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Aerospace, Volume 8, Issue 10 (October 2021) – 36 articles

Cover Story (view full-size image): The on-board tilting mirror calibration mechanism (TMCM) has a mechanical driving part that helps to achieve the main functional modes of deployment and stow when calibrating a spaceborne imaging sensor. In general, it is necessary to consider a holding and release device (HRM) in the mechanism design, to secure the structural safety of the mechanical driving part in severe launch environments. However, in this study, we proposed a novel design strategy based on mass balancing, to guarantee mechanical safety on the driving part of the TMCM, although the implementation of the HRM was not considered in the design. The effectiveness of the proposed design was experimentally verified via launch vibration and life cycle tests, etc.View this paper
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Article
A Control Method of Space Manipulator for Peg-in-Hole Assembly Task Considering Equivalent Stiffness Optimization
Aerospace 2021, 8(10), 310; https://doi.org/10.3390/aerospace8100310 - 19 Oct 2021
Viewed by 193
Abstract
To meet the control requirements of high precision and high robustness for peg-in-hole assembly tasks, an optimized control method for a peg-in-hole assembly task of a space manipulator is proposed to reduce the system disturbance caused by the change contact status during the [...] Read more.
To meet the control requirements of high precision and high robustness for peg-in-hole assembly tasks, an optimized control method for a peg-in-hole assembly task of a space manipulator is proposed to reduce the system disturbance caused by the change contact status during the assembly process. The first step is to build an equivalent stiffness model, which considers the structure and control characteristics of the space manipulator. Flexibility indices along the assembly direction are then created. On completion of the flexibility indices, the assembly configuration of the manipulator is optimized with the gain of the joint controller. After that, based on the sliding mode impedance control law, the disturbance of contact force is compensated using a zero-sum optimal control compensation strategy. Finally, the correctness and effectiveness of the control method are verified through simulation experiments. The results of the simulation experiments show that the contact force of the space manipulator can be precisely controlled by the method proposed in this paper. Compared with existing methods, the sudden change of contact force and the disturbing force of the base are reduced by 90% and 54%, respectively. A control method of the space manipulator for a peg-in-hole assembly task considering the equivalent stiffness optimization is proposed, which effectively reduces the influence of disturbance caused by contact collision and improves the control robustness of peg-in-hole assembly tasks. Full article
(This article belongs to the Section Astronautics & Space Science)
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Article
Movement Characteristics of a Dual-Spin Guided Projectile Subjected to a Lateral Impulse
Aerospace 2021, 8(10), 309; https://doi.org/10.3390/aerospace8100309 - 19 Oct 2021
Viewed by 181
Abstract
In this paper, a new dual-spin guided projectile that is equipped with ten lateral impulse jets is proposed for trajectory correction. To guide the overall design of the projectile and the control system, a linear motion model of the projectile that was subjected [...] Read more.
In this paper, a new dual-spin guided projectile that is equipped with ten lateral impulse jets is proposed for trajectory correction. To guide the overall design of the projectile and the control system, a linear motion model of the projectile that was subjected to a lateral impulse was obtained based on a full nonlinear seven-degree-of-freedom (7-DOF) dynamic model. The trajectory correction process of a lateral impulse was divided into two stages. To explain the principle of lateral impulse trajectory correction, the analytical solutions of the linear model of these two stages were obtained. Analytical and numerical solutions were compared to verify the accuracy of the linear model. It is concluded that the analytical and numerical solutions are in good agreement. Full article
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Article
Nonlinear Aeroelastic Simulations and Stability Analysis of the Pazy Wing Aeroelastic Benchmark
Aerospace 2021, 8(10), 308; https://doi.org/10.3390/aerospace8100308 - 18 Oct 2021
Viewed by 204
Abstract
The Pazy wing aeroelastic benchmark is a highly flexible wind tunnel model investigated in the Large Deflection Working Group as part of the Third Aeroelastic Prediction Workshop. Due to the design of the model, very large elastic deformations in the order of 50% [...] Read more.
The Pazy wing aeroelastic benchmark is a highly flexible wind tunnel model investigated in the Large Deflection Working Group as part of the Third Aeroelastic Prediction Workshop. Due to the design of the model, very large elastic deformations in the order of 50% span are generated at highest dynamic pressures and angles of attack in the wind tunnel. This paper presents static coupling simulations and stability analyses for selected onflow velocities and angles of attack. Therefore, an aeroelastic solver developed at the German Aerospace Center (DLR) is used for static coupling simulations, which couples a vortex lattice method with the commercial finite element solver MSC Nastran. For the stability analysis, a linearised aerodynamic model is derived analytically from the unsteady vortex lattice method and integrated with a modal structural model into a monolithic aeroelastic discrete-time state-space model. The aeroelastic stability is then determined by calculating the eigenvalues of the system’s dynamics matrix. It is shown that the stability of the wing in terms of flutter changes significantly with increasing deflection and is heavily influenced by the change in modal properties, i.e., structural eigenvalues and eigenvectors. Full article
(This article belongs to the Special Issue Aeroelasticity, Volume III)
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Article
Generalized Guidance Formulation for Impact Angle Interception with Physical Constraints
Aerospace 2021, 8(10), 307; https://doi.org/10.3390/aerospace8100307 - 18 Oct 2021
Viewed by 230
Abstract
This paper proposes an optimal impact angle control guidance law for homing missiles with a narrow field-of-view of the seekers. As groundwork for designing a guidance law, we first present a general guidance structure that can achieve any terminal constraint of the line-of-sight [...] Read more.
This paper proposes an optimal impact angle control guidance law for homing missiles with a narrow field-of-view of the seekers. As groundwork for designing a guidance law, we first present a general guidance structure that can achieve any terminal constraint of the line-of-sight rate based on the optimal control theory. We configure the desired profile of the line-of-sight rate using a saturation function whose exact form is determined to satisfy the required boundary conditions. By combining the line-of-sight rate profile with the optimal guidance structure, we develop a guidance law that achieves an impact angle interception with the field-of-view constraint. Herein, as the entire guidance structure is derived based on exact kinematics without any approximation, the proposed law ensures the accurate impact angle interception for various engagement scenarios. This precise consideration of the engagement kinematics also accurately ensures the energy optimality of preventing the excessive use of control inputs when homing. To evaluate the performance of the proposed method, numerical simulations with various engagement scenarios are conducted, and the results demonstrate that the proposed law allows missiles to accurately intercept their targets with the desired impact angles and without violating the prescribed field-of-view constraint. Full article
(This article belongs to the Section Aeronautics)
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Article
Relief Aircraft Dispatch Strategies Based on Different Levels of Information Sharing Systems
Aerospace 2021, 8(10), 306; https://doi.org/10.3390/aerospace8100306 - 17 Oct 2021
Viewed by 204
Abstract
In the wake of a disaster, relief activities are expected to start immediately. To determine a better approach in dispatchment and transportation during relief activities, the primary factor is the communication and information sharing between the various parties such as airports, relief shelters [...] Read more.
In the wake of a disaster, relief activities are expected to start immediately. To determine a better approach in dispatchment and transportation during relief activities, the primary factor is the communication and information sharing between the various parties such as airports, relief shelters and aircraft pilots. However, the effect of the information-sharing systems on the efficiency of transportation is yet to be clarified, and the differences between transport methods under different information-sharing systems are not yet known. Therefore, in this paper, we proposed different dispatch strategies corresponding to different information sharing levels and utilized the agent-based simulation modeling dynamic system to compare the air relief efficiency of different dispatch strategies. The simulation results demonstrate that the efficiency of relief activities increases as the level of information sharing improves, and different dispatch strategies have an impact on the effect of relief activities. Full article
(This article belongs to the Section Air Traffic and Transportation)
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Article
Thermo-Mechanical Design and Validation of Spaceborne High-Speed Digital Receiver Unit for Synthetic Aperture Radar Application
Aerospace 2021, 8(10), 305; https://doi.org/10.3390/aerospace8100305 - 16 Oct 2021
Viewed by 274
Abstract
This paper presents the effectiveness of the thermo-mechanical design of a high-speed digital receiver unit (HSDRU) developed for spaceborne synthetic aperture radar applications. The main features of HSDRU’s thermo-mechanical design include the thermal management of high-heat dissipation units by adopting heat sinks with [...] Read more.
This paper presents the effectiveness of the thermo-mechanical design of a high-speed digital receiver unit (HSDRU) developed for spaceborne synthetic aperture radar applications. The main features of HSDRU’s thermo-mechanical design include the thermal management of high-heat dissipation units by adopting heat sinks with the additional function of structural stiffeners and securing the heat rejection path to the upper side of electronics that interfaces the foil radiator for the on-orbit passive thermal control of electronics exposed to deep space environments. The thermal design, which adopts a thermal gap pad, is closely related to the solder joint fatigue life in a launch vibration environment, owing to its initial compressive static load between the heat sink and heat dissipation units that enhances the heat transfer capability. The effectiveness of the design was validated via the qualification level of launch environment tests. Full article
(This article belongs to the Special Issue Vibration Control for Space Application)
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Article
Design of Robust Control System of Magnetic Suspension and Balance System through Harmonic Excitation Simulation
Aerospace 2021, 8(10), 304; https://doi.org/10.3390/aerospace8100304 - 15 Oct 2021
Viewed by 91
Abstract
The magnetic suspension and balance system (MSBS) uses magnetic force and moment to precisely control the movement of the test object located at the center of the test section without mechanical contact, and at the same time measure the external force acting on [...] Read more.
The magnetic suspension and balance system (MSBS) uses magnetic force and moment to precisely control the movement of the test object located at the center of the test section without mechanical contact, and at the same time measure the external force acting on the test object. If such an MSBS is installed around the test section of the wind tunnel so that the position and attitude angle of the test object follow the harmonic function, various vibration tests can be performed on structures subjected to aerodynamic loads without the influence of the mechanical support. Because the control force and moment in the MSBS is generated by a number of electromagnets located around the test section, it is necessary to apply the adaptive control algorithm to the position and attitude control system so that the experiment can be carried out stably despite the sudden performance change of each electromagnet and electric power supply. In this study, a fault-tolerant position and attitude angle control system was designed through an adaptive control algorithm, and the effectiveness was verified through simulation under the condition that the electric power supply of MSBS failed. Full article
(This article belongs to the Special Issue Vibration Control for Space Application)
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Article
A Case for User-Centered Design in Satellite Command and Control
Aerospace 2021, 8(10), 303; https://doi.org/10.3390/aerospace8100303 - 15 Oct 2021
Viewed by 190
Abstract
The prevalence of unique, disparate satellite command and control (SATC2) systems in current satellite operations is problematic. As such, the United States Air Force aims to consolidate SATC2 systems into an enterprise solution that utilizes a common Human–Machine Interface (HMI). We employed a [...] Read more.
The prevalence of unique, disparate satellite command and control (SATC2) systems in current satellite operations is problematic. As such, the United States Air Force aims to consolidate SATC2 systems into an enterprise solution that utilizes a common Human–Machine Interface (HMI). We employed a User-Centered Design (UCD) approach including a variety of methods from design thinking and human factors engineering to develop a solution that is effective, efficient, and meets operator needs. During a summative test event, we found that users had significantly higher situation awareness, lower workload, and higher subjective usability while using the HMI developed via UCD over the existing, or legacy, HMI. This case study serves as evidence to support the assertion that involving users early and often has positive and tangible effects on the development of aerospace systems. Full article
(This article belongs to the Section Astronautics & Space Science)
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Article
An Evaluation Method for Dry Friction Damping of Ring Damper in Gas Turbine Engines under Axial Vibration
Aerospace 2021, 8(10), 302; https://doi.org/10.3390/aerospace8100302 - 15 Oct 2021
Viewed by 96
Abstract
The blisks and labyrinth seals in gas turbine engines are typical rotating periodic structures. Vibration problems will inevitably occur during the operation, which can easily lead to High Cycle Fatigue failure of the structure. Adding ring damper is an effective means of structural [...] Read more.
The blisks and labyrinth seals in gas turbine engines are typical rotating periodic structures. Vibration problems will inevitably occur during the operation, which can easily lead to High Cycle Fatigue failure of the structure. Adding ring damper is an effective means of structural vibration reduction. The damper uses the dry friction of the contact surface to dissipate the vibration energy, improve the damping of the system, and then reduce the vibration response of the structure. The structures have a nodal diameter and modal shape, and the forced vibration often presents the characteristics of traveling wave. In this paper, an evaluation method for dry friction damping of ring damper under the axial component of traveling wave vibration is established. For the given vibration stress at the critical location, the equivalent damping ratio provided by the ring damper is calculated based on the friction energy dissipation and the damping characteristic curve that is the equivalent damping ratio varying with the vibration stress is obtained. This method can avoid calculating the nonlinear dry friction forced response and is suitable for the design stage. The damping of split ring dampers with rectangular section for one blisk and labyrinth seal is analyzed in this paper. It is shown that rotating speed, friction coefficient, section area and material density significantly influence the damping characteristics. There are many factors affecting the damping characteristics of the damping, so it is necessary to comprehensively consider various factors and multiple modes for vibration reduction design. Full article
(This article belongs to the Special Issue Vibration Control for Space Application)
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Communication
Air Traffic Prediction as a Video Prediction Problem Using Convolutional LSTM and Autoencoder
Aerospace 2021, 8(10), 301; https://doi.org/10.3390/aerospace8100301 - 14 Oct 2021
Viewed by 217
Abstract
Accurate prediction of future air traffic situations is an essential task in many applications in air traffic management. This paper presents a new framework for predicting air traffic situations as a sequence of images from a deep learning perspective. An autoencoder with convolutional [...] Read more.
Accurate prediction of future air traffic situations is an essential task in many applications in air traffic management. This paper presents a new framework for predicting air traffic situations as a sequence of images from a deep learning perspective. An autoencoder with convolutional long short-term memory (ConvLSTM) is used, and a mixed loss function technique is proposed to generate better air traffic images than those obtained by using conventional L1 or L2 loss function. The feasibility of the proposed approach is demonstrated with real air traffic data. Full article
(This article belongs to the Special Issue Aircraft Operations and CNS/ATM)
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Article
Post-COVID-19 Scenarios of Global Airline Traffic until 2040 That Reflect Airport Capacity Constraints and Mitigation Strategies
Aerospace 2021, 8(10), 300; https://doi.org/10.3390/aerospace8100300 - 14 Oct 2021
Viewed by 194
Abstract
Although there has been an unprecedented decline in traffic volume due to the COVID-19 crisis, robust growth in global demand for air transport services in the past means that air traffic is expected to recover in the long term. While capacity constraints are [...] Read more.
Although there has been an unprecedented decline in traffic volume due to the COVID-19 crisis, robust growth in global demand for air transport services in the past means that air traffic is expected to recover in the long term. While capacity constraints are currently not a major topic at airports due to the extremely low levels of traffic, there is growing evidence to suggest that important nodes of the worldwide airport network will struggle to deal with capacity constraints after the recovery. The objectives of this research were therefore as follows: to elaborate long-term global passenger and flight volume scenarios in a post-COVID-19 world; to conduct an empirical and model-based analysis of the impact of limited airport capacity on the future development of air traffic in these scenarios; and to derive general strategies for mitigating capacity constraints at certain international airports. Thus, the main aim of this paper is to present a model-based scenario analysis of the long-term impact of the COVID-19 crisis on the capacity situation for airports. Our results indicate that once the pandemic is over, the capacity crunch will remain on the airports’ agenda for some time. Full article
(This article belongs to the Section Air Traffic and Transportation)
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Article
Two-Stage Pursuit Strategy for Incomplete-Information Impulsive Space Pursuit-Evasion Mission Using Reinforcement Learning
Aerospace 2021, 8(10), 299; https://doi.org/10.3390/aerospace8100299 - 14 Oct 2021
Viewed by 183
Abstract
This paper presents a novel and robust two-stage pursuit strategy for the incomplete-information impulsive space pursuit-evasion missions considering the J2 perturbation. The strategy firstly models the impulsive pursuit-evasion game problem into a far-distance rendezvous stage and a close-distance game stage according to the [...] Read more.
This paper presents a novel and robust two-stage pursuit strategy for the incomplete-information impulsive space pursuit-evasion missions considering the J2 perturbation. The strategy firstly models the impulsive pursuit-evasion game problem into a far-distance rendezvous stage and a close-distance game stage according to the perception range of the evader. For the far-distance rendezvous stage, it is transformed into a rendezvous trajectory optimization problem and a new objective function is proposed to obtain the pursuit trajectory with the optimal terminal pursuit capability. For the close-distance game stage, a closed-loop pursuit approach is proposed using one of the reinforcement learning algorithms, i.e., the deep deterministic policy gradient algorithm, to solve and update the pursuit trajectory for the incomplete-information impulsive pursuit-evasion missions. The feasibility of this novel strategy and its robustness to different initial states of the pursuer and evader and to the evasion strategies are demonstrated for the sun-synchronous orbit pursuit-evasion game scenarios. The results of the Monte Carlo tests show that the successful pursuit ratio of the proposed method is over 91% for all the given scenarios. Full article
(This article belongs to the Special Issue Spacecraft Dynamics and Control)
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Article
Short-Arc Association and Orbit Determination for New GEO Objects with Space-Based Optical Surveillance
Aerospace 2021, 8(10), 298; https://doi.org/10.3390/aerospace8100298 - 14 Oct 2021
Viewed by 194
Abstract
For Geosynchronous Earth Orbit (GEO) objects, space-based optical surveillance has advantages over regional ground surveillance in terms of both the timeliness and space coverage. However, space-based optical surveillance may only collect sparse and short orbit arcs, and thus make the autonomous arc association [...] Read more.
For Geosynchronous Earth Orbit (GEO) objects, space-based optical surveillance has advantages over regional ground surveillance in terms of both the timeliness and space coverage. However, space-based optical surveillance may only collect sparse and short orbit arcs, and thus make the autonomous arc association and orbit determination a challenge for new GEO objects without a priori orbit information. In this paper, a three-step approach tackling these two critical problems is proposed. First, under the near-circular orbit assumption, a multi-point optimal initial orbit determination (IOD) method is developed to improve the IOD convergence rate and the accuracy of the IOD solution with angles-only observations over a short arc. Second, the Lambert equation is applied to associate two independent short arcs in an attempt to improve accuracy of the single-arc IOD semi-major axis (SMA) with the use of virtual ranges between the optical sensor and GEO object. The key idea in the second step is to generate accurate ranges at observation epochs, which, along with the real angle data, are then used to achieve much improved SMA accuracy. The third step is basically the repeated application of the second step to three or more arcs. The high success rate of arc associations and accurate orbit determination using the proposed approach are demonstrated with simulated space-based angle data over short arcs, each being only 3 min. The results show that the proposed approach is able to determine the orbit of a new GEO at a three-dimensional accuracy of about 15 km from about 10 arcs, each having a length of about 3 min, thus achieving reliable cataloguing of uncatalogued GEO objects. The IOD and two-arc association methods are also tested with the real ground-based observations for both GEO and LEO objects of near-circular orbits, further validating the effectiveness of the proposed methods. Full article
(This article belongs to the Section Astronautics & Space Science)
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Article
Development and Characterization of a Novel Porous-Media Borosilicate Glass Ion Sources for Electrospray Thruster
Aerospace 2021, 8(10), 297; https://doi.org/10.3390/aerospace8100297 - 14 Oct 2021
Viewed by 176
Abstract
The porous-media-based electrospray thruster is a cutting-edge micropropulsion technology that can revolutionize the capabilities of microsatellites. This paper reports the design, fabrication, and characterization of a novel porous-media borosilicate glass electrospray thruster. The porous glass used here is integrally formed by the phase [...] Read more.
The porous-media-based electrospray thruster is a cutting-edge micropropulsion technology that can revolutionize the capabilities of microsatellites. This paper reports the design, fabrication, and characterization of a novel porous-media borosilicate glass electrospray thruster. The porous glass used here is integrally formed by the phase separation method, which make it display outstanding pore uniformity and processability. The picosecond ultraviolet laser processing technique is applied to machine 361 emitters out of glass. Performance characteristic experiments are conducted with the thruster passively fed with ionic EMI-BF4 liquid. The results reveal that the per-emitter can emit up to 200.46 nA of ion current at 2 kV. The novel porous glass and the corresponding machine method present an opportunity to attain more-controllable emitter shapes, which has a positive impact on thruster lifetime and performance improvement. Full article
(This article belongs to the Section Astronautics & Space Science)
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Article
Innovative Acoustic Treatments of Nacelle Intakes Based on Optimised Metamaterials
Aerospace 2021, 8(10), 296; https://doi.org/10.3390/aerospace8100296 - 14 Oct 2021
Viewed by 197
Abstract
Modern turbofans with high bypass ratios, low blade passage frequencies and short nacelles require continuous development of acoustic linings to achieve the noise reductions expected by the international aviation authorities. Metamaterials and metafluids have been recently proposed as promising technologies for designing innovative [...] Read more.
Modern turbofans with high bypass ratios, low blade passage frequencies and short nacelles require continuous development of acoustic linings to achieve the noise reductions expected by the international aviation authorities. Metamaterials and metafluids have been recently proposed as promising technologies for designing innovative acoustic treatments dedicated to reducing aeronautic turbofan noise emissions. In this work, a phase-gradient metasurface treatment is investigated as a way to tackle the noise radiation from an axially symmetric nacelle. This paper aims to study the potential benefits of the mentioned technology, and is not an attempt to design a complete new liner or nacelle. The metasurface is modelled through an equivalent metafluid, and a simulation-based optimisation is used in defining the design parameters. The tonal contribution of the blade passage frequency is considered, and the numerical results with the metafluid optimised on one azimuthal mode at a time show a significant effect in terms of acoustic levels and directivity over an arc of virtual receivers. Full article
(This article belongs to the Special Issue Aeroacoustic Analysis)
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Review
The Progress of Aerodynamic Mechanisms Based on Avian Leading-Edge Alula and Future Study Recommendations
Aerospace 2021, 8(10), 295; https://doi.org/10.3390/aerospace8100295 - 13 Oct 2021
Viewed by 230
Abstract
Birds in nature have many unique devices to help them acquire excellent flight abilities under various complex flight conditions. One of the unique devices is the leading-edge alula, located at the junction of the arm wing and the hand wing of most birds. [...] Read more.
Birds in nature have many unique devices to help them acquire excellent flight abilities under various complex flight conditions. One of the unique devices is the leading-edge alula, located at the junction of the arm wing and the hand wing of most birds. It often spreads out during takeoff and landing, probably playing a similar role to high-lift devices in fixed-wing aircraft. This paper analyzed and reviewed the results of current research on leading-edge alula, finding some important factors, such as the complex flapping motions, flexibility, and the plane and section shape of the wing, that have been ignored in current research to a certain extent. These would greatly affect the conclusions obtained. Hence, for a deeper understanding of the aerodynamic mechanisms and functions of the alula, some new study predictions for future research are presented. In addition, the feasible models and methods for further research based on these predictions are discussed and proposed. For example, the higher-accuracy LES or hybrid LES/RANS method and the combinations of these methods with wind-tunnel experiments using PIV technology are recommended. Full article
(This article belongs to the Section Aeronautics)
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Article
Evaluation of Anti-Icing Performance for an NACA0012 Airfoil with an Asymmetric Heating Surface
Aerospace 2021, 8(10), 294; https://doi.org/10.3390/aerospace8100294 - 12 Oct 2021
Viewed by 234
Abstract
Heating devices on airfoil surfaces are widely used as an anti-icing technology. This study investigated the aerodynamic performance with a static heating surface based on the modified extended Messinger model. The predicted ice shape was validated through a comparison with the experimental results [...] Read more.
Heating devices on airfoil surfaces are widely used as an anti-icing technology. This study investigated the aerodynamic performance with a static heating surface based on the modified extended Messinger model. The predicted ice shape was validated through a comparison with the experimental results for HAARP-II. A reasonable agreement was found for both the icing area and the ice mass on the suction surface. Then, the prediction method was adopted for an NACA0012 airfoil at an attack angle of 4.0 under a glaze ice condition. An asymmetric heating area was imposed on the suction and pressure surfaces considering a temperature of 10C near the leading edge. As a result of heating, the round ice formation when was no longer observed, and the formed ice volume decreased. However, bump-shaped pieces of ice were formed downstream of the heater owing to runback water; these bump-shaped pieces of ice formed on the suction surface significantly increased the flow drag and reduced the lift. The results indicated that extending the heating area on the suction surface can improve the aerodynamic performance. Consequently, the overall aerodynamic performance is deteriorated by adding static heating compared to the case without heating. Full article
(This article belongs to the Special Issue Deicing and Anti-Icing of Aircraft (Volume II))
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Article
Turbojet Thrust Augmentation through a Variable Exhaust Nozzle with Active Disturbance Rejection Control
Aerospace 2021, 8(10), 293; https://doi.org/10.3390/aerospace8100293 - 11 Oct 2021
Viewed by 376
Abstract
Turbojets require variable exhaust nozzles to fit high-demanding applications; however, few reports on nozzle control are available. The purpose of this paper is to investigate the possible advantages of an exhaust gas control through a variable exhaust nozzle. The control design method combines [...] Read more.
Turbojets require variable exhaust nozzles to fit high-demanding applications; however, few reports on nozzle control are available. The purpose of this paper is to investigate the possible advantages of an exhaust gas control through a variable exhaust nozzle. The control design method combines successful linear active disturbance rejection control (LADRC) capabilities with a loop shaping controller (LSC) to: (i) allow designing the closed-loop characteristics in terms of gain margin, phase margin and bandwidth, and (ii) increase the LSC disturbance rejection capabilities with an extended state observer. A representation of the nozzle dynamics is obtained from first principles and adapted to achieve a stream-velocity-based control loop. The results show that the resulting controller allows improving the expansion of the exhaust gas to the ambient pressure for the whole operating range of the turbojet, increasing the estimated thrust by 14.23% during the tests with experimental data. Full article
(This article belongs to the Special Issue Technologies for Future Distributed Engine Control Systems)
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Article
A Physics-Based Multidisciplinary Approach for the Preliminary Design and Performance Analysis of a Medium Range Aircraft with Box-Wing Architecture
Aerospace 2021, 8(10), 292; https://doi.org/10.3390/aerospace8100292 - 09 Oct 2021
Viewed by 351
Abstract
The introduction of disruptive innovations in the transport aviation sector is becoming increasingly necessary. This is because there are many very demanding challenges that the transport aviation system will have to face in the years ahead. In particular, the reduction in pollutant emissions [...] Read more.
The introduction of disruptive innovations in the transport aviation sector is becoming increasingly necessary. This is because there are many very demanding challenges that the transport aviation system will have to face in the years ahead. In particular, the reduction in pollutant emissions from air transport, and its impact on climate change, clearly must be addressed; moreover, sustainable solutions must be found to meet the constantly increasing demand for air traffic, and to reduce the problem of airport saturation at the same time. These three objectives seem to be in strong contrast with each other; in this paper, the introduction of a disruptive airframe configuration, called PrandtlPlane and based on a box-wing lifting system, is proposed as a solution to face these three challenges. This configuration is a more aerodynamically efficient alternative candidate to conventional aircraft, introducing benefits in terms of fuel consumption and providing the possibility to increase the payload without enlarging the overall aircraft wingspan. The development and analysis of this configuration, applied to a short-to-medium range transport aircraft, is carried out through a multi-fidelity physics-based approach. In particular, following an extensive design activity, the aerodynamic performance in different operating conditions is investigated in detail, the structural behaviour of the lifting system is assessed, and the operating missions of the aircraft are simulated. The same analysis methodologies are used to evaluate the performance of a benchmark aircraft with conventional architecture, with the aim of making direct comparisons with the box-wing aircraft and quantifying the performance differences between the two configurations. Namely, the CeRAS CSR-01, an open-access virtual representation of an A320-like aircraft, is selected as the conventional benchmark. Following such a comparative approach, the paper provides an assessment of the potential benefits of box-wing aircraft in terms of fuel consumption reduction and increase in payload capability. In particular, an increase in payload capability of 66% and a reduction in block fuel per pax km up to 22% is achieved for the PrandtlPlane with respect to the conventional benchmark, while maintaining the same maximum wingspan. Full article
(This article belongs to the Special Issue Aircraft Design (SI-3/2021))
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Article
Classification and Analysis of Go-Arounds in Commercial Aviation Using ADS-B Data
Aerospace 2021, 8(10), 291; https://doi.org/10.3390/aerospace8100291 - 09 Oct 2021
Viewed by 247
Abstract
Go-arounds are a necessary aspect of commercial aviation and are conducted after a landing attempt has been aborted. It is necessary to conduct go-arounds in the safest possible manner, as go-arounds are the most safety-critical of operations. Recently, the increased availability of data, [...] Read more.
Go-arounds are a necessary aspect of commercial aviation and are conducted after a landing attempt has been aborted. It is necessary to conduct go-arounds in the safest possible manner, as go-arounds are the most safety-critical of operations. Recently, the increased availability of data, such as ADS-B, has provided the opportunity to leverage machine learning and data analytics techniques to assess aviation safety events. This paper presents a framework to detect go-around flights, identify relevant features, and utilize unsupervised clustering algorithms to categorize go-around flights, with the objective of gaining insight into aspects of typical, nominal go-arounds and factors that contribute to potentially abnormal or anomalous go-arounds. Approaches into San Francisco International Airport in 2019 were examined. A total of 890 flights that conducted a single go-around were identified by assessing an aircraft’s vertical rate, altitude, and cumulative ground track distance states during approach. For each flight, 61 features relevant to go-around incidents were identified. The HDBSCAN clustering algorithm was leveraged to identify nominal go-arounds, anomalous go-arounds, and a third cluster of flights that conducted a go-around significantly later than other go-around trajectories. Results indicate that the go-arounds detected as being anomalous tended to have higher energy states and deviations from standard procedures when compared to the nominal go-arounds during the first approach, prior to the go-around. Further, an extensive comparison of energy states between nominal flights, anomalous flights, the first approach prior to the go-around, and the second approach following the go-around is presented. Full article
(This article belongs to the Special Issue Machine Learning Applications in Aviation Safety)
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Article
Comparative Study of Different Algorithms for a Flight Control System Design and the Potentiality of Their Integration with a Sidestick
Aerospace 2021, 8(10), 290; https://doi.org/10.3390/aerospace8100290 - 07 Oct 2021
Viewed by 329
Abstract
The modern trend of developing highly automated aircraft is characterized by a transition from traditional methods and technical solutions to innovative approaches in order to control the system, inceptor and display design. This paper deals with the development and comparison of flight control [...] Read more.
The modern trend of developing highly automated aircraft is characterized by a transition from traditional methods and technical solutions to innovative approaches in order to control the system, inceptor and display design. This paper deals with the development and comparison of flight control system algorithms based on inverse dynamics, H-infinity and traditional feedback methods. The integration of a controller based on inverse dynamics with a novel type of sidestick, shaping the pilot output signal such that it is proportional to the control force (force sensing control—FSC), is studied. The inverse dynamics-based controller is chosen, as it provides a variance of error that is up to 2.3 times less than that of the feedback gains and up to 1.5 times less than that of the H-infinity controller in a pitch tracking task. The synergetic effect arising from the proposed integration is also evaluated. The evaluation of the effectiveness of the methods is carried out through mathematical modeling of the pilot–aircraft system and ground-based simulations on a helicopter mathematical model in a pitch tracking task. Full article
(This article belongs to the Special Issue Aerospace Guidance, Navigation and Control)
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Article
Air-Launch Experiment Using Suspended Rail Launcher for Rockoon
Aerospace 2021, 8(10), 289; https://doi.org/10.3390/aerospace8100289 - 06 Oct 2021
Viewed by 335
Abstract
The method of air-launching a rocket using a launcher suspended from a balloon, referred to as a rockoon, can improve the flight performance of small rockets. However, there have been safety issues and flight trajectory errors due to uncertainty with respect to the [...] Read more.
The method of air-launching a rocket using a launcher suspended from a balloon, referred to as a rockoon, can improve the flight performance of small rockets. However, there have been safety issues and flight trajectory errors due to uncertainty with respect to the launch direction. Air-launch experiments were performed to demonstrate a rail launcher equipped with a control moment gyroscope to actively control the azimuth angle. As a preliminary study, it was suspended via a crane instead of a balloon. The rockets successfully flew along the target azimuth line and impacted the predicted safe area. The elevation angle of the launcher rail exhibited a fluctuation composed of two frequency components. A double-pendulum model with a rigid rod suspended by a wire was proposed to predict this behavior. Significant design parameters and error sources were investigated using this model, revealing the constraining effect of a large mass above the wire and elevation angle fluctuation, which caused trajectory errors due to the friction force on the rail guide and thrust misalignment. Finally, tradeoffs in designing the rail length were found between the launcher clear velocity and elevation fluctuations. Full article
(This article belongs to the Section Astronautics & Space Science)
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Article
Selective Simulated Annealing for Large Scale Airspace Congestion Mitigation
Aerospace 2021, 8(10), 288; https://doi.org/10.3390/aerospace8100288 - 05 Oct 2021
Viewed by 315
Abstract
This paper presents a methodology to minimize the airspace congestion of aircraft trajectories based on slot allocation techniques. The traffic assignment problem is modeled as a combinatorial optimization problem for which a selective simulated annealing has been developed. Based on the congestion encountered [...] Read more.
This paper presents a methodology to minimize the airspace congestion of aircraft trajectories based on slot allocation techniques. The traffic assignment problem is modeled as a combinatorial optimization problem for which a selective simulated annealing has been developed. Based on the congestion encountered by each aircraft in the airspace, this metaheuristic selects and changes the time of departure of the most critical flights in order to target the most relevant aircraft. The main objective of this approach is to minimize the aircraft speed vector disorder. The proposed algorithm was implemented and tested on simulated trajectories generated with real flight plans on a day of traffic over French airspace with 8800 flights. Full article
(This article belongs to the Special Issue Aircraft Operations and CNS/ATM)
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Article
Aerodynamic Characteristics of Re-Entry Capsules with Hyperbolic Contours
Aerospace 2021, 8(10), 287; https://doi.org/10.3390/aerospace8100287 - 03 Oct 2021
Viewed by 308
Abstract
For most re-entry capsules, the shape of the forebody of the capsule is designed based on the blunted nose cone. A similar shape can be created using a hyperboloid of revolution that can control the nose bluntness and the half angle of the [...] Read more.
For most re-entry capsules, the shape of the forebody of the capsule is designed based on the blunted nose cone. A similar shape can be created using a hyperboloid of revolution that can control the nose bluntness and the half angle of the cone easily. In this study, the hypersonic aerodynamic characteristics of re-entry capsules designed with hyperbolic contours were investigated using the CFD code, FaSTAR, developed by Japan Aerospace Exploration Agency (JAXA). The CFD results showed that, using the hyperbolic contours, the drag and lift coefficients can be increased compared to those for the Hayabusa re-entry capsule without changing the shape of the capsule drastically. This suggests that shape design based on the hyperbolic contours can improve the aerodynamic characteristics of re-entry capsules. Full article
(This article belongs to the Collection Hypersonics: Emerging Research)
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Article
Towards Flocking Navigation and Obstacle Avoidance for Multi-UAV Systems through Hierarchical Weighting Vicsek Model
Aerospace 2021, 8(10), 286; https://doi.org/10.3390/aerospace8100286 - 02 Oct 2021
Viewed by 355
Abstract
Flocking navigation and obstacle avoidance in complex environments remain challenging for multiple unmanned aerial vehicle (multi-UAV) systems, especially when only one UAV (termed as information UAV) knows the predetermined path and the communication range is limited. To this end, we propose a hierarchical [...] Read more.
Flocking navigation and obstacle avoidance in complex environments remain challenging for multiple unmanned aerial vehicle (multi-UAV) systems, especially when only one UAV (termed as information UAV) knows the predetermined path and the communication range is limited. To this end, we propose a hierarchical weighting Vicsek model (HWVEM). In this model, a hierarchical weighting mechanism and an obstacle avoidance mechanism are designed. Based on the hierarchical weighting mechanism, all the UAVs are divided into different layers, and assigned with different weights according to the layer to which they belong. The purpose is to align the rest of UAVs with the information UAV more efficiently. Subsequently, the obstacle avoidance mechanism that utilizes only the local information is developed to ensure the system safety in an environment filled with obstacles differing in size and shape. A series of simulations have been conducted to demonstrate the high performance of HWVEM in terms of convergence time, success rate, and safety. Full article
(This article belongs to the Section Aeronautics)
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Article
Clocking and Potential Effects in Combustor–Turbine Stator Interactions
Aerospace 2021, 8(10), 285; https://doi.org/10.3390/aerospace8100285 - 02 Oct 2021
Viewed by 269
Abstract
Investigations of combustors and turbines separately have been carried out for years by research institutes and aircraft engine companies, but there are still many questions about the interaction effect. In this paper, a prediction of a turbine stator’s potential effect on flow in [...] Read more.
Investigations of combustors and turbines separately have been carried out for years by research institutes and aircraft engine companies, but there are still many questions about the interaction effect. In this paper, a prediction of a turbine stator’s potential effect on flow in a combustor and the clocking effect on temperature distribution in a nozzle guide vane are discussed. Numerical simulation results for the combustor simulator and the nozzle guide vane (NGV) of the first turbine stage are presented. The geometry and flow conditions were defined according to measurements carried out on a test section within the framework of the EU FACTOR (full aerothermal combustor–turbine interactions research) project. The numerical model was validated by a comparison of results against experimental data in the plane at a combustor outlet. Two turbulence models were employed: the Spalart–Allmaras and Explicit Algebraic Reynolds Stress models. It was shown that the NGV potential effect on flow distribution at the combustor–turbine interface located at 42.5% of the axial chord is weak. The clocking effect due to the azimuthal position of guide vanes downstream of the swirlers strongly affects the temperature and flow conditions in a stator cascade. Full article
(This article belongs to the Special Issue Technologies for Future Distributed Engine Control Systems)
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Article
Development of On-Board Tilt Mirror Calibration Mechanism without Holding and Release Mechanism
Aerospace 2021, 8(10), 284; https://doi.org/10.3390/aerospace8100284 - 01 Oct 2021
Viewed by 367
Abstract
The on-board tilting mirror calibration mechanism has a mechanical driving part that helps to achieve the main functional modes of deployment and stow when calibrating a spaceborne imaging sensor. In general, it is necessary to consider a holding and release device in the [...] Read more.
The on-board tilting mirror calibration mechanism has a mechanical driving part that helps to achieve the main functional modes of deployment and stow when calibrating a spaceborne imaging sensor. In general, it is necessary to consider a holding and release device in the mechanism design, to secure the structural safety of the mechanical driving part in severe launch environments. However, in the present study, we proposed a novel design strategy based on mass balancing, to guarantee mechanical safety on the driving part of the tilt mirror mechanism, although the implementation of the holding and release mechanism was not considered in the design. The effectiveness of the proposed design was experimentally verified via launch vibration and life cycle tests. The test results demonstrated that the mechanism fulfills all the required functions, and the design approach proposed in this study is effective for ensuring mechanical safety on the driving part of the tilting mirror mechanism in severe launch vibration environments. Full article
(This article belongs to the Special Issue Vibration Control for Space Application)
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Article
Multimodal Analysis of Eye Movements and Fatigue in a Simulated Glass Cockpit Environment
Aerospace 2021, 8(10), 283; https://doi.org/10.3390/aerospace8100283 - 01 Oct 2021
Viewed by 332
Abstract
Pilot fatigue is a critical reason for aviation accidents related to human errors. Human-related accidents might be reduced if the pilots’ eye movement measures can be leveraged to predict fatigue. Eye tracking can be a non-intrusive viable approach that does not require the [...] Read more.
Pilot fatigue is a critical reason for aviation accidents related to human errors. Human-related accidents might be reduced if the pilots’ eye movement measures can be leveraged to predict fatigue. Eye tracking can be a non-intrusive viable approach that does not require the pilots to pause their current task, and the device does not need to be in direct contact with the pilots. In this study, the positive or negative correlations among the psychomotor vigilance test (PVT) measures (i.e., reaction times, number of false alarms, and number of lapses) and eye movement measures (i.e., pupil size, eye fixation number, eye fixation duration, visual entropy) were investigated. Then, fatigue predictive models were developed to predict fatigue using eye movement measures identified through forward and backward stepwise regressions. The proposed approach was implemented in a simulated short-haul multiphase flight mission involving novice and expert pilots. The results showed that the correlations among the measures were different based on expertise (i.e., novices vs. experts); thus, two predictive models were developed accordingly. In addition, the results from the regressions showed that either a single or a subset of the eye movement measures might be sufficient to predict fatigue. The results show the promise of using non-intrusive eye movements as an indicator for fatigue prediction and provides a foundation that can lead us closer to developing a near real-time warning system to prevent critical accidents. Full article
(This article belongs to the Special Issue Aircraft Operations and CNS/ATM)
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Article
Orbital Design and Control for Jupiter-Observation Spacecraft
Aerospace 2021, 8(10), 282; https://doi.org/10.3390/aerospace8100282 - 01 Oct 2021
Viewed by 364
Abstract
This paper investigates the evolution of orbits around Jupiter and designs a sun-synchronous repeating ground track orbit. In the dynamical models, the leading terms of the Jupiter’s oblateness are J2 and J4 terms. A reasonable range of ground track repetition parameter [...] Read more.
This paper investigates the evolution of orbits around Jupiter and designs a sun-synchronous repeating ground track orbit. In the dynamical models, the leading terms of the Jupiter’s oblateness are J2 and J4 terms. A reasonable range of ground track repetition parameter Q is given and the best observation orbit elements are selected. Meanwhile, the disturbing function acting on the navigation spacecraft is the atmospheric drag and the third body. The law of altitude decay of the spacecraft’s semimajor orbit axis caused by the atmospheric drag is studied, and the inclination perturbation caused by the sun’s gravity is analyzed. This paper designs a semimajor axis compensation strategy to maintain the orbit’s repeatability and proposes an initial inclination prebiased strategy to limit the local time at the descending node in a permitted range. In particular, these two methods are combined in the context of sun-synchronous repeating ground track orbit for better observation of the surface of Jupiter. Full article
(This article belongs to the Special Issue Spacecraft Dynamics and Control)
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Article
Analytical and FEM Analyses of High-Speed Impact Behaviour of Al 2024 Alloy
Aerospace 2021, 8(10), 281; https://doi.org/10.3390/aerospace8100281 - 30 Sep 2021
Viewed by 261
Abstract
The present work investigates the impact behaviour of Al 2024-T3 alloy using FEM analysis performed through LS DYNA software. Johnson–Cookvisco-plastic model is used to study the ballistic impact resistance of target Al alloy impacted by a rigid steel cylindrical projectile. The tensile properties [...] Read more.
The present work investigates the impact behaviour of Al 2024-T3 alloy using FEM analysis performed through LS DYNA software. Johnson–Cookvisco-plastic model is used to study the ballistic impact resistance of target Al alloy impacted by a rigid steel cylindrical projectile. The tensile properties of Al 2024-T3 alloy reported in the literature are used to estimate the J.C. model parameters. Impact velocities within a range of 50 m/s–900 m/s of the projectile were triggered onto Al alloy target thicknesses in the range of 3.18 mm–6.35 mm. To understand the accuracy of the FEM model, an analytical model proposed by Chen et al. for blunt-nosed projectiles on the ductile targets was used to compare with the obtained residual velocities from FEM simulations. It was observed that the ballistic limit velocities have led to the highest energy absorption behaviour of the Al 2024-T3 alloy for an impact velocity of 183 m/s and a 6.35 mm target thickness. The ballistic limit velocities have increased from 97 m/s to 183 m/s for the considered thickness range of 3.18 mm–6.35 mm. The impact failure was observed to have a petalling formation with two petals for thinner targets, while a full-fledged plugging with no petal formation for the 4.00 mm and 6.35 mm target thicknesses was observed. Full article
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