Journal Description
Aerospace
Aerospace
is a peer-reviewed, open access journal of aeronautics and astronautics published monthly online by MDPI. The European Aeronautics Science Network (EASN), and the ECATS International Association are affiliated with Aerospace and their members receive a discount on the article processing charges.
- Open Access— free for readers, with article processing charges (APC) paid by authors or their institutions.
- High Visibility: indexed within Scopus, SCIE (Web of Science), Inspec, and other databases.
- Journal Rank: JCR - Q1 (Engineering, Aerospace) / CiteScore - Q2 (Aerospace Engineering)
- Rapid Publication: manuscripts are peer-reviewed and a first decision is provided to authors approximately 22.3 days after submission; acceptance to publication is undertaken in 2.7 days (median values for papers published in this journal in the second half of 2023).
- Recognition of Reviewers: reviewers who provide timely, thorough peer-review reports receive vouchers entitling them to a discount on the APC of their next publication in any MDPI journal, in appreciation of the work done.
- Companion journal: Astronomy.
Impact Factor:
2.6 (2022);
5-Year Impact Factor:
2.6 (2022)
Latest Articles
Gaze Movements of Helicopter Pilots during Real and Simulated Take-Off and Landing Maneuvers
Aerospace 2024, 11(6), 429; https://doi.org/10.3390/aerospace11060429 (registering DOI) - 24 May 2024
Abstract
Most accidents and serious incidents of commercial air transport helicopters occur during standard flight phases, whereby a main cause is pilots’ situational awareness. Enabling pilots to better assess their situational awareness can make an important contribution in reducing the risk of fatal accidents.
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Most accidents and serious incidents of commercial air transport helicopters occur during standard flight phases, whereby a main cause is pilots’ situational awareness. Enabling pilots to better assess their situational awareness can make an important contribution in reducing the risk of fatal accidents. One approach is to examine a pilot’s gaze behavior with the help of eye tracking. This paper reports the results of a case study with eye tracking measurements during real flight and simulator studies of a standard mission profile. The general gaze behavior is characterized by a dominant, external view, and the airspeed and altitude indicator as the most important flight instruments. A real-world applicability of gaze data obtained in the simulator could be shown.
Full article
(This article belongs to the Special Issue Vertical Lift: Rotary- and Flapping-Wing Flight)
Open AccessArticle
Tailoring 3D Star-Shaped Auxetic Structures for Enhanced Mechanical Performance
by
Yulong Wang, Naser A. Alsaleh, Joy Djuansjah, Hany Hassanin, Mahmoud Ahmed El-Sayed and Khamis Essa
Aerospace 2024, 11(6), 428; https://doi.org/10.3390/aerospace11060428 - 24 May 2024
Abstract
Auxetic lattice structures are three-dimensionally designed intricately repeating units with multifunctionality in three-dimensional space, especially with the emergence of additive manufacturing (AM) technologies. In aerospace applications, these structures have potential for use in high-performance lightweight components, contributing to enhanced efficiency. This paper investigates
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Auxetic lattice structures are three-dimensionally designed intricately repeating units with multifunctionality in three-dimensional space, especially with the emergence of additive manufacturing (AM) technologies. In aerospace applications, these structures have potential for use in high-performance lightweight components, contributing to enhanced efficiency. This paper investigates the design, numerical simulation, manufacturing, and testing of three-dimensional (3D) star-shaped lattice structures with tailored mechanical properties. Finite element analysis (FEA) was employed to examine the effect of a lattice unit’s vertex angle and strut diameter on the lattice structure’s Poisson’s ratio and effective elastic modulus. The strut diameter was altered from 0.2 to 1 mm, while the star-shaped vertex angle was adjusted from 15 to 90 degrees. Laser powder bed fusion (LPBF), an AM technique, was employed to experimentally fabricate 3D star-shaped honeycomb structures made of Ti6Al4V alloy, which were then subjected to compression testing to verify the modelling results. The effective elastic modulus was shown to decrease when increasing the vertex angle or decreasing the strut diameter, while the Poisson’s ratio had a complex behaviour depending on the geometrical characteristics of the structure. By tailoring the unit vertex angle and strut diameter, the printed structures exhibited negative, zero, and positive Poisson’s ratios, making them applicable across a wide range of aerospace components such as impact absorption systems, aircraft wings, fuselage sections, landing gear, and engine mounts. This optimization will support the growing demand for lightweight structures across the aerospace sector.
Full article
Open AccessArticle
Solar Sail Optimal Performance in Heliocentric Nodal Flyby Missions
by
Giovanni Mengali, Marco Bassetto and Alessandro A. Quarta
Aerospace 2024, 11(6), 427; https://doi.org/10.3390/aerospace11060427 - 24 May 2024
Abstract
Solar sails are propellantless propulsion systems that extract momentum from solar radiation pressure. They consist of a large ultrathin membrane, typically aluminized, that reflects incident photons from the Sun to generate thrust for space navigation. The purpose of this study is to investigate
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Solar sails are propellantless propulsion systems that extract momentum from solar radiation pressure. They consist of a large ultrathin membrane, typically aluminized, that reflects incident photons from the Sun to generate thrust for space navigation. The purpose of this study is to investigate the optimal performance of a solar sail-based spacecraft in performing two-dimensional heliocentric transfers to inertial points on the ecliptic that lie within an assigned annular region centered in the Sun. Similar to ESA’s Comet Interceptor mission, this type of transfer concept could prove useful for intercepting a potential celestial body, such as a long-period comet, that is passing close to Earth’s orbit. Specifically, it is assumed that the solar sail transfer occurs entirely in the ecliptic plane and, in analogy with recent studies, the flyby points explored are between and from the Sun. The heliocentric dynamics of the solar sail is described using the classical two-body model, assuming the spacecraft starts from Earth orbit (assumed circular), and an ideal force model to express the sail thrust vector. Finally, no constraint is imposed on the arrival velocity at flyby. Numerical simulation results show that solar sails are an attractive option to realize these specific heliocentric transfers.
Full article
(This article belongs to the Special Issue Spacecraft Orbit Transfers)
Open AccessArticle
An Engine Deterioration Model for Predicting Fuel Consumption Impact in a Regional Aircraft
by
Manuel de Jesús Gurrola Arrieta, Ruxandra M. Botez and Axel Lasne
Aerospace 2024, 11(6), 426; https://doi.org/10.3390/aerospace11060426 - 24 May 2024
Abstract
A deterioration cycle model is presented, designed to consider the turbomachinery efficiency losses that are expected during real engine in-service operations. The cycle model was developed using information from practical experience found in the literature to account for both short- and long-term deterioration
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A deterioration cycle model is presented, designed to consider the turbomachinery efficiency losses that are expected during real engine in-service operations. The cycle model was developed using information from practical experience found in the literature to account for both short- and long-term deterioration effects; the former occurring during the first flight cycles, the latter due to regular in-service operation. This paper highlights the importance of analyzing the inter-turbine temperature margin () to track engine deterioration to determine the extent of an in-service engine life. The proposed model was used to assess the and fuel consumption impact in the CRJ-700 regional aircraft (powered by two CF34-8C5B1 engines) for three representative missions: short (0.4 h), average (1.4 h), and long (2.5 h), considering different levels of engine deterioration, from the new engine level up to fully deteriorated. The fuel consumption at the new engine level (zero deterioration) was validated against a real-time engine model embedded in a Level-D flight simulator, the so-called Virtual Research Flight Simulator located at the Laboratory of Applied Research in Active Control, Avionics, and AeroServoElasticity. The errors found in this validation for the trip mission fuel consumption in the short, average, and long missions were −3.6, +0.9, and +0.6%, respectively. The cycle model predictions suggest the for a new engine is 55.2 °C, whereas for a fully deteriorated engine, it is 26.4 °C. Finally, in terms of fuel consumption, the results presented here show that an average CF34-8C5B1 engine shows an increase in the cumulative fuel consumption of 2.25% during its life in service, which translates to a 4.5% impact in aircraft fuel consumption.
Full article
(This article belongs to the Section Aeronautics)
Open AccessArticle
Flutter Characteristics of a Modified Z-Shaped Folding Wing Using a New Non-Intrusive Model
by
Wuchao Qi, Shimiao Wu and Sumei Tian
Aerospace 2024, 11(6), 425; https://doi.org/10.3390/aerospace11060425 - 24 May 2024
Abstract
Unmanned aerial vehicles (UAVs) with folding wings can serve in multiple mission profiles, usually accompanied by sudden changes in flight speed. These bring great challenges to the aeroelastic design of UAVs, especially in the calculation of flutter characteristics. This paper developed a new
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Unmanned aerial vehicles (UAVs) with folding wings can serve in multiple mission profiles, usually accompanied by sudden changes in flight speed. These bring great challenges to the aeroelastic design of UAVs, especially in the calculation of flutter characteristics. This paper developed a new non-intrusive aeroelastic model to quickly calculate the flutter characteristics of Z-shaped folding wings at different folding angles. First, the original Z-shaped folding wing was designed to be enhanced. Beams and ribs were arranged inside each wing segment to enhance the structural strength performance. Control surfaces were arranged in the middle-wing and outer-wing to enhance the aerodynamic control performance. Second, a parametric aeroelastic model at any folding angle was reconstructed based on the input file of Nastran software for the flutter calculation of the folding wing in the unfolded state. Finally, the effects of parameters such as folding angle, hinge stiffness between different wing segments, and hinge stiffness of the control surfaces on the flutter characteristics of the folding wing were investigated. The results show that the enhancement scheme could significantly increase the flutter speed and flutter frequency of the folding wing. The hinge stiffness between each wing segment had a significant impact on the flutter characteristics of the folding wing, but flutter at the control surface basically did not occur.
Full article
(This article belongs to the Special Issue Active Flutter Suppression and Gust Load Alleviation)
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Open AccessArticle
Design and Analysis of Low-Gravity Simulation Scheme for Mars Ascent Vehicle
by
Chen Li, Huijuan Wang, Zhicheng Hu, Chen Wang and Jinbao Chen
Aerospace 2024, 11(6), 424; https://doi.org/10.3390/aerospace11060424 - 23 May 2024
Abstract
The sample carried back by the Mars Ascent Vehicle (MAV) is a potential flagship mission of deep space exploration in recent years. A low-gravity simulation experiment is an effective method and a necessary stage for verifying the performance of the MAV launch dynamic
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The sample carried back by the Mars Ascent Vehicle (MAV) is a potential flagship mission of deep space exploration in recent years. A low-gravity simulation experiment is an effective method and a necessary stage for verifying the performance of the MAV launch dynamic in Earth’s gravity. In this paper, the uniqueness of low-gravity simulation is illustrated by the classical pulley balance method for the high dynamic process of a test model of the MAV. Its movement direction is the same as the compensation force, which leads to the relaxation of the sling and the failure of the compensation force in traditional cable suspension. Here, three cable suspension schemes including an improved pulley balancing scheme based on a coordinate transformation scheme and based on a dynamic pulley group scheme are proposed. For the actual launch condition of the MAV, the motion state of the ascent under the schemes and the real Mars launch are compared, which proves the feasibility of the schemes. Among them, the improved pulley balancing scheme has the best gravity compensation effect, and the error between the average value and the required value is the smallest, only 1%.
Full article
(This article belongs to the Section Aeronautics)
Open AccessArticle
A Multisubstructure-Based Method for the Assessment of Displacement and Stress in a Fluid–Structure Interaction Framework
by
Changchuan Xie, Kunhui Huang, Yang Meng, Nongyue Gao and Zhitao Zhang
Aerospace 2024, 11(6), 423; https://doi.org/10.3390/aerospace11060423 - 23 May 2024
Abstract
A multisubstructure-based method for assessing the deformation and stress of a fine-meshed model according to a coarse model was proposed. Integrating boundary conditions in a local fine-meshed model, a displacement mapping matrix from the coarse model to the fine-meshed model was constructed. The
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A multisubstructure-based method for assessing the deformation and stress of a fine-meshed model according to a coarse model was proposed. Integrating boundary conditions in a local fine-meshed model, a displacement mapping matrix from the coarse model to the fine-meshed model was constructed. The method was verified by a three-level panel in a fluid–structure interaction (FSI) framework by integrating the steady vortex lattice method (VLM). A comparison between the inner deformation distribution of the coarse model and that of the global fine-meshed model obtained from MSC.Nastran was carried out, and the results showed that the coarse model failed to demonstrate reliable strains and stresses. In contrast, the proposed method in this paper can effectively depict the inner deformation and critical stress distribution. The deformation error was lower than 8%, meeting engineering requirements. Moreover, the results of different working conditions can achieve a similar relative error of displacement for an identical position. The easy storage of the displacement mapping matrix and the convenience of the boundary information transformation among all substructure levels are prominent aspects. As a result, there is a solid foundation for addressing the time-dependent problem in spite of the simultaneity and region.
Full article
(This article belongs to the Special Issue Multiscale Modelling in Aerospace Engineering)
Open AccessArticle
Enhancing Flow Separation Control Using Hybrid Passive and Active Actuators in a Matrix Configuration
by
Songqi Li and Ping Zhang
Aerospace 2024, 11(6), 422; https://doi.org/10.3390/aerospace11060422 - 23 May 2024
Abstract
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Efficient control of flow separation holds significant economic promise. This study investigates flow separation mitigation using an experimental platform featuring a combination of passive and active actuators arranged in a matrix configuration. The platform consists of 5 × 6 hybrid actuator units, each
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Efficient control of flow separation holds significant economic promise. This study investigates flow separation mitigation using an experimental platform featuring a combination of passive and active actuators arranged in a matrix configuration. The platform consists of 5 × 6 hybrid actuator units, each integrating a height-adjustable vortex generator and a micro-jet actuator. Inspired by the distributed pattern of V-shaped scales on shark skin, these actuator units are strategically deployed in a matrix configuration to reduce flow separation on a backward-facing ramp. Distributed pressure taps encircling the hybrid actuators monitor the flow state. Parametric analyses examine the effect of different control strategies. By adopting appropriate passive and active actuation patterns, effective pressure recovery on the ramp surface can be achieved. The most significant flow control outcome occurs when the actuators operate under combined active and passive excitation, harnessing the benefits of both control strategies. Particle image velocimetry (PIV) results confirm a notable reduction in flow separation under the best-controlled case. These findings suggest a promising future for flow control devices employing combined passive and active actuation in matrix-like configurations.
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Open AccessArticle
Investigation of Spray Characteristics for Detonability: A Study on Liquid Fuel Injector and Nozzle Design
by
Myeung Hwan Choi, Yoojin Oh and Sungwoo Park
Aerospace 2024, 11(6), 421; https://doi.org/10.3390/aerospace11060421 - 23 May 2024
Abstract
Detonation engines are gaining prominence as next-generation propulsion systems that can significantly enhance the efficiency of existing engines. This study focuses on developing an injector utilizing liquid fuel and a gas oxidizer for application in detonation engines. In order to better understand the
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Detonation engines are gaining prominence as next-generation propulsion systems that can significantly enhance the efficiency of existing engines. This study focuses on developing an injector utilizing liquid fuel and a gas oxidizer for application in detonation engines. In order to better understand the spray characteristics suitable for the pulse detonation engine (PDE) system, an injector was fabricated by varying the Venturi nozzle exit diameter ratio and the geometric features of the fuel injection hole. Analysis of high-speed camera images revealed that the Venturi nozzle exit diameter ratio plays a crucial role in determining the characteristics of air-assist or air-blast atomization. Under the conditions of an exit diameter ratio of Re/Ri = 1.0, the formation of a liquid film at the exit was observed, and it was identified that the film’s length is influenced by the geometric characteristics of the fuel injection hole. The effect of the fuel injection hole and Venturi nozzle exit diameter ratio on SMD was analyzed by using droplet diameter measurement. The derived empirical correlation indicates that the atomization mechanism varies depending on the Venturi nozzle exit diameter ratio, and it also affects the distribution of SMD. The characteristics of the proposed injector, its influence on SMD, and its velocity, provide essential groundwork and data for the design of detonation engines employing liquid fuel.
Full article
(This article belongs to the Special Issue Supersonic Combustion in Scramjet Engine)
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Open AccessArticle
Constrained Parameterized Differential Dynamic Programming for Waypoint-Trajectory Optimization
by
Xiaobo Zheng, Feiran Xia, Defu Lin, Tianyu Jin, Wenshan Su and Shaoming He
Aerospace 2024, 11(6), 420; https://doi.org/10.3390/aerospace11060420 - 22 May 2024
Abstract
Unmanned aerial vehicles (UAVs) are required to pass through multiple important waypoints as quickly as possible in courier delivery, enemy reconnaissance and other tasks to eventually reach the target position. There are two important problems to be solved in such tasks: constraining the
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Unmanned aerial vehicles (UAVs) are required to pass through multiple important waypoints as quickly as possible in courier delivery, enemy reconnaissance and other tasks to eventually reach the target position. There are two important problems to be solved in such tasks: constraining the trajectory to pass through intermediate waypoints and optimizing the flight time between these waypoints. A constrained parameterized differential dynamic programming (C-PDDP) algorithm is proposed for meeting multiple waypoint constraints and free-time constraints between waypoints to deal with these two issues. By considering the intermediate waypoint constraints as a kind of path state constraint, the penalty function method is adopted to constrain the trajectory to pass through the waypoints. For the free-time constraints, the flight times between waypoints are converted into time-invariant parameters and updated at the trajectory instants corresponding to the waypoints. The effectiveness of the proposed C-PDDP algorithm under waypoint constraints and free-time constraints is verified through numerical simulations of the UAV multi-point reconnaissance problem with five different waypoints. After comparing the proposed algorithm with fixed-time constrained DDP (C-DDP), it is found that C-PDDP can optimize the flight time of the trajectory with three segments to 7.35 s, 9.50 s and 6.71 s, respectively. In addition, the maximum error of the optimized trajectory waypoints of the C-PDDP algorithm is 1.06 m, which is much smaller than that (7 m) of the C-DDP algorithm used for comparison. A total of 500 Monte Carlo tests were simulated to demonstrate how the proposed algorithm remains robust to random initial guesses.
Full article
(This article belongs to the Topic Target Tracking, Guidance, and Navigation for Autonomous Systems, 2nd Edition)
Open AccessArticle
Rigid–Flexible Coupling Dynamics Analysis of Coordination Arm and Application of a New Directional Subinterval Uncertainty Analysis Method
by
Xuan Gao, Longmiao Chen and Jingsong Tang
Aerospace 2024, 11(6), 419; https://doi.org/10.3390/aerospace11060419 - 22 May 2024
Abstract
Cartridge delivery systems are commonly employed in aerospace engineering for the transportation of cylindrical projectiles. The coordination mechanism plays a pivotal role in ensuring reliable cartridge conveying, with its positioning accuracy being of utmost importance. However, accurately depicting the nonlinear relationship between input
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Cartridge delivery systems are commonly employed in aerospace engineering for the transportation of cylindrical projectiles. The coordination mechanism plays a pivotal role in ensuring reliable cartridge conveying, with its positioning accuracy being of utmost importance. However, accurately depicting the nonlinear relationship between input parameters and output response is challenging due to the involvement of numerous complex, uncertain factors during the movement process of the coordination mechanism. To address this issue, this study proposes a dynamics model that incorporates hinged gaps to represent rigid–flexible coupling within the coordination mechanism. Experimental validation confirms its effectiveness, while computational efficiency is enhanced through the utilization of a deep learning neural network surrogate model. Furthermore, an improved method for the uncertainty analysis of directional subintervals is introduced and applied to analyze uncertainty in coordination mechanisms, yielding results that demonstrate superior efficiency compared to other approaches.
Full article
(This article belongs to the Topic Uncertainty Quantification in Design, Manufacturing and Maintenance of Complex Systems)
Open AccessArticle
Numerical Investigation of the Vortex Ring Phenomena in Rotorcraft
by
Vytautas Rimša and Mykolas Liugas
Aerospace 2024, 11(6), 418; https://doi.org/10.3390/aerospace11060418 - 22 May 2024
Abstract
Due to their complex aerodynamics, helicopters may enter different dangerous aerodynamic conditions under certain adverse circumstances. In this paper, we examine one such phenomenon—the Vortex Ring State (VRS). We present a simulation of the formation and evolution of a vortex ring around a
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Due to their complex aerodynamics, helicopters may enter different dangerous aerodynamic conditions under certain adverse circumstances. In this paper, we examine one such phenomenon—the Vortex Ring State (VRS). We present a simulation of the formation and evolution of a vortex ring around a helicopter’s main rotor. The calculations were carried out by solving Navier–Stokes equations using the Ansys CFX code. The simulations modeled a real helicopter using the rotor wing concept, assuming that only the main rotor blade’s geometry was modeled. A sensitivity study assessed the impact of the calculation domain and mesh size on main rotor thrust and required moment parameters. Simulations were conducted to determine the VRS region by observing the transition of the helicopter from a level flight, with the main rotor blades held at a fixed pitch position, to a gradual increase in vertical descent. The VRS region was compared with experimental results obtained from other authors, revealing sufficient coincidences. The main characteristics of the identified region were then described.
Full article
(This article belongs to the Special Issue Advances in Rotorcraft Dynamics)
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Open AccessArticle
Crater Triangle Matching Algorithm Based on Fused Geometric and Regional Features
by
Mingda Jin and Wei Shao
Aerospace 2024, 11(6), 417; https://doi.org/10.3390/aerospace11060417 - 21 May 2024
Abstract
Craters are regarded as significant navigation landmarks during the descent and landing process in small body exploration missions for their universality. Recognizing and matching craters is a crucial prerequisite for visual and LIDAR-based navigation tasks. Compared to traditional algorithms, deep learning-based crater detection
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Craters are regarded as significant navigation landmarks during the descent and landing process in small body exploration missions for their universality. Recognizing and matching craters is a crucial prerequisite for visual and LIDAR-based navigation tasks. Compared to traditional algorithms, deep learning-based crater detection algorithms can achieve a higher recognition rate. However, matching crater detection results under various image transformations still poses challenges. To address the problem, a composite feature-matching algorithm that combines geometric descriptors and region descriptors (extracting normalized region pixel gradient features as feature vectors) is proposed. First, the geometric configuration map is constructed based on the crater detection results. Then, geometric descriptors and region descriptors are established within each feature primitive of the map. Subsequently, taking the salience of geometric features into consideration, composite feature descriptors with scale, rotation, and illumination invariance are generated through fusion geometric and region descriptors. Finally, descriptor matching is accomplished by computing the relative distances between descriptors and adhering to the nearest neighbor principle. Experimental results show that the composite feature descriptor proposed in this paper has better matching performance than only using shape descriptors or region descriptors, and can achieve a more than 90% correct matching rate, which can provide technical support for the small body visual navigation task.
Full article
(This article belongs to the Special Issue Space Navigation and Control Technologies)
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Open AccessArticle
Design and Analysis of the Integrated Drag-Free and Attitude Control System for TianQin Mission: A Preliminary Result
by
Liwei Hao and Yingchun Zhang
Aerospace 2024, 11(6), 416; https://doi.org/10.3390/aerospace11060416 - 21 May 2024
Abstract
This article explores novel in-orbit drag-free technology that can be utilized for deep space detection scientific missions. In this study, we considered a two-test-mass drag-free method and analyzed the design of the drag-free and attitude control system for the TianQin mission. The entire
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This article explores novel in-orbit drag-free technology that can be utilized for deep space detection scientific missions. In this study, we considered a two-test-mass drag-free method and analyzed the design of the drag-free and attitude control system for the TianQin mission. The entire control system was comprehensively designed, including an actuator allocation design and controllers for two test masses and one spacecraft, with a total of 18 degrees of freedom. Furthermore, stability analysis was conducted. Based on our design, numerical analysis and simulations were performed assuming geocentric orbit conditions in the TianQin mission, confirming the feasibility of this aerospace engineering concept. The versatility of the design allows for its application to scientific observations across various disciplines by modifying the structure of the simulation environment, and consequently, the approach discussed in this study holds significant practical implications for effectively accomplishing deep space observation tasks.
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(This article belongs to the Special Issue Space Systems Preliminary Design)
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Towards Global Explainability of Artificial Intelligence Agent Tactics in Close Air Combat
by
Emre Saldiran, Mehmet Hasanzade, Gokhan Inalhan and Antonios Tsourdos
Aerospace 2024, 11(6), 415; https://doi.org/10.3390/aerospace11060415 - 21 May 2024
Abstract
In this paper, we explore the development of an explainability system for air combat agents trained with reinforcement learning, thus addressing a crucial need in the dynamic and complex realm of air combat. The safety-critical nature of air combat demands not only improved
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In this paper, we explore the development of an explainability system for air combat agents trained with reinforcement learning, thus addressing a crucial need in the dynamic and complex realm of air combat. The safety-critical nature of air combat demands not only improved performance but also a deep understanding of artificial intelligence (AI) decision-making processes. Although AI has been applied significantly to air combat, a gap remains in comprehensively explaining an AI agent’s decisions, which is essential for their effective integration and for fostering trust in their actions. Our research involves the creation of an explainability system tailored for agents trained in an air combat environment. Using reinforcement learning, combined with a reward decomposition approach, the system clarifies the agent’s decision making in various tactical situations. This transparency allows for a nuanced understanding of the agent’s behavior, thereby uncovering their strategic preferences and operational patterns. The findings reveal that our system effectively identifies the strengths and weaknesses of an agent’s tactics in different air combat scenarios. This knowledge is essential for debugging and refining the agent’s performance and to ensure that AI agents operate optimally within their intended contexts. The insights gained from our study highlight the crucial role of explainability in improving the integration of AI technologies within air combat systems, thus facilitating more informed tactical decisions and potential advancements in air combat strategies.
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(This article belongs to the Section Aeronautics)
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Structural Strength Analysis and Optimization of Commercial Aircraft Nose Landing Gear under Towing Taxi-Out Conditions Using Finite Element Simulation and Modal Testing
by
Qiwei Lin, Chang Yang, Yuhao Bai and Jiahao Qin
Aerospace 2024, 11(5), 414; https://doi.org/10.3390/aerospace11050414 - 20 May 2024
Abstract
In the field of civil aviation, the nose landing gear is a critical component that is prone to damage during taxiing. With the advent of new technologies such as towing taxi-out and hub motors, the nose landing gear faces increasingly complex operational environments,
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In the field of civil aviation, the nose landing gear is a critical component that is prone to damage during taxiing. With the advent of new technologies such as towing taxi-out and hub motors, the nose landing gear faces increasingly complex operational environments, thereby imposing higher performance demands. Ensuring the structural safety of the nose landing gear is fundamental for the successful application of these technologies. However, current research on aircraft nose landing gear under these new conditions is somewhat lacking, particularly in terms of reliable analysis models for real-world scenarios. This study focuses on a typical Class C aircraft, specifically the B-727 model, for which a finite element model of the nose landing gear is developed. Modal testing of the aircraft’s nose landing gear is conducted using the impact hammer method, and the results are compared with those from the simulations. The experimental data indicate that the error range for the first seven natural frequencies is between 0.23% and 9.27%, confirming the high accuracy of the developed landing gear model. Furthermore, with towing taxi-out as the primary scenario, a dynamic model of the aircraft towing system is established, and an analysis on the structural strength and topological optimization of the nose landing gear under various conditions, including high speeds and heavy loads, is performed. The results show that the developed model can effectively support the analysis and prediction of the mechanical behavior of the nose landing gear. Under high-speed, heavy-load conditions, the nose landing gear experiences significantly increased loads, with the maximum deformation primarily occurring at the lower section of the shock strut’s outer cylinder. However, no damage occurred. Additionally, under these conditions, an optimized structural design for the landing gear was identified, which, while ensuring structural strength, achieves a 22.32% reduction in the mass of the outer cylinder, also ensuring safety in towing taxi-out conditions.
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(This article belongs to the Special Issue Recent Advances in Flight Testing)
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Refined Aircraft Positioning Based on Stochastic Hybrid Estimation with Adaptive Square-Root Unscented Particle Filtering
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Yangyang Zhang, Zhenxing Gao, Kai Qi and Jiawei Li
Aerospace 2024, 11(5), 413; https://doi.org/10.3390/aerospace11050413 - 20 May 2024
Abstract
The positioning of civil aviation aircraft relative to a geographic reference point on Earth in a Cartesian frame is significant to detect the deviations from the desired path, especially for high-altitude airports or special airports based on performance-based navigation (PBN). To obtain these
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The positioning of civil aviation aircraft relative to a geographic reference point on Earth in a Cartesian frame is significant to detect the deviations from the desired path, especially for high-altitude airports or special airports based on performance-based navigation (PBN). To obtain these critical deviations during aircraft approach and landing, it is fundamental to estimate the continuous flight variables and discrete flight modes simultaneously with enough accuracy. With the coordinate conversion between the North, East, and Down (NED) frame and the geographic coordinate system based on World Geodetic System 1984 (WGS-84) considered, this study proposed a non-linear stochastic hybrid estimation algorithm with adaptive square-root unscented particle filtering (ASR-UPF) to estimate the true path. The probabilities of mode transition, represented by the normal cumulative density function of continuous states, determine whether to proceed with mode transitions. In addition, the adaptive update characterized by tracking variable noise and the importance sampling distributions based on the results of square-root unscented Kalman filtering (SR-UKF), as a comparative study of continuous system filtering, were used. The experiments illustrated the ASR-UPF is able to reduce the state estimation error more effectively, and more promptly track the error caused by incorrect mode estimation with adaptability compared to the SR-UKF. A further test with real flight data indicates that the proposed method gives the refined estimation of position and azimuth in NED frame.
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(This article belongs to the Section Aeronautics)
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Open AccessArticle
The Impact of Upstream Static Deformation on Flow Past a Cylinder/Flare
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Aaron Becks, Tyler Korenyi-Both, Jack J. McNamara and Datta V. Gaitonde
Aerospace 2024, 11(5), 412; https://doi.org/10.3390/aerospace11050412 - 20 May 2024
Abstract
Reynolds-averaged Navier–Stokes simulations are performed for supersonic turbulent flow over a cylinder/flare with upstream surface distortion representative of structural deformation induced via fluid–structural and fluid–thermal–structural behavior. Broad parametric analysis is carried out through the generation of Kriging-response surfaces from a database of general
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Reynolds-averaged Navier–Stokes simulations are performed for supersonic turbulent flow over a cylinder/flare with upstream surface distortion representative of structural deformation induced via fluid–structural and fluid–thermal–structural behavior. Broad parametric analysis is carried out through the generation of Kriging-response surfaces from a database of general simulations. A posteriori simulations are then carried out at parametric combinations that correspond to extrema in the Kriging response surfaces to gain deeper insights into the interaction between the surface distortion and flow responses. Upstream distortions tend to decrease, rather than increase, the peak pressure and heat flux loads on the flare compared to an undeformed cylinder. Furthermore, decreases in these quantities reach up to O(10%) compared to up to O(1%) for increases. Integrated quantities over the flare are relatively insensitive to upstream distortion. The corner separation length is the most sensitive quantity to upstream distortion, with protrusions tending to increase the separation length and recessions reducing the separation length. Modifications in the separation length of up to 40% are observed. Reductions in peak loads tend to correspond to increases in the corner separation length. The movement of the surface distortion relative to the corner indicates a negligible impact beyond 1.5 distortion lengths from the corner, and the largest impact on the corner separation length occurs when distortion is directly adjacent. These results are an important step toward understanding and quantifying the impact of surface deformations on downstream components.
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(This article belongs to the Special Issue Flight at Supersonic and Hypersonic Velocities: Aerodynamics, Flow Control, Propulsion)
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Open AccessArticle
A Framework for Rapidly Predicting the Dynamics of Flexible Solar Arrays in the China Space Station with a Verification Based on On-Orbit Measurement Data
by
Song Wu, Han Yan, Yuzhen Zhao, Yanhao Chen and Guoan Tang
Aerospace 2024, 11(5), 411; https://doi.org/10.3390/aerospace11050411 - 20 May 2024
Abstract
The Chinese space station is a complex structure with large flexible appendages. Obtaining the on-orbit response characteristics of such a structure under different working conditions is a traditional and classic challenge in the field of dynamics. To address the on-orbit dynamics of the
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The Chinese space station is a complex structure with large flexible appendages. Obtaining the on-orbit response characteristics of such a structure under different working conditions is a traditional and classic challenge in the field of dynamics. To address the on-orbit dynamics of the China Space Station, the basic equations for dynamic reduction, assembly and data recovery of linear and nonlinear substructures are derived based on the reduction and recovery theory, and a fast coupling analysis framework for flexible systems with nonlinear attachments is formed. This coupling analysis framework is adopted to quickly acquire the dynamic response of the China Space Station during in-orbit operation, thereby guiding the design. Taking SZ-15 radial docking to the Chinese Space Station as the object, the substructure of six nonlinear flexible arrays is reduced, the full flexible dynamic equation of the space station is assembled, and the response of each part of the flexible wing during the docking process is analyzed and recovered. By designing a reasonable and reliable flexible wing test scheme in-orbit, the acceleration at the root and top of the flexible wing during the docking of SZ-15 is obtained. The measured data in-orbit show that the acceleration analysis results of the typical parts of the flexible wing have a good agreement, which verifies the correctness of the fast coupling analysis framework of the flexible system. Hence, the dynamic coupling characteristics analysis of the main structure of the space station and the flexible wing based on this method can better guide the rationality of the design of the dynamic characteristics of the Chinese Space Station.
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(This article belongs to the Section Astronautics & Space Science)
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Open AccessArticle
Experimental Investigation of Solid Rocket Scramjet Based on Central Strut
by
Jia Zeng, Guohui Wang, Hui Huang, Jian Fan and Haosu Wang
Aerospace 2024, 11(5), 410; https://doi.org/10.3390/aerospace11050410 - 19 May 2024
Abstract
Scramjet based on solid propellant has become a potential choice for the development of future hypersonic vehicles. In this paper, a boron-containing solid rocket scramjet based on the central strut injection was proposed, and the ground direct-connect experiment with the equivalence ratios of
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Scramjet based on solid propellant has become a potential choice for the development of future hypersonic vehicles. In this paper, a boron-containing solid rocket scramjet based on the central strut injection was proposed, and the ground direct-connect experiment with the equivalence ratios of 0.43 to 2.4 under the flight condition of Mach 6, 25 km was carried out. The pressure and flow rate over time were measured in the experiment. The results show that the engine can realize stable supersonic mode or subsonic mode combustion by changing the gas flow rate. The engine can effectively increase the combustor pressure, reduce the unstable combustion time, and advance the strong combustion position by increasing the gas flow rate. The engine achieved high combustion efficiency when the equivalence ratio was about 1, with a maximum of 88.28%. A numerical simulation analysis was also carried out in this paper. Compared to the experimental results, the pressure error obtained by numerical simulation was less than 4%, and the typical position error was less than 3%, suggesting that the simulation model can be used to predict the behavior of scramjet.
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(This article belongs to the Special Issue Advanced Chemical Propulsion and Electric Propulsion)
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