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In the realm of prognosticating the remaining useful life (RUL) of pivotal components, such as aircraft engines, a prevalent challenge persists where the available historical life data often proves insufficient. This insufficiency engenders obstacles such as impediments in performance degradation feature extraction, inadequacies in capturing temporal relationships comprehensively, and diminished predictive accuracy. To address this issue, a 1D CNN-GRU prediction model for few-shot conditions is proposed in this paper. In pursuit of more comprehensive data feature extraction and enhanced RUL prognostication precision, the Convolutional Neural Network (CNN) is selected for its capacity to discern high-dimensional features amid the intricate dynamics of the data. Concurrently, the Gated Recurrent Unit (GRU) network is leveraged for its robust capability in extracting temporal features inherent within the data. We combine the two to construct a CNN-GRU hybrid network. Moreover, the integration of data distribution alongside correlation and monotonicity indices is employed to winnow the input of multi-sensor monitoring parameters into the CNN-GRU network. Finally, the engine RULs are predicted by the trained model. In this paper, experiments are conducted on a sub-dataset of the National Aeronautics and Space Administration (NASA) C-MAPSS multi-constraint dataset to validate the effectiveness of the method. Experimental results have demonstrated that this method has high accuracy in RUL prediction tasks, which can powerfully demonstrate its effectiveness. [ABSTRACT FROM AUTHOR]

Global navigation satellite system (GNSS) integrity monitoring (IM) has been introduced in aviation, but remains challenging for urban scenarios because of limited satellite visibility and strong multipath and non-line-of-sight effects. Consequently, factors such as limited measurement redundancy and inaccurate uncertainty modeling significantly compromise positioning and IM performance. To alleviate these issues, this paper proposes an integrity-constrained factor graph optimization model for GNSS positioning augmented by switch variables. In contrast to conventional IM methods, this method enhances redundancy through the factor graph structure. Instead of directly excluding measurements, the proposed method reweights the measurements by using switch variables to satisfy a chi-square test constraint within the optimization, ultimately yielding optimal positioning accuracy. Moreover, a proper protection level that conservatively bounds the positioning error can be derived by using the modified weighting matrix under a single-fault assumption. The effectiveness of the proposed method was verified based on data sets collected in open-sky and urban-canyon areas in Hong Kong. [ABSTRACT FROM AUTHOR]

Global navigation satellite systems have enabled significant improvements in aeronautical navigation. However, in recent years, a growing number of interference events have been reported by flight crews. In this paper, we first identify such events using crowd-sourced surveillance data collected between February and December 2022 for three different regions: the Baltic states, eastern Europe bordering the Black Sea, and the eastern Mediterranean. Then, we assess the extent and duration of these events to determine their impact on civil aviation. The analysis shows different characteristics, ranging from isolated events to regular large-scale and recurrent disruptions. Next, we identify aircraft types for the affected flights and evaluate flight plan data with respect to navigation equipment in order to identify flights that rely solely on satellite navigation and that might require assistance in the case of a loss of satellite navigation. Finally, we show the impact of radio frequency interference (RFI) on a selected passenger flight by analyzing automatic dependent surveillance-broadcast data as well as avionics data obtained from the airline's flight data monitoring department for that specific flight and link the observations to the warnings triggered by the aircraft to alert the flight crew while encountering RFI. [ABSTRACT FROM AUTHOR]

SMA actuators are a group of lightweight actuators that offer advantages over conventional technology and allow for simple and compact solutions to the increasing demand for electrical actuation. In particular, an increasing number of SMA torsional actuator applications have been published recently due to their ability to supply rotational motion under load, resulting in advantages such as module simplification and the reduction of overall product weight. This paper presents the conceptual design, operating principle, experimental characterization and working performance of torsional actuators applicable in active rudder in aeronautics. The proposed application comprises a pair of SMA torsion springs, which bi-directionally actuate the actuator by Joule heating and natural cooling. The experimental results confirm the functionality of the torsion springs actuated device and show the rotation angle of the developed active rudder was about 30° at a heating current of 5 A. After the design and experiment, one of their chief drawbacks is their relatively slow operating speed in rudder positioning, but this can be improved by control strategy and small modifications to the actuator mechanism described in this work. [ABSTRACT FROM AUTHOR]

Hydrofoil trailing edge shape directly influences its downstream flow state. Due to the non-streamlined shape, alternating vortices will form downstream, resulting in complex pressure pulsations. Different shapes of the trailing edge lead to varying pressure pulsations downstream. In this paper, four different trailing edge shapes were selected for numerical simulation based on the National Advisory Committee for Aeronautics 0009 hydrofoil. The main difference lies in trimming one side of the trailing edge to different degrees, making it asymmetrical. Large Eddy Simulation was used and the results were accurate. The optimized multivariate variational mode decomposition was used to extract and reconstruct effective components of pressure pulsation in the flow, and satisfactory reconstruction results were obtained. This combined method effectively identifies key components influencing flow field and enables reasonable reconstruction. Results show that shedding vortices on both sides of an asymmetric hydrofoil's tailing edge exhibit noticeable differences in morphology. Pressure pulsation distribution in the trailing-edge flow field was primarily influenced by components near vortex-shedding frequency. With the deepening of the asymmetric trimming degree, the pressure pulsation influenced by this component on that side is gradually weakened, but the energy peak of pressure pulsation in the flow field is less reduced. [ABSTRACT FROM AUTHOR]

This note discusses environmental aspects of the planning and consultation process undertaken for the UK aviation White Paper. The process as a whole has involved some three years of forecasting and assessment of the operational, economic and environmental implications of some 28 options for airport expansion at 14 UK locations. Unconstrained passenger demand forecasts have been used as a basis for the planning and consultation, and a mitigation approach to environment has predominated. This is inadequate, given the climate impacts of the forecast aviation expansion. Greenhouse gas emissions reduction should be a high priority in transport infrastructure planning, not the subject of post-hoc analysis. [ABSTRACT FROM AUTHOR]

This study evaluates differences between two-year and four-year schools offering a Federal Aviation Administration (FAA) Part 147 aviation maintenance technician program. The actual average test scores were analyzed to determine whether students from four-year university programs were better prepared for the test than students from two-year college or technical school programs. Test scores can be viewed as a direct indication of the quality of the aviation maintenance programs at these schools. The study found that there was no statistically significant difference in the test scores between two-year college and four-year university students taking the FAA examinations. These results support previous studies that found the learning outcomes of two-year and four-year students on general subjects to be comparable. [ABSTRACT FROM AUTHOR]

The present paper examines the use of modified dual-wavelength sawtooth serrations introduced at the trailing edge (TE) of a National Advisory Committee for Aeronautics (NACA) 65 (12)-10 airfoil as a passive means for the control of airfoil broadband noise. The studies are conducted for different parameters such as serration wavelengths (λ), serration amplitudes (h) as well as (hꞌ) modified amplitude to determine the best serration parameter which provides higher noise reductions. The reduction of noise level brought by the modified dual-wavelength sawtooth serrations at the TE is about 4 dB, while it is about 3.3 dB for the simple ones. It reveals that the modified sawtooth can provide a substantial reduction of self-noise alongside the interaction noise over an extensive range of frequencies which indicates the existence of strong far-field destructive interference (i.e., feedback) from low to mid-frequency ranges (i.e., 1.5 - 5 kHz). The TE serrated airfoils show lower acoustic emissions as compared to baseline although they exhibit a common behavior for all emission angles. The large noise decrease provided by the dual-wavelength sawtooth may be because of the significant reductions in the scattering intensity of sound as well as strong far-field destructive interference owing to the presence of two roots between the two successive maximum amplitude peaks. [ABSTRACT FROM AUTHOR]

Flight Operations Quality Assurance (FOQA)-derived data was used to develop parsimonious model(s) for fuel consumption on a Boeing 757 airplane using regression analysis. Using the model(s), it should be possible to identify outliers (specific flights) with respect to fuel consumption, which will enable the air carrier to investigate the cause of excessive fuel consumption and remedy the problem A major air carrier provided the database used for the study. Fuel flow was predicted by calibrated airspeed, gross weight, and n2 (ENG[1 or 2]n2). The models containing these three variables explained approximately 85% of the variation in fuel flow. A reporting routine using these models and FOQA data should be incorporated into the ongoing quality assurance program of the air carrier. [ABSTRACT FROM AUTHOR]

In this paper, we study the influence of an original airship design on its stability modes. Based on the verified model of the YEZ-2A airship, the Sobol sensitivities are calculated to filter the design parameters. The airship hull length, the slenderness ratio of the airship hull, the exponent of the tail, the fin installation position on the hull, and the fin half-span are found to be of large influences on all stability modes, whereas the stability modes are comparatively insensitive to the exponent of the bow and the fin relative thickness. The empirical formulas for mapping relationships are fitted to the experimental data and are verified by both sensitivities and root locus diagrams. The empirical formulas representing the mapping relationships between the original design parameters and the stability mode parameters of the airship can be used as references to simplify and estimate the stability and performance in the preliminary design of the airship. [ABSTRACT FROM AUTHOR]

This paper combines shape optimization and homogenization techniques in searching for the optimal design of microstructures in elastic scaffolds. The development of materials with specific properties is of practical interest, for example, for medical applications or for the development of lightweight structures in aeronautics. In particular, the optimal design of microstructures leads to fundamental questions for elastic porous media: how to calculate a microstructure leading to a target effective Hooke tensor. We propose a robust approach to find a design that is as insensitive as possible to domain variations. Our strategy is based on the shape derivative for the problem of achieving a prescribed effective tensor. We demonstrate the applicability and feasibility of our approach through numerical experiments. [ABSTRACT FROM AUTHOR]

In this paper, we investigate the three-dimensional nature of dynamic stall. Conducting the investigation, the flow around a harmonically pitching National Advisory Committee for Aeronautics (NACA) 0012 airfoil is numerically simulated using Unsteady-Reynolds-Averaged Navier–Stokes (URANS) and multiple detached eddy simulation (DES) solvers: the Delayed-DES (DDES) and the Improved-DDES (IDDES). Two- and three-dimensional simulations are performed for each solver, and the results are compared against experimental measurements in the literature. The results showed that three-dimensional simulations surpass two-dimensional ones in capturing the stages of dynamic stall and predicting the lift coefficient values, with a distinguished performance of the DES solvers over the URANS ones. For instance, the IDDES simulations, as an inherently three-dimensional solver, predicted the necessary cascaded amalgamation process of vortices to form the adequate strength of the dynamic stall vortex. This vortex size and timing provided accurate and sufficient suction that resulted in identical matching of the numerical and experimental lift coefficients at the peak value. Hence, the hypothesis that dynamic stall has a three-dimensional nature is supported by the superiority of the three-dimensional simulation in all aspects. In conclusion, it is found that dynamic stall is intrinsically a three-dimensional phenomenon. [ABSTRACT FROM AUTHOR]

Background: Cognitive load (CL) management is essential in safety‐critical fields so that professionals can monitor and control their cognitive resources efficiently to perform and solve scenarios in a timely and safe manner, even in complex and unexpected circumstances. Thus, cognitive load theory (CLT) can be used to design virtual reality (VR) training programmes for professional learning in these fields. Objectives: We studied CL management performance through behavioural indicators in authentic VR flight training and explored if and to what extent physiological data was associated with CL management performance. Methods: The expert (n = 8) and novice pilots (n = 6) performed three approach and landing scenarios with increasing element interactivity. We used video recordings of the training to assess CL management performance based on the behavioural indicators. Then, we used the heart rate (HR) and heart rate variability (HRV) data to study the associations between the physiological data and CL management performance. Results and Conclusions: The pilots performed effectively in CL management. The experience of the pilots did not remarkably explain the variation in CL management performance. The scenario with the highest element interactivity and an increase in the very low‐frequency band of HRV were associated with decreased performance in CL management. Takeaways: Our study sheds light on the association between physiological indicators and CL management performance, which has traditionally been assessed with behavioural indicators in professional learning in safety‐critical fields. Thus, physiological measurements can be used to supplement the assessment of CL management performance, as relying solely on behavioural indicators can be time consuming. Lay Description: What is currently known about the subject matter: The advantages of VR training systems are clear in the safety‐critical fields.Cognitive load (CL) theory may help design of VR training.CL management is part of the professional competence in these fields. What this paper adds: The pilots performed well in CL management in VR flight training.The work experience of the pilot was not associated with the performance.The physiological data improved the explanatory level of the performance. The implications of study findings for practitioners: Pilots need time to get used to the immersive learning environment.Typical 1–2‐hour intensive VR flight training is not too demanding.The physiological data could complement CL management assessment. [ABSTRACT FROM AUTHOR]

In structural bonds, the interface between adherend and adhesive is nearly two-dimensional making the interface susceptible to minute quantities of contamination, which can cause weak bonds. Regulatory organizations such as the Federal Aviation Administration (FAA) often require redundant load paths in secondary-bonded primary-structures due to uncertainty in bond performance. To address this issue, the NASA Convergent Aeronautics Solutions (CAS): Adhesive Free Bonding of Composites (AERoBOND) project is investigating reformulated aerospace epoxy-matrix resins to enable reflow and diffusion of the resin at the joint interface during a secondary bonding and cure process that can eliminate the material discontinuity at the interface. Implementing in-situ process monitoring enables assessing the bond quality during processing rather than waiting for post-fabrication mechanical testing to be completed. In this paper, an in-situ ultrasonic inspection system is used to monitor the joining of three composite laminates assembled using the AERoBOND technique. For each panel, the amplitude of the wave reflection at the joint was measured throughout the cure cycle. The results indicate the timing and extent of reflow and cure of the epoxy resin at the joint. Factors indicating end of cure were ascertained and a metric was developed to qualitatively predict acceptable mode-II fracture toughness based on the ultrasonic amplitude at the joint line during cure. In addition, since the inspection system scans an area of the joint, high-resolution localized results can be obtained across the joint. [ABSTRACT FROM AUTHOR]

Canada's airports are unique in the world as a system of private, no-share capital, not-for-profit organizations. This paper reviews the evolution Canada's airport system and airport policy over the last 30 years and provides an overview of airport performance including an assessment of the likely proceeds should the Canadian government decide to sell its eight largest airports to private investors. The review reveals an airport system with a heavy "user pay" orientation that has become reliant on "airport improvement fees" charged to passengers, over and above regular aeronautical charges, in order to finance the substantial investments in infrastructure made by airport authorities. The paper highlights criticisms of the current airport system that have endured for over 20 years and shows how recent recommendations to sell our airports to private investors reveals an underlying tension regarding whether airports should be regarded as "spark plugs" that create wider economic benefits or "toll booths" that generate government revenues. The paper argues that a viable alternative to selling off airports to private investors is to reintroduce legislation first introduced in 2003 and again in 2006, which, despite broad political support, never became law. [ABSTRACT FROM AUTHOR]

This paper analyses the development level and trend of grey system theory (GST) over the past 40 years based on bibliometrics. Literature was searched using the Web of Science (WoS) databases. Literature analysis was carried out from eight aspects: paper publication, main journals publishing GST and its application, 20 highly cited articles, hot research topics, high-output scholars and their cooperation networks, the geographical distribution of scholars, finding agencies, and a comparison between papers obtained from the China National Knowledge Infrastructure (CNKI) and WoS databases. Bibliometric analysis showed that while GST had developed slowly over the initial 20 years, it experienced a period of high-speed development over the last 20 years. Two journals the Journal of Grey System and Grey Systems: Theory and Application-play key roles in promoting the international development of GST. Professor Sifeng Liu and Nanjing University of Aeronautics and Astronautics have been the most influential scholar and research center in GST, respectively. GST has attracted many scholars worldwide, and the number of papers published in international journals is increasing. A comparison of publications related to GST between CNKI and WoS databases showed that more efforts are required for GST to become more international. [ABSTRACT FROM AUTHOR]

Supercooled large droplet (SLD) icing is beyond of the protection ability of the conventional antiicing system. SLD is a more serious icing environment and could badly affect the flight safety. In order to ensure flight safety in the SLD icing condition, the precondition is that the SLD should be detected explicitly required by the 14 CFR 25.140 of Federal Aeronautics Administration. It is found that the breakup of droplets will change their trajectory and distribution, and reduce the impingement limit on the wing-leading edge, while the splash of droplets has little effect on the impingement limit. Therefore, ice detection technologies satisfying airworthiness compliance of SLD is studied in this paper considering the characteristics of a various range of large and small droplets. Conventional ice detectors with mature technologies are used and are located in the ice sensitive zones according to the collection range of water droplets. It can detect the whole ice environment in the methods above. [ABSTRACT FROM AUTHOR]

The paper presents the results of a cavitation in a slit channel study and offers an analytical description of cavity development. Special emphasis was placed on examining partial cavitation near a NACA 0012 hydrofoil (NACA – the National Advisory Committee for Aeronautics) inside slit channels of different geometries. Experimental investigation was carried out via high-speed imaging and the laser Doppler anemometry (LDA) method. The experimental data showed that the local flow velocity in hydrofoil leading edge area increased abruptly under arising cavitation. In addition, occurrence of cavitation raised flow velocity pulsation by 20%. In the case of a shorter channel, cavity growth occurred at higher cavitation numbers than for a longer channel. The cavity growth velocity was higher for a shorter channel. We showed that the tendency of partial cavitation development in the slit channel can be described as follows: L / C ∼ σ −1, where L is the cavity length; C is the hydrofoil chord; σ is the cavitation number; and parameter A changes as the slit channel length is varied. Comparison of cavitation development near hydrofoil at different attack angles α inside the slit channel with a three-dimensional (3D) cavitation tunnel was conducted. Cavitation in the slit channel occurred at lower σ /2 α values compared to 3D cavitation flow around the hydrofoil. To directly compare lengths of the attached cavities arising in slit channels and 3D cavitation tunnels, an additional parameter is proposed, taking into account friction of the slit channel: K = λ · l / D. This parameter allowed us to quantitatively compare the characteristics of cavitating hydrofoils in slit channels and 3D tunnels. The paper provides the governing criteria of the cavitation in the slit channel. Our results propose the physical foundations for the development of cavities in the slit channel. [ABSTRACT FROM AUTHOR]

The present study investigates the efficacy of sinusoidal trailing-edge (TE) serrations as a passive means for the reductions of airfoil broadband noise, theoretically and experimentally. Comprehensive parametric studies were conducted to determine the effect of serration amplitudes and wavelengths on the noise reduction performance of a National Advisory Committee for Aeronautics (NACA) airfoil. Initially, the present paper shows the use of the trailing-edge noise (TNO) model for the accurate predictions of the surface pressure spectrum near the TE and hence the far-field noise using the Wiener-Hopf method. The predicted spectra and the noise reduction levels showed good agreement with the measurements for a wide range of frequencies. The present study reveals that the local maximums of the overall noise reductions occur when the transverse turbulence integral length scale is either 1.2 or 0.2 times the serration wavelength, which corresponds to λ/Λt=0.833 or 5, where λ and Λt are the serration wavelength and integral length scale. One of the key findings of the paper is that the serration wavelength at which the highest noise reductions occur when the acoustic emissions vary inversely with the modified Strouhal number Sthm [i.e., wsste(ω)/wbl(ω)∝1/Sthm ] for narrow (i.e., small wavelengths) and wider serrations (i.e., large wavelengths), where wsste and wbl are the acoustic emissions radiated from the serrated and baseline airfoils. Further, the TE serrations are also observed to reduce leading-edge (LE) noise along with the self-noise, which indicates the efficacy of TE serrations in reducing the total far-field noise. [ABSTRACT FROM AUTHOR]

In an innovative system, it is essential to keep under control the crucial development phases, which should consider several aspects involving, for instance, the modeling or the assessment of suitable analytical representations. Aiming to pursue a final demonstration to verify the actual capability of an engineering idea, however, some fundamental elements may have been partially considered. Many projects state the initial and final technology readiness level based on the famous scale introduced by the US National and Aeronautics Space Administration (NASA) many years ago and now widespread in many fields of technology innovation. Its nine-step definition provides a high-level indication of the maturity of the observed innovative system. Trivially, the resolution of that macroscopic meter is not made for catching advancement details, but it rather provides comprehensive information on the examined technology. It is, therefore, necessary to refer to more sophisticated analysis tools that can show a more accurate picture of the development stage and helps designers to highlight points that deserve further attention and deeper analysis. The risk is to perform a very good demonstration test that can miss generality and remain confined only to that specific experimental campaign. Moving on to these assumptions, the authors expose three realizations of theirs concerning aeronautic morphing systems, to the analysis of a well-assessed Technology Readiness Level instrument. The aim is to define the aspects to be further assessed, the aspect to be considered fully mature, and even aspects that could miss some elementary point to attain full maturation. Such studies are not so frequent in the literature, and the authors believe to give a valuable, yet preliminary, contribution to the engineering of breakthrough systems. Without losing generality, the paper refers to the 2.2 version of a tool set up by the US Air Force Research Laboratory (AFRL), and NASA, with the aim to standardize the evaluation process of the mentioned nine-step TRL. [ABSTRACT FROM AUTHOR]

Purpose -- With the predicted rise in air traffic, a growing need exists to make the aviation industry more environmentally sustainable in the long-term future. Research has shown that the turbo-electric distributed propulsion system (TeDP) could be the next disruptive technology that has the potential to meet the ambitious environmental goals set for the N + 3 time frame. This however will require the use of superconductivity, application of high-temperature superconducting materials and cryogenic liquids. This paper provides a brief overview of the technology and further discusses the benefits, advantages and new opportunities that may arise from the application of the technology. Design/methodology/approach -- This paper provides a brief overview of the technology and further discusses the benefits, advantages and new opportunities that may arise from the application of the technology. Findings -- Implementation of superconducting technology is currently one of the greater challenges faced and hence this article also reviews some of the key considerations to enable utilisation of cryogenic fuels in the future. Originality/value -- This paper provides a viewpoint and reviews some of the work undertaken in the field. It also provides a perspective on some new possibilities and advantages from using TeDP with cryogenic fuels. [ABSTRACT FROM AUTHOR]

Pulse-power technology has been widely used in inertial-confinement fusion, electron-beam accelerators, and the aeronautics and astronautics fields. However, particle contamination can reduce operational stability by altering the breakdown process. The objective of this paper is to study the effects of large numbers of metallic submicron particles on the breakdown characteristics. Particles were spontaneously generated via consecutive high-pulse-power breakdowns in compressed N2. In this paper, we adopted a plasma-diagnosis system that combines a laser scattering technique with laser shadow photography to detect particles originating from different materials. To distinguish the specific effects of particles, a double-electrode/double-pulse method was used to eliminate the unwanted effects of electrode erosion. After thousands of consecutive breakdowns, numerous particles were unexpectedly found to suspend and accumulate in the inter-electrode gap rather than fall to the bottom. These particles mainly stemmed from the anode and were identified as either metallic conducting nanoparticles or submicron particles. Furthermore, their density continuously increased and remained at a high level for a long time. This converted the insulating medium from a pure gas to a mixture with numerous metallic particles. In this case, the probability of breakdowns involving particles increased and their mean breakdown voltage showed a downward trend. According to our analysis of the field-enhancement process, these small particles alone can neither cause field emission nor trigger a microdischarge. However, their collective effects could be significant if they were involved in the breakdown channel. [ABSTRACT FROM AUTHOR]

Satellites have provided decades of valuable cloud observations, but the data from conventional passive radiometers are biased toward information from at or near cloud top. Tied with the Joint Polar Satellite System (JPSS) Visible Infrared Imaging Radiometer Suite (VIIRS) Cloud Calibration/Validation research, we developed a statistical Cloud Base Height (CBH) algorithm using the National Aeronautics and Space Administration (NASA) A-Train satellite data. This retrieval, which is currently part of the National Oceanic and Atmospheric Administration (NOAA) Enterprise Cloud Algorithms, provides key information needed to display clouds in a manner that goes beyond the typical top-down plan view. The goal of this study is to provide users with high-quality three-dimensional (3D) cloud structure information which can maximize the benefits and performance of JPSS cloud products. In support of the JPSS Proving Ground Aviation Initiative, we introduced Cloud Vertical Cross-sections (CVCs) along flight routes over Alaska where satellite data are extremely helpful in filling significant observational gaps. Valuable feedback and insights from interactions with aviation users allowed us to explore a new approach to provide satellite-based 3D cloud data. The CVC is obtained from multiple cloud retrieval products with supplementary data such as temperatures, Pilot Reports (PIREPs), and terrain information. We continue to improve the product demonstrations based on user feedback, extending the domain to the contiguous United States with the addition of the Geostationary Operational Environmental Satellite (GOES)-16 Advanced Baseline Imager (ABI). Concurrently, we have refined the underlying science algorithms for improved nighttime and multilayered cloud retrievals by utilizing Day/Night Band (DNB) data and exploring machine learning approaches. The products are evaluated using multiple satellite data sources and surface measurements. This paper presents our accomplishments and continuing efforts in both scientific and user-engagement improvements since the beginning of the VIIRS era. [ABSTRACT FROM AUTHOR]

Balanced systems have extensive applications in engineering fields such as new energy storage and aeronautics. The reliability analysis of such systems has been reported in literature. However, most existing studies focus on the binary-state situation, and research on multi-state cases and the relevant rebalancing mechanism is still limited. To fill this gap, a multi-state k-out-of-n:F balanced system with a rebalancing mechanism is studied in this paper. Both components and the system have multiple states, and all the components are required to be working in similar states to ensure that the system operates in a balanced condition. It means that the difference between the maximum and minimum component states should not exceed a threshold. Otherwise, the system is out of balance and should be rebalanced by identifying the components whose states are too high and adjusting them into lower states. A continuous-time Markov process is used to describe the component operation process and relevant reliability indices are derived accordingly. An age maintenance strategy is also proposed and an optimization model is constructed to obtain the optimal results. Finally, numerical examples based on a product line balancing problem are presented to demonstrate the application of the proposed model. [ABSTRACT FROM AUTHOR]

By using the self-developed unmanned aerial vehicle (UAV) borne mini synthetic aperture radar (MiniSAR) system, all-directional echoes for multiple types of representative ground targets are collected and used for image processing by the Radar Detection and Imaging Techniques Research Group of Nanjing University of Aeronautics & Astronantics (NUAA). A proprietary SAR database for complex targets is constructed, based on which artificial-intelligence-inspired target recognition approaches are studied. To solve the challenging issue of SAR image defocus caused by unstable movement of the UAV platform and the limited accuracy provided by the accessory sensors, novel movement compensation and auto-focus processing methods are proposed. The impact of the image defocus on the classification accuracies provided by the neural networks is revealed, and the limited generalizability of the existing neural networks is demonstrated. Simulation results show that although the classic neural networks, such as AlexNet, ResNet-18, AConvNet, and VGG offer a near-100% accuracy for the MSTAR 10-target classification problem, the 9-class target classification accuracies provided by these networks for the MiniSAR dataset are all much lower than 90%. Since the experiment method employed in this paper closely resembles the practical application scenario, the proposed database will be of great reference value to the development of SAR target recognition algorithms for engineering applications. [ABSTRACT FROM AUTHOR]

Purpose: Since the inception of aerospace engineering, reducing drag is of eternal importance. Over the years, researchers have been trying to improve the aerodynamics of National Advisory Committee for Aeronautics (NACA) aerofoils in many ways. It is proved that smooth-surfaced NACA 0012 aerofoil produces more drag in compressible flow. Recent research on shark-skin pattern warrants a feasible solution to many fluid-engineering problems. Several attempts were made by many researchers to implement the idea of shark skin in the form of coatings, texture and more. However, those ideas are at greater risk when it comes to wing maintenance. The purpose of this paper is to implement a relatively larger biomimetic pattern which would make way for easy maintenance of patterned wings with improved performance. Design/methodology/approach: In this paper, two biomimetic aerofoils are designed by optimizing the surface pattern of shark skin and are tested at different angles of attack in the computational flow domain. Findings: The results of the biomimetic aerofoils prove that viscous and total drag can be reduced up to 33.08% and 3.68%, respectively, at high subsonic speed when validated against a NACA 0012 aerofoil. With the ample effectiveness of patched shark-skin pattern, biomimetic aerofoil generates as high as 10.42% lift than NACA 0012. Originality/value: In this study, a feasible shark-skin pattern is constructed for NACA 0012 in a transonic flow regime. Computational results achieved using the theoretical model agree with experimental data. [ABSTRACT FROM AUTHOR]

COVID-19 pandemic has posed a major occupational and economical risk to the commercial aviation industry, although risk assessment remains unaccounted for. The described in this paper sleep and mental health disturbances due to the pandemic, of personel responsible for the operational safety of flights should be implemented in aeromedical assessment. Objective: The aim of this study was to assess the mental health and sleep quality of aviation workers in Greece during the pandemic. Methods: A cross-sectional study of aviation workers in Greece was conducted. Results: Sleep disturbances were observed in 25.4% of our 548 participants, whereas 8.2% and 5.8% reported at least mild depressive and anxiety symptoms, respectively. The impact of the pandemic on their mental health was their primary concern, which increased for many active pilots according to their workload. Those infected mainly faced daily tiredness and fatigue. Smoking habits and high body mass index were a predisposition for more physical symptoms. Cabin crew and women generally yielded worse scores than the other groups. Conclusion: Fear of infection could explain mental health issues, whereas physical symptoms of those infected could be attributed to long-COVID (coronavirus disease) syndrome. Flight attendants' lower ratings may be due to more occupational exposure. [ABSTRACT FROM AUTHOR]

In this paper, the potential of a novel active flow control strategy by means of a modulated pulse jet vortex generator to enhance high-lift performance is demonstrated on a two-dimensional supercritical National Aeronautics and Space Administration (NASA) SC(2)-0714 airfoil with a single slotted trailing-edge flap at a high deflection angle. Fast-switching solenoid valves and compressed air were used as actuators to excite the flow. The vortex generator slot pairs were incorporated into the shoulder of the trailing-edge flap, where the flow separation occurs due to the high flow deflection and severe adverse pressure gradient. In these experiments, in addition to the simple square-wave excitation signal, a burst-modulated excitation signal as a novel pulse jet sequence was implemented to produce the unsteady blowing. The burst-modulation signal was used for the first time for a fast-switching solenoid valve actuator. The experiments were performed at a freestream velocity of 25 m/s with a corresponding Reynolds number of about 1×106 for a range of angles of attack from 0° to 20° at flap deflection angles from 0° to 35°. The results indicated that the ejection from vortex generator slot pairs was able to prevent flow separation completely in most conditions. These measurements revealed that the burst-modulated excitation was accompanied by more aerodynamic improvements and less air consumption relative to the simple pulsed jet excitation. In the best flow control mode, the results showed about a 12.6% increase in the lift coefficient and a 19.8% decrease in the drag coefficient. [ABSTRACT FROM AUTHOR]

The problem of uniformly placing N points onto a sphere finds applications in many areas. For example, points on the sphere correspond to unit quaternions as well as to the group of rotations SO(3) and the online version of generating uniform rotations (known as "incremental generation") plays a crucial role in a large number of engineering applications ranging from robotics and aeronautics to computer graphics. An online version of this problem was recently studied with respect to the gap ratio as a measure of uniformity. The first online algorithm of Chen et al. was upper-bounded by 5.99 and later improved to 3.69, which is achieved by considering a circumscribed dodecahedron followed by a recursive decomposition of each face. In this paper we provide a more efficient tessellation technique based on the regular icosahedron, which improves the upper-bound for the online version of this problem, decreasing it to approximately 2.84. Moreover, we show that the lower bound for the gap ratio of placing at least three points is (1 + 5) / 2 ≈ 1.618 and for at least four points is no less than 1.726. [ABSTRACT FROM AUTHOR]

We report on results of an intercomparison of 10 global sea-ice concentration (SIC) data products at 12.5 to 50.0 km grid resolution from satellite passive microwave (PMW) observations. For this we use SIC estimated from >350 images acquired in the visible–near-infrared frequency range by the joint National Aeronautics and Space Administration (NASA) and United States Geological Survey (USGS) Landsat sensor during the years 2003–2011 and 2013–2015. Conditions covered are late winter/early spring in the Northern Hemisphere and from late winter through fall freeze-up in the Southern Hemisphere. Among the products investigated are the four products of the European Organisation for the Exploitation of Meteorological Satellites (EUMETSAT) Ocean and Sea Ice Satellite Application Facility (OSI SAF) and European Space Agency (ESA) Climate Change Initiative (CCI) algorithms SICCI-2 and OSI-450. We stress the importance to consider intercomparison results across the entire SIC range instead of focusing on overall mean differences and to take into account known biases in PMW SIC products, e.g., for thin ice. We find superior linear agreement between PMW SIC and Landsat SIC for the 25 and the 50 km SICCI-2 products in both hemispheres. We discuss quantitatively various uncertainty sources of the evaluation carried out. First, depending on the number of mixed ocean–ice Landsat pixels classified erroneously as ice only, our Landsat SIC is found to be biased high. This applies to some of our Southern Hemisphere data, promotes an overly large fraction of Landsat SIC underestimation by PMW SIC products, and renders PMW SIC products overestimating Landsat SIC particularly problematic. Secondly, our main results are based on SIC data truncated to the range 0 % to 100 %. We demonstrate using non-truncated SIC values, where possible, can considerably improve linear agreement between PMW and Landsat SIC. Thirdly, we investigate the impact of filters often used to clean up the final products from spurious SIC over open water due to weather effects and along coastlines due to land spillover. Benefiting from the possibility to switch on or off certain filters in the SICCI-2 and OSI-450 products, we quantify the impact land spillover filtering can have on evaluation results as shown in this paper. [ABSTRACT FROM AUTHOR]

Major surgical events/incidents onboard are rare but can be catastrophic to any mission. National Aeronautics and Space Administration (NASA) uses the Integrated Medical Model (IMM) to develop an integrated, quantified, evidence-based decision support tool useful for crew health and mission planners to assess risk and design medical systems. In 2017, the IMM of the NASA Human Research Program included a list of 100 medical conditions that could be anticipated during space flight. Of those conditions, 27 are expected to need surgical treatment. Consequently, there has been a continuing interest in surgical capabilities for exploration space flight. The surgical system capabilities aboard all space stations and analogue flights have been designed and implemented with an emphasis on stabilisation, medical evacuation, and ATLS capabilities. However, with future missions to the Moon and Mars, evacuation is not a possibility and astronauts will need to troubleshoot, adapt, and self-administer complex surgical care autonomously. This narrative review aims to examine the published work on surgical care in space, discuss the inherent challenges, and identify scope for future studies. The review evaluates and analyses results from several landmark experiments covering important technical aspects such as basic surgical skills, laparoscopic surgery, robotic surgery, and tele surgery. Relevant studies for the review were identified from the MEDLINE, PubMed, and EMBASE databases. Eligible studies were published between 1960 and June 2021 and were identified using the terms "space surgery", "microgravity", "zero gravity", "weightlessness", "parabolic flight", "neutral buoyancy", and "spaceflight". Only articles in English were selected and references cited in the selected publications were followed up and included where appropriate. Documents available in the public domain and/or archives of National Space agencies were also included. The search yielded a total of 86 hits including review articles, commentaries, studies, meeting summaries and technical reports submitted to National Space agencies. Results were then filtered for eligible papers relevant to this narrative review. Challenges on a long-duration mission will be unique, unlike anything we have faced so far in the last 60 years of space travel. Despite the progress in space surgery in the last 40 years, there are several challenges to achieving a fully functional surgical care system on any mission outside Low Earth Orbit. The microgravity environment presents unique challenges related to altered physiology as well as mechanics and techniques pertinent to surgical care. Some of the challenges include but are not limited to crew selection, role of prophylactic surgery, adaptation to zero gravity, lack of ground support, training and maintenance of surgical skills and limitation of weight and volume for hardware. Ultrasound imaging, 3D printing and AI-based surgical assistance coupled with robotic surgery have shown promise, but their real efficacy and functionality remains to be tested. • Inability to repatriate has highlighted need for autonomous surgical care. • Adaptation to weightlessness for the patient and surgeon is important to consider. • Crew selection, training and maintenance of skills will be critical. • Conservative and minimal access management of surgical conditions is predicted. • Ultrasound and 3D printing will play an important role in surgical care. [ABSTRACT FROM AUTHOR]

Abstract From the perspective of the history of technology, this paper reviews the development of a hypersonic wind tunnel in China. The key figure is Yu Hongru 俞鸿儒, who began his research into shock tube wind tunnels in the 1950s, and proposed ways to use detonation driver technology. His insight, however, was stymied during China's "Cultural Revolution." After China's reform and opening-up began in the late 1970s, Yu 俞 designed a hypersonic tunnel driven by backward hydrogen-oxygen detonation utilizing a dumping section and carried out verification experiments with RWTH Aachen University. After 2000, the high-temperature gas dynamics team of the Institute of Mechanics of the Chinese Academy of Sciences built the first long test-duration detonation-driven shock tunnel. This case study draws extensively upon Chinese literature, documents, and interviews. It adds to the history exploring Cold War science and technology. While much research has focused on activities in the USA and the USSR, this article contributes to the less-explored history of scientific research and development in China after 1950, demonstrating the importance of knowledge flows within the wider concept of Cold War transnational science. In addition, this transnational emphasis contributes a non-western chapter to the western-centric history of aerospace technology development. [ABSTRACT FROM AUTHOR]

This paper reviews jet noise research conducted at the National Aeronautics and Space Administration (NASA) from the early 1950s to the present day. Research conducted by NASA's predecessor, the National Advisory Committee for Aeronautics (NACA), and during the early years of NASA focused on turbojet noise, where a common approach for reducing jet noise was to limit the jet exit velocity to speeds that provided acceptable noise levels. Suppressors tested during this time resulted in thrust losses that were too severe to be implemented. With the introduction of turbofan engines in the 1960s, NASA shifted research to programs for both subsonic and supersonic aircraft applications with specific noise reduction goals. Subsonic research focused on increasing the bypass ratio of the engine to reduce the jet exit velocity of the core exhaust and adding mixers to the dual exhaust streams. Advances in computational methods improved aerodynamic designs and jet noise prediction tools. Supersonic applications proved to be more troublesome as programs aimed at large commercial transports required higher specific thrust engines. Changing the engine cycle to reduce jet noise was not compatible with mission range and speed requirements. Research for supersonic commercial aircraft remains an area of interest today at NASA. [ABSTRACT FROM AUTHOR]

This paper describes the design, development, and flight testing of a mesoscale cyclocopter. Weighing 29 g, the present vehicle is the smallest cycloidal rotor-based aircraft at the time of writing of this paper. Unlike the larger cyclocopters, the prototype utilizes a lightweight (3 g) cycloidal rotor design with no exposed rotor shaft and cantilevered blades that have a semielliptical planform. To minimize bending deflections, the blades use a lightweight (0.1 g each) unidirectional carbon fiber-based structural design and are fabricated using a specialized manufacturing process. The cycloidal rotor design was chosen through systematic performance measurements conducted using a custom-built miniature three-component force balance. Based on experimental parametric studies, a four-bladed rotor and symmetric blade kinematics with a pitch amplitude of 45° provided the highest thrust and power loading (thrust/power) and was used in the final rotor design. The airframe is fabricated using a combination of carbon fiber and three-dimensional printed material. The attitude control strategy utilizes a combination of RPM-control of the two cycloidal rotors/tail rotor and thrust vectoring of the cycloidal rotors. The control strategy is implemented on a custom-built 1.3 g autopilot, which uses a closed-loop proportionalderivative controller for hover stability. The vehicle has been flight-tested and has demonstrated stable hovering flight after tuning the feedback gains. [ABSTRACT FROM AUTHOR]

Abstract Identification of nonlinear roll dynamics of finned cylindrical bodies is a critical step when assessing free motion stability and trajectories of aerially dispensed munitions or decoys. In this paper the authors present a parameter estimation process that focuses on identifying nonlinear aerodynamic models that characterize the roll dynamics of a cylindrical body with wrap around fins using data from a series of dynamic wind tunnel tests. This is a three step approach that combines ordinary least squares, stepwise regression and the augmented output-error method, and it is initially tested using simulation data corrupted by white Gaussian noise and then applied to the wind tunnel data. Roll and roll rate dynamics were captured through a series of high angle of attack free-to-roll tests carried out at an airspeed of 35 m / s corresponding to a Reynolds number of 800 , 000. The results and discussion in this paper demonstrate how simulation can be used to develop and mature a system identification routine followed by its assessment through wind tunnel test data. It is shown that high order nonlinear models with up to 14 terms can be parameterized to provide high levels of agreement with roll and roll rate dynamics observed in the dynamic wind tunnel tests. [ABSTRACT FROM AUTHOR]

Abstract The development of supersonic and hypersonic aeronautical projects has led to a renewal of interest and research in supersonic mixing processes and methods to control them. Due to the compressibility effects, the mixing process in supersonic condition is significantly inhibited. Limited flow residence time (at the order of microseconds) for mixing of supersonic airstream and fuel in a scramjet combustor calls for the development of techniques for mixing enhancement. In the present paper, the applicable techniques for mixing enhancement of supersonic mixing layer flows are reviewed comprehensively. Following the brief introduction of fundamentals of supersonic mixing layer, this paper discusses the mixing enhancement methods in the categories of: passive flow control techniques, active flow control techniques and shock wave induced mixing enhancement strategy. Based on the review of former progress, the gaps in current knowledge and areas where more research is needed are pointed out. Meanwhile, the mechanisms of different enhanced mixing methods are summarized, which can be a reference and guidance for the future techniques design for mixing enhancement of supersonic flows. Highlights • Enhanced mixing methods for supersonic mixing layers are reviewed. • Overview of the fundamentals of supersonic mixing layers is presented. • The mechanisms of different methods for mixing enhancement are revealed. • The present review can be a reference and guidance for future strategy design. [ABSTRACT FROM AUTHOR]

Abstract Hybrid-electric propulsion is an interesting alternative for the light aviation market, carrying the advantages of electric propulsion in terms of lower noise and pollutive emissions in terminal maneuvers, while not renouncing to the flight performance – especially range – typical to conventional propulsion, based on hydrocarbon fuel. Some difficulty in the spreading of this new technology in light aviation may be ascribed to the lack of consolidated techniques to preliminary design hybrid-electric aircraft, complicating the negotiation of specifications and making design choices difficult. This is also the effect of a notable increase in the number of design variables needed to describe the hybrid-electric power-train, which include characteristics of both its thermal and electric parts, with respect to conventionally powered aircraft. The present paper presents a methodology to efficiently cope with this design problem. The procedure is based on an optimal approach where take-off weight is minimized, and constraints are included to assure meeting the mission performance requirements while not exceeding any technological limit. The paper recalls at first some simple mathematical models, allowing to translate flight performance requirements into constraints on the power-train. Then the proposed optimal design approach is thoroughly presented at a theoretical level. Finally, an example design of a hybrid-electric motor-glider is shown, where the optimal design tool is used both to find a baseline solution and to investigate the sensitivity of that design point with respect to constraints due to performance requirements and technological specifications. [ABSTRACT FROM AUTHOR]

In this paper, an indirect lightning-induced transient protection circuit for avionics system is proposed, and its effectiveness is verified. The proposed circuit consists of a metal oxide varistor (MOV), a transient voltage suppression (TVS) diode, and a resistor. Compared with the conventional circuits (MOV or TVS diode), the improved noise suppression of the proposed circuit against indirect lightning strikes are experimentally verified in accordance with radio technical commission for aeronautics (RTCA) DO-160G Sec. 22. The highest attenuation levels of indirect lightning strike WF5A reference voltage and current signals are approximately 91.0% and approximately 98.4% for the input lightning signals, respectively. [ABSTRACT FROM AUTHOR]