuel engine was calculated by taking into account the flow parameters in the engine chamber. Consequently, it was found that as wet move to the nozzle, heat transfer coefficient increases with velocity of the flow. This results revealed that in analytical methods, the maximum convective heat transfer coefficient occurs in the nozzle throat, while CFD results show that the maximum occurs upstream of the nozzle throat. These methods require less computational time than CFD, however CFD has to be considered more accurately. As a result, during a preliminary design procedure, the much faster and slightly less precise method can be used, in particular at the throat where the relative difference between the methods is quite low. Finally, it was shown that the innovative approach of combining Adami and Bartz methods has the lowest possible error, compared to the CFD.