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Volume 11
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Aerospace, Volume 11, Issue 12 (December 2024) – 45 articles

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16 pages, 690 KiB  
Article
Characterization of an Ignition System for Nitromethane-Based Monopropellants
by Maxim Kurilov, Christoph U. Kirchberger and Stefan Schlechtriem
Aerospace 2024, 11(12), 1001; https://doi.org/10.3390/aerospace11121001 (registering DOI) - 3 Dec 2024
Abstract
This paper presents the results of a hot-fire test campaign aimed at characterizing a newly developed ignition system for nitromethane-based green monopropellants. Nitromethane-based propellants are a cost-effective replacement for hydrazine and energetic ionic liquid hydrazine alternatives such as LMP-103S and ASCENT. The developed [...] Read more.
This paper presents the results of a hot-fire test campaign aimed at characterizing a newly developed ignition system for nitromethane-based green monopropellants. Nitromethane-based propellants are a cost-effective replacement for hydrazine and energetic ionic liquid hydrazine alternatives such as LMP-103S and ASCENT. The developed system uses a glow plug as the ignition source. Additionally, gaseous oxygen is injected simultaneously into the combustion chamber at the beginning of a firing. After closing the oxygen valve, a pure monopropellant operation follows. Three test series were carried out using NMP-001, a previously characterized nitromethane-based monopropellant. During the first test series, the required ROF for ignition was identified to be above 0.3. In the second test series, the low-pressure combustion limit was shown to be 13.9 bar, which is significantly lower than the 30 bar limit of heritage nitromethane-based monopropellants. In the third test series, the oxygen injection timing was optimized to minimize the required amount of oxygen for successful ignition to 1.5 g per ignition in this test setup. This approach to ignition is more cost effective than the catalytic initiation used for other monopropellants because neither costly precious-metal catalytic materials nor lengthy preheating procedures are required. Full article
(This article belongs to the Special Issue Green Propellants for In-Space Propulsion)
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24 pages, 6066 KiB  
Article
Three-Dimensional Event-Triggered Predefined-Time Cooperative Guidance Law
by Dingye Zhang, Hang Yu, Keren Dai, Wenjun Yi, He Zhang, Jun Guan and Shusen Yuan
Aerospace 2024, 11(12), 999; https://doi.org/10.3390/aerospace11120999 (registering DOI) - 2 Dec 2024
Viewed by 210
Abstract
To address the problem of multiple missiles attacking a maneuvering target simultaneously in three-dimensional space, we propose a new predefined-time cooperative guidance law based on an event-triggered mechanism. The settling time of the system states under this guidance law is independent of the [...] Read more.
To address the problem of multiple missiles attacking a maneuvering target simultaneously in three-dimensional space, we propose a new predefined-time cooperative guidance law based on an event-triggered mechanism. The settling time of the system states under this guidance law is independent of the initial states, and the upper bound of the settling time can be directly set by the explicit parameters in the guidance law. Firstly, the time-to-go estimate is taken as a consistency variable, and the communication failure and time-delay that are easily encountered during the communication process are taken into account; the event-triggered mechanism is introduced into the guidance law along the line of sight (LOS) direction, and the event-triggered threshold is given. Then, a predefined-time extended state observer is used to accurately estimate disturbances. In addition, the stability of the proposed guidance laws along and perpendicular to the LOS direction is proven by the Lyapunov theory. Finally, the superiority of the proposed guidance law introducing the event-triggered mechanism in reducing energy consumption and its effectiveness in encountering communication failure and time-delay are verified through simulations. Full article
(This article belongs to the Section Aeronautics)
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28 pages, 37860 KiB  
Article
Study on Novel Radar Absorbing Grilles of Aircraft Engine Inlet Based on Metasurface Design Theory
by Xufei Wang, Yongqiang Shi, Qingzhen Yang, Huimin Xiang and Jin Bai
Aerospace 2024, 11(12), 998; https://doi.org/10.3390/aerospace11120998 (registering DOI) - 2 Dec 2024
Viewed by 218
Abstract
In modern warfare, the advancement of low detectable technology has made the reduction of an aircraft radar cross section (RCS) crucial for survivability, while engine inlets significantly impact the overall detectability index as major forward scattering sources. Inspired by radar absorbing structures (RASs) [...] Read more.
In modern warfare, the advancement of low detectable technology has made the reduction of an aircraft radar cross section (RCS) crucial for survivability, while engine inlets significantly impact the overall detectability index as major forward scattering sources. Inspired by radar absorbing structures (RASs) based on metasurface theory, as well as the spoof surface plasmon polariton (SSPP) theory, this paper proposes a comprehensive design of radar absorbing grilles (RAGs) which are installed at the inlet aperture of the aircraft intake, where RAGs allow airflow to cross through and absorb the detecting radar wave. To enhance the ability of electromagnetic wave attenuation, an indium tin oxide (ITO) film is added in the middle of the RAGs to change the impedance characteristics. This study clarifies the mechanism influencing radar wave absorption characteristics through design parameters (unit length and sheet resistance) and radar characteristic parameters (frequency, incident angle, and polarization mode). The absorption peak gradually shifts towards lower frequencies with the increase in unit length from 8 to 16 mm of the grille. The integrated average absorption first increases and then decreases with the increase in sheet resistance from 100 to 800 Ω/□ applied as ITO film in the middle of the grille. When the unit length of RAG is 12 mm and 400 Ω/□, the sheet resistance is applied, and a 90% absorption bandwidth is achieved to 100% within the 8–18 GHz band. The 90% absorption bandwidth reaches 72.3% in the 2–18 GHz band while maintaining absorption above 40% in the 2–8 GHz band. The integrated average absorption reaches 0.887, and the 90% absorption bandwidth increases to 255.6% of the original model’s bandwidth. The results indicate that the proposed RAGs based on metasurface exhibit broadband absorption performance and high angular stability, providing technical support for further application of these grilles in aircraft engine inlets. Full article
(This article belongs to the Section Aeronautics)
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23 pages, 3113 KiB  
Article
Allocating New Slots in a Multi-Airport System Based on Capacity Expansion
by Sichen Liu, Shuce Wang, Minghua Hu, Lei Yang, Lei Liu and Yan Wang
Aerospace 2024, 11(12), 1000; https://doi.org/10.3390/aerospace11121000 - 2 Dec 2024
Viewed by 335
Abstract
Over time, the rapid expansion of civil aviation infrastructure has led to the establishment of multi-airport systems (MASs) or Metroplex, where airports situated in close proximity form interconnected networks. Given that individual airport capacities often fall short of meeting flight scheduling demands, devising [...] Read more.
Over time, the rapid expansion of civil aviation infrastructure has led to the establishment of multi-airport systems (MASs) or Metroplex, where airports situated in close proximity form interconnected networks. Given that individual airport capacities often fall short of meeting flight scheduling demands, devising effective multi-airport flight scheduling methods becomes imperative. This article introduces a novel MAS slot expansion configuration framework centered on coupling terminal areas. In contrast to conventional airport capacity slot expansion approaches, this framework demonstrates superior configurational efficacy within respective airport terminal environments. The model outlined in this research identifies the terminal control sector as the pivotal resource node within the interconnected terminal area, aiming to maximize the total expanded slots while minimizing the overall unfairness among airports within the terminal airspace. Employing the ε-constraint method facilitates the transformation of the minimization objective into solvable constraint conditions. Subsequently, leveraging Beijing Metroplex as a case study, the research devises benchmark, single-airport, multi-airport minimum, and multi-airport maximum scenarios to compare and analyze configuration outcomes in terms of key resource allocation impacts and coupled resource utilization efficiencies. Ultimately, employing the AirTOp fast-time simulation model validates each scenario, demonstrating that the proposed configuration method yields reduced delay levels and fewer conflicts in simulation environments. Full article
(This article belongs to the Special Issue Advances in Air Traffic and Airspace Control and Management (2nd Edition))
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17 pages, 2812 KiB  
Article
Neural Field-Based Space Target 3D Reconstruction with Predicted Depth Priors
by Tao Fu, Yu Zhou, Ying Wang, Jian Liu, Yamin Zhang, Qinglei Kong and Bo Chen
Aerospace 2024, 11(12), 997; https://doi.org/10.3390/aerospace11120997 (registering DOI) - 1 Dec 2024
Viewed by 466
Abstract
As space technology advances, an increasing number of spacecrafts are being launched into space, making it essential to monitor and maintain satellites to ensure safe and stable operations. Acquiring 3D information of space targets enables the accurate assessment of their shape, size, and [...] Read more.
As space technology advances, an increasing number of spacecrafts are being launched into space, making it essential to monitor and maintain satellites to ensure safe and stable operations. Acquiring 3D information of space targets enables the accurate assessment of their shape, size, and surface damage, providing critical support for on-orbit service activities. Existing 3D reconstruction techniques for space targets, which mainly rely on laser point cloud measurements or image sequences, cannot adapt to scenarios with limited observation data and viewpoints. We propose a novel method to achieve a high-quality 3D reconstruction of space targets. The proposed approach begins with a preliminary 3D reconstruction using the neural radiance field (NeRF) model, guided by observed optical images of the space target and depth priors extracted from a customized monocular depth estimation network (MDE). A NeRF is then employed to synthesize optical images from unobserved viewpoints. The corresponding depth information for these viewpoints, derived from the same depth estimation network, is integrated as a supervisory signal to iteratively refine the 3D reconstruction. By exploiting MDE and the NeRF, the proposed scheme iteratively optimizes the 3D reconstruction of spatial objects from seen viewpoints to unseen viewpoints. To minimize excessive noise from unseen viewpoints, we also incorporate a confident modeling mechanism with relative depth ranking loss functions. Experimental results demonstrate that the proposed method achieves superior 3D reconstruction quality under sparse input, outperforming traditional NeRF and DS-NeRF models in terms of perceptual quality and geometric accuracy. Full article
(This article belongs to the Section Astronautics & Space Science)
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17 pages, 5693 KiB  
Article
Predesign of a Radial Inflow Turbine That Uses Supercritical Methane for a Mid-Scale Thruster for Upper Stage Application
by Alexandru-Claudiu Cancescu, Daniel-Eugeniu Crunteanu, Anna-Maria Theodora Andreescu and Simona-Nicoleta Danescu
Aerospace 2024, 11(12), 996; https://doi.org/10.3390/aerospace11120996 (registering DOI) - 1 Dec 2024
Viewed by 449
Abstract
The worldwide concern regarding the harmful effects of old polluting and toxic propellants has led to increased interest in new, green propellants and higher efficiency thrusters. This fact requires that a new generation of turbopumps, fit for these propellants, is developed. This paper [...] Read more.
The worldwide concern regarding the harmful effects of old polluting and toxic propellants has led to increased interest in new, green propellants and higher efficiency thrusters. This fact requires that a new generation of turbopumps, fit for these propellants, is developed. This paper focuses on the design of a radial inflow turbine, which was developed to power a single-shaft turbopump system for a 30 kN upper stage expander cycle thruster engine. The objective was to create a high-efficiency, compact, cheap-to-manufacture, 3D-printable turbine suitable to simultaneously power the methane and Oxygen pumps that feed the thruster. The total power consumed by the pumps for which this turbine was designed is 152 kW. The solution proposed in this paper includes measures such as elimination of the bladed diffuser, which was carried out to reduce the weight and the overall dimensions of the turbine. Comparing it with an axial turbine with the same power output, it has lower overall dimensions because it does not require a direction change at the inlet to the turbine bladed components, it does not require a stator to work, and its casing has a conical shape and is not cylindrical like the axial construction one. The proposed design has been analysed by CFD, which revealed that it can power the pumps. Analysis performed in off-design conditions indicated that the turbine has the best efficiency if the rotation speed and mass flow are varied at the same time. A breadboard model of the turbopump for which the turbine in this paper has been designed has been built using plastic and tested at pressures up to 6 bars using compressed air. The results indicate that above 1.5 bars of inlet pressure the turbine can overcome the internal resistances of the components and the rotor starts to spin. No indication of imbalance of the rotor was observed at maximum test pressure. Two configurations of the seals between the turbine and the adjacent pump have been tested, indicating that labyrinth seals must be doubled by floating ring seals. Full article
(This article belongs to the Special Issue Progress in Turbomachinery Technology for Propulsion)
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24 pages, 10035 KiB  
Article
Numerical Study of Supersonic Cavity Flows with Different Turbulent Models
by Hongpeng Liu, Shufan Zou, Fangcheng Shi and Shengye Wang
Aerospace 2024, 11(12), 995; https://doi.org/10.3390/aerospace11120995 (registering DOI) - 1 Dec 2024
Viewed by 380
Abstract
A numerical study of supersonic cavity flows is conducted with different turbulent models, including RANS, LES, DES, DDES, and IDDES. Firstly, a supersonic cavity-ramp flow with Ma∞ = 2.92 is simulated numerically. It shows that the results of DDES and IDDES are [...] Read more.
A numerical study of supersonic cavity flows is conducted with different turbulent models, including RANS, LES, DES, DDES, and IDDES. Firstly, a supersonic cavity-ramp flow with Ma∞ = 2.92 is simulated numerically. It shows that the results of DDES and IDDES are nearly equivalent. The wall skin-friction coefficients obtained by these two models are in better agreement with the experimental measurement than those of DES. The reason is that the RANS region of DDES and IDDES is larger than that of DES, so it produces more turbulence in the near-wall region. In comparison, RANS cannot accurately predict large separation flows. The shear layer’s reattachment point on the ramp predicted by RANS is biased downstream compared to the experimental measurement, making its overall prediction accuracy worse than other models. The results obtained by LES are comparable to those obtained by DDES and IDDES except for the wall skin-friction coefficient, which is much smaller because the grid resolution is not high enough to accurately resolve the near-wall turbulent flow. Secondly, the effect of different aft-wall angles (θ) on the flow characteristics of the supersonic cavity is investigated numerically with IDDES. We find that as θ decreases, the oscillation intensity of the cavity flow continuously decreases. However, the change in cavity drag with θ is non-monotonic, which means that there might be a critical θ at which the drag penalties of a cavity are minimal. Therefore, an optimal design should be achieved when changing θ to control the oscillation intensity of supersonic cavity flows. Full article
(This article belongs to the Section Aeronautics)
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14 pages, 6632 KiB  
Article
Estimating Drone Visual Line-of-Sight Distance Using Machine Learning Approaches
by Gyoubeom Kim, Inje Cho, Junghoi Jin, Keecheon Kim, Shinui Kim and Heejeong Choi
Aerospace 2024, 11(12), 994; https://doi.org/10.3390/aerospace11120994 (registering DOI) - 1 Dec 2024
Viewed by 278
Abstract
In this study, we conducted flight tests to establish a clear standard for the visual line-of-sight (VLOS) distance of drones using machine learning models, as outlined in the Aviation Safety Act. Various machine learning models were applied and compared to predict the VLOS [...] Read more.
In this study, we conducted flight tests to establish a clear standard for the visual line-of-sight (VLOS) distance of drones using machine learning models, as outlined in the Aviation Safety Act. Various machine learning models were applied and compared to predict the VLOS distance based on flight data. The analysis revealed that factors such as flight altitude, drone size, and observer’s vision significantly influence the VLOS distance. In particular, drone volume and observer’s vision were identified as the most important factors in predicting VLOS distance. The Random Forest Regression model demonstrated the best predictive performance, followed by the Polynomial Regression model. This study provides fundamental data to ensure safe drone operations and compliance with aviation regulations. The findings can also serve as practical resources for drone operators in planning safe flights. Future works should focus on collecting data from diverse environmental conditions to improve the generalization of prediction models. Additional research is also needed on beyond visual line-of-sight (BVLOS) and night flights, as these are critical areas for drone commercialization and require new predictive models and technological advancements to ensure safety. Full article
(This article belongs to the Section Aeronautics)
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25 pages, 8085 KiB  
Article
Orbital Analysis of a Dual Asteroid System Explorer Based on the Finite Element Method
by Linli Su, Wenyu Feng, Lie Yang, Zichen Fan, Mingying Huo and Naiming Qi
Aerospace 2024, 11(12), 993; https://doi.org/10.3390/aerospace11120993 (registering DOI) - 30 Nov 2024
Viewed by 308
Abstract
In the study of dual asteroid systems, a model that can rapidly compute the motion and orientation of these bodies is essential. Traditional modeling techniques, such as the double ellipsoid or polyhedron methods, fail to deliver sufficient accuracy in estimating the interactions between [...] Read more.
In the study of dual asteroid systems, a model that can rapidly compute the motion and orientation of these bodies is essential. Traditional modeling techniques, such as the double ellipsoid or polyhedron methods, fail to deliver sufficient accuracy in estimating the interactions between dual asteroids. This inadequacy primarily stems from the non-tidally locked nature of asteroid systems, which necessitates continual adjustments to account for changes in gravitational fields. This study adopts the finite element method to precisely model the dynamic interaction forces within irregular, time-varying dual asteroid systems and, thereby, enhance the planning of spacecraft trajectories. It is possible to derive the detailed characteristics of a spacecraft’s orbital patterns via the real-time monitoring of spacecraft orbits and the relative positions of dual asteroids. Furthermore, this study examines the orbital stability of a spacecraft under various trajectories, revealing that orbital stability is intrinsically linked to the geometric configuration of the orbits. And considering the influence of solar pressure on the orbit of asteroid detectors, a method was proposed to characterize the stability of detector orbits in the time-varying gravitational field of binary asteroids using cloud models. The insights gained from the analysis of orbital characteristics can inform the design of landing trajectories for binary asteroid systems and provide data for deep learning algorithms that are aimed at optimizing such orbits. By introducing the application of the finite element method, detailed analysis of spacecraft orbit characteristics, and a stability characterization method based on a cloud model, this paper systematically explores the logic and structure of spacecraft orbit planning in a dual asteroid system. Full article
(This article belongs to the Section Astronautics & Space Science)
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13 pages, 9839 KiB  
Article
Nonlinear Aero-Thermo-Elastic Stability Analysis of a Curve Panel in Supersonic Flow Based on Approximate Inertial Manifolds
by Wei Kang, Kang Liang, Bingzhou Chen and Shilin Hu
Aerospace 2024, 11(12), 992; https://doi.org/10.3390/aerospace11120992 (registering DOI) - 30 Nov 2024
Viewed by 289
Abstract
The stability of a nonlinear aero-thermo-elastic panel in supersonic flow is analyzed numerically. In light of Hamilton’s principle, the governing equation of motion for a two-dimensional aero-thermo-elastic panel is established taking geometric nonlinearity and curvature effect into account. Coupling with the panel vibration, [...] Read more.
The stability of a nonlinear aero-thermo-elastic panel in supersonic flow is analyzed numerically. In light of Hamilton’s principle, the governing equation of motion for a two-dimensional aero-thermo-elastic panel is established taking geometric nonlinearity and curvature effect into account. Coupling with the panel vibration, aerodynamic pressure is evaluated by first order supersonic piston theory and aerothermal load is approximated by the quasi-steady theory of thermal stress. A Galerkin method based on approximate inertial manifolds is deduced for low-dimensional dynamic modeling. The efficiency of the method is discussed. Finally, the complex stability regions of the system are presented within the parametric space. The Hopf bifurcation is found during the onset of flutter as the dynamic pressure increases. The temperature rise imposes a significant effect on the stability region of the panel. Since the material parameters of the panel (elastic modulus and thermal expansion coefficient in this case) are the function of temperature, the panel tends to lose its stability as the temperature gets higher. Full article
(This article belongs to the Special Issue Advances in Thermal Fluid, Dynamics and Control)
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21 pages, 799 KiB  
Article
Predictability of Flight Arrival Times Using Bidirectional Long Short-Term Memory Recurrent Neural Network
by Vladimir Socha, Miroslav Spak, Michal Matowicki, Lenka Hanakova, Lubos Socha and Umer Asgher
Aerospace 2024, 11(12), 991; https://doi.org/10.3390/aerospace11120991 (registering DOI) - 30 Nov 2024
Viewed by 281
Abstract
The rapid growth in air traffic has led to increasing congestion at airports, creating bottlenecks that disrupt ground operations and compromise the efficiency of air traffic management (ATM). Ensuring the predictability of ground operations is vital for maintaining the sustainability of the ATM [...] Read more.
The rapid growth in air traffic has led to increasing congestion at airports, creating bottlenecks that disrupt ground operations and compromise the efficiency of air traffic management (ATM). Ensuring the predictability of ground operations is vital for maintaining the sustainability of the ATM sector. Flight efficiency is closely tied to adherence to assigned airport arrival and departure slots, which helps minimize primary delays and prevents cascading reactionary delays. Significant deviations from scheduled arrival times—whether early or late—negatively impact airport operations and air traffic flow, often requiring the imposition of Air Traffic Flow Management (ATFM) regulations to accommodate demand fluctuations. This study leverages a data-driven machine learning approach to enhance the predictability of in-block and landing times. A Bidirectional Long Short-Term Memory (BiLSTM) neural network was trained using a dataset that integrates flight trajectories, meteorological conditions, and airport operations data. The model demonstrated high accuracy in predicting landing time deviations, achieving a Root-Mean-Square Error (RMSE) of 8.71 min and showing consistent performance across various long-haul flight profiles. In contrast, in-block time predictions exhibited greater variability, influenced by limited data on ground-level factors such as taxi-in delays and gate availability. The results highlight the potential of deep learning models to optimize airport resource allocation and improve operational planning. By accurately predicting landing times, this approach supports enhanced runway management and the better alignment of ground handling resources, reducing delays and increasing efficiency in high-traffic airport environments. These findings provide a foundation for developing predictive systems that improve airport operations and air traffic management, with benefits extending to both short- and long-haul flight operations. Full article
(This article belongs to the Section Air Traffic and Transportation)
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24 pages, 20801 KiB  
Article
Four-Dimensional Generalized AMS Optimization Considering Critical Engine Inoperative for an eVTOL
by Jiannan Zhang, Max Söpper, Florian Holzapfel and Shuguang Zhang
Aerospace 2024, 11(12), 990; https://doi.org/10.3390/aerospace11120990 (registering DOI) - 29 Nov 2024
Viewed by 417
Abstract
In this paper, we present a method to optimize the attainable moment set (AMS) to increase the control authority for electrical vertical take-off and landing vehicles (eVTOLs). As opposed to 3D AMSs for conventional airplanes, the hover control of eVTOLs requires vertical thrust [...] Read more.
In this paper, we present a method to optimize the attainable moment set (AMS) to increase the control authority for electrical vertical take-off and landing vehicles (eVTOLs). As opposed to 3D AMSs for conventional airplanes, the hover control of eVTOLs requires vertical thrust produced by the powered lift system in addition to three moments. The limits of the moments and vertical thrust are coupled due to input saturation, and, as a result, the concept of the traditional AMS is extended to the 4D generalized moment set to account for this coupling effect. Given a required moment set (RMS) derived from system requirements, the optimization is formulated as a 4D convex polytope coverage problem, i.e., the AMS coverage over the RMS, such that the system’s available control authority is maximized to fulfill the prescribed requirements. The optimization accounts for not only nominal flight, but also for one critical engine inoperative situation. To test the method, it is applied to an eVTOL with eight rotors to optimize for the rotors’ orientation with respect to the body axis. The results indicate highly improved coverage of the RMS for both failure-free and one-engine-inoperative situations. Closed-loop simulation tests are performed for both optimal and non-optimal configurations to further validate the results. Full article
(This article belongs to the Special Issue Recent Research on UAM/AAM Aircraft and Systems: Modeling, Advanced Control, and Emerging Technologies)
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36 pages, 14204 KiB  
Article
A Novel Algorithm for Precise Orbit Determination Using a Single Satellite Laser Ranging System Within a Single Arc for Space Surveillance and Tracking
by Dong-Gu Kim, Sang-Young Park and Eunji Lee
Aerospace 2024, 11(12), 989; https://doi.org/10.3390/aerospace11120989 (registering DOI) - 29 Nov 2024
Viewed by 235
Abstract
A satellite laser ranging (SLR) system uses lasers to measure the range from ground stations to space objects with millimeter-level precision. Recent advances in SLR systems have increased their use in space surveillance and tracking (SST). The problem we are addressing, the precise [...] Read more.
A satellite laser ranging (SLR) system uses lasers to measure the range from ground stations to space objects with millimeter-level precision. Recent advances in SLR systems have increased their use in space surveillance and tracking (SST). The problem we are addressing, the precise orbit determination (POD) using one-dimensional range observations within a single arc, is challenging owing to infinite solutions because of limited observability. Therefore, general orbit determination algorithms struggle to achieve reasonable accuracy. The proposed algorithm redefines the cost value for orbit determination by leveraging residual tendencies in the POD process. The tendencies of residuals are quantified as R-squared values using Fourier series fitting to determine velocity vector information. The algorithm corrects velocity vector errors through the grid search method and least squares (LS) with a priori information. This approach corrects all six dimensions of the state vectors, comprising position and velocity vectors, utilizing only one dimension of the range observations. Simulations of three satellites using real data validate the algorithm. In all cases, the errors of the two-line element data (three-dimensional position error of 1 km and velocity error of 1 m/s, approximately) used as the initial values were reduced by tens of meters and the cm/s level, respectively. The algorithm outperformed the general POD algorithm using only the LS method, which does not effectively reduce errors. This study offers a more efficient and accurate orbit determination method, which improves the safety, cost efficiency, and effectiveness of space operations. Full article
(This article belongs to the Section Astronautics & Space Science)
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28 pages, 11196 KiB  
Article
Surface Charging Analysis of Ariel Spacecraft in L2-Relevant Space Plasma Environment and GEO Early Transfer Orbit
by Marianna Michelagnoli, Mauro Focardi, Maxsim Pudney, Ian Renouf, Pierpaolo Merola, Vladimiro Noce, Marina Vela Nunez, Giacomo Dinuzzi and Simone Chiarucci
Aerospace 2024, 11(12), 988; https://doi.org/10.3390/aerospace11120988 (registering DOI) - 29 Nov 2024
Viewed by 244
Abstract
Ariel (Atmospheric Remote-sensing Infrared Exoplanet Large-survey) is the ESA Cosmic Vision M4 mission, selected in March 2018 and officially adopted in November 2020, whose launch is scheduled by 2029. It aims at characterizing the atmospheres of hundreds of exoplanets orbiting nearby stars by [...] Read more.
Ariel (Atmospheric Remote-sensing Infrared Exoplanet Large-survey) is the ESA Cosmic Vision M4 mission, selected in March 2018 and officially adopted in November 2020, whose launch is scheduled by 2029. It aims at characterizing the atmospheres of hundreds of exoplanets orbiting nearby stars by low-resolution primary and secondary transit spectroscopy. The Ariel spacecraft’s operational orbit is baselined as a large-amplitude, eclipse-free halo orbit around the second Lagrangian (L2) point, a virtual point located at about 1.5 million km from the Earth in the anti-Sun direction, as it offers the possibility of long uninterrupted observations in a fairly stable radiative and thermo-mechanical environment. A direct escape injection with a single passage through the Van Allen radiation belts is foreseen. During both the injection trajectory and the final orbit around L2, Ariel will be immersed in and interact with Sun radiation and the plasma environment. These interactions usually result in the accumulation of net electrostatic charge on the external surfaces of the spacecraft, leading to a potentially hazardous configuration for the nominal operation and survivability of the Ariel platform and its payload, as it may induce harmful electrostatic discharges (ESDs). This work presents the latest results collected from surface charging analyses conducted using the SPIS tool of the European SPINE community along the GEO insertion orbit segment and operational orbit. Full article
(This article belongs to the Section Astronautics & Space Science)
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23 pages, 2184 KiB  
Article
Research on High-Dynamic Tracking Algorithms for FH-BOC Signals
by Xue Li, Shun Zhao, Xinyue Hou, Lulu Wang and Yinsen Zhang
Aerospace 2024, 11(12), 987; https://doi.org/10.3390/aerospace11120987 (registering DOI) - 28 Nov 2024
Viewed by 264
Abstract
The rapid development of Low Earth Orbit (LEO) satellite navigation systems requires modulation schemes with strong anti-jamming capabilities, high spectral efficiency, and the ability to achieve precise tracking in high-dynamic environments. Traditional Binary Offset Carrier (BOC) modulation suffers from multi-peak ambiguity, leading to [...] Read more.
The rapid development of Low Earth Orbit (LEO) satellite navigation systems requires modulation schemes with strong anti-jamming capabilities, high spectral efficiency, and the ability to achieve precise tracking in high-dynamic environments. Traditional Binary Offset Carrier (BOC) modulation suffers from multi-peak ambiguity, leading to false lock issues. To address this, FH-BOC modulation, which integrates BOC modulationand frequency hopping, significantly improves both anti-jamming performance and spectral efficiency. Against this background, this paper proposes a comprehensive high-dynamic tracking algorithm for FH-BOC signals. (1) Based on the adaptive Kalman filter algorithm, high-precision carrier tracking was achieved in high-dynamic environments. (2) By leveraging the correlation between the ranging code and frequency-hopping offset carrier, a composite pseudo-code is generated through the XOR operation, and a corresponding composite code-tracking loop is introduced. (3) Based on code loop tracking results, the frequency-hopping moments of the subcarrier are detected, and a phase-locked loop for the frequency-hopping subcarrier is established. Simulation results indicate that the algorithm achieves centimeter-level pseudorange measurement accuracy for FH-BOC navigation signals under the JPL high-dynamic model. Full article
(This article belongs to the Section Astronautics & Space Science)
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22 pages, 6877 KiB  
Article
Optimization of Temperature Measurement Method for High-Pressure Gas Flow Standard Facility Based on Sonic Nozzle Array
by Zhihao Zhang, Jiaxi Zhao, Tingting Liu and Rongping Zhang
Aerospace 2024, 11(12), 986; https://doi.org/10.3390/aerospace11120986 (registering DOI) - 28 Nov 2024
Viewed by 209
Abstract
To improve the accuracy of the wind tunnel test, relying on the high-pressure gas source of the China Aerodynamic Research and Development Center, a secondary flow standard facility based on a sonic nozzle array was developed, with a pressure range of (1~6) MPa [...] Read more.
To improve the accuracy of the wind tunnel test, relying on the high-pressure gas source of the China Aerodynamic Research and Development Center, a secondary flow standard facility based on a sonic nozzle array was developed, with a pressure range of (1~6) MPa and a flow range of (0.12~5.55) kg/s. Currently, most facilities use the average temperature measured by the temperature array to represent the upstream temperature of the sonic nozzle array. However, the small flow calibration test results showed that the maximum temperature difference upstream of the standard sonic nozzle array was 1.97 K, and the temperature field upstream of the sonic nozzle array showed non-uniformity, so the above method cannot accurately obtain the upstream temperature. To solve this problem, each nozzle used in the standard sonic nozzle array was accurately measured by temperature sensors. The uncertainty of the facility and the discharge coefficient of the calibrated nozzle between the two methods were compared. The results showed that compared with the discharge coefficient obtained using the temperature sensor array of 0.9902, the accurate measurement of 0.9904 was closer to the National Institute of Metrology, China (NIM) traceable result of 0.9907, and the relative uncertainty of the facility was reduced from 0.124% (k = 2) to 0.120% (k = 2). Full article
(This article belongs to the Section Aeronautics)
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20 pages, 4526 KiB  
Article
Transient Energy Growth in a Free Cylindrical Liquid Jet
by Dongqi Huang, Qingfei Fu and Lijun Yang
Aerospace 2024, 11(12), 985; https://doi.org/10.3390/aerospace11120985 - 28 Nov 2024
Viewed by 224
Abstract
The stability and behavior of jet flows are critical in various engineering applications, yet many aspects remain insufficiently understood. Previous studies predominantly relied on modal methods to describe small perturbations on jet flow surfaces through the linear superposition of modal waves. However, these [...] Read more.
The stability and behavior of jet flows are critical in various engineering applications, yet many aspects remain insufficiently understood. Previous studies predominantly relied on modal methods to describe small perturbations on jet flow surfaces through the linear superposition of modal waves. However, these approaches largely neglected the interaction between different modes, which can lead to transient energy growth and significantly impact jet stability. This work addresses this gap by focusing on the transient growth of disturbances in jet flows through a comprehensive non-modal analysis, which captures the short-term energy evolution. Unlike modal analysis, which provides insights into the overall trend of energy changes over longer periods, non-modal analysis reveals the instantaneous dynamics of the disturbance energy. This approach enables the identification of transient growth mechanisms that are otherwise undetectable using modal methods, which treat disturbance waves as independent and fail to account for their coupling effects. The results demonstrate that non-modal analysis effectively quantifies the interplay between disturbance waves, capturing the nonlinearity inherent in transient energy growth. This method highlights the short-term amplification of disturbances, providing a more accurate understanding of jet flow stability. Furthermore, the impact of dimensionless parameters such as the Reynolds number, Weber number, and initial wave number on transient energy growth is systematically analyzed. Key findings reveal the optimal conditions for maximizing energy growth and elucidate the mechanisms driving these phenomena. By integrating non-modal analysis, this study advances the theoretical framework of transient energy growth, offering new insights into jet flow stability and paving the way for practical improvements in fluid dynamic systems. Full article
(This article belongs to the Section Aeronautics)
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26 pages, 10668 KiB  
Article
Data-Driven Sensitivity Analysis of the Influence of Geometric Parameterized Variables on Flow Fields Under Different Design Spaces
by Xiaoyu Xu, Hongbo Chen, Chenliang Zhang, Yanhui Duan and Guangxue Wang
Aerospace 2024, 11(12), 984; https://doi.org/10.3390/aerospace11120984 - 28 Nov 2024
Viewed by 362
Abstract
In aerodynamic shape optimization, geometric parameterized variables have a significant impact on the flow field, thereby influencing both the effectiveness and efficiency of the optimization process. This paper utilizes flow field data from computational fluid dynamics (CFD) to develop a data-driven approach for [...] Read more.
In aerodynamic shape optimization, geometric parameterized variables have a significant impact on the flow field, thereby influencing both the effectiveness and efficiency of the optimization process. This paper utilizes flow field data from computational fluid dynamics (CFD) to develop a data-driven approach for analyzing the influence of geometric parameterized variables on the objective function and flow field across various design spaces. A data-driven method, namely a sensitivity analysis based on the Kriging model, is proposed along with three design space variation schemes (scaling, translation, and their combination) to evaluate the influence of geometric parameters on the objective function under varying design spaces. Furthermore, the study investigates the effects of these design space variation schemes on the sensitivity results using two test functions and a wave drag reduction case. The results of the wave drag reduction case are further analyzed in relation to flow conditions, including the Mach number and shock-wave strength. The findings indicate that design space variations alter the relationship between geometric parameters and the flow field, particularly affecting the shock-wave position and strength, as reflected by the sensitivity indices of the variables. Additionally, the sensitivity results show a strong dependence on the Mach number under varying design space configurations. Full article
(This article belongs to the Section Aeronautics)
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11 pages, 3469 KiB  
Article
Resolving Visible Emission Lines in Hydrogen Diffusion Flames
by Muyi Pan, Xuanqi Liu, Yufeng Lai, Yuchen Zhang and Yang Zhang
Aerospace 2024, 11(12), 983; https://doi.org/10.3390/aerospace11120983 - 28 Nov 2024
Viewed by 285
Abstract
The hydrogen diffusion flame is commonly described as difficult to see in the visible range. However, even in controlled laboratory conditions with careful imaging, the flame appears reddish. Previous research has reported a variety of colours generated from hydrogen flames. Some researchers believe [...] Read more.
The hydrogen diffusion flame is commonly described as difficult to see in the visible range. However, even in controlled laboratory conditions with careful imaging, the flame appears reddish. Previous research has reported a variety of colours generated from hydrogen flames. Some researchers believe that the visible colour is due to sodium in airborne dust. Other studies suggest the flame colour is caused by the vibration–rotation band of water vapour. In addition, H−α emits radiance in the visible range; therefore, the visible colour of the hydrogen flame could be contributed from the H−α emission. Nevertheless, a definitive conclusion to explain the visible reddish colour of the hydrogen flame is lacking. This paper reports precisely instrumented spectroscopic imaging tests, calibration, and data processing in order to resolve the spectral lines in the red colour zone (580–700 nm). This study used a spectrograph and a DSLR camera to capture the spectrum of hydrogen diffusion flames under different co-flow conditions. The values of emission lines in this range were compared with the databases provided by HITRAN molecular spectroscopy and the National Institute of Standards and Technology (NIST). The results of this study show that H−α emission is highly likely to appear in a hydrogen diffusion flame, which contradicts the previous hypothesis. This work may provide new insight into hydrogen-based combustion. Full article
(This article belongs to the Special Issue Revolutionizing Aerospace Mobility: Green Hydrogen As the Sustainable Fuel of the Future)
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19 pages, 8144 KiB  
Article
Thermal Optimization Design for a Small Flat-Panel Synthetic Aperture Radar Satellite
by Tian Bai, Yuanbo Zhang, Lin Kong, Hongrui Ao, Jisong Yu and Lei Zhang
Aerospace 2024, 11(12), 982; https://doi.org/10.3390/aerospace11120982 - 27 Nov 2024
Viewed by 312
Abstract
This article introduces a small microwave remote sensing satellite weighing 310 kg, operating in low earth orbit (LEO). It is equipped with an X-band synthetic aperture radar (SAR) antenna, capable of a maximum imaging resolution of 0.6 m. To achieve the objectives of [...] Read more.
This article introduces a small microwave remote sensing satellite weighing 310 kg, operating in low earth orbit (LEO). It is equipped with an X-band synthetic aperture radar (SAR) antenna, capable of a maximum imaging resolution of 0.6 m. To achieve the objectives of lower cost, reduced weight, minimized power consumption, and enhanced temperature stability, an optimized thermal design method tailored for satellites has been developed, with a particular focus on SAR antennas. The thermal control method of the antenna is closely integrated with structural design, simplifying the thermal design and its assembly process, reducing the resource consumption of thermal control systems. The distribution of thermal interface material (TIM) in the antenna assembly has been carefully calculated, achieving a zero-consumption thermal design for the SAR antenna. And the temperature difference of the entire antennas when powered on and powered off would not exceed 17 °C, meeting the specification requirements. In addition, to ensure the accuracy of antenna pointing, the support plate of antennas requires stable temperature. The layout of the heaters on the board has been optimized, reducing the use of heaters by 30% while ensuring that the temperature variation of the support board remains within 5 °C. Then, an on-orbit thermal simulation analysis of the satellite was conducted to refine the design and verification. Finally, the thermal test of the SAR satellite under vacuum conditions was conducted, involving operating the high-power antenna, verifying that the peak temperature of T/RM is below 29 °C, the temperature fluctuation amplitude during a single imaging task is 10 °C, and the lowest temperature point of the support plate is 16 °C. The results of the thermal simulation and test are highly consistent, verifying the correctness and effectiveness of the thermal design. Full article
(This article belongs to the Section Astronautics & Space Science)
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18 pages, 1429 KiB  
Article
Fatigue Detection of Air Traffic Controllers Through Their Eye Movements
by Yi Hu, Haoran Shen, Hui Pan and Wenbin Wei
Aerospace 2024, 11(12), 981; https://doi.org/10.3390/aerospace11120981 - 27 Nov 2024
Viewed by 384
Abstract
Eye movement patterns have become an essential element in modern approaches for identifying air traffic controller fatigue. By observing eye movements among various individuals and environments, researchers have discovered correlations with multiple physiological metrics and cognitive processing abilities. This study involved human-in-the-loop simulations [...] Read more.
Eye movement patterns have become an essential element in modern approaches for identifying air traffic controller fatigue. By observing eye movements among various individuals and environments, researchers have discovered correlations with multiple physiological metrics and cognitive processing abilities. This study involved human-in-the-loop simulations to collect eye movement and fatigue data from air traffic controllers and students. The eye movements were classified into three main types: fixation, saccade, and blink. Statistical analyses were performed to determine the most important indicators. Using support vector machine and random forest models for training and prediction, it was found that the fixation characteristic is significantly important for monitoring air traffic controller fatigue. The implementation of this model has the potential to identify forthcoming instances of controller fatigue during their shifts, thereby helping to avert the possibility of unsafe situations. Full article
(This article belongs to the Section Air Traffic and Transportation)
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20 pages, 3891 KiB  
Article
A Robust Adaptive PID-like Controller for Quadrotor Unmanned Aerial Vehicle Systems
by Ahsene Boubakir, Toufik Souanef, Salim Labiod and James F. Whidborne
Aerospace 2024, 11(12), 980; https://doi.org/10.3390/aerospace11120980 - 27 Nov 2024
Viewed by 366
Abstract
This paper introduces a stable adaptive PID-like control scheme for quadrotor Unmanned Aerial Vehicle (UAV) systems. The PID-like controller is designed to closely estimate an ideal controller to meet specific control objectives, with its gains being dynamically adjusted through a stable adaptation process. [...] Read more.
This paper introduces a stable adaptive PID-like control scheme for quadrotor Unmanned Aerial Vehicle (UAV) systems. The PID-like controller is designed to closely estimate an ideal controller to meet specific control objectives, with its gains being dynamically adjusted through a stable adaptation process. The adaptation process aims to reduce the discrepancy between the ideal controller and the PID-like controller in use. This method is considered model-free, as it does not require knowledge of the system’s mathematical model. The stability analysis performed using a Lyapunov method demonstrates that every signal in the closed-loop system is Uniformly Ultimately Bounded (UUB). The effectiveness of the proposed PID-like controller is validated through simulations on a quadrotor for path following, ensuring accurate monitoring of the target positions and yaw angle. Simulation results highlight the performance of this control scheme. Full article
(This article belongs to the Special Issue Challenges and Innovations in Aircraft Flight Control)
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33 pages, 5587 KiB  
Article
Full Envelope Control of Over-Actuated Fixed-Wing Vectored Thrust eVTOL
by Emmanuel Enenakpogbe, James F. Whidborne and Linghai Lu
Aerospace 2024, 11(12), 979; https://doi.org/10.3390/aerospace11120979 - 27 Nov 2024
Viewed by 326
Abstract
A novel full-envelope controller for an over-actuated fixed-wing vectored thrust eVTOL aircraft is presented. It proposes a generic control architecture, which is applicable to piloted, semi-automatic, and fully automated flight, consisting of an aircraft-level controller (high-level controller) and a control allocation scheme. The [...] Read more.
A novel full-envelope controller for an over-actuated fixed-wing vectored thrust eVTOL aircraft is presented. It proposes a generic control architecture, which is applicable to piloted, semi-automatic, and fully automated flight, consisting of an aircraft-level controller (high-level controller) and a control allocation scheme. The aircraft-level controller consists of a main inner loop classical nonlinear dynamic inversion controller and an outer loop proportional–integral linear controller. The inner loop nonlinear dynamic inversion controller is a velocity controller that cancels the nonlinear bare airframe dynamics, while the outer loop proportional–integral linear controller is an attitude and navigation position controller. Together, they are used for hover/low-speed control and forward flight. The control allocation scheme uses a novel architecture, which transfers the nonlinearity in the vectored thrust effector model formulation to the computation of the actuator limits by converting the effector model from polar to rectangular form, thus allowing the use of classical control allocation linear optimisation technique. The linear optimisation technique is an active set linear quadratic programming constrained optimisation algorithm with a weighted least squares formulation. The control allocation allocates the overall control demand (virtual controls) to individual redundant effectors while performing control error minimisation, control channel prioritisation and control effort minimisation. Simulation results show the transition from hover to cruise, climb and descent, and coordinated turn clearly demonstrate that the controller can handle actuator saturation (position or rate). Full article
(This article belongs to the Special Issue Recent Research on UAM/AAM Aircraft and Systems: Modeling, Advanced Control, and Emerging Technologies)
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19 pages, 12795 KiB  
Article
Dual-Metric-Based Assessment and Topology Generation of Urban Airspace with Quadrant Analysis and Pareto Ranking
by Weizheng Zhang, Hua Wu, Yang Liu, Suyu Zhou, Hailong Dong and Huayu Liu
Aerospace 2024, 11(12), 978; https://doi.org/10.3390/aerospace11120978 - 27 Nov 2024
Viewed by 398
Abstract
In this study, an urban airspace assessment mechanism is proposed and validated using the actual urban building data, offering a systematic approach to airspace selection for unmanned aerial vehicle (UAV) operations. Two metrics are involved to assess the urban airspace accurately, which are [...] Read more.
In this study, an urban airspace assessment mechanism is proposed and validated using the actual urban building data, offering a systematic approach to airspace selection for unmanned aerial vehicle (UAV) operations. Two metrics are involved to assess the urban airspace accurately, which are the airspace availability and risk to ground population. The former is measured by analyzing the connectivity of the urban airspace which particularly emphasizes the impact of urban features like buildings and obstacles. The latter is quantized by using a previously proposed risk estimation model, with which an urban risk map can be generated. Quadrant analysis and Pareto ranking are then employed to evaluate the available airspace for UAVs. Quadrant analysis maps the urban airspace availability and risk to ground population onto a two-dimensional space. Additionally, Pareto ranking determines a set of Pareto-optimal solutions wherein no objective can be improved without compromising at least one other objective. The topology of urban airspace could be constructed by using the top 50% of grids ranked by Pareto ranking based on the actual building data. A case study is conducted in a densely populated urban area in Changqing District, Jinan, Shandong Province, China. The connectivity of the airspace topology is verified by employing the A-star algorithm to generate a feasible path for UAVs. Full article
(This article belongs to the Section Air Traffic and Transportation)
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20 pages, 6165 KiB  
Article
Micro UAVs with Fixed Wings: Design, Technological Solutions, and Tests
by Daniel Iorga, Constantin Georgescu, Sorin Constantinescu, George Ghiocel Ojoc, Alexandru Viorel Vasiliu, Mihai Constantinescu, Constantin Cristian Andrei and Lorena Deleanu
Aerospace 2024, 11(12), 977; https://doi.org/10.3390/aerospace11120977 - 27 Nov 2024
Viewed by 424
Abstract
Considering the advantages of using expanded polystyrene (EPS) reinforced with adhesive tape made of glass fibers, this paper presents a design and technological solution for a functional drone of class C1, meaning a maximum take-off mass of 900 g, and tests validating the [...] Read more.
Considering the advantages of using expanded polystyrene (EPS) reinforced with adhesive tape made of glass fibers, this paper presents a design and technological solution for a functional drone of class C1, meaning a maximum take-off mass of 900 g, and tests validating the use of EPS for small UAVs under flight conditions. The selected profile was MH-49, which had a maximum chord thickness of 10.5%. This profile demonstrated a much lower coefficient of pitching moment than that of the NACA 63215 profile, giving this flying-wing UAV superior governability. This airfoil implies a geometry with greater attenuation of the trailing edge, and the design favors the placement of stress concentrators towards the trailing edge. Due to the use of fiberglass tape reinforcement technology, it is possible to address this profile, implying improved aerodynamic performance. The use of EPS in the disposable UAV industry may bring significant benefits, contributing to the development of high-performance, versatile, and low-cost UAVs, suitable for a wide range of tactical and logistic applications. This study presents the design, the fabrication, and testing of this drone, highlighting the advantages and possible challenges of the proposed solution. Full article
(This article belongs to the Special Issue Selected Papers from the 11th Edition of the “AEROSPATIAL” Conference (AEROSPATIAL 2024))
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18 pages, 8899 KiB  
Article
Feature Coding and Graph via Transformer: Different Granularities Classification for Aircraft
by Jianghao Rao, Senlin Qin, Zongyan An, Jianlin Zhang, Qiliang Bao and Zhenming Peng
Aerospace 2024, 11(12), 976; https://doi.org/10.3390/aerospace11120976 - 26 Nov 2024
Viewed by 258
Abstract
Against the background of the sky, imaging and perception of aircraft are crucial for various vision applications. Thanks to the ever-evolving nature of the convolutional neural network (CNN), it has become easier to distinguish and recognize different types of aircraft. Nevertheless, accurate classification [...] Read more.
Against the background of the sky, imaging and perception of aircraft are crucial for various vision applications. Thanks to the ever-evolving nature of the convolutional neural network (CNN), it has become easier to distinguish and recognize different types of aircraft. Nevertheless, accurate classification for sub-categories of aircraft still poses great challenges. On one hand, fine-grained recognition focuses on exploring and studying such problems. On the other hand, aircraft under different sub-categories and granularities put forward higher requirements for feature representation to classify, which led us to rethink the in-depth application of features. We noticed that information in the swin-transformer effectively represents the features in neural network layers, fully showcasing encoding and indexing for information. Through further research based on this, we proposed a better understanding of encoding and reuse for features, and innovatively performed feature coding graphically for classification. In this paper, our approach shows the effects on aircraft feature representation and classification, manifested from the flexible recognition effect at different aircraft category granularities, and outperforms other famous fine-grained classification models on this vision task. Not only did the approach we proposed demonstrate adaptability to aircraft at different classification granularities, but it also revealed the mechanisms and characteristics of feature encoding under different sample space partitions for classification. The relationship between the oriented representation of aircraft features and various classification granularities, which is manifested through different classification criteria, shows that feature coding and graph construction via the transformer opens a new door for specific defined classification tasks where objects are divided under various partition criteria, and provides another perspective on calculation and feature extraction in fine-grained classification. Full article
(This article belongs to the Section Aeronautics)
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25 pages, 4818 KiB  
Article
Research and Flight Test on the Terminal Guidance Control Technology for Cruising Unmanned Aerial Vehicles
by Xiaoru Cai, Chao Yang, Zhiming Guo, Zonghua Sun, Liaoni Wu, Fuqiang Bing and Guoqiang Su
Aerospace 2024, 11(12), 975; https://doi.org/10.3390/aerospace11120975 - 26 Nov 2024
Viewed by 304
Abstract
The Cruising Unmanned Aerial Vehicle (CUAV) exemplifies an advanced system integrating UAV and munitions technology. The primary challenge lies in devising strategies to achieve precision strikes. Achieving precision strikes is a critical combat mission for CUAV and serves as the primary focus of [...] Read more.
The Cruising Unmanned Aerial Vehicle (CUAV) exemplifies an advanced system integrating UAV and munitions technology. The primary challenge lies in devising strategies to achieve precision strikes. Achieving precision strikes is a critical combat mission for CUAV and serves as the primary focus of this research. This paper introduces a three-loop pseudo-angle-of-attack acceleration autopilot design with proportional–integral (PI) correction, overcoming the limitations of existing two-loop and three-loop systems. The existing two-loop acceleration autopilot with PI correction suffers from low robustness, whereas the three-loop autopilot exhibits slow response to acceleration deviations. The proposed design overcomes these shortcomings by optimizing the autopilot for high-dynamic and fast-response scenarios. The design methodology leverages pole assignment, referencing the pole co-circle method and accommodating servo bandwidth limitations. A comparison of the designed three-loop acceleration autopilot with PI correction with other acceleration autopilots reveals superior accuracy advantages. The reliability and robustness of the proposed autopilot were validated through flight tests, achieving a drop point accuracy of less than 0.5 m. This study demonstrates the engineering application of a pseudo-angle-of-attack three-loop acceleration autopilot with PI correction, designed using the pole assignment method, on a short-range CUAV. Future efforts will focus on optimizing the autopilot to further enhance its adaptability and robustness. Full article
(This article belongs to the Section Aeronautics)
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19 pages, 7127 KiB  
Article
Refinement of Control Strategies for Wheel-Fan Systems in High-Speed Air-Floating Vehicles Operating in Atmospheric Pressure Pipelines
by Kun Zhang, Bin Jiao, Yuliang Bian, Zeming Liu, Tiehua Ma and Changxin Chen
Aerospace 2024, 11(12), 974; https://doi.org/10.3390/aerospace11120974 - 26 Nov 2024
Viewed by 352
Abstract
This study explored the optimization of control systems for atmospheric pipeline air-floating vehicles traveling at ground level by introducing a novel composite wheel-fan system that integrates both wheels and fans. To evaluate the control impedance, the system simulates road conditions like inclines, uneven [...] Read more.
This study explored the optimization of control systems for atmospheric pipeline air-floating vehicles traveling at ground level by introducing a novel composite wheel-fan system that integrates both wheels and fans. To evaluate the control impedance, the system simulates road conditions like inclines, uneven surfaces, and obstacles by using fixed, random, and high torque settings. The hub motor of the wheel fan is managed through three distinct algorithms: PID, fuzzy PID, and the backpropagation neural network (BP). Each algorithm’s control strategy is outlined, and tracking experiments were conducted across straight, circular, and curved trajectories. Analysis of these experiments supports a hybrid control approach: initiating with fuzzy PID, employing the PID algorithm on straight paths, and utilizing the BP neural network for sinusoidal and circular paths. The adaptive capacity of the BP neural network suggests its potential to eventually supplant the PID algorithm in straight path scenarios over extended testing and operation, ensuring improved control performance. Full article
(This article belongs to the Section Aeronautics)
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28 pages, 17406 KiB  
Article
Enhancing Multi-Hole Pressure Probe Data Processing in Turbine Cascade Experiments Using Structural Risk Minimization Principle
by Ming Ni, Zuojun Wei, Weimin Deng, Haibo Tao, Guangming Ren and Xiaohua Gan
Aerospace 2024, 11(12), 973; https://doi.org/10.3390/aerospace11120973 - 26 Nov 2024
Viewed by 382
Abstract
Multi-hole pressure probes are crucial for turbomachinery flow measurements, yet conventional data processing methods often lack generalization for complex flows. This study introduces an innovative approach by integrating machine learning techniques with the structural risk minimization (SRM) principle, significantly enhancing the generalization capability [...] Read more.
Multi-hole pressure probes are crucial for turbomachinery flow measurements, yet conventional data processing methods often lack generalization for complex flows. This study introduces an innovative approach by integrating machine learning techniques with the structural risk minimization (SRM) principle, significantly enhancing the generalization capability of regression models. A comprehensive framework has been developed, combining SRM-based machine learning regression methods, such as ridge regression and kernel ridge regression, with hyperparameter optimization and S-fold cross-validation, to ensure robust model selection and accuracy. Validated using the McCormick function and applied to VKI-RG transonic turbine cascade measurements, the SRM-based methods demonstrated superior performance over traditional empirical risk minimization approaches, with lower error ratios and higher R2 values. Novel insights from SHAP analysis revealed subtle but significant differences in aerodynamic parameters, including a 0.63122° discrepancy in exit flow angle predictions, guiding the probe design and calibration strategies. This study presents a holistic workflow for improving multi-hole pressure probe measurements under high-subsonic conditions, representing a meaningful enhancement over traditional empirical methods and providing valuable references for practical applications. Full article
(This article belongs to the Special Issue Machine Learning for Aeronautics (2nd Edition))
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15 pages, 5977 KiB  
Article
Predicting Wall Pressure Fluctuations on Aerospace Launchers Through Machine Learning Approaches
by Elisa de Paola, Roberto Camussi, Fabio Gasparetti, Alessandro Di Marco, Luana G. Stoica, Giorgia Capobianchi and Fabio Paglia
Aerospace 2024, 11(12), 972; https://doi.org/10.3390/aerospace11120972 - 26 Nov 2024
Viewed by 290
Abstract
Artificial intelligence (AI) can be used to optimize the prediction of pressure fluctuations over the external surfaces of aerospace launchers and minimize the number of wind tunnel tests. In the present research, various machine learning (ML) techniques capable of predicting the acoustic load [...] Read more.
Artificial intelligence (AI) can be used to optimize the prediction of pressure fluctuations over the external surfaces of aerospace launchers and minimize the number of wind tunnel tests. In the present research, various machine learning (ML) techniques capable of predicting the acoustic load were tested and validated. The methods included decision trees, Gaussian Process Regression (GPR), Support Vector Machines (SVMs), artificial neural networks (ANNs), linear regression, and ensemble methods such as bagged and boosted trees. These algorithms were trained using experimental data from an extensive wind tunnel test campaign conducted to support the design of a VEGA (Advanced Generation European Vehicle) launcher vehicle and provide wall pressure fluctuations in many configurations. The main objective of this study was to identify, among several algorithms, the most suitable method able to process such complex databases efficiently and to provide reliable predictions. Different statistical indices, including the root mean square error (RMSE), the mean square error (MSE), and a correlation coefficient (R-squared), were employed to evaluate the performance of the ML methods. Among all the methods, the bagged tree algorithm outperformed the others, providing the most accurate predictions, with low RMSE and high R-squared values across all test cases. Other methods, such as the ANNs and GPR, exhibited higher errors, indicating their reduced suitability for this dataset. The results demonstrate that ensemble decision tree methods are highly effective in predicting acoustic loads, offering reliable predictions, even for configurations outside the training database. These findings support the application of ML-based models to optimize experimental campaigns and enhance the design of aerospace launch vehicles. Full article
(This article belongs to the Special Issue Artificial Intelligence in Aeroacoustics for Aerospace Applications)
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