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Aerospace, Volume 7, Issue 6 (June 2020) – 19 articles

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Cover Story (view full-size image) The emergence of selective laser melting (SLM) as a promising additive manufacturing (AM) technique [...] Read more.
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Open AccessArticle
Winging It: Key Issues and Perceptions around Regulation and Practice of Aircraft Maintenance in Australian General Aviation
Aerospace 2020, 7(6), 84; https://doi.org/10.3390/aerospace7060084 - 26 Jun 2020
Viewed by 1004
Abstract
The very diverse character of General Aviation (GA) within Australia poses challenges for its effective management of risk and safety in the sector. Improvements for human performance and perceptions of safety within the maintenance environment are among the areas which regulators have targeted [...] Read more.
The very diverse character of General Aviation (GA) within Australia poses challenges for its effective management of risk and safety in the sector. Improvements for human performance and perceptions of safety within the maintenance environment are among the areas which regulators have targeted for continuous improvement. This paper provides a timely empirical exploration of maintenance engineer perspectives around: (1) Changes in the role of the regulator/regulation that have impacted the sector and diminished safe operations; and (2) specific practical and operational challenges that the GA industry must deal with to sustain safe operations going forward. A thematic analysis of transcribed qualitative data revealed five key themes and identified a number of key issues from sector changes including a decline in training and education, drift in working practices, and wider power-distance gap. Issues with auditing and bureaucratization, negative safety climate, and underlying values and philosophies were also found. Practical and operational challenges going forward included an array of concerns associated with safety, the mismatch between GA and commercial aviation, workforce development and the financial burden in the sector. The results draw attention to the interconnectedness between various components of the GA system, and carry timely implications for regulation in the GA sector. Future research directions are discussed. Full article
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Open AccessArticle
Segmented Standard Taxi Routes—A New Way to Integrate Remotely Piloted Aircraft into Airport Surface Traffic
Aerospace 2020, 7(6), 83; https://doi.org/10.3390/aerospace7060083 - 25 Jun 2020
Viewed by 638
Abstract
The safe and orderly integration of unmanned aircraft in the airspace is surely among the most difficult challenges to be solved in the near future. However, a safe and fluid traffic management on the ground is not less important and not less challenging, [...] Read more.
The safe and orderly integration of unmanned aircraft in the airspace is surely among the most difficult challenges to be solved in the near future. However, a safe and fluid traffic management on the ground is not less important and not less challenging, as completely different aspects have to be considered here. Much less work has been done yet to solve this question. In the frame of the project Surface Management Operations (SuMO), a procedural solution has been developed to enable fully integrated unmanned airport ground movements while allowing air traffic controllers to guarantee a safe, orderly and expeditious flow of traffic. This concept is based on the idea of segmented standard taxi routes for unmanned aircraft, while maintaining current procedures for manned aircraft. From 2017 to 2019, a two-stage validation campaign validated this new solution. No concerns regarding safety or human factors issues were revealed. Access and Equity, as well as Interoperability, were found to be very satisfying. A fast time simulation of mixed manned and unmanned traffic, using the proposed solution, was almost as efficient as pure manned traffic and can easily be implemented at medium-size airports. This article provides information about the experimental setup and the conduction of both validations stages, and illustrates obtained results. It closes with a discussion and an outlook. Full article
(This article belongs to the Special Issue Unmanned Aircraft Traffic Management)
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Open AccessArticle
Characterization of Vacuum Arc Thruster Performance in Weak Magnetic Nozzle
Aerospace 2020, 7(6), 82; https://doi.org/10.3390/aerospace7060082 - 19 Jun 2020
Viewed by 739
Abstract
Vacuum arc thruster performance in a magnetic nozzle configuration is experimentally characterized. Measurements are performed on a miniature coaxial thruster with an anode inner diameter of 1.8 mm. The magnetic field B is produced by a single air coil, 18 mm in diameter. [...] Read more.
Vacuum arc thruster performance in a magnetic nozzle configuration is experimentally characterized. Measurements are performed on a miniature coaxial thruster with an anode inner diameter of 1.8 mm. The magnetic field B is produced by a single air coil, 18 mm in diameter. Direct measurement of thrust, mass consumption and arc current are performed. To obtain statistically viable results 6000 arc pulses are analyzed at each operational point. Cathode mass erosion is measured using laser profilometry. To sustain thruster operation over several measurement cycles, an active cathode feeding system is used. For 0 < B 0.2 T, performance increase over the non-magnetic case is observed with the best thrust to arc power ratio T / P 9 μ N/W obtained at B 0.2 T. A parametric model is provided that captures the performance enhancement based on beam collimation and acceleration by the magnetic nozzle. For B > 0.2 T, the arc discharge is shown to be suppressed nullifying any additional gains by the nozzle effect. Full article
(This article belongs to the Special Issue Electric Propulsion)
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Open AccessArticle
A Contemporary Analysis of Aircraft Maintenance-Related Accidents and Serious Incidents
Aerospace 2020, 7(6), 81; https://doi.org/10.3390/aerospace7060081 - 17 Jun 2020
Viewed by 862
Abstract
Aircraft maintenance has been identified as a key point of concern within many high-risk areas of aviation; still being a casual/contributory factor in a number of accidents and serious incidents in commercial air transport industry. The purpose of this study is to review [...] Read more.
Aircraft maintenance has been identified as a key point of concern within many high-risk areas of aviation; still being a casual/contributory factor in a number of accidents and serious incidents in commercial air transport industry. The purpose of this study is to review and analyse the aircraft maintenance-related accidents and serious incidents which occurred between 2003 and 2017, to provide a better understanding of the causal and contributory factors. To achieve this, a dataset of maintenance-related accidents and serious incidents was compiled and then qualitatively analysed by thematic analysis method. Coding these events by using NVivo software enabled the development of a taxonomy, MxFACS. The coded output was then evaluated by subject matter experts, and an inter-rater concordance value determined to demonstrate the rigour of the research process. Subsequently, the events were evaluated in terms of their relationship to known accident categories such as loss of control, runway excursions. The most frequent maintenance event consequences were found to be runway excursions and air turnbacks, with the second level categories being related to failures in engine and landing gear systems. The greatest maintenance factor issues were ‘inadequate maintenance procedures’ and ‘inspections not identifying defects’. In terms of fatalities, ‘collision events’ were the most prominent consequence, ‘engine-related events’ were the most significant event, and ‘inadequate maintenance procedures’ were the most concerning maintenance factor. The study’s findings may be used in conjunction with existing risk analysis methodologies and enable the stakeholders to develop generic or customised bowties. This may identify the existing barriers in the system as well as weaknesses which will enable the development of mitigation strategies on both organisational and industry-wide levels. Full article
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Open AccessCommunication
Temperature Effects on Polymer-Ceramic Pressure-Sensitive Paint as a Luminescent Pressure Sensor
Aerospace 2020, 7(6), 80; https://doi.org/10.3390/aerospace7060080 - 17 Jun 2020
Viewed by 666
Abstract
Polymer-ceramic pressure-sensitive paint (PC-PSP) has been used for capturing unsteady pressure over aerodynamic surfaces. Spatial and temporal pressure information is calculated from the luminescent intensity produced by a PC-PSP, which provides a nonintrusive pressure measurement. Despite its benefits, the temperature dependency of PC-PSP [...] Read more.
Polymer-ceramic pressure-sensitive paint (PC-PSP) has been used for capturing unsteady pressure over aerodynamic surfaces. Spatial and temporal pressure information is calculated from the luminescent intensity produced by a PC-PSP, which provides a nonintrusive pressure measurement. Despite its benefits, the temperature dependency of PC-PSP makes extraction of quantitative pressure data challenging. The temperature dependency in terms of the static and dynamic characteristics of a ruthenium-based PC-PSP is studied herein. The impact of temperature dependency on PC-PSP characteristics is also discussed in the context of an unsteady pressure measurement. Full article
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Open AccessReview
Review of Conflict Resolution Methods for Manned and Unmanned Aviation
Aerospace 2020, 7(6), 79; https://doi.org/10.3390/aerospace7060079 - 16 Jun 2020
Viewed by 754
Abstract
Current investigations into urban aerial mobility, as well as the continuing growth of global air transportation, have renewed interest in Conflict Detection and Resolution (CD&R) methods. With the new applications of drones, and the implications of a profoundly different urban airspace, new demands [...] Read more.
Current investigations into urban aerial mobility, as well as the continuing growth of global air transportation, have renewed interest in Conflict Detection and Resolution (CD&R) methods. With the new applications of drones, and the implications of a profoundly different urban airspace, new demands are placed on such algorithms, further spurring new research. This paper presents a review of current CR methods for both manned and unmanned aviation. It presents a taxonomy that categorises algorithms in terms of their approach to avoidance planning, surveillance, control, trajectory propagation, predictability assumption, resolution manoeuvre, multi-actor conflict resolution, considered obstacle types, optimization, and method category. More than a hundred CR methods were considered, showing how most work on a tactical, distributed framework. To enable a reliable comparison between methods, this paper argues that an open and ideally common simulation platform, common test scenarios, and common metrics are required. This paper presents an overview of four CR algorithms, each representing a commonly used CR algorithm category. Both manned and unmanned scenarios were tested, through fast-time simulations on an open-source airspace simulation platform. Full article
(This article belongs to the Special Issue Unmanned Aircraft Traffic Management)
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Open AccessArticle
Evaluation of Asphalt Concrete Airport Pavement Conditions Based on the Airfield Pavement Condition Index (APCI) in Scope of Flight Safety
Aerospace 2020, 7(6), 78; https://doi.org/10.3390/aerospace7060078 - 15 Jun 2020
Viewed by 705
Abstract
Airoport infrastructure development requires care to maintain it in proper technical condition. Due to this, airport pavements should be constantly monitored, and, above all, correctly managed. High-level airport pavement management requires access to reliable information about their current technical condition as well as [...] Read more.
Airoport infrastructure development requires care to maintain it in proper technical condition. Due to this, airport pavements should be constantly monitored, and, above all, correctly managed. High-level airport pavement management requires access to reliable information about their current technical condition as well as proper forecasting of this condition in the future. Obtaining good quality information about the technical condition of airport pavement should be based on a proven methodology, taking into account the introduced quality management system. The authors propose a method of technical pavement condition assessment based on the Airfield Pavement Condition Index (APCI), taking into account not only the results of the surface deterioration inventory, but also repair overviews, load bearing capacity, evenness and roughness of the surface, as well as the surface tensile bond strength. The method was developed during long-term work financed by the Ministry of Science and Higher Education. At the beginning of the article, the authors focus on reviewing the currently available methods of assessing the technical condition of the pavement. Then they briefly present the most popular surface assessment method based on the PCI indicator. Afterwards, a proprietary asphalt pavement assessment method based on the APCI indicator is proposed and an example of how to use the method is presented. Finally, they discuss the results and summarize the work done, and present further directions of work. Full article
(This article belongs to the collection Air Transportation—Operations and Management)
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Open AccessReview
Selective Laser Melting of Aluminum and Titanium Matrix Composites: Recent Progress and Potential Applications in the Aerospace Industry
Aerospace 2020, 7(6), 77; https://doi.org/10.3390/aerospace7060077 - 11 Jun 2020
Viewed by 880
Abstract
Selective laser melting (SLM) is a near-net-shape time- and cost-effective manufacturing technique, which can create strong and efficient components with potential applications in the aerospace industry. To meet the requirements of the growing aerospace industrial demands, lighter materials with enhanced mechanical properties are [...] Read more.
Selective laser melting (SLM) is a near-net-shape time- and cost-effective manufacturing technique, which can create strong and efficient components with potential applications in the aerospace industry. To meet the requirements of the growing aerospace industrial demands, lighter materials with enhanced mechanical properties are of the utmost need. Metal matrix composites (MMCs) are extraordinary engineering materials with tailorable properties, bilaterally benefiting from the desired properties of reinforcement and matrix constituents. Among a wide range of MMCs currently available, aluminum matrix composites (AMCs) and titanium matrix composites (TMCs) are highly potential candidates for aerospace applications owing to their outstanding strength-to-weight ratio. However, the feasibility of SLM-fabricated composites utilization in aerospace applications is still challenging. This review addresses the SLM of AMCs/TMCs by considering the processability (densification level) and microstructural evolutions as the most significant factors determining the mechanical properties of the final part. The mechanical properties of fabricated MMCs are assessed in terms of hardness, tensile/compressive strength, ductility, and wear resistance, and are compared to their monolithic states. The knowledge gained from process–microstructure–mechanical properties relationship investigations can pave the way to make the existing materials better and invent new materials compatible with growing aerospace industrial demands. Full article
(This article belongs to the Special Issue Additive Manufacturing for Aerospace and Defence)
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Open AccessArticle
Drone Launched Short Range Rockets
Aerospace 2020, 7(6), 76; https://doi.org/10.3390/aerospace7060076 - 08 Jun 2020
Viewed by 827
Abstract
A concept of drone launched short range rockets (DLSRR) is presented. A drone or an aircraft rises DLSRR to a release altitude of up to 20 km. At the release altitude, the drone or an aircraft is moving at a velocity of up [...] Read more.
A concept of drone launched short range rockets (DLSRR) is presented. A drone or an aircraft rises DLSRR to a release altitude of up to 20 km. At the release altitude, the drone or an aircraft is moving at a velocity of up to 700 m/s and a steep angle of up to 68° to the horizontal. After DLSRRs are released, their motors start firing. DLSRRs use slow burning motors to gain altitude and velocity. At the apogee of their flight, DLSRRs release projectiles which fly to the target and strike it at high impact velocity. The projectiles reach a target at ranges of up to 442 km and impact velocities up to 1.88 km/s. We show that a rocket launched at high altitude and high initial velocity does not need expensive thermal protection to survive ascent. Delivery of munitions to target by DLSRRs should be much less expensive than delivery by a conventional rocket. Even though delivery of munitions by bomber aircraft is even less expensive, a bomber needs to fly close to the target, while a DLSRR carrier releases the rockets from a distance of at least 200 km from the target. All parameters of DLSRRs, and their trajectories are calculated based on theoretical (mechanical and thermodynamical) analysis and on several MatLab programs. Full article
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Open AccessArticle
The Effect of Post-Processing on the Mechanical Behavior of Ti6Al4V Manufactured by Electron Beam Powder Bed Fusion for General Aviation Primary Structural Applications
Aerospace 2020, 7(6), 75; https://doi.org/10.3390/aerospace7060075 - 05 Jun 2020
Viewed by 841
Abstract
In this work a mechanical characterization of Ti6Al4V processed by electron beam powder bed fusion additive manufacturing was carried out to investigate the viability of this technology for the manufacturing of flyable parts for general aviation aircraft. Tests were performed on different manufacturing [...] Read more.
In this work a mechanical characterization of Ti6Al4V processed by electron beam powder bed fusion additive manufacturing was carried out to investigate the viability of this technology for the manufacturing of flyable parts for general aviation aircraft. Tests were performed on different manufacturing conditions in order to investigate the effect of post processing as machining on the mechanical behavior. The study provides useful information to airframe designers and manufacturing specialists that work with this technology. The investigation confirms the low process variability and provides data to be used in the design loop of general aviation primary structural elements. The test results show a high level of repeatability indicating that the process is well controlled and reliable enough to match the airworthiness requirements. In addition, the so-called “as-built specimens”, i.e., specimens produced by the electron beam melting machine without any major post-processing, have lower mechanical performances than specimens subjected to a machining phase after the electron beam melting process. Specific primary structural elements will be designed and flight cleared, resulting from the findings presented herein. Full article
(This article belongs to the Special Issue Additive Manufacturing for Aerospace and Defence)
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Open AccessArticle
Sequential Low-Thrust Orbit-Raising of All-Electric Satellites
Aerospace 2020, 7(6), 74; https://doi.org/10.3390/aerospace7060074 - 04 Jun 2020
Viewed by 824
Abstract
In this paper, we consider a recently developed formulation of the electric orbit-raising problem that utilizes a novel dynamic model and a sequence of optimal control sub-problems to yield fast and robust computations of low-thrust trajectories. This paper proposes two enhancements of the [...] Read more.
In this paper, we consider a recently developed formulation of the electric orbit-raising problem that utilizes a novel dynamic model and a sequence of optimal control sub-problems to yield fast and robust computations of low-thrust trajectories. This paper proposes two enhancements of the computational framework. First, we use thruster efficiency in order to determine the trajectory segments over which the spacecraft coasts. Second, we propose the use of a neural network to compute the solar array degradation in the Van Allen radiation belts. The neural network is trained on AP-9 data and SPENVIS in order to compute the associated power loss. The proposed methodology is demonstrated by considering transfers from different geosynchronous transfer orbits. Numerical simulations analyzing the effect of thruster efficiency and average power degradation indicate the suitability of starting the maneuver from super-geosynchronous transfer orbits in order to limit fuel expenditure and radiation damage. Furthermore, numerical simulations demonstrate that proposed enhancements are achieved with only marginal increase in computational runtime, thereby still facilitating rapid exploration of all-electric mission scenarios. Full article
(This article belongs to the Special Issue Electric Propulsion)
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Open AccessArticle
Critical Parameter Identification for Safety Events in Commercial Aviation Using Machine Learning
Aerospace 2020, 7(6), 73; https://doi.org/10.3390/aerospace7060073 - 04 Jun 2020
Viewed by 824
Abstract
In recent years, there has been a rapid growth in the application of data science techniques that leverage aviation data collected from commercial airline operations to improve safety. This paper presents the application of machine learning to improve the understanding of risk factors [...] Read more.
In recent years, there has been a rapid growth in the application of data science techniques that leverage aviation data collected from commercial airline operations to improve safety. This paper presents the application of machine learning to improve the understanding of risk factors during flight and their causal chains. With increasing complexity and volume of operations, rapid accumulation and analysis of this safety-related data has the potential to maintain and even lower the low global accident rates in aviation. This paper presents the development of an analytical methodology called Safety Analysis of Flight Events (SAFE) that synthesizes data cleaning, correlation analysis, classification-based supervised learning, and data visualization schema to streamline the isolation of critical parameters and the elimination of tangential factors for safety events in aviation. The SAFE methodology outlines a robust and repeatable framework that is applicable across heterogeneous data sets containing multiple aircraft, airport of operations, and phases of flight. It is demonstrated on Flight Operations Quality Assurance (FOQA) data from a commercial airline through use cases related to three safety events, namely Tire Speed Event, Roll Event, and Landing Distance Event. The application of the SAFE methodology yields a ranked list of critical parameters in line with subject-matter expert conceptions of these events for all three use cases. The work concludes by raising important issues about the compatibility levels of machine learning and human conceptualization of incidents and their precursors, and provides initial guidance for their reconciliation. Full article
(This article belongs to the Special Issue Machine Learning Applications in Aviation Safety)
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Open AccessArticle
A Nonlinear Ultrasonic Modulation Method for Crack Detection in Turbine Blades
Aerospace 2020, 7(6), 72; https://doi.org/10.3390/aerospace7060072 - 04 Jun 2020
Viewed by 820
Abstract
In modern gas turbines, efforts are being made to improve efficiency even further. This is achieved primarily by increasing the generated pressure ratio in the compressor and by increasing the turbine inlet temperature. This leads to enormous loads on the components in the [...] Read more.
In modern gas turbines, efforts are being made to improve efficiency even further. This is achieved primarily by increasing the generated pressure ratio in the compressor and by increasing the turbine inlet temperature. This leads to enormous loads on the components in the hot gas region in the turbine. As a result, non-destructive testing and structural health monitoring (SHM) processes are becoming increasingly important to gas turbine manufacturers. Initial cracks in the turbine blades must be identified before catastrophic events occur. A proven method is the linear ultrasound method. By monitoring the amplitude and phase fluctuations of the input signal, structural integrity of the components can be detected. However, closed cracks or small cracks cannot be easily detected due to a low impedance mismatch with the surrounding materials. By contrast, nonlinear ultrasound methods have shown that damages can be identified at an early stage by monitoring new signal components such as sub- and higher harmonics of the fundamental frequency in the frequency spectrum. These are generated by distortion of the elastic waveform due to damage/nonlinearity of the material. In this paper, new global nonlinear parameters were derived that result from the dual excitation of two different ultrasound frequencies. These nonlinear features were used to assess the presence of cracks as well as their qualitative sizes. The proposed approach was tested on several samples and turbine blades with artificial and real defects. The results were compared to samples without failure. Numerical simulations were conducted to investigate nonlinear elastic interaction of the stress waves with the damage regions. The results show a clear trend of nonlinear parameters changing as a function of the crack size, demonstrating the capability of the proposed approach to detect in-service cracks. Full article
(This article belongs to the Special Issue Selected Papers from IWSHM 2019)
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Open AccessArticle
Pareto Optimal PID Tuning for Px4-Based Unmanned Aerial Vehicles by Using a Multi-Objective Particle Swarm Optimization Algorithm
Aerospace 2020, 7(6), 71; https://doi.org/10.3390/aerospace7060071 - 04 Jun 2020
Viewed by 1086
Abstract
Unmanned aerial vehicles (UAVs) are affordable these days. For that reason, there are currently examples of the use of UAVs in recreational, professional and research applications. Most of the commercial UAVs use Px4 for their operating system. Even though Px4 allows one to [...] Read more.
Unmanned aerial vehicles (UAVs) are affordable these days. For that reason, there are currently examples of the use of UAVs in recreational, professional and research applications. Most of the commercial UAVs use Px4 for their operating system. Even though Px4 allows one to change the flight controller structure, the proportional-integral-derivative (PID) format is still by far the most popular choice. A selection of the PID controller parameters is required before the UAV can be used. Although there are guidelines for the design of PID parameters, they do not guarantee the stability of the UAV, which in many cases, leads to collisions involving the UAV during the calibration process. In this paper, an offline tuning procedure based on the multi-objective particle swarm optimization (MOPSO) algorithm for the attitude and altitude control of a Px4-based UAV is proposed. A Pareto dominance concept is used for the MOPSO to find values for the PID comparing parameters of step responses (overshoot, rise time and root-mean-square). Experimental results are provided to validate the proposed tuning procedure by using a quadrotor as a case study. Full article
(This article belongs to the collection Unmanned Aerial Systems)
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Open AccessArticle
Impulse and Performance Measurements of Electric Solid Propellant in a Laboratory Electrothermal Ablation-Fed Pulsed Plasma Thruster
Aerospace 2020, 7(6), 70; https://doi.org/10.3390/aerospace7060070 - 30 May 2020
Viewed by 850
Abstract
Electric solid propellants are advanced solid chemical rocket propellants that can be controlled (ignited, throttled and extinguished) through the application and removal of an electric current. This behavior may enable the propellant to be used in multimode propulsion systems utilizing the ablative pulsed [...] Read more.
Electric solid propellants are advanced solid chemical rocket propellants that can be controlled (ignited, throttled and extinguished) through the application and removal of an electric current. This behavior may enable the propellant to be used in multimode propulsion systems utilizing the ablative pulsed plasma thruster. The performance of an electric solid propellant operating in an electrothermal ablation-fed pulsed plasma thruster was investigated using an inverted pendulum micro-newton thrust stand. The impulse bit and specific impulse of the device using the electric solid propellant were measured for short-duration test runs of 100 pulses and longer-duration runs to end-of-life, at energy levels of 5, 10, 15 and 20 J. Also, the device was operated using the current state-of-the-art ablation-fed pulsed plasma thruster propellant, polytetrafluoroethylene (PTFE). Impulse bit measurements for PTFE indicate 100 ± 20 µN-s at an initial energy level of 5 J, which increases linearly with energy by approximately 30 µN-s/J. Within the error of the experiment, measurements of the impulse bit for the electric solid propellant are identical to PTFE. Specific impulse when operating on PTFE is calculated to be about 450 s. It is demonstrated that a surface layer in the hygroscopic electric solid propellant is rapidly ablated over the first few discharges of the device, which decreases the average specific impulse relative to the traditional polytetrafluoroethylene propellant. Correcting these data by subtracting the early discharge ablation mass loss measurements yields a corrected electric solid propellant specific impulse of approximately 300 s. Full article
(This article belongs to the Special Issue Electric Propulsion)
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Open AccessArticle
Data-Driven Analysis of Airport Security Checkpoint Operations
Aerospace 2020, 7(6), 69; https://doi.org/10.3390/aerospace7060069 - 29 May 2020
Viewed by 806
Abstract
Airport security checkpoints are the most important bottleneck in airport operations, but few studies aim to empirically understand them better. In this work we address this lack of data-driven quantitative analysis and insights about the security checkpoint process. To this end, we followed [...] Read more.
Airport security checkpoints are the most important bottleneck in airport operations, but few studies aim to empirically understand them better. In this work we address this lack of data-driven quantitative analysis and insights about the security checkpoint process. To this end, we followed a total of 2277 passengers through the security checkpoint process at Rotterdam The Hague Airport (RTM), and published detailed timing data about their journey through the process. This dataset is unique in scientific literature, and can aid future researchers in the modelling and analysis of the security checkpoint. Our analysis showed important differences between six identified passenger types. Business passengers were found to be the fastest group, while passengers with reduced mobility (PRM) and families were the slowest two groups. We also identified events that hindered the performance of the security checkpoint, in which groups of passengers had to wait long for security employees or other passengers. A total of 335 such events occurred, with an average of 2.3 passengers affected per event. It was found that a passenger that had a high luggage drop time was followed by an event in 27% of the cases, which was the most frequent cause. To mitigate this waiting time of subsequent passengers in the security checkpoint process, we performed an experiment with a so-called service lane. This lane was used to process passengers that are expected to be slow, while the remaining lanes processed the other passengers. It was found that the mean throughput of the service lane setups was higher than the average throughput of the standard lanes, making it a promising setup to investigate further. Full article
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Open AccessArticle
Computational Evaluation of Aerodynamic Loading on Retractable Landing-Gears
Aerospace 2020, 7(6), 68; https://doi.org/10.3390/aerospace7060068 - 29 May 2020
Viewed by 785
Abstract
Computational fluid dynamics is employed to evaluate the mean aerodynamic loading on the retractable landing-gears of a regional transport commercial aircraft. The mean turbulent flow around simplified landing-gear systems including doors is simulated by using the Reynolds-averaged Navier–Stokes approach, where the governing equations [...] Read more.
Computational fluid dynamics is employed to evaluate the mean aerodynamic loading on the retractable landing-gears of a regional transport commercial aircraft. The mean turbulent flow around simplified landing-gear systems including doors is simulated by using the Reynolds-averaged Navier–Stokes approach, where the governing equations are solved with a finite volume-based numerical method. Using a dynamic meshing method, the computational grid is automatically and continuously adapted to the time-changing geometry, while following the extension/retraction of the landing-gear systems. The temporal evolution of the aerodynamic forces on both the nose and the main landing-gears, along with the hinge moments of the doors, is numerically predicted. The proposed computational modeling approach is verified to have good practical potential when compared with reference experimental data provided by the Leonardo Aircraft structural loads group. Full article
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Open AccessReview
A Review of Low-Power Electric Propulsion Research at the Space Propulsion Centre Singapore
Aerospace 2020, 7(6), 67; https://doi.org/10.3390/aerospace7060067 - 28 May 2020
Cited by 1 | Viewed by 972
Abstract
The age of space electric propulsion arrived and found the space exploration endeavors at a paradigm shift in the context of new space. Mega-constellations of small satellites on low-Earth orbit (LEO) are proposed by many emerging commercial actors. Naturally, the boom in the [...] Read more.
The age of space electric propulsion arrived and found the space exploration endeavors at a paradigm shift in the context of new space. Mega-constellations of small satellites on low-Earth orbit (LEO) are proposed by many emerging commercial actors. Naturally, the boom in the small satellite market drives the necessity of propulsion systems that are both power and fuel efficient and accommodate small form-factors. Most of the existing electric propulsion technologies have reached the maturity level and can be the prime choices to enable mission versatility for small satellite platforms in Earth orbit and beyond. At the Plasma Sources and Applications Centre/Space Propulsion Centre (PSAC/SPC) Singapore, a continuous effort was dedicated to the development of low-power electric propulsion systems that can meet the small satellites market requirements. This review presents the recent progress in the field of electric propulsion at PSAC/SPC Singapore, from Hall thrusters and thermionic cathodes research to more ambitious devices such as the rotamak-like plasma thruster. On top of that, a review of the existing vacuum facilities and plasma diagnostics used for electric propulsion testing and characterization is included in the present research. Full article
(This article belongs to the Special Issue Electric Propulsion)
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Open AccessArticle
Probabilistic Model for Aero-Engines Fleet Condition Monitoring
Aerospace 2020, 7(6), 66; https://doi.org/10.3390/aerospace7060066 - 26 May 2020
Viewed by 795
Abstract
Since aeronautic transportation is responsible for a rising share of polluting emissions, it is of primary importance to minimize the fuel consumption any time during operations. From this perspective, continuous monitoring of engine performance is essential to implement proper corrective actions and avoid [...] Read more.
Since aeronautic transportation is responsible for a rising share of polluting emissions, it is of primary importance to minimize the fuel consumption any time during operations. From this perspective, continuous monitoring of engine performance is essential to implement proper corrective actions and avoid excessive fuel consumption due to engine deterioration. This requires, however, automated systems for diagnostics and decision support, which should be able to handle large amounts of data and ensure reliability in all the multiple conditions the engines of a fleet can be found in. In particular, the proposed solution should be robust to engine-to-engine deviations and different sensors availability scenarios. In this paper, a probabilistic Bayesian network for fault detection and identification is applied to a fleet of engines, simulated by an adaptive performance model. The combination of the performance model and the Bayesian network is also studied and compared to the probabilistic model only. The benefit in the suggested hybrid approach is identified as up to 50% higher accuracy. Sensors unavailability due to manufacturing constraints or sensor faults reduce the accuracy of the physics-based method, whereas the Bayesian model is less affected. Full article
(This article belongs to the Special Issue Progress in Jet Engine Technology)
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