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ABSTRACT This study analyzed Remotely Piloted Aircraft System (RPAS) deployment in the Regional Services of Aeronautical Accidents Investigation and Prevention (SERIPA – Brazil) as a support tool to investigate aviation accidents. Such review is justified by the acquisition and use of this equipment and new technology by investigators since 2017. Research aim was to analyze the perception of SERIPA investigators regarding the usefulness and ease of use of the RPAS equipment. We applied an adaptation of the Theoretical Model of Technology. Methodologically, the study was characterized as exploratory and carried out through an inductive logic and qualitative approach. A case study has been done with 14 investigators belonging to six Brazilian SERIPA units. In conclusion, the respondents deem the RPAS to be useful for aircraft accident investigation, and the equipment is of easy use. RPAS was observed as a tool capable of replacing manned aircraft in some crash sites. The external variable, i.e. crash site characteristics, emerged as a factor that influences the use of RPAS, as well as the transport of RPAS in commercial aircraft.

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ABSTRACT With the help of gathered data and formulas extracted from a previous conference paper, the all-electric geostationary Earth orbit (GEO) communication satellite statistical design was conducted and further studied with analytic hierarchy process (AHP) and technique for order of preference by similarity to ideal solution (TOPSIS) methods. Moreover, with the help of previously determined system parameters, the orbital ascension, orbital maintenance and deorbiting specifications, calculations and simulations were persuaded. Furthermore, a parametric subsystem design was conducted to test the methods reliability and prove the feasibility of such approach. The parametric subsystem design was used for electrical power subsystem (EPS), attitude determination and control system (ADCS), electric propulsion, telemetry, tracking and control (TT&C) in conceptual subsystem design level, which highly relies on the satellite type and other specifications, were concluded in this paper; other subsystem designs were not of a significant difference to hybrid and chemical satellites. Eventually, the verification of the mentioned subsystems has been evaluated by contrasting the results with the Space mission engineering: the new SMAD, and subsystem design book reference.

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ABSTRACT The aerospace industry is experiencing an unprecedented scenario. The air travel drifted from years of constant growth and positive expectations to a place where the uncertainty is the most predominant distinctive. Consequently, the aerospace ecosystem needs to adapt to cope with challenges never faced before. Understanding the evolution of the aerospace ecosystem is thus essential to foster its progression. This research aims at the identification and categorisation of key enablers that have been linked to the growth of aerospace ecosystems. To this extent, key enablers are first identified and then categorised using interpretive structural modelling (ISM) and cross-impact matrix multiplication applied to classification (MICMAC) methodologies. An analysis is elaborated for a developed aerospace ecosystem, the United Kingdom, and an emergent aerospace ecosystem, Mexico. Results evidence a contrasting categorisation of key enablers among both ecosystems. On the other hand, the automotive ecosystem and geopolitical factors are considered as underpinning enablers for both aerospace ecosystems evolution.

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ABSTRACT Since Gagarin’s flight on April 12th, 1961, the dream of making human space flight routine and making Homo sapiens a multiplanetary species seemed to have become closer to reality. Nonetheless, on average less than 10 human flights a year have happened along the past 60 years. Unmanned spacecrafts, on the other hand, have changed the way the human race sees itself and the universe it is surrounded by. They have explored all planets in the solar system, as well as comets, asteroids and the Sun. Presently, there are four unmanned spacecrafts on Mars’ surface and eight satellites in its orbit. Since the launching of Sputnik in 1957, more than 11,000 satellites have been sent into Earth’s orbit. Nowadays, it is impossible to imagine life on Earth without the services provided by the space-based infrastructure resulting from the Space Age. They have changed the modus vivendi of the human civilization and become a commodity, like potable water and electricity. The so-called satellite industry generates around US$ 300 billion a year, mostly related to the sale of satellite services and ground equipment. The era of exponential growth and disruption has reached Earth’s orbit, and beyond, through the minds, initiatives and boldness of the NewSpace generation, from which Elon Musk is its exponent. Twenty-five thousand satellites are expected to be launched in the next 10 years to provide, among other applications, worldwide broadband internet access. The scientific community and the military, however, have already expressed their concerns regarding space debris and, as a consequence, space sustainability. For the scientific community, the long-waited launch of the James Webb Space Telescope (JWST) promises to be the 2021 main event. In a time in which Spaceship Earth faces so many challenges, the dream of making its dwellers a multiplanetary species got a revival trough the minds and actions of Elon Musk and Jeff Bezos. There are those who, through public-private partnerships, intend to establish a 1,000 people community working and living in space by 2045. Cooperation among nations has been usual in space, but they are still shy when compared to the efforts required to colonize the Moon, Mars and other places in the solar system. As the 21st century advances, Spaceship Earth faces its greatest challenge ever. Space-based assets provide all the tools required to monitor Earth’s health, but if the human species intends to survive as the only identified intelligent civilization, it will have to think and act united in a truly cooperative way. Otherwise, the civilizational and technological effort hitherto undertaken may prove to be useless.

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ABSTRACT Unmanned vehicles/systems (UVs/USs) technology has exploded in recent years. Unmanned vehicles are operated in the air, on the ground, or on/in the water. Unmanned vehicles play a more significant role in many civil application domains, such as remote sensing, surveillance, precision agriculture and rescue operations rather than manned systems. Unmanned vehicles outperform manned systems in terms of mission safety and operational costs. Unmanned aerial vehicles (UAVs) are widely utilized in the civil infrastructure because of their low maintenance costs, ease of deployment, hovering capability, and excellent mobility. The UAVs can gather photographs faster and more accurately than satellite imagery, allowing for more prompt assessment. This study provides a comprehensive overview of UAV civil applications, including classification and requirements. Also encompassed with research trends, critical civil challenges, and future insights on how UAVs with artificial intelligence (smart AI). Furthermore, this paper discusses the specifications of several drone models and simulators. According to the literature review, precision agriculture is one of the civil applications of smart UAVs. Unmanned aerial vehicles aid in the detection of weeds, crop management, and the identification of plant diseases, among other issues, paving the path for researchers to create drone applications in the future.

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ABSTRACT Ground-based augmentation systems (GBASs) were designed to support civil aviation precision approach and landing with safety and integrity. It has several advantages over traditional navigation aids, allowing airspace usage optimization and reduction of fuel consumption. However, in low-latitude regions such as Brazil, this technology is still not operational due to the strong influence of ionospheric variability. Considering the increased interest in deploying a GBAS station in Brazil along with efforts toward this goal over the last decade, this paper is the first of a two-part series that provides an overview of the key aspects of this technology and the challenges posed when using it in low-latitude regions. The context in which GBAS operates today in midlatitudes is presented along with its fundamental principles and methods of guaranteeing sufficient accuracy, continuity, and integrity for precision operations, particularly those dealing with threatening ionospheric conditions. Finally, the evolution of GBAS to include multiple Global Navigation Satellite System (GNSS) satellite constellations and signal frequencies are discussed with respect to their ability to mitigate ionospheric effects. The conclusion is that the use of these new elements of GBAS seem to be the most viable solution for operating GBAS in low latitudes with high availability.

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ABSTRACT Ionospheric dynamics over low latitudes, especially in Brazil, are highly active, with several phenomena resulting from the complex interaction between space weather and atmospheric elements. These phenomena may cause disruptions to aviation communications, navigation and surveillance systems. Motivated by the issues posed by the ionosphere to the operation of ground-based augmentation of global navigation satellite systems (GNSS) in Brazil, this review paper presents fundamental physical aspects of space weather and low-latitude ionospheric dynamics to show how and why the ionosphere over Brazil is much more challenging for satellite-based positioning technologies. Solar influence, geomagnetic field configurations under quiet and storm periods, and the ensuing ionospheric dynamics over low latitudes occasionally lead to the development of structures known as equatorial plasma bubbles. These structures can produce strong plasma gradients within the ionosphere and cause scintillation on transionospheric signals. The consequences of these structures for GNSS users are specifically addressed.

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ABSTRACT This work presents selected results of an unconventional aircraft development campaign. Engine installation at the rear part of the fuselage imposed design constraints for air intakes that should be used for cooling purposes. Trial and error flight tests increased the development cost and time which required a more sophisticated analysis through computational fluid dynamics (CFD) techniques and robust semiempirical approach. The carried-out investigation of the air intakes started with an empirical approach from guidelines for designing NACA and scoops. Numerical studies via computational fluid dynamics were performed with the air intakes installed in the aircraft fuselage. An analysis based on the air intake efficiency, drag and the effect of angle of attack are detailed in this work. Different air intakes designs, such as scoops of different shapes, were evaluated seeking for improved air intake efficiency and low drag while providing enough air for cooling the engine compartment. The results showed that the numerical approach used herein decreased the development cost and time of the aircraft, providing a reasonable low-cost approach and leading to a design selection more easily. Based on the current approach the canard airplane geometry was changed to account for the new selected air intake for engine cooling purposes.

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ABSTRACT The life test of the 30 cm diameter ion thruster developed by the Lanzhou institute of physics began in Apr. 2018 and ended in Jan. 2020, lasting 6,500 h. This paper introduces the results of the 6,500-h life test of the 30 cm diameter ion thruster completed on the ground, including the ground facility for life test, the variations of the thrusters working performance, the times of the breakdown and power restart, and the erosion of the key components. The results show that the performance parameters, such as thrust, specific impulse and efficiency, do not change obviously during the test and magnetic field of the discharge chamber has no change. With the increase of test time, breakdown times increased significantly, whereas the power restart time decreased correspondingly. The diameter of the cathode orifice decreases gradually and there is a blockage risk of orifice. However, the diameter of the keeper orifice increases and presents an inverted cone erosion pattern. The diameter of the decelerator grid aperture expanded from 1.6 to 1.8 mm from 0 to 1,000 h and slightly enlarged after that. The aperture diameter of the accelerator grid presented linear enlargement but the pits-and-grooves erosion is obvious.

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ABSTRACT Combustion instability can severely impair the operation of many kinds of combustion engines. Acoustic resonators are widely used to suppress the pressure oscillations caused by the coupling between the combustion process and the combustion chamber acoustic modes. Combustion chambers with subsonic flow in its inlets and outlets, like gas turbine combustors, exhibit some acoustical damping due to the presence of openings. In such chambers, the acoustic modes are complex. In a complex mode, the antinode regions can be shifted from its position in the corresponding real mode. In this work an experimental acoustic modal analysis of a cavity with an opening was performed. Acoustic frequency response functions were obtained by using a volume acceleration source, a microphone and a data acquisition system. The PolyMAX algorithm was used to estimate longitudinal modes in its real and complex versions. A comparison was performed and the results show that, for some modes, the antinode region placement could change reasonably. This suggests that the use of complex modes for location of antinode regions provides more accurate results and consequently could be a better way to identify positions, where resonators provide maximum damping in order to minimize combustion instability in subsonic combustion chambers.

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ABSTRACT Traditional airplanes with fixed frequency and unipolar DC bus (270 V) commonly use 12-pulse passive rectifiers. The increase of power demand and the concern with aircraft efficiency boost the electrification of airplanes using variable frequency(360-800 Hz) and bipolar DC buses (± 270 V). Thus, this paper analyses the 12-pulse passive rectifiers in this new scenario. It is proposed an accurate model, describing its design, to verify if passive rectifiers are suitable for aircraft application complying with current standards. The analysis of the 12-pulse rectifier is done by an association of two 6-pulse rectifiers and considering both sorts of an input filter, L and LC. The mathematical model is presented and considers typical harmonic components, allowing precise analysis of input current and output voltage. Simulation and experimental results are provided to validate the mathematical model. The paper shows that the 12-pulse passive rectifier is not a viable solution when operating under variable frequency, which was verified by the violation of the electricity quality standards.

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ABSTRACT Radar absorbing materials (RAMs) are composites made with a polymeric matrix and an electromagnetic absorbing filler, such as carbon black (CB), silicon carbide (SiC) or manganese zinc ferrite (MnZn). To enhance their performances to attenuate an incident wave through reflection loss (RL), RAMs can be produced in multilayer structures. Usually, the RL analysis is done theoretically and experimentally validated with free space analysis. Here, it was demonstrated that multilayer structure can be designed and easily validated using rectangular waveguide, using a simpler setup and small samples. Three composites were produced using 2 wt% of CB (CB2), 40 wt% of SiC (SiC40) and 60 wt% of MnZn (MnZn60). They were characterized over the Ku-band and used to validate the multilayer structures, that were prepared by simply stacking each material inside the waveguide sample holder. One of the best results was obtained with structure SiC40+CB2 with 5.85 mm thickness, that presented a calculated RL of -21 dB at 17.8 GHz and a measured RL of -36 dB at the same frequency. In conclusion, using rectangular waveguide has been proven to be an easy, cheap, precise and fast approach to validate multilayer structures designs.

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ABSTRACT Generally, micro gas turbines are in the range of 15 to 300 kW. However, recent applications in unmanned aerial vehicles (UAVs) and polygeneration require a small micro gas turbine. So, here a small swirl combustor designed for micro gas turbine engine of capacity less than 1 kW is analyzed under nonreacting flow conditions. Simulations have been carried out to study the flow field inside the can combustor. Flow field characteristics, like velocity, path lines, turbulent intensity and total pressure loss are studied. The total pressure loss across the combustor is also measured experimentally and compared with that of simulation results. Good agreement is achieved between experimental and numerical results. The combustor total pressure drop was found to be negligible in the range of 0.002 to 0.06% at an inlet velocity ranges from 1.7 to 10.19 m/s. Flow pattern indicates a strong swirling pattern and strong interaction between the secondary air entrainment inside the flame tube.

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ABSTRACT Ethylene propylene diene monomer rubber is used as flexible thermal protection for rocket engines, as well as in blends with polychloroprene, which can be applied in the aeronautical sector, and with great potential in the defense sector. However, there is not a considerable number of studies considering both polymers as a blend. In general, elastomer content quantification in blends is done by more complex instrumental methods. When performed by Fourier transform-infrared spectroscopy, the conventional transmission mode is used, usually without including the developed methodology error. Therefore, the Fourier transform infrared spectroscopy (FT-IR) methodology is proposed using the universal attenuated total reflection mode, with sample treatment (pyrolysis) to determine polychloroprene content in the mixture with ethylene propylene diene monomer. In accordance with the infrared spectrometer precision limits and rubber blends studies data found in the literature, the methodology error analysis shows a value close to 2%. In addition, it has the advantage of being a less complex methodology. This actual study uses a simple FT-IR analytical tool, scarce, especially for the rubber research community, to determine the content of rubber minor phase within the major phase. It is valuable in weapons reverse engineering, aiming at the knowledge of new thermal protections.

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ABSTRACT Methods based on received signal strength measurements (RSS measurements) are used to determine the unmanned aerial vehicle (UAV) location using a wireless sensor network. The UAV transmitter power is usually unknown. In real conditions, it often becomes necessary to consider existence of anomalous measurement results. The reasons for the violation of the measurement process can be: the influence of interference, errors in the identification of signals during primary processing, failures of the equipment and similar. The optimum and quasi-optimal adaptive algorithms of UAV movement parameters filtration based on the RSS-measurement sensor networks in the presence of anomalous measurements at the unknown power of the transmitter are developed. These algorithms are obtained using Bayes’ theorems and the Markov property of a mixed process, including a vector of target movement parameters and a discrete component characterizing the type of measurement. Analysis of developed algorithm performance was carried out by Monte Carlo method on 2D plane. The quasi-optimal adaptive filtering algorithm detects the appearance of anomalous measurements with probabilities close to unity and allows one to eliminate their influence on the accuracy of UAV movement parameters estimation and also to estimate the UAV unknown transmitter power.

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ABSTRACT This research investigated how the variation of temperature and shear rate affects the viscosity of ethanol gel propellants that use methyl cellulose as gellant and, in parts, use boron as energetic additive. Using a rotational viscometer in a cone-and-plate configuration, propellant viscosity data was recorded across a range of temperatures and applied shear rates. The temperaturedependence of the viscosity was modelled using an Arrhenius-type equation. For the high shear rates, the data was modelled using the Power Law, Herrschel–Bulkley model, Carreau model, and Cross model. For low shear rates the used model was the rearranged Herrschel–Bulkley model. The temperature investigation suggested that the trend of decreasing viscosity with increasing temperature, predicted by the Arrhenius-type equation, is only applicable until approximately 320 K, after which the gel viscosity increased strongly. At high shear rates, the gel behaved in a shear thinning manner and was modelled most accurately by the Cross model. At low shear rates, the gel was shear thickening up to its elastic limit, which was found to lie at 0.41 s–1.

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ABSTRACT Many researchers developed new algorithms to predict the faults of unmanned aerial vehicles (UAV). These algorithms detect anomalies in the streamed data of the UAV and label them as potential faults. Most of these algorithms consider neither the complex relationships among the UAV variables nor the temporal patterns of the previous instances, which leaves a potential opportunity for new ideas. A new method for analyzing the relationships and the temporal patterns of every two variables to detect the potentially defected sensors. The proposed method depends on a new platform, which is composed of multiple deep neural networks. The method starts by building and training this platform. The training step requires reshaping the dataset into a set of subdatasets. Each new subdataset is used to train one deep neural network. In the testing phase, the method reads new instances of the UAV testing dataset. The output of the algorithm is the predicted potential faults. The proposed approach is evaluated and compared it with other well-known algorithms. The proposed approach showed promising results in predicting different kinds of faults.

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This paper addresses problems on the interception of hypersonic vehicles in near-space. The main contribution is to study a head pursuit guidance law based on fractional-order sliding mode theory and analyze the stability of the guidance law provided. Firstly, the fractional-order differential operator, which has characteristics such as fast convergence and memory, is introduced into the design of sliding mode surface, based on which a head pursuit guidance can be designed to improve the performance of the guidance system. The stability of this guidance law is proved by Lyapunov stability theory. Based on this, a head pursuit guidance law considering autopilot dynamic characteristic is designed and the stability is also analyzed. Finally, numerical simulations are presented and the results verify that the guidance laws designed in this paper can avoid overload saturation at the initial moment of the terminal guidance stage and improve the convergence speed.

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ABSTRACT Turboelectric distributed propulsion systems are paving the way for more electric aircraft systems (TeDP). This type of system provides a solution for some of the drawbacks of current low-energy-density batteries, which limit the ability of long-endurance electric aircraft. However, turboelectric propulsion requires the use of advanced turboelectric motors, superconductive materials and cryogenic cooling technologies, which are still under development and may be in production in the near future. This paper investigates a turboelectric propulsion system that can be considered an initial step in the production of TeDP in a remotely piloted aircraft system with the use of existing technology. This is achieved by replacing the gear and the starter motor of a turboprop with a high-speed permanent magnet electric machine to generate electrical power and propelling the aircraft through a distributed electric propulsion system. In this theoretical study, an augmentation to Breguet’s range and endurance equation is developed. This study confirmed that the new system is 31% lighter than the turboprop engine. Then the effect of the weight savings is used in the distributed electric propulsion (DEP) aerodynamic studies and found that there is a drastic increase in the range for a TeDP developed with the high-speed machine.

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ABSTRACT This case study, using a regional climate model (RegCM-4.7) in high horizontal resolution, allowed to obtain information on the intensity of the average vertical wind profile over the Alcântara Launch Center (ALC), Brazil. In the literature, on the wind intensity, the lack of continuous monitoring of the existence of flows in the vertical profile of the wind at heights of 400 to 600 m and the measurement of its magnitude make it possible to have an estimate lower than what can occur in reality at a low level in the region for operational purposes for the rocket launch. Therefore, this works results points to an intraseasonal variability of the wind intensity with maximum winds of the order of 14 to 20 m·s-1 in the core wind intensity at heights of 600 m, corresponding to pressure levels of the order of 930 hPa, in August, September and October 2020. These intensity values should be further studied with the use of observation equipment such as sound detection and ranging (SODAR) in the continuation of this research, in moment future, as well; the global models of reanalysis have low resolution and are not suitable for comparisons.

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ABSTRACT The paper is focused on numerical modeling of the aerodynamic characteristics of a full-scale coaxial main rotor in hover. The simulation was performed using two approaches of computational fluid dynamics (CFD): the original free wake model (FWM) developed by the authors and the unsteady Reynolds-averaged Navier–Stokes (URANS) equations method based on the Ansys Fluent software. The structure of the rotor vortex wake, flow images, vorticity and induced velocity fields, total and distributed aerodynamic characteristics of the rotor, including the rotor performance and figure of merit diagrams, have been analyzed. A comparison between FWM/URANS based calculations and calculated/experimental data by other authors has been performed. A satisfactory match of these data confirms reliability of used methods when modeling the aerodynamic characteristics of coaxial rotors. The FMW demonstrates a significant advantage in speed and resources intensity when calculating the total aerodynamic characteristics of a coaxial rotor. The URANS method makes it possible to model with significant accuracy the effects associated with the blade vortex interactions and pressure distribution over the blade surface. Finally, conclusions about most effectiveness of joint application of considered methods in solving complex problems of coaxial rotor aerodynamics has been made.

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ABSTRACT The light-emitting diode (LED) is the main lighting solution currently adopted in aircraft cabin lighting. This technology offers high durability, energy efficiency and luminosity, bringing plenty of benefits for being utilized in an aircraft. Despite its high initial price, it has many advantages, and the operational cost is lower than other types of illumination, such as fluorescent lamps. Additionally, LED illumination may improve the flight experience, making it more comfortable and pleasant for the passengers. Aircraft that have fluorescent lamps in their cabin should consider the possibility to make an illumination retrofit to LED lamps, because weight is directly correlated to the fuel consumption and operational costs and the energy economy can bring new improvements to the aircraft. The objective of this work is to evaluate the economic viability of the LED system installation compared with a fluorescent lamps illumination system in a regional aircraft. The study of the data shows that the usage of LED lights could save up to 68% of the energy in a month compared to conventional fluorescent lamps in the ceiling lights and reduce by 38% the monthly operational costs of illumination. The payback period is 4.2 years according to the proposed system.

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ABSTRACT Suborbital flight experiments, carried out through sounding rockets, have been employed for scientific and technological research since the beginning of the space age, in the late 1950s. In Brazil, sounding rocket campaigns have been carried out since 1965, when the Centro de Lançamento Barreira do Inferno (CLBI) began its operation, having the Instituto de Aeronáutica e Espaço (IAE) as the primary provider of vehicles. IAE has also provided vehicles for international programs, such as the TEXUS and MASER microgravity programs, implemented by the European Space Agency (ESA), with launching campaigns based in the European territory. To implement each Brazilian mission that uses IAE’s sounding rockets, a set of activities focused on mission objectives is planned and implemented. Although structured and executed quite similarly to a project, such sounding rocket campaigns do not have their complete life-cycle studied and formally described in phases, review meetings, management processes and verification and validation philosophy. In the present work, the attempt has been to characterize a sounding rocket mission as a project and then, based on European Cooperation for Space Standardization (ECSS) standards, propose a reduced life-cycle to develop such projects, tailored to meet Brazilian sounding rocket missions. The proposed life-cycle, adapted to Brazilian sounding rocket missions, is then compared with two other sounding rocket campaigns life-cycles: one from the European Programme for Life and Physical Sciences in Space and the other from the National Aeronautics and Space Administration (NASA) sounding rocket program. The study and availability of a framework for implementing and managing sounding rocket missions will improve the reliability of such endeavors and speed up their organization.

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Abstract This article discusses the jet mixing effectiveness of rectangular tab with slots to distort the jet, thereby creating vortices of differing sizes to enhance the mixing. This article numerically investigates the effectiveness of slanted slotted/perforated rectangular tabs with the slot connecting the adjacent faces of the tab to control Mach 0.4 jet. To intensify the jet mixing process, two similar tabs with equal blockage ratio of 7% are placed at diametrically opposite locations of the convergent nozzle exit. The jet flow development in the axial and radial directions of the jet are investigated in detail. To measure the effectiveness of the slotted tabs, the results are compared with the free jet and with the jet operated with solid rectangular tab. The percentage reduction in the core length obtained is 84.1 and 74% for the jet employed with the slotted tab and the solid tab, respectively, when compared with the free jet. The results exhibit that the slotted tab distorts the jet in the near field to a greater extent when compared with the solid rectangular tab.

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Abstract Advanced tactical fighter (ATF) configurations are bound to perform high angle of attack (AoA) maneuvers. However, existing conceptual design tools available in aerospace industry are based on empirical or potential flows that cannot predict aerodynamic data in nonlinear regimes. High-fidelity computational fluid dynamics algorithms have to be incorporated during conceptual design phase for better assessment between competing configurations. In this research, steady state aerodynamic analysis is conducted to compare four conceptual designs of advanced tactical fighters through Reynolds-averaged Navier–Stokes (RANS) simulations. Prior to the study, two validation test cases were conducted based on ONERA M6 Wing and benchmark unmanned combat air vehicle (UCAV) design to assess the computational setup for the problem. Pressure based solver is used to model the flow field in subsonic, transonic and supersonic regimes at sea level for all four competing designs. The quantitative results include the aerodynamic forces and the longitudinal stability coefficient comparisons among the models and its components. The qualitative analyses include pressure distribution, eddy shedding and behavior of vortices at varying flow angle. Additionally, the empirical estimation for interpolation and post-stall extrapolation are carried out for further flight performance studies.

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ABSTRACT With the continuous development and application of modeling technology, civil aircraft designers urgently need to apply model-based systems engineering (MBSE) theory and methods into the field of civil aircraft development. However, the existing modeling tools, which combined with MBSE methodologies, only focus on one particular area, such as requirement modeling, functional modeling and design synthesis. This kind of low coupling design system makes it difficult to link the upstream and downstream designers in the early stage of system development. This paper introduces the MBSE development process of civil aircraft and then establishes an integrated platform composed of six work stations for civil aircraft development based on this process. Commercially available modeling tools, such as IBM Rational DOORS and enterprise architect (EA), are conducted in the platform. The development of flight control system is taken as an example to test the feasibility and efficiency of our integrated platform in logic layer. This platform can complete the activities of aircraft life cycle function analysis, requirement and model management. The loose coupling between the modules and the high cohesive nature allows different system engineers to maintain their design independence and consistency at different stages of development.

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ABSTRACT The thrust produced by a hybrid rocket motor (HRM) can be controlled by varying the oxidizer flow rate to the combustion chamber. This feature is useful in shaping motor thrust profiles and optimizing a vehicle flight trajectory, but propellant throttling in solid-fuel hybrids is limited to the liquid component only, complicating the control scheme and potentially destabilizing combustion in the motor. While hybrid motor throttling ability remains a subject of considerable interest, there has been little investigation of throttling in motors that use high regression rate, liquefying fuels such as paraffin wax. This article describes the development and implementation of a closed loop thrust control scheme for a laboratory-scale paraffin wax/nitrous oxide HRM using a low-cost ball valve as the controlling hardware element. A model of motor performance is first developed from which proportional-integral-derivative (PID) controller constants are obtained through experimental testing. The control scheme is demonstrated through closed loop hot fire tests of a laboratory-scale motor in which thrust tracks a set-point value with feedback provided through a load cell. Upon reaching the setpoint, the motor remains throttled within ± 2.4% of the maximum thrust of the motor. Constant and ramping thrust profiles are demonstrated.

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ABSTRACT The purpose of the paper is to study the effect of temperature change on the theory of inner product vector (IPV). The IPV method can be used to detect structural damage. This study evaluates the IPV method ability to detect damage of an Airbus A320 slat-track, which is in the form of a longitudinal crack. The results show that the IPV method is able to detect defects in the structure as well as its location, with close approximation. Then, the Airbus A320 slat-track was investigated for the effect of changes in temperature on the IPV method, evaluated over a temperature between –73 and 260 °C. The effect of temperature on the performance of IPV damage detection method has not been investigated so far. The results of the IPV method show a spurious defect in the structure as the temperature changes; therefore, the IPV method is temperature-sensitive. Also, this study highlighted the importance of applying simulation methods to develop vibration-based damage detection (VBDD) techniques, especially for evaluating the effect of changes in environmental temperature when the structure is complex.

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ABSTRACT Aircraft noise emissions are a problem that negatively affects human health, directly or indirectly. For this reason, examining and managing the noise effects caused by aircrafts at the airports is important for the sustainable development of aviation. In the present study, a noise management model based on the multiapproach method, including some actions related to aircraft noise, has been created. The model was applied to the International Eskisehir Hasan Polatkan Airport (LTBY). Within the scope of the model, in the first stage, in 365 days, day, evening and night noise levels around the airport were simulated using IMMI software under the European noise directive and European Civil Aviation Conference (ECAC) doc 29-interim was also used to measure aircraft noise. In the second stage, the noise generated by the Cessna 172-S aircraft under different operating conditions experimentally measured was carried out. After the model had been applied to LTBY, improvement opportunities for aircraft noise were evaluated. It is thought that the study and its results will help other civil airports on the issue of noise problem at airports.

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ABSTRACT Aircraft fuels, called jet propulsion, are used in several areas of activity within aeronautics. There are jet fuels based on kerosene, that is, those obtained commercially, and there are synthetics produced in the laboratory. All of these fuels are included within the so-called propellants. In this article, Jet propulsion-8 (JP 8) fuel was used as the basis for data analysis, and thus two temperature ranges were analyzed. The first range, from 300 to 2500 K, was analyzed for specific heat, enthalpy and entropy. Based on theoretical and experimental data, artificial neural networks (ANNs) were developed to identify these properties in other working conditions, that is, at other temperatures.

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ABSTRACT Lifetime is a main factor restraining the application of low-power Hall thruster. Magnetic shielding configuration is regarded as a promising method to prolong the lifespan of Hall thruster. Aiming to demonstrate the feasibility and effectiveness of magnetic shielding configuration applying on low-power Hall thruster, a 60-mm diameter Hall thruster in partial magnetic shielding configuration was designated. Both the numerical and experimental methods were used to investigate the discharge characteristics of the Hall thruster and help understand the mechanism behind. The maximum anode efficiency was achieved as high as 29.7% with 1.7 mg•s–1 anode mass flow and 320 V discharge voltage. To evaluate the effectiveness of the magnetic shielding used for low-power Hall thruster, a 2000 h lifetime test has been carried out and the results indicate that the erosion rate has been decreased below 0.2 μm•h–1.

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ABSTRACT Paraffin wax has been identified as a hybrid rocket motor fuel, which offers enhanced regression rates and improved combustion performance. While various investigations into the performance of this class of fuels are being conducted around the world, the consideration of its structural performance is often overlooked. The research presented here establishes a simplified, yet accurate method of defining the structural performance of a paraffin wax hybrid fuel grain to be introduced early in the design phase of a motor. The use of the Johnson–Cook (J–C) material model has been verified to work within the “low speed” ignition range experienced in paraffin wax/N2O hybrid motors, and therefore is used to predict failure in a variety of motors. The resultant stress profiles within the grains indicate that the grain outer to inner diameter (OD/ID) ratio, as well as the outer diameter (OD) itself, play an important role in the grain ability to withstand the loading conditions applied. Additionally, the grain structural properties, and the stiffness of the combustion chamber affect the severity of the internal stresses in the grain. The feasibility of large-scale pure paraffin wax grains without structural enhancement additives is thus found to be poor. Fuel additives should be considered for structural enhancement.

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ABSTRACT The main points to the evaluation of effectiveness for the collaborative combat of the unmanned aerial vehicle (UAV) lie within the construction of a reasonable indicator system and an accurate contribution model. As for point one, this article introduces a new method combining the Delphi consulting method and the principal component analysis method to avoid the underlying subjective and time-consuming defects of the existing methods. As for another point, a weighting method is adopted combining the subjective and objective parameters to minimize the errors caused by a single entity. Firstly, the modified grey relational degree analysis method is used to obtain the subjective weight, which can reduce the influence of the extreme values and outliers by enhancing the selection process of the reference sequence. Secondly, this paper adopts the weight of minimum entropy weight method to obtain the objective weight; it can avoid the information loss caused by the original method, which only determines the weight based on the frequency of each element present in the effective combination. At last, the principle of minimum relative entropy is adopted to obtain a more reasonable weight distribution coefficient. The simulation experiments established the rationality and effectiveness of the proposed method.

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ABSTRACT In this study, surface features such as dimples and bumps are introduced to the surface of a NACA 0012 airfoil to study their effect on boundary layer separation, particularly at high angles of attack. Six modified airfoils were designed with dimples and bumps of spherical and pyramidical shapes. A computational fluid dynamics (CFD) analysis was conducted on these models at subsonic flow using Ansys Fluent. The analysis used the Shear Stress Transport k – ω turbulence model at a varying angle of attack (AOA) from 0 to 15°. The velocity contours and streamlines were generated. Also, the lift coefficient, drag coefficient and the lift-to-drag performance ratio were computed and analyzed. The results showed that all surface modifications led to delayed flow separation and flow recirculation. All surface modification also resulted in a decrease in drag at 15°. All designs, except pyramidical protrusions, increased the lift-to-drag ratio (L/D) performance at 15°. It was found that dimples are better than bumps and spherical features are better than pyramidical ones.

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ABSTRACT The regional navigation satellite system (RNSS) is recently used in some countries to cover or enhance their local navigation. The most important satellite navigation systems to date are in the Earth medium orbit (MEO) and Earth synchronous Earth orbit (GEO), which are characterized by big satellites, and high launch, construction, and operation costs. In contrast, low Earth orbit (LEO) small-satellite constellations have recently become attractive because of their advantages, such as a significant reduction in system cost, an increase in communication volume, and a reduction in latency. Therefore, in this study, the spatial geometry of a LEO constellation is designed for Iran to increase the required regional navigation performance. For this purpose, the optimal constellation configuration is obtained through a multi-objective genetic algorithm (MOGA) utilizing a cost function with a combination of the geometry dilution of precision (GDOP), the number of satellites, and orbital height in the form of a design procedure. Moreover, reducing the feasible region of longitude of the ascending nodes of orbit planes is applied in the design process to reduce the search space. The simulation results indicate the constellation designed performance.

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ABSTRACT For evaluating the cooperative combat effectiveness of unmanned aerial vehicles (UAVs), traditional entropy methods have an undue weight coefficient of the index due to its high degree of dispersion, and the interrelationship between the indices are not considered. To deal with this problem, this paper proposes a conditional entropy combination weighting method for evaluating the cooperative combat effectiveness of UAVs. Firstly, with the aim of establishing the UAV cooperative combat index system, the modified Delphi method has been combined with analytic hierarchy process (AHP) and interval estimation. This method has been used for estimating the degree of contribution of each index and to remove the indices that have a low contribution. Secondly, the principle of conditional entropy has been introduced for modifying the entropy method with the consideration of the interrelation between the indices. Finally, the modified entropy and AHP have been combined to assign the final weight in the UAV cooperative combat system. Testing results demonstrate that the index system established by this method is more comprehensive and reasonable as compared to that established by the traditional Delphi method. Compared with the single weighted method, this method is more suitable for the evaluation system of UAVs cooperative combat effectiveness.

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ABSTRACT This paper is concerned with the three-dimensional constrained optimal path planning. To this end, an objective function is defined as the shortest trajectory length in such a way that some constraints including rough terrain avoidance, forbidden zone avoidance, initial and terminal constraints, allowable altitude constraint and maximum allowable curvature of trajectory are satisfied. These leads to a challenging problem for aircraft guidance and control that solution requires great experience, skill, accuracy, and a powerful strategy. For this purpose, pseudospectral technique, which is one of the direct methods, is applied in this paper based on the Chebyshev nodes through which the complexity of the problem is reduced by transforming the optimal control problem into the parametric optimization one. The efficacy of the proposed method is demonstrated by extensive simulations, and it is particularly verified that this method is able to produce a solution satisfying all hard constraints of the underlying problem.

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ABSTRACT In a beyond visual range (BVR) air combat, one of the challenges is identifying the best time to launch a missile, which is a decision that must be made quickly. The decision involves combining knowledge about altitude, speed, distance, onboard sensor systems information, aircraft type, and type of missile on the aircraft, as well as intelligence on the opponent’s behavior. This paper discusses an approach to evaluate the probability of shoot-down of an unmanned combat air vehicle (UCAV) in a BVR air combat, based on a decision support system model that makes use of parameters available from the onboard sensors of the shooter UCAV. The strategic options development and analysis (SODA) method is applied to select the main features available in the on-board sensor systems of the shooter aircraft required to launch a missile successfully. Such features help us to develop an artificial neural network (ANN) for shoot-down prediction. The ANN was trained with a data set with 1093 registered shoots in military exercises, and it shows 78.0% accuracy with the cross-validation procedure.

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ABSTRACT For the aircraft, the engine is its core component. Once the engine fails, the flight safety will be seriously affected; therefore, it is necessary to diagnose the failure in time. This paper briefly introduced three aircraft engine fault diagnosis algorithms based on support vector machine (SVM), random forest, and particle swarm optimization-back-propagation (PSO-BP) and carried out a simulation experiment on the performance of the three algorithms in MATLAB software. The results showed that the PSO-BP-based diagnosis algorithm had the highest recognition accuracy and the SVM-based diagnosis algorithm had the lowest, both for artificial fault data and real fault data. The PSO-BP-based diagnosis algorithm took the least average recognition time, and the SVM-based diagnosis algorithm took the longest time.

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ABSTRACT This work experimentally investigates the effects that a different number of blades, three and five, has in the dynamic torque, acceleration, and power performance of a horizontal-axis small wind turbine. It presents the methodology used for calculating the temporal behavior of the aerodynamic torque generated by the blades during their acceleration phase. The tests were performed in an open section wind tunnel of 1.0 × 0.8 m. The model was produced by additive manufacturing and had two possible assemblies, with three and five blades. An in-line dynamic torque meter acquired the torque and angular speed data, and a National Instruments USB-6009 device processed the signal. The resistive torques were calculated by spin-down tests. The tests were executed at a wind speed of 10 m·s–1. The measurements displayed the five blades assembly having improved performance compared to the three blades: a higher static torque, which resulted in shorter stating time, and a power coefficient 39% higher.

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ABSTRACT Knowledge creation projects are essential for today’s business. It is common to observe in these projects, in all their dimensions, the presence of the uncertainty factor. Effectively, managing uncertainties is seen nowadays as a necessary condition for project success. This article aimed to present a study on the intensity that the hard and soft paradigms appear in knowledge creation projects and, consequently, identify the levels of uncertainty presented in its projects. To make this study possible, we adopted the hard and soft analysis framework. A case study on knowledge creation, managed by the aeronautical certification department of EMBRAER S.A, was analyzed under the aspects of this framework. It was expected, as a result of this study, to empirically validate the concepts about the uncertainty levels presented in projects of this nature.

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ABSTRACT The discharge characteristics of hollow cathode directly affect the performance of thruster. In order to obtain the plasma parameters of the 20 A emission current hollow cathode, COMSOL software is used to simulate the potential distribution, neutral fluid distribution and plasma parameters of the cathode, then the test is carried out to verify the simulations. The results show that the fluid velocity in the emitter region is about 20 ms–1 and is uniform in the radial direction. The electron density throughout the cathode discharge zone is almost uniform within the range of 1.09 × 1020 ~ 1.2 × 1020 m–3. The electron temperature increased from 2.8 to 4.9 eV throughout the cathode discharge zone. The electron collision frequency is in the order of 1023 Hz. The test results show that the electron temperature is increased from 2.4 to 5.2 eV from outlet of the emitter region to the plume region, and which presents an opposite trend to the electron density. There is a small error between the test results and the simulation results, and this error is mainly caused by the flow boundary setting.

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ABSTRACT In this study, the numerical simulations are used to simulate the discharge process of a 10-cm dual-stage 4-grid (DS4G) radiofrequency (RF) ion thruster, and the effects of RF coil turns, and electrical parameters on the key plasma parameters inside the discharge chamber are investigated. Thus, the optimal design parameters of the thruster are obtained. The RF plasma source has high inductive coupling discharge efficiency when the number of coil turns is six and the operational frequency is 2 MHz. The simulation results show that increasing the number of coil turns can effectively increase the plasma density inside the discharge chamber, and thus improve the efficiency of the inductive coupling discharge, and the operational frequency affects the characteristics of the inductively coupled discharge by influencing the depth of the plasma skinning layer. An experimental thruster demonstrated the 10-cm DS4G RF ion thruster can achieve super high specific impulse. The correctness of the simulation model is verified by the experiment results of the thruster, which will be useful for the optimal design of radio ion thruster or ion sources.

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ABSTRACT The design of the magnetic field is crucial to the performance of the hall thruster. This paper investigates the effects of magnetic field on the discharge characteristics of the low-power hall thruster in the method of combining simulation and experiment. Based on a 40-mm-diameter hall thruster (LHT-40) operating with hundreds of Watts, a two-dimensional axisymmetric model is established in fluid method to investigate the mechanism, how the magnetic field influences the performance of the thruster, and the experiments are also carried out to investigate the performance effected by magnetic field. Both the numerical and the experimental results indicate that there is an optimal magnetic flux density in which the thruster could achieve a higher efficiency compared with other conditions. And in order to maintain its high efficiency, the line of magnetic-curve inflexion inside the discharge channel should coincide with the center line of the channel to decrease the interaction between the plasma and the wall. The LHT-40 could generate about 12.2 mN of thrust at an optimal efficiency of 27% when the maximum magnetic flux density along the center line of the channel is about 200 Gs.

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ABSTRACT The development and proliferation of small unmanned aerial vehicles (UAVs) have led to the need to create systems for tracking UAVs and monitoring their authorized activities. The presence of electromagnetic radiation makes it possible to use passive radio monitoring systems, based on wireless sensor networks, for tracking UAVs. Methods, based on angle-of-arrival (AOA) measurements, are widely used for determining the location of a radio source using wireless sensor networks. In practice, it becomes necessary to take into account the appearance of abnormal (rough) measurements, which lead to a sharp deterioration in the accuracy characteristics of Kalman filtration algorithms. In this work, to synthesize an optimal adaptive filtering algorithm, the Markov property of a mixed process was used, which includes a continuous-valued vector of UAV movement parameters and discrete parameters that characterize the type of measurements of the sensors of the sensor network. A quasi-optimal algorithm of adaptive filtering of UAV movement parameters when using AOA measurements of the sensor network was obtained using the Gaussian approximation method of the posterior probability density. Its analysis is carried out using a model example. The quasi-optimal adaptive filtering algorithm allows to eliminate the uncontrolled increase of estimates errors of the UAV movement parameters and it does not require significant computational costs.

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ABSTRACT Objectives of this article are to create a method that should identify distortion of navigation signals using supplementary information obtained whilst processing the navigation parameters in the calculator of the navigation receiver. To develop this method, a comparative evaluation of the actual data of the navigation measurements with the calculated data values and a Bayesian probabilistic approach for detecting the navigation field distortion and identifying the interference. Test of results of the developed method showed that it enables a highly reliable assessment of the state of the navigation field and, if distorted, the identification of the distortion type: normal (undistorted) condition; abnormal state: when abnormally high errors appear spasmodically in the positioning estimation within individual measuring channels of the navigation receiver; slightly distorted state leading to a slow change in positioning accuracy; active spoofing manifested in the substitution of positioning coordinates. The article provides a new method for processing navigation parameters allowing to detect the fact of the navigation fields (NF) distortion and identify the interference effect on the navigation receiver (NR) of UAV.

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ABSTRACT This paper provides an overview of the design and development process for the L75 liquid propellant rocket engine (LPRE) foreseen as upper stage of a satellite launch vehicle application. Emphasis is put on the choice of available technologies, an adequate operational cycle, and the most suitable propellant combination. Problems encountered during the development and resulting solution approaches are described. Furthermore, a survey of upper stages including their main performance data currently in operation worldwide is presented. Since economical constraints are more important today compared to previous developments schedule and cost figures and their drawbacks are investigated as well. Finally, a summary regarding the development status of the Brazilian L75 engine is reported.