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ABSTRACT: There are many problems facing aircraft in the air during flight, such as lightning strikes and ice accumulation on aircraft surfaces. These problems usually reduce aircraft efficiency and lead to serious accidents and fatalities. However, the current protection systems used to solve these problems of aircraft represent excessive energy usage, a hazard to the environment, and they are generally bulky, heavy and costly. Therefore, there are new conductive composites containing an embedded layer of conductive fibers such as graphene and carbon nanotube designed to carry lightning currents, in addition to that, there is a new deicing heater element made of graphene nanoribbons films to be used in ice protection systems. This paper presents a review of some problems facing aircraft in the air, such as lightning and ice accumulation on the surfaces of the aircraft and the significant efforts that have been exerted to address and solve these issues. Also, this paper reviews the contribution of composite materials in reducing the weight of the aircraft and fuel consumption as well as increasing the efficiency of aircraft. This paper also will review the conductive composite materials and its application for aviation, in addition to their contribution to solving the most important problems in aviation.

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ABSTRACT This paper reviews various power device components of solar-powered aircraft such as photovoltaic (PV) cells, maximum power point tracker (MPPT) and rechargeable batteries. The various power device components were highlighted, and the ones applicable to aircraft were analyzed, based on criteria as efficiency for photovoltaic cells; energy densities about rechargeable batteries; and maximum power point tracker on quick response to achieve maximum power point on I-V curve. Emerging technologies like photovoltaic cells, thin film cell, organic photovoltaic cell, multi-junction cell and silicon quantum dot cell, with the future potential of high efficiencies that can be used in solar-powered aircraft, were all examined. Regarding battery technology, Lithium-air battery (Li-air) was reported as having great opportunities for high energy densities capable of improving the efficiency of the solar-powered aircraft, for the greater prospect of the aviation industry. The design of efficient power device for solar-powered aircraft application is proposed. Gallium Arsenide (GaAs) solar cells were used because of its high energy conversion efficiency of 30 to 40%. A smart and intelligent MPPT Artificial Neural Network (ANN) is chosen because of its efficiency in partial shading and fast response and speed. The Li-air rechargeable battery is proposed because of its theoretical energy density of 11680 Wh/Kg.

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ABSTRACT: Increased congestion at hub airports affects on-time airline performance to the detriment of customer satisfaction and may have substantially negative repercussions for airlines in a hypercompetitive environment. This paper concentrates on the on-time performance of British Airways (BA) at London Heathrow Airport (LHR) to identify BA's delays/disruption management; measure the passengers' expectations in case of a delay; and investigate the passenger satisfaction levels. A survey of 160 BA passengers based on a close-ended questionnaire was conducted, complemented by semi-structured interviews with four members of staff at BA's network operations department. The survey results show that BA has been able to satisfy its customers by matching or exceeding their expectations and that those customers will travel with BA again.Interestingly, the results contradict the widespread belief that BA passengers are annoyed by a service failure/delay at LHR; this is because they expect to experience such a delay anyway.

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ABSTRACT Experimental investigations were carried out to study the wake profile of a supercritical airfoil at Mach numbers of 0.4 and 0.6 in a pitching motion. Both static and dynamic tests were conducted in a tri-sonic wind tunnel. Flow field inside the wake was measured by hot wire anemometry at downstream distances of 0.25 and 0.5 times the chord length from trailing edge. All data were taken at mean incidence angle of 3º; the amplitude of oscillation was 3º and the oscillation frequencies were 3 and 6 Hz. Moreover, numerical study was applied for the same airfoil under similar experimental test conditions; finally, wake profiles obtained from both numerical and experimental methods were compared.

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ABSTRACT In large-scale natural disasters and military supplies, multiple parafoils are more capable of performing actual tasks. The cooperative paths planning for multiple parafoils with different initial positions and headings is an important step in multiple parafoils airdrop, which has to satisfy multiple objectives, namely, parafoils can’t collide with each other, parafoils should rendezvous at same target area, most of parafoils need to keep alignment against wind, and planned paths should be in the range of maneuver performance constraints to ensure that every parafoil’s path is flyable. Due to more factors need to be considered, it is more difficult to plan paths for multiple parafoils than single parafoil. In this paper an improved genetic algorithm is used to solve the multi-objective cooperative paths planning problem of multiple parafoils system. Parafoils’ paths are encoded by real matrix, and the cooperative relationship between parafoils is realized by paths fitness function. The random single point crossover and Gaussian mutation are introduced to accelerate algorithm convergence rate. Finally, a simulation example is given, simulation results show that proposed method can plan feasible paths for all parafoils, meanwhile, it satisfies the requirements of anti-collision, rendezvous to target point, and keep alignment against the wind.

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ABSTRACT Optimization is now an established tool for obtaining better solutions in engineering design. Nevertheless, the multiplicity of possible applications and the continuing search for better computational performance has motivated researchers in continuing to propose new methods, as well as improvements on existing ones. Not only optimization has allowed a better exploration of the design space, it also can significantly reduce the time of the design process. In this paper the advantages of using a fully multiobjective and multicase approach for the design of space radiators is presented. The optimization of Amazonia-1 satellite batteries panel thermal design is investigated. Instead of conventional space radiators, in this work an innovative solution considering the fin as heat absorber is analyzed. The results have shown that there are several viable configurations regarding to fin coating material, heater power consumption and additional mass, and the choice of the appropriate radiator configuration shall be evaluated based on system impact. The possibility of testing automatically different coatings and sizes for the fin, allowed by the optimization approach, increased significantly the probability of finding viable solutions on the design space.

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ABSTRACT Ethylene-propylene-diene elastomer (EPDM) is employed as thermal insulation for rocket motors, as well as EPDM blends with ethylene vinyl acetate (EVA) have been used in the aerospace industry. The quantification of these blends is more common using Fourier Transform Infrared Spectrometry (FT-IR) by transmission mode, but without discussing sample preparation and methodology error. Considering this fact, a methodology was developed for determining EVA content in binary blend with EPDM samples, by Universal Attenuated Total Reflection (UATR) technique, associated to thermogravimetric analysis (TGA). This last one, it was applied to determine Vinyl Acetate (VA) content in EVA and to identify differences between EPDM/EVA blends. Samples of the analyzed blends showed two VA contents and five proportions of EPDM/EVA: 90/10, 70/30, 50/50, 30/70, and 10/90. The carbonyl stretching vibration band C=O at 1740 cm-1 was used as analytical band in FT-IR quantification. Finally, the results presented excellent accuracy with a good linear correlation coefficient (R > 0.940) and with relative error values lower than 2%, respecting the precision limits of the FT-IR spectrometer.

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ABSTRACT This paper presents a wind tunnel study of the flow patterns in the main Brazilian Space Port, the Alcântara Launch Center (ALC), located in the Northwest region, over an irregular coastal cliff of 40 m height. In the ALC region, constant winds of strong incidence are very common, which can change the characteristics of the atmospheric boundary layer and affect safety conditions during launching operations. This study was conducted using a scaled model of the Launching Pad Area (LPA) in ALC complex with the purpose of getting insights about the wind flow patterns, as zones of strong vorticity, in that region when the wind incidence angle and coastal cliff characteristics change. The experiments were carried out in an aerodynamic wind tunnel, and for this reason it was necessary to use some techniques described in the literature to simulate an atmospheric boundary layer in a short test section wind tunnel. Hot-wire anemometer measurements were carried out for turbulence level evaluation with empty wind tunnel test section, and a two-dimensional Particle Image Velocimetry (PIV) was used for flow field velocity measurements in different configurations of wind incidence angle (α), Reynolds number and coastal cliff slope angle (β).

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ABSTRACT Based on adaptive sliding mode-control and back-stepping design method, an integrated guidance and control method with less calculation is proposed, which is designed for air-to-ground missile during the terminal course in three-dimensional space. The model of the control system with nonlinear and coupling is simplified, then the integrated guidance and control model in pitch and yaw channel is established. The coupling terms and modeling error between channels is considered as unknown bounded disturbance. An extended state observer is developed to estimate and compensate the unknown disturbance. In the design process, the block dynamic surface method is adopted, and the first order low pass filter is introduced to avoid the problem of differential explosion present in the traditional back-stepping design method during the process of differentiating virtual control variable. The Lyapunov stability theory is used to prove the stability of the system. Finally, in the case of nominal and positive and negative perturbations of model parameters, the simulation experiments are carried outto verify the effectiveness of the proposed IGC algorithm.

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ABSTRACT This paper presents a detailed analysis about the implementation of a washout filter on the SIVOR (Simulador de Voo Robótico - Robotic Flight Simulator) project. The main objective of this project is to develop, on an anthropomorphic robot, a flight simulator which can be used as an Engineering Development System (EDS) and a pilot training platform, capable of providing feelings the pilot would only have in more intensive maneuvers, such as losses/gains of G in aircraft flight tests. The SIVOR project also has the objective of providing a cost-efficient and flexible tool that can be used during the design phases of aircrafts. One of the demanded features of such simulator is a representative behavior of its motion system, which is achieved by an adequate implementation of the washout filter. To the best knowledge of the authors, there are no works in the literature that present a detailed discussion about the implementation of a classical washout filter in such flight simulator, especially when the translational channel is used to its limits. Experimental results to support the proposed solutions are presented herein.

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ABSTRACT Thermoacoustic instability in liquid rocket engines can have potentially catastrophic consequences. Active control based on feedback promises improved stability margin over a wider range of operating conditions than passive control. In the present work, the thermoacoustic characteristics of a trim adjustment active control system based on variable volume tunable Helmholtz resonator are investigated in open loop. The effect of variation of parameters for a ducted resonator in relation to a duct alone is brought out for the fundamental and first harmonic mode in a closed-open duct using a mode tracking technique. Thermoacoustic instability of the first harmonic is predicted for lean mixtures. Combustion delay has an optimum with regard to the combustion stability of the flame in a duct. Introduction of the resonator stabilizes the fundamental mode completely with respect to flame position. Increasing the volume of the resonator is destabilizing for both fundamental and harmonic modes in fuel rich mixtures. The resonator has maximum effect in controlling instability when placed near the antinode of the standing wave pattern and when its characteristic frequency matches the modal frequency. Volume variable resonators are seen to be effective for control of thermoacoustic instability in open loop.

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ABSTRACT The structure of mission management and maneuver planning for multiple UAVs in close formation flight is investigated. This article provides a distributed and priority-based platform of guidance and control model to meet requirements for each coordinated maneuver. To accomplish the coordinated maneuvers of multiple UAVs, some levels of hierarchy from mission planning to accurate guidance law are presented. The main focuses have been on the structure of equations and vicinity pattern to avoid a probable collision during maneuver so the high-level decision-maker can integrate all irregularities and solve them at the same time. Unlike complex control systems, the proposed algorithm provides outstanding following performance and inherent collision avoidance pattern due to prioritized tracking. The results show the admissible performance of the framework designed for implementing coordinated maneuvers due to its lower collision probability and noise resistance. According to the simulations, this method also resolves irregularity and disarrangements in the close formation flights and tracking media.

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ABSTRACT: The existing relations between the supply of air transport services and economic development have been a relevant area of research in transport management. This study aims to analyze the influence of the productive performance of some Brazilian exported commodities over the demand for regional passenger air transportation on the regions where those commodities are produced. In order to do so, this study used the linear regression method, checking what the relations are, if any exist, between the productive performance of those areas and the supply and demand for passenger seats in airports located in areas producing those commodities. The mathematical model used was validated with a control model that, in its turn, examined the correlation between macroeconomic and population aggregates and the global domestic demand for passenger air travel. The results show ambiguous relations between explicative and dependent variables, because in some localities the correlation was significantly higher than in others. The main contribution is to analyze how the regional aviation market is exposed to the productive performance on markets with high level of economic specialization.

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ABSTRACT: This paper investigates the influences of three different input parameters, such as feed rate, insert nose radius, and insert coating methods, in the turning operation of Inconel 718. The coating methods were selected as medium temperature chemical vapor deposition (MT-CVD) and physical vapor deposition (PVD) and in addition to coating methods, the role of various coating materials was discussed since the inserts were coated with multi-layers of TiCN/Al2O3/TiN and single-layer of TiAlN on carbide substrates. The results were discussed in terms of wear behavior of cutting tools and surface quality of the workpiece, which is indicated by surface roughness. A full factorial experimental design was employed in the present work and the results were evaluated using main effects plots. Furthermore, the analysis of variance (ANOVA) method was applied to specify both reactive and non-reactive effects of experimental parameter reactions. The results showed that surface roughness is reduced using low feed rates and large nosed inserts in the operations. Furthermore, TiAlN-coated inserts with PVD method provided better surface finish than with MT-CVD method. It was also found that surface roughness increases as the wear rate of inserts increases.

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ABSTRACT: To improve the speed and accuracy of the photoelectric tracking and pointing platform stable tracking, we took the three-axis photoelectric tracking platform, of which the coupling among the rings is ignored, as the research object. Considering the effects of various disturbances, the stable tracking double closed-loop servo control system was built for the azimuth, pitch, and roll rings. In the stabilization loop, output-feedback H∞ controller based on linear matrix inequality was designed to reduce the effects of model perturbations and uncertainties and to maintain the stability of the platform’s inertial space. In the tracking loop, the integral-separation proportional integral derivative (PID) controller was designed to achieve fast and accurate tracking. Smith estimated compensation was adopted to compensate the pure lag caused by video tracking. Finally, the double closed-loop servo control system was built to complete the simulation. The simulation results show that the system not only has good robustness under external disturbances, but also completes the attitude tracking quickly and accurately. Besides, the tracking error is |error| < 5∙e-4 rad, which meets the tracking accuracy requirements.

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ABSTRACT: The aerodynamic characteristics of a NACA0012 wing geometry at low Reynold’s numbers and angle of attack ranging from 0º to 90º are investigated using numerical simulations and the results are validated by wind tunnel experiments. Further experiments are conducted at low Reynold’s numbers of 1 × 105, 2 × 105 and 3 × 105. Findings of the study show a similar trend for the lift and drag coefficients at all the investigated Reynold’s numbers. The lift coefficient is linearly increased with angle of attack until it reaches its maximum value at 32º which is the stall angle. It is observed that further increment in angle of attack results in decrement of lift coefficient until it reaches its minimum value at 90º angle of attack. The drag force acting on the airfoil increases as the angle of attack is increased and increment in the drag force results in change of laminar flow to turbulent flow. As the turbulence gets higher the flow starts to separate from the airfoil surface due to eddies generated by turbulence. Hence, the lift force generated by the wing is reduced and drag force is increased simultaneously, which results in poor performance of the wing.

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ABSTRACT: The moment of inertia parameters play a critical role in assuring the spacecraft mission throughout its lifetime. However, determination of the moment of inertia is a key challenge in operating satellites. During satellite mission, those parameters can change in orbit for many reasons such as sloshing, fuel consumption, etc. Therefore, the inertia matrix should be estimated in orbit to enhance the attitude estimation and control accuracy. This paper investigates the use of gyroscope to estimate the attitude rate and inertia matrix for low earth orbit satellite via extended Kalman filter. Simulation results show the effectiveness and advantages of the proposed algorithm in estimating these parameters without knowing the nominal inertia. The robustness of the proposed algorithm has been validated using the Monte-Carlo method. The obtained results demonstrate that the accuracy of the estimated inertia and angular velocity parameters is satisfactory for satellite with coarse accuracy mission requirements. The proposed method can be used for different types of satellites.

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ABSTRACT: This paper presents the overall pros and cons of the effect of surface roughness elements over a NACA 4412 tapered, swept back half wing with a sweep angle of 30º and a dihedral angle of 5º. The tests were conducted at a Reynolds number of 4 × 105 in the IIUM Low Speed wind tunnel. Different roughness sizes and roughness locations were tested for a range of angle of attack. Lift, drag and pitching moment coefficients were measured for the smooth wing and with roughness elements. Surface roughness delays the stall angle and decreases the lift. The wing with the roughness elements located at 75% to 95% of mean chord from leading edge shows minimum drag and maximum lift compared to other locations. Significant increase in the pitching moment coefficient was found for flexible roughness elements. In case of rigid surface roughness, the effect on pitching moment is small.

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ABSTRACT: This paper provides a real example of applying COCOMO II as an estimation technique for the required software development effort in a safety-critical software application project following the DO-178C processes. The main goal and contribution of the case study is to support the research on software effort estimation and to provide software practitioners with useful data based on a real project. We applied the method as it is, by correlating the effort multiplier factors with the complexity and objectives introduced by the DO-178C level A application, resulting in an estimated effort. The rationales for each scale factor and effort multiplier selection were also described in detail. By comparing the estimated values with the actual required data, we found a magnitude of relative error (MRE) of 40% and provided alternatives for future work in order to increase the effort estimation accuracy in safety-critical software projects.

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ABSTRACT When some materials need to be characterized, the hydroxyl number (IOH) determination is especially useful, mainly for those applied in the aerospace field. Usually, this characterization is performed by wet chemistry, using methodologies involving several steps, such as derivatization. This is a time-consuming and costly step. On the other hand, when the analysis is performed by Fourier transform infrared (FT-IR) spectroscopy, the most used region is the medium infrared (MIR) and transmission techniques are usually employed. However, FT-IR methodology developed error is usually not discussed. FT-IR methodology was developed in near infrared (NIR) and MIR regions, including non-conventional techniques, such as universal attenuated total reflection (UATR) and transflectance (near infrared reflection accessory [NIRA]), and transmission, to determine IOH in surfactants, used in aerospace catalysts/cosmetic products, and polyesters, applied in paints. According to the samples’ characteristics, surfactants were analyzed by transmission/solution and, as received, by NIRA. Polyesters were analyzed by UATR and NIRA, as received. The IOH values for all samples were also measured by wet chemistry and/or potentiometry (supplier’s data) and used as reference. Good linear correlations were observed between 0.939 and 0.976, being considered with good precision, and between 88% (NIRA) and 98% (MIR) of the results were explained by developed methodologies.

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ABSTRACT In this study, an improved cooperative integrated guidance and control (IGC) design method is proposed based on distributed networks to address the guidance and control problem of multiple interceptor missiles. An IGC model for a leading interceptor is constructed based on the relative kinematic relations between missiles and a target and the kinematic equations of the missiles in a pitch channel. The unknown disturbances of the model are estimated using a finite-time disturbance observer (FTDO). Then, the control algorithm for the leading interceptor is designed according to the disturbance estimation and nonsingular fast dynamic surface sliding mode control (SMC). To enhance the rate of convergence of the cooperative control commands for the interceptors, an improved cooperative control strategy is proposed based on the leader-follower distributed network. Consequently, the two velocity components of the interceptor in the pitch channel can be obtained, which are subsequently converted to the total velocity and flight path angle commands of the interceptor using kinematic relations. The control algorithm for the following interceptor is similarly designed using an FTDO and dynamic surface SMC. The effectiveness of the improved distributed cooperative control strategy for multiple interceptors is validated through simulations.

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ABSTRACT: The radar detection with decision making in the moments space (DRACEC method) is based on a statistical analysis to determine the boundary between the background (absent target) and the anomaly (present target) classes. In this article, the boundary is taken as an ellipse and is calculated for two dimensions, emphasizing its geometric interpretation. The procedures to establish the shape, location, and size of the ellipse are highlighted, guaranteeing the probability of false alarm by applying the Neyman-Pearson criterion. The proposal establishes a methodology for calculation of the boundary when it is required to use the moments directly as a sufficient decision statistic.

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ABSTRACT: Small satellites are growing in use for educational, scientific, and commercial purposes, usually in Low Earth Orbit (LEO) flights, given their lower costs and associated risks, as well as smaller lead times for assembling and testing. However, the typically short periods of LEO passes bring the need to find ways of optimizing the communication between the ground and space segments. In that direction, several projects have relied on ground station networks to increase the total time of contact with the satellites. In this type of arrangement, the stations agree in monitoring one or more satellites in such a way that, as the spacecraft exits one station’s field of view, another station assumes its tracking, extending the total communication time and compensating the short passes. This type of solution, while very efficient in terms of costs, on the other hand demands a good synchronization procedure, so that all constraints present in its operations are taken into account and the network can operate effectively. This paper aims at describing a model implemented for orchestrating ground station networks that optimizes the communication capacity of the ground network, while taking into account physical constraints not usually considered in other models currently proposed.

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ABSTRACT Brazil has a Microgravity Program mainly based on experiments using sounding rockets. Up to now, four missions have been carried out with approximately 35 experiments submitted in total. In all flights, the Associate Laboratory of Sensors and Materials of the Brazilian Space Research Institute (LABAS/INPE) participated with a fast solidification furnace, capable of producing temperatures up to 900 °C, which was tested with semiconductor and metal alloys. This paper describes the construction and the performance of that furnace during the last parabolic flight, Rio Verde Mission, occurred in 2016. The solidification furnace is now qualified and ready to be used by other institutions in sounding rocket flights.

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ABSTRACT: Trailing edge surface of aerofoil is an important source of broadband aerodynamic noise production. In this paper, three aerofoil self-noise mechanisms from turbulent boundary layer near trailing edge surface are studied. Numerical computations were performed for a three bladed 2 MW horizontal axis upwind turbine of blade length 37 m and source height of 80 m, for wind speeds of 8-15 m/s. A weighted 1/3rd octave band sound power levels (SPL) are evaluated for receiver located at distance of total turbine height and at 2 m above ground. The results obtained for sound power level using baseline models showed maximum values occurring between 300 Hz and 1 kHz region of spectrum. The trends for BPM model showed a reduction of ~2 dBA near 1 kHz region of spectrum at 10 m/s, but Grosveld’s and Lowson model were identical and agreed over the entire spectrum. The effect of rotational speed on sound power levels using three baseline models are illustrated at a wind speed of 8 m/s for 2 MW turbine. Results showed that for a change of ±10% rotor speed from the rated value, there is an increase of 2 to 6 dBA over the entire sound spectrum due to differences in blade tip speed.

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ABSTRACT The aim of this work is to propose an accurate and reliable numerical simulation method of gust response, so as to analyze longitudinal stability characteristics of high-aspect-ratio unmanned aerial vehicles (UAVs) under gust response. Based on the dual-time stepping method, the unsteady Navies-Stokes equation was solved. By introducing grid velocity to study the effects of gust, the numerical simulation of gust response was realized. Moreover, the numerical simulation method was verified to be accurate by using the theoretical value and reference value obtained in previous research. The calculation results of the high-aspect-ratio UAV under the 1-cos gust reveal that longitudinal aerodynamic forces of high-aspect-ratio UAVs changed. In the whole range of gust gradient length, the UAVs were always in the state of static stability. However, with the increase of gust velocity, static stability margin decreased. The numerical simulation method of gusts established in this study preferably overcomes the possible numerical oscillations and divergence problems caused by excessive gust velocity. The analysis on longitudinal static stability and stability margin of high-aspect-ratio UAVs under the effects of gusts can ensure flight quality and safety of UAVs under the effects of gusts.

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ABSTRACT: Zirconium diboride is an ultra high temperature ceramic material that leads this emerging class of materials because of its distinct combination of properties, including high melting temperature (> 3000 °C) and the lowest theoretical density (6.09 g·cm-3) among the borides. This combination of properties makes ZrB2 candidate for airframe leading edges on sharp-bodied reentry vehicles. In this work, the effect of particle size of ZrB2 on the pressureless sintering of ZrB2-SiC composites was studied, using ZrB2 powder with average particle size of 2.6 and 14.2µm. Four different vol% concentration of ß-SiC (0, 10, 20 and 30 vol%) were added to as-received and planetary milled ZrB2 powder. Samples were pressureless sintered at 2050 °C/1h in argon atmosphere. The reduction of initial ZrB2 particle size led to composites with better results of densification, mechanical properties and oxidation resistance regardless ß-SiC addition, showing relative densities around 92.5 %Theoretical Density (Td) and flexural strength and microhardness around 260 MPa and 17.5 GPa, respectively. Composites processed with as-received ZrB2 powder showed increasing in densification and flexural strength with the SiC content increasing. Relative density varied from 74.7 to 90.8 %TD and flexural strength from 102 to 241 MPa, for 0 and 30 vol% of SiC, respectively.

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ABSTRACT In the present paper, thermomechanical attributes of a power-law graded uniform mounted disc with or without rigid casing are investigated analytically under centrifugal and steady-state thermal loads within the framework of axisymmetric infinitesimal plane-stress elasticity theory. Young's modulus, material density, thermal expansion coefficient and thermal conductivity are all assumed to be constantly changed in the radial direction with different inhomogeneity indexes while Poisson's ratio is kept constant. Two parametric studies are conducted by both hypothetically and physically chosen metal-ceramic pairs namely nickel-silicon nitride (Ni-Si3N4), aluminum-aluminum oxide (Al-Al2O3), and stainless steel-zirconium oxide (SUS304-ZrO2).

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ABSTRACT In order to make reasonable suggestions for the expansion of the Air Traffic Management Technical Support System (ATMTSS), it is necessary to conduct a comprehensive analysis of the ATMTSS network. This paper constructs a multi-source weighted ATMTSS network which considers the working characteristics and geographical locations of the facilities. The complex network metrics, such as degree, node strength, clustering coefficient, average path length, diameter, and the improved Fast-Newman (FN) algorithm, are used in the analysis of the network. The results show that the ATMTSS network is a complex network with small-world characteristics and random characteristics, and that the distribution of ATMTSS network support capability is not the same as the topology network structure. The weighted network is looser than the non-weighted network. The air traffic management in remote areas is less affected by facilities than that in developed areas.

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ABSTRACT Thermal insulation inside the rocket motor experience severe pressure and temperature conditions. Experimental determination of heat flux imparted to thermal insulator inside the rocket motor during the static firing is a challenging task. This paper reports experimental determination of heat flux for double base propellant (DBP) in small rocket motor. It includes development of experimental rocket motor, adaptation of water-cooled heat flux sensor on rocket motor, required instrumentation for heat flux time recording and analysis of data. Data are recorded in real time for double base propellant combustion up to the pressure level ~3.6 MPa. Average heat flux imparted to the rocket motor casing is found in the range of 230-300 × 104 W/m2. Heat flux inside the rocket motor varies nearly linear with pressure. A correlation between the heat flux and pressure is also established for measured pressure range.

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ABSTRACT: Precipitation events are infrequent in the dry quarter (SON) of the Alcântara Launch Center (Centro de Lançamento de Alcântara, CLA), the main launch site of the Brazilian Space Program. However, their occurrence could be a risk for activities during launch missions. In this work, the observational features of wet days (daily precipitation total ≥ 1 mm/day) in the dry quarter of the CLA region were studied. Daily precipitation totals over the course of 37 years (1979-2016, except 2006), outgoing longwave radiation (OLR) data and ERA-Interim reanalysis data were used. On average, in the dry quarter, there were 9 wet days, which accumulated 32 mm. The number and quarterly precipitation total of wet days showed pronounced interannual variability. This variability was negatively and significantly correlated with the interhemispheric sea surface temperature anomalies gradient in the Atlantic Ocean and the wind speed at 925 hPa over the CLA region. Based on a theoretical distribution (log-normal), the probability of occurrence of heavy precipitation days (daily total ≥ 10 mm/day) was only 0.5%. For days with heavy precipitation and deep convection (OLR ≤ 230 W·m-2), over a large area along the northeastern coast of South America including the CLA region, negative OLR differences (from the mean) and the strengthening of favorable conditions for deep convection were found. The large-scale organization of the convective activity and atmospheric features for higher precipitation events obtained in this work could be helpful for nowcasting and short-range weather forecasting during launch missions at the CLA.

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ABSTRACT: Two stiffness models for a flexible hinge with large rotation angle are established based on the pseudo-rigid body method and the series or parallel relationship of flexible units. Finite element simulation of the flexible hinge is conducted in ANSYS to verify the two stiffness models of the flexible hinge. A multi-objective optimization method is used to optimize the design parameters of the hinge. The stiffness models of the flexible hinge are used to establish the optimized objective function of an optimization model to improve the rotation angle of the hinge under a certain radial stiffness. After optimization, the rotation angle can reach 70 deg when the rotational and radial stiffnesses are 1.29 N·mm/rad and 1.37 N/mm.

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ABSTRACT: Pintle technology is currently a versatile technology used in a solid rocket motor (SRM) to control the desired thrust by changing the nozzle throat area, while effectively controlling the chamber pressure at the same time. The sudden movement of the pintle can induce rapid changes in the flow field and the occurrence of pressure oscillations inside the combustion chamber. The analysis of such rapid changes is essential to design an efficient controllable pintle rocket motor for a better thrust regulation. Two-dimensional axisymmetric models with mesh generation and required boundary condition were designed to analyze the effects of three different pintle head shape models in SRM thrust regulation effect. Dynamic mesh method was used with specific velocity for moving plug/pintle in the numerical analysis of SRM thrust regulation. The effects of different pintle head models on the flow field, combustion chamber pressure, mass-flow rate, thrust and Mach number were investigated. According to the analysis of total pressure response time, the simulation data revealed that circular pintle head model responded faster among three different models. According to the thrust effect, parabolic pintle has the maximum value of thrust and the greatest total pressure recovery coefficient among all pintle head models.

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ABSTRACT: In modern conditions unmanned aerial vehicles (UAVs) generate new classes of threats, including their use for terrorist purposes. A feature of modern UAVs is the ability to perform sudden maneuvers and to keep the same position in the point in space. For the description of the UAV movement with various types of maneuver it is used a rectangular coordinate system. We use the model in the form of stochastic dynamic system with random structure in the discrete time in which the change type UAV movement occurs at random times. When a UAV emits a sign, its location can be determined by wireless sensor networks (WSN) using the TDOA method. On the basis of a mathematical apparatus of the mixed Markov processes for in discrete time optimal and quasi-optimal adaptive algorithms for filtration of UAV movement parameters based on the TDOA-measurement, sensor networks are synthesized. Devices that realize these algorithms are multichannel and belong to the class of devices with feedback between channels. At the same time, in a quasi-optimal algorithm, a sequential procedure of the arriving measurements from sensors of a sensor network is realized, which allows to avoid the inversion of large-dimensional matrices. An analysis of the quasi-optimal adaptive algorithm is performed using statistical modeling. On the intervals of hovering and of the UAV movements without maneuver, the developed algorithm allows to increase significantly the accuracy of the estimation of the UAV coordinates, and also to recognize various types of its movement with high probability level.

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ABSTRACT: To meet the high precision sun tracking needs of a space deployable membrane solar concentrator and other equipment, an existing algorithm for accurately computing the sun position is improved. Firstly, compared with other theories, the VSOP (variation seculaires des orbits planetaires) 87 theory is selected and adopted to obtain the sun position in the second equatorial coordinate system. Comparing the results with data of the astronomical almanac from 2015, it is found that the deviation of the apparent right ascension does not exceed 0.17 arc seconds, while that of the apparent declination does not exceed 1.2 arc seconds. Then, to eliminate the difference in the direction of the sun position with respect to the satellite caused by the size of the satellite’s orbit, a translation transform is introduced in the proposed algorithm. Finally, the proposed algorithm is applied to the orbit of the satellite designated by SJ-4 (shijian-4). Under the condition that both of the existing and improved algorithms adopt the VSOP87 theory to compute sun position in the second equatorial coordinate system, the maximum deviation of the azimuth angle on the SJ-4 is 35.19 arc seconds and the one of pitch angle is 19.93 arc seconds, when the deviation is computed by subtracting the results given by both algorithms. In summary, the proposed algorithm is more accurate than the existing one.

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ABSTRACT: Spacecrafts in space environment are exposed to several kinds of thermal sources such as radiation, albedo and emitted IR from the earth. The thermal control subsystem in spacecraft is used to keep all parts operating within allowable temperature ranges. A failure in one or many temperature sensors could lead to abnormal operation. Consequently, a prediction process must be performed to replace the missing data with estimated values to prevent abnormal behavior. The goal of the proposed model is to predict the failed or missing sensor readings based on artificial neural networks (ANN). It has been applied to EgyptSat-1 satellite. A backpropagation algorithm called Levenberg-Marquardt is used to train the neural networks (NN). The proposed model has been tested by one and two hidden layers. Practical metrics such as mean square error, mean absolute error and the maximum error are used to measure the performance of the proposed network. The results showed that the proposed model predicted the values of one failed sensor with adequate accuracy. It has been employed for predicting the values of two failed sensors with an acceptable mean square and mean absolute errors; whereas the maximum error for the two failed sensors exceeded the acceptable limits.

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ABSTRACT: Accurate determination of heat flux is an important task not only in the designing aspect, but also in the performance analysis of rocket engines. In this purpose, this work deals with the heat flux determination in a combustion chamber through the inverse method. In this approach, the transient heat flux is determined from the experimental temperature data measured at the outer sidewall of the rocket engine. In this work the physical phenomenon was modeled by the transient one-dimensional heat equation in cylindrical coordinates and the material properties of the chamber were considered constant. Furthermore, the model is solved using the inverse heat conduction problem with least squares modified by the addition of Tikhonov regularization term of zero-order. Moreover, the sensitivity coefficients were obtained by Duhamel’s theorem. Through the regularization parameter, it was able to generate acceptable results even when using data with considerable experimental errors.

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ABSTRACT: Poor lateral-directional stability due to the absence of vertical stabilizer is a great risk to the aircraft with flying wing layout. In this paper, an unmanned aerial vehicle with this kind of configuration is chosen as the research object. A three-dimensional model of the unmanned aerial vehicle is established, and then the sensitivity analysis is performed to obtain the effects of main aerodynamic shape parameters on lateral-directional flying quality. The results show that the roll mode and spiral mode of the aircraft meet the requirements of Level 1 flying quality in MIL-F-8785C. But the Dutch roll mode is generally divergent, which means that the flying quality of the aircraft is unacceptable. Thus it can be seen that the Dutch roll mode is the key to the dynamic stability of the aircraft. Further studies show that increasing the value of wing aspect ratio or decreasing the values of dihedral angle and torsion angle are useful for improving the Dutch roll mode. It is valuable to reveal the influence mechanism of aerodynamic shape parameters on lateral-directional flying quality for the design of flying wing aircraft.

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ABSTRACT: Rotary friction welding process (RFW) is one of the most used processes in the world for manufacturing bimetallic components that require high mechanical strength. All process occurs in solid state at temperatures below the melting point of the involved materials, having as the main bonding mechanisms the diffusion and mechanical mixture. The purpose of this work was to carry out an experimental thermal analysis of the dissimilar joint AA6351 T6 aluminum and AISI 304L stainless steel during the friction welding operation through system of thermocouples. Gradients of temperature obtained had their data analyzed and recorded. Results of the experimental thermal analysis showed the behavior of the temperature in the bonding interface, how the dissipation occurs in the radial and longitudinal direction, heating rates, cooling, maximum temperatures reached, its relationship with the different stages of the process and the influence on mechanical properties of welded joint. This study is of great importance for relating the temperature distribution in the bonding interface with atomic diffusion and mechanical resistance of junction.

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ABSTRACT Research on broadband aerodynamic noise from wind turbine blades is becoming important in several countries. In this work, computer simulation of acoustic emissions from wind turbine blades are predicted using quasi empirical model for a three-bladed horizontal axis 3 MW turbine with blade length ~47 m. Sound power levels are investigated for source and receiver height of 80 m and 2 m above ground and located at a distance equal to total turbine height. The results are validated using existing experimental data for Siemens SWT-2.3 MW turbine having blade length of 47 m, as well as with 2.5 MW turbine. Aerofoil self-noise mechanisms are discussed in present work and results are demonstrated for wind speed of 8 m/s. Overall sound power levels for 3 MW turbine showed good agreements with the existing experiment data obtained for SWT-2.3 MW turbine. Noise map of single source sound power level, dBA of an isolated blade segment located at 75 %R for single blade is illustrated for wind speed of 8 m/s. The results demonstrated that most of the noise production occurred from outboard section of blade and for blade azimuth positions between 80° and 170°.

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ABSTRACT Stainless steel and copper alloys joints are often applied in aerospace, marine and power industries where both high thermal and electrical conductivity (Cu) and corrosion resistance (steel) are required. In the aerospace industry, in particular for the combustion chamber of rocket engines, copper and steel combinations offer perfect materials selection due to their combined high thermal conductivity and good stiffness. In this work, laser welds were produced with intensity between 3.8 × 104 and 5.7 × 104 W/mm2 and a heat input between 72 and 108 J/mm, giving an aspect ratio of 1.8. The microstructure of the weld beads was marked by chemical heterogeneities due to the phase separation between Cu and Fe in the liquid state. The phase separation gave rise to globular precipitates which further transform due to a secondary precipitation at temperatures below 1000 °C. The steel side part of the weld presents around 20% Cu, leading to a liquation of the grain boundaries and cracking at high heat inputs. The hardness values situated between both base materials and the tensile shear behavior, when the weld is sufficiently tough, present strength up to 350 MPa and elongation up to 10%.

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ABSTRACT Nowadays, it has become possible for universities and new businesses to launch satellites of reduced size and cost fulfilling viable missions. Nevertheless, there is still a considerable failure rate that reduces the expected lifetime of these spacecraft. One of the main causes of failure is the power system. Redundancy is one of the main options to enhance its lifetime and lower the failure rate. However, cost, mass, and complexity increase due to redundancy, making it more difficult to complete the projects. Thus, it is necessary to enhance the lifetime of power systems while keeping the development process simple and fast. This paper proposes two configurations of an electrical power system with duplicate components: single-bus configuration has been designed for a nanosatellite not yet launched and dual-bus configuration for a micro deep-space probe launched into a heliocentric orbit. The design and implementation of two dual electrical power systems are described; measurements and on-orbit data of the electrical power system of the micro deep-space probe are also presented, demonstrating that the dual-bus electrical power system can be successfully used in spacecraft. Lastly, conclusions regarding the redundancy considerations for small satellite electrical power systems are drawn based on these two examples.

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ABSTRACT: Boundary layers over concave surfaces may become unstable due to centrifugal instability that manifests itself as stationary streamwise counter rotating vortices. The centrifugal instability mechanism in boundary layers has been extensively studied and there is a large number of publications addressing different aspects of this problem. The results on the effect of pressure gradient show that favorable pressure gradients are stabilizing and adverse pressure gradient enhances the instability. The objective of the present investigation is to complement those works, looking particularly at the effect of pressure gradient on the stability diagram and on the determination of the spanwise wave number corresponding to the fastest growth. This study is based on the classic linear stability theory, where the parallel boundary layer approximation is assumed. Therefore, results are valid for Görtler numbers above 7, the lower limit where local mode linear stability analysis was identified in the literature as valid. For the base flow given by the Falkner-Skan solution, the linear stability equations are solved by a shooting method where the eigenvalues are the Görtler number, the spanwise wavenumber and the growth rate. The results show stabilization due to favorable pressure gradient as the constant amplification rate curves are displaced to higher Görtler numbers, with the opposite effect for adverse pressure gradient. Results previously unavailable in the literature identifying the fastest growing mode spanwise wavelength for a range of Falkner-Skan acceleration parameters are presented.

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ABSTRACT: Nanosatellite missions are becoming increasingly popular nowadays, especially because of their reduced cost. Therefore, many organizations are entering the space sector due to the paradigm shift caused by nanosatellites. Despite the reduced size of these spacecrafts, their Flight Software (FSW) complexity is not proportional to the satellite volume, thus creating a great barrier for the entrance of new players on the nanosatellite market. On the other side, there are some available frameworks that can provide mature FSW design approaches, implying in considerable reduction in software project timeframe and cost. This paper presents a comparative survey between six relevant flight software frameworks, compared according to commonly required ‘New Space’ criteria, and finally points out the most suitable one to the VCUB1 reference nanosatellite mission.

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ABSTRACT: Natural (Terrestrial & Space) Environment (NE) phenomena play a significant role in the design and flight of aerospace vehicles and in the integrity of the associated aerospace systems and structures. Natural environmental design criteria guidelines described here are based on measurements and modeling of atmospheric and climatic phenomena relative to various aerospace vehicle development and mission/operational procedures, and for vehicle launch locations. Both the terrestrial environment (0-90 km altitude) and the space environment (Earth orbital altitudes) parameters and their engineering application philosophy are given with emphasis on launch vehicle-affected terrestrial environment elements. This paper also addresses the basis for the NE guidelines presented, the interpretation of the guidelines, and application to the development of launch or space vehicle design requirements. This paper represents the first of three on this subject.

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ABSTRACT: In this research, viscous, unsteady and turbulent fluid flow is simulated numerically around a pitching NACA0012 airfoil in the dynamic stall area. The Navier-Stokes equations are discretized based on the finite volume method and are solved by the PIMPLE algorithm in the open source software, namely OpenFOAM. The SST k - ω model is used as the turbulence model for Low Reynolds Number flows in the order of 105. A homogenous dynamic mesh is used to reduce cell skewness of mesh to prevent non-physical oscillations in aerodynamic forces unlike previous studies. In this paper, the effects of Reynolds number, reduced frequency, oscillation amplitude and airfoil thickness on aerodynamic force coefficients and dynamic stall delay are investigated. These parameters have a significant impact on the maximum lift, drag, the ratio of aerodynamic forces and the location of dynamic stall. The most important parameters that affect the maximum lift to drag coefficient ratio and cause dynamic stall delaying are airfoil thickness and reduced frequency, respectively.

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ABSTRACT: This communication presents a comparative analysis of tuning techniques for satellite launch vehicle attitude controllers. The investigated tuning techniques consist in the minimization of specific performance indexes, namely the Integral Absolute Error (IAE) index, the Integral of Time Multiplied Absolute Error (ITAE) index, the Integral Squared Error (ISE) index, and the Integral of Time Multiplied Squared Error (ITSE) index, being hence, termed optimal. By defining adequate figures of merit, relevant for evaluating the overall performance of satellite launch vehicles, and also taking into account requirements related to the physical limitations of the latter, the performance of attitude controllers tuned by the investigated techniques is compared to the one tuned by the methodology currently employed in the Brazilian Satellite Launch Vehicle (VLS), namely, the Linear Quadratic (LQ) methodology. Through simulation results, it is demonstrated that, despite sparse benefits produced by the alternative tuning techniques, in particular ITAE and ISE, the LQ methodology remains globally superior.