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Methods of Identifying Correlated Model Parameters with Noise in Prognostics -
Modular Impulsive Green Monopropellant Propulsion System (MIMPS-G): For CubeSats in LEO and to the Moon -
Fixed Wing Aircraft Automatic Landing with the Use of a Dedicated Ground Sign System -
Radiation Risks in a Mission to Mars for a Solar Particle Event Similar to the AD 993/4 Event -
Online Model-Based Remaining-Useful-Life Prognostics for Aircraft Cooling Units Using Time-Warping Degradation Clustering
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 many other databases.
- Journal Rank: JCR - Q2 (Engineering, Aerospace) / CiteScore - Q2 (Aerospace Engineering)
- Rapid Publication: manuscripts are peer-reviewed and a first decision provided to authors approximately 17.1 days after submission; acceptance to publication is undertaken in 4.6 days (median values for papers published in this journal in the first half of 2021).
- 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.
Impact Factor:
1.659 (2020)
;
5-Year Impact Factor:
1.688 (2020)
Latest Articles
Unscented Kalman Filter-Aided Long Short-Term Memory Approach for Wind Nowcasting
Aerospace 2021, 8(9), 236; https://doi.org/10.3390/aerospace8090236 - 26 Aug 2021
Abstract
Obtaining reliable wind information is critical for efficiently managing air traffic and airport operations. Wind forecasting has been considered one of the most challenging tasks in the aviation industry. Recently, with the advent of artificial intelligence, many machine learning techniques have been widely
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Obtaining reliable wind information is critical for efficiently managing air traffic and airport operations. Wind forecasting has been considered one of the most challenging tasks in the aviation industry. Recently, with the advent of artificial intelligence, many machine learning techniques have been widely used to address a variety of complex phenomena in wind predictions. In this paper, we propose a hybrid framework that combines a machine learning model with Kalman filtering for a wind nowcasting problem in the aviation industry. More specifically, this study has three objectives as follows: (1) compare the performance of the machine learning models (i.e., Gaussian process, multi-layer perceptron, and long short-term memory (LSTM) network) to identify the most appropriate model for wind predictions, (2) combine the machine learning model selected in step (1) with an unscented Kalman filter (UKF) to improve the fidelity of the model, and (3) perform Monte Carlo simulations to quantify uncertainties arising from the modeling process. Results show that short-term time-series wind datasets are best predicted by the LSTM network compared to the other machine learning models and the UKF-aided LSTM (UKF-LSTM) approach outperforms the LSTM network only, especially when long-term wind forecasting needs to be considered.
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(This article belongs to the Special Issue Application of Data Science to Aviation)
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10-Year Anniversary of the European Proximity Operations Simulator 2.0—Looking Back at Test Campaigns, Rendezvous Research and Facility Improvements
Aerospace 2021, 8(9), 235; https://doi.org/10.3390/aerospace8090235 - 24 Aug 2021
Abstract
Completed in 2009, the European Proximity Operations Simulator 2.0 (EPOS 2.0) succeeded EPOS 1.0 at the German Space Operations Center (GSOC). One of the many contributions the old EPOS 1.0 facility made to spaceflight rendezvous is the verification of the Jena-Optronik laser-based sensors
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Completed in 2009, the European Proximity Operations Simulator 2.0 (EPOS 2.0) succeeded EPOS 1.0 at the German Space Operations Center (GSOC). One of the many contributions the old EPOS 1.0 facility made to spaceflight rendezvous is the verification of the Jena-Optronik laser-based sensors used by the Automated Transfer Vehicle. While EPOS 2.0 builds upon its heritage, it is a completely new design aiming at considerably more complex rendezvous scenarios. During the last ten years, GSOC’s On-Orbit-Servicing & Autonomy group, who operates, maintains and evolves EPOS 2.0, has made numerous contributions to the field of uncooperative rendezvous, using EPOS as its primary tool. After general research in optical navigation in the early 2010s, the OOS group took a leading role in the DLR project “On-Orbit-Servicing End-to-End Simulation” in 2014. EPOS 2.0 served as the hardware in the loop simulator of the rendezvous phase and contributed substantially to the project’s remarkable success. Over the years, E2E has revealed demanding requirements, leading to numerous facility improvements and extensions. In addition to the OOS group’s research work, numerous and diverse open-loop test campaigns for industry and internal (DLR) customers have shaped the capabilities of EPOS 2.0 significantly.
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(This article belongs to the Section Astronautics & Space Science)
Open AccessReview
Development of Green Storable Hybrid Rocket Propulsion Technology Using 98% Hydrogen Peroxide as Oxidizer
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, , , , , , , , and
Aerospace 2021, 8(9), 234; https://doi.org/10.3390/aerospace8090234 - 24 Aug 2021
Abstract
This paper presents the development of indigenous hybrid rocket technology, using 98% hydrogen peroxide as an oxidizer. Consecutive steps are presented, which started with interest in hydrogen peroxide and the development of technology to obtain High Test Peroxide, finally allowing concentrations of up
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This paper presents the development of indigenous hybrid rocket technology, using 98% hydrogen peroxide as an oxidizer. Consecutive steps are presented, which started with interest in hydrogen peroxide and the development of technology to obtain High Test Peroxide, finally allowing concentrations of up to 99.99% to be obtained in-house. Hydrogen peroxide of 98% concentration (mass-wise) was selected as the workhorse for further space propulsion and space transportation developments. Over the course nearly 10 years of the technology’s evolution, the Lukasiewicz Research Network—Institute of Aviation completed hundreds of subscale hybrid rocket motor and component tests. In 2017, the Institute presented the first vehicle in the world to have demonstrated in-flight utilization for 98% hydrogen peroxide. This was achieved by the ILR-33 AMBER suborbital rocket, which utilizes a hybrid rocket propulsion as the main stage. Since then, three successful consecutive flights of the vehicle have been performed, and flights to the Von Karman Line are planned. The hybrid rocket technology developments are described. Advances in hybrid fuel technology are shown, including the testing of fuel grains. Theoretical studies and sizing of hybrid propulsion systems for spacecraft, sounding rockets and small launch vehicles have been performed, and planned further developments are discussed.
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(This article belongs to the Special Issue Hybrid Rocket(Volume II))
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Development of a Numerical Model to Simulate Laser-Shock Paint Stripping on Aluminum Substrates
Aerospace 2021, 8(9), 233; https://doi.org/10.3390/aerospace8090233 - 24 Aug 2021
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An explicit 3D Finite Element (FE) model was developed in the LS-Dyna code to simulate the laser shock paint stripping on aircraft aluminum substrates. The main objective of the model is to explain the physical mechanisms of the laser shock stripping process in
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An explicit 3D Finite Element (FE) model was developed in the LS-Dyna code to simulate the laser shock paint stripping on aircraft aluminum substrates. The main objective of the model is to explain the physical mechanisms of the laser shock stripping process in terms of shock wave propagation, stress and strain evolution and stripping shape and size and to evaluate the effects of laser and material parameters on the stripping pattern. To simulate the behavior of aluminum, the Johnson–Cook plasticity model and the Gruneisen equation of state were applied. To simulate stripping, the cohesive zone modeling method was applied. The FE model was compared successfully against experiments in terms of back-face velocity profiles. The parameters considered in the study are the aluminum thickness, the epoxy paint thickness, the laser spot diameter, the fracture toughness of the aluminum/epoxy interface and the maximum applied pressure. In all cases, a circular solid or hollow stripping pattern was predicted, which agrees with the experimental findings. All parameters were found to affect the stripping pattern. The numerical results could be used for the design of selective laser shock stripping tests.
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Aircraft Engine Gas-Path Monitoring and Diagnostics Framework Based on a Hybrid Fault Recognition Approach
Aerospace 2021, 8(8), 232; https://doi.org/10.3390/aerospace8080232 - 22 Aug 2021
Abstract
Considering the importance of continually improving the algorithms in aircraft engine diagnostic systems, the present paper proposes and benchmarks a gas-path monitoring and diagnostics framework through the Propulsion Diagnostic Methodology Evaluation Strategy (ProDiMES) software developed by NASA. The algorithm uses fleet-average and individual
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Considering the importance of continually improving the algorithms in aircraft engine diagnostic systems, the present paper proposes and benchmarks a gas-path monitoring and diagnostics framework through the Propulsion Diagnostic Methodology Evaluation Strategy (ProDiMES) software developed by NASA. The algorithm uses fleet-average and individual engine baseline models to compute feature vectors that form a fault classification with healthy and faulty engine classes. Using this classification, a hybrid fault-recognition technique based on regularized extreme learning machines and sparse representation classification was trained and validated to perform both fault detection and fault identification as a common process. The performance of the system was analyzed along with the results of other diagnostic frameworks through four stages of comparison based on different conditions, such as operating regimes, testing data, and metrics (detection, classification, and detection latency). The first three stages were devoted to the independent algorithm development and self-evaluation, while the final stage was related to a blind test case evaluated by NASA. The comparative analysis at all stages shows that the proposed algorithm outperforms all other diagnostic solutions published so far. Considering the advantages and the results obtained, the framework is a promising tool for aircraft engine monitoring and diagnostic systems.
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(This article belongs to the Special Issue Aircraft Fault Detection)
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Impact Time Control Cooperative Guidance Law Design Based on Modified Proportional Navigation
Aerospace 2021, 8(8), 231; https://doi.org/10.3390/aerospace8080231 - 22 Aug 2021
Abstract
The paper proposes a two-dimensional impact time control cooperative guidance law under constant velocity and a three-dimensional impact time control cooperative guidance law under time-varying velocity, which can both improve the penetration ability and combat effectiveness of multi-missile systems and adapt to the
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The paper proposes a two-dimensional impact time control cooperative guidance law under constant velocity and a three-dimensional impact time control cooperative guidance law under time-varying velocity, which can both improve the penetration ability and combat effectiveness of multi-missile systems and adapt to the complex and variable future warfare. First, a more accurate time-to-go estimation method is proposed, and based on which a modified proportional navigational guidance (MPNG) law with impact time constraint is designed in this paper, which is also effective when the initial leading angle is zero. Second, adopting cooperative guidance architecture with centralized coordination, using the MPNG law as the local guidance, and the desired impact time as the coordination variables, a two-dimensional impact time control cooperative guidance law under constant velocity is designed. Finally, a method of solving the expression of velocity is derived, and the analytic function of velocity with respect to time is given, a three-dimensional impact time control cooperative guidance law under time-varying velocity based on desired impact time is designed. Numerical simulation results verify the feasibility and applicability of the methods.
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(This article belongs to the Section Astronautics & Space Science)
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Stereo Vision-Based Relative Position and Attitude Estimation of Non-Cooperative Spacecraft
Aerospace 2021, 8(8), 230; https://doi.org/10.3390/aerospace8080230 - 20 Aug 2021
Abstract
In on-orbit services, the relative position and attitude estimation of non-cooperative spacecraft has become the key issues to be solved in many space missions. Because of the lack of prior knowledge about manual marks and the inability to communicate between non-cooperative space targets,
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In on-orbit services, the relative position and attitude estimation of non-cooperative spacecraft has become the key issues to be solved in many space missions. Because of the lack of prior knowledge about manual marks and the inability to communicate between non-cooperative space targets, the relative position and attitude estimation system poses great challenges in terms of accuracy, intelligence, and power consumptions. To address these issues, this study uses a stereo camera to extract the feature points of a non-cooperative spacecraft. Then, the 3D position of the feature points is calculated according to the camera model to estimate the relationship. The optical flow method is also used to obtain the geometric constraint information between frames. In addition, an extended Kalman filter is used to update the measurement results and obtain more accurate pose optimization results. Moreover, we present a closed-loop simulation system, in which the Unity simulation engine is employed to simulate the relative motion of the spacecraft and binocular vision images, and a JetsonTX2 supercomputer is involved to conduct the proposed autonomous relative navigation algorithm. The simulation results show that our approach can estimate the non-cooperative target’s relative pose accurately.
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(This article belongs to the Special Issue Spacecraft Dynamics and Control)
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Performance Enhancement by Wing Sweep for High-Speed Dynamic Soaring
Aerospace 2021, 8(8), 229; https://doi.org/10.3390/aerospace8080229 - 19 Aug 2021
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Dynamic soaring is a flight mode that uniquely enables high speeds without an engine. This is possible in a horizontal shear wind that comprises a thin layer and a large wind speed. It is shown that the speeds reachable by modern gliders approach
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Dynamic soaring is a flight mode that uniquely enables high speeds without an engine. This is possible in a horizontal shear wind that comprises a thin layer and a large wind speed. It is shown that the speeds reachable by modern gliders approach the upper subsonic Mach number region where compressibility effects become significant, with the result that the compressibility-related drag rise yields a limitation for the achievable maximum speed. To overcome this limitation, wing sweep is considered an appropriate means. The effect of wing sweep on the relevant aerodynamic characteristics for glider type wings is addressed. A 3-degrees-of-freedom dynamics model and an energy-based model of the vehicle are developed in order to solve the maximum-speed problem with regard to the effect of the compressibility-related drag rise. Analytic solutions are derived so that generally valid results are achieved concerning the effects of wing sweep on the speed performance. Thus, it is shown that the maximum speed achievable with swept wing configurations can be increased. The improvement is small for sweep angles up to around 15 deg and shows a progressive increase thereafter. As a result, wing sweep has potential for enhancing the maximum-speed performance in high-speed dynamic soaring.
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Design of Low Altitude Long Endurance Solar-Powered UAV Using Genetic Algorithm
Aerospace 2021, 8(8), 228; https://doi.org/10.3390/aerospace8080228 - 16 Aug 2021
Abstract
This paper presents a novel framework for the design of a low altitude long endurance solar-powered UAV for multiple-day flight. The genetic algorithm is used to optimize wing airfoil using CST parameterization, along with wing, horizontal and vertical tail geometry. The mass estimation
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This paper presents a novel framework for the design of a low altitude long endurance solar-powered UAV for multiple-day flight. The genetic algorithm is used to optimize wing airfoil using CST parameterization, along with wing, horizontal and vertical tail geometry. The mass estimation model presented in this paper is based on structural layout, design and available materials used in the fabrication of similar UAVs. This model also caters for additional weight due to the change in wing airfoil. The configuration is optimized for a user-defined static margin, thereby incorporating static stability in the optimization. Longitudinal and lateral control systems are developed for the optimized configuration using the inner–outer loop strategy with an LQR and PID controller, respectively. A six degree-of-freedom nonlinear simulation is performed for the validation of the proposed control scheme. The results of nonlinear simulations are in good agreement with static analysis, validating the complete design process.
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(This article belongs to the Collection Unmanned Aerial Systems)
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Small Hall Effect Thruster with 3D Printed Discharge Channel: Design and Thrust Measurements
Aerospace 2021, 8(8), 227; https://doi.org/10.3390/aerospace8080227 - 15 Aug 2021
Abstract
This paper presents the design and performance of the UAH-78AM, a low-power small Hall effect thruster. The goal of this work is to assess the feasibility of using low-cost 3D printing to create functioning Hall thrusters, and study how 3D printing can expand
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This paper presents the design and performance of the UAH-78AM, a low-power small Hall effect thruster. The goal of this work is to assess the feasibility of using low-cost 3D printing to create functioning Hall thrusters, and study how 3D printing can expand the design space. The thruster features a 3D printed discharge channel with embedded propellant distributor. Multiple materials were tested including ABS, ULTEM, and glazed ceramic. Thrust measurements were obtained at the NASA Glenn Research Center. Measured thrust ranged from 17.2–30.4 mN over a discharge power of 280 W to 520 W with an anode ISP range of 870–1450 s. The thruster has a similar performance range to conventional thrusters at the same power levels. However, the polymer ABS and ULTEM materials have low temperature limits which made sustained operation difficult.
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(This article belongs to the Section Astronautics & Space Science)
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Open AccessReview
Hybrid Rocket Engine Design Optimization at Politecnico di Torino: A Review
Aerospace 2021, 8(8), 226; https://doi.org/10.3390/aerospace8080226 - 13 Aug 2021
Abstract
Optimization of Hybrid Rocket Engines at Politecnico di Torino began in the 1990s. A comprehensive review of the related research activities carried out in the last three decades is here presented. After a brief introduction that retraces driving motivations and the most significant
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Optimization of Hybrid Rocket Engines at Politecnico di Torino began in the 1990s. A comprehensive review of the related research activities carried out in the last three decades is here presented. After a brief introduction that retraces driving motivations and the most significant steps of the research path, the more relevant aspects of analysis, modeling and achieved results are illustrated. First, criteria for the propulsion system preliminary design choices (namely the propellant combination, the feed system and the grain design) are summarized and the engine modeling is presented. Then, the authors describe the in-house tools that have been developed and used for coupled trajectory and propulsion system design optimization. Both deterministic and robust-based approaches are presented. The applications that the authors analyzed over the years, starting from simpler hybrid powered sounding rocket to more complex multi-stage launchers, are then presented. Finally, authors’ conclusive remarks on the work done and their future perspective in the context of the optimization of hybrid rocket propulsion systems are reported.
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(This article belongs to the Special Issue Hybrid Rocket(Volume II))
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Experimental Research on the Influence of Roughness on Water Film Flow
Aerospace 2021, 8(8), 225; https://doi.org/10.3390/aerospace8080225 - 13 Aug 2021
Abstract
Icing phenomena are one of the hot issues in the aviation field, which has attracted the attention of many manufacturers. The physical process of water film flow determines the position and amount of icing. In this paper, the flow process of water film
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Icing phenomena are one of the hot issues in the aviation field, which has attracted the attention of many manufacturers. The physical process of water film flow determines the position and amount of icing. In this paper, the flow process of water film on a rough surface is studied. An experimental platform was built in a wind tunnel, and the digital image processing (DIP) technology was used to measure the water film flow. The water film flow under different roughness conditions of the plate was obtained in the experiments. The correction model of interfacial shear coefficient is established, and the influence of roughness on water film flow is deduced. The relationship obtained in this paper can provide data support for the study of gas-water coupled flows on rough surfaces.
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(This article belongs to the Special Issue Fluid Dynamic Measurement Technologies: Optical and Nanophotonic Methods)
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Explanation of Machine-Learning Solutions in Air-Traffic Management
Aerospace 2021, 8(8), 224; https://doi.org/10.3390/aerospace8080224 - 12 Aug 2021
Abstract
Advances in the trusted autonomy of air-traffic management (ATM) systems are currently being pursued to cope with the predicted growth in air-traffic densities in all classes of airspace. Highly automated ATM systems relying on artificial intelligence (AI) algorithms for anomaly detection, pattern identification,
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Advances in the trusted autonomy of air-traffic management (ATM) systems are currently being pursued to cope with the predicted growth in air-traffic densities in all classes of airspace. Highly automated ATM systems relying on artificial intelligence (AI) algorithms for anomaly detection, pattern identification, accurate inference, and optimal conflict resolution are technically feasible and demonstrably able to take on a wide variety of tasks currently accomplished by humans. However, the opaqueness and inexplicability of most intelligent algorithms restrict the usability of such technology. Consequently, AI-based ATM decision-support systems (DSS) are foreseen to integrate eXplainable AI (XAI) in order to increase interpretability and transparency of the system reasoning and, consequently, build the human operators’ trust in these systems. This research presents a viable solution to implement XAI in ATM DSS, providing explanations that can be appraised and analysed by the human air-traffic control operator (ATCO). The maturity of XAI approaches and their application in ATM operational risk prediction is investigated in this paper, which can support both existing ATM advisory services in uncontrolled airspace (Classes E and F) and also drive the inflation of avoidance volumes in emerging performance-driven autonomy concepts. In particular, aviation occurrences and meteorological databases are exploited to train a machine learning (ML)-based risk-prediction tool capable of real-time situation analysis and operational risk monitoring. The proposed approach is based on the XGBoost library, which is a gradient-boost decision tree algorithm for which post-hoc explanations are produced by SHapley Additive exPlanations (SHAP) and Local Interpretable Model-Agnostic Explanations (LIME). Results are presented and discussed, and considerations are made on the most promising strategies for evolving the human–machine interactions (HMI) to strengthen the mutual trust between ATCO and systems. The presented approach is not limited only to conventional applications but also suitable for UAS-traffic management (UTM) and other emerging applications.
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(This article belongs to the Collection Air Transportation—Operations and Management)
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Multidisciplinary Optimisation of Aircraft Structures with Critical Non-Regular Areas: Current Practice and Challenges
Aerospace 2021, 8(8), 223; https://doi.org/10.3390/aerospace8080223 - 12 Aug 2021
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The design optimisation of aerostructures is largely based on Multidisciplinary Design Optimisation (MDO), which is a set of tools used by the aircraft industry to size primary structures: wings, large portions of the fuselage or even an entire aircraft. The procedure is computationally
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The design optimisation of aerostructures is largely based on Multidisciplinary Design Optimisation (MDO), which is a set of tools used by the aircraft industry to size primary structures: wings, large portions of the fuselage or even an entire aircraft. The procedure is computationally expensive, as it must account for several thousands of loadcases, multiple analyses with hundreds of thousands of degrees of freedom, thousands of design variables and millions of constraints. Because of this, the coarse Global Finite Element Model (GFEM), on which the procedure is based, cannot be further refined. The structures represented in the GFEM contain many components and non-regular areas, which require a detailed modelling to capture their complex mechanical behaviour. Instead, in the GFEM, these components are represented by simplified models with approximated stiffness, whose main role is to contribute to the identification of the load paths over the whole structure. Therefore, these parts are kept fixed and are not constrained during the optimisation, as the description of their internal deformation is not sufficiently accurate. In this paper, we show that it would nevertheless be desirable to size the non-regular areas and the overall structures at once. Firstly, we introduce the concept of non-regular areas in the context of a structural airframe MDO. Secondly, we present a literature survey on MDO with a critical review of several architectures and their current applications to aircraft design optimisation. Then, we analyse and demonstrate with examples the possible consequences of neglecting non-regular areas when MDO is applied. In the conclusion, we analyse the requirements for alternative approaches and why the current ones are not viable solutions. Lastly, we discuss which characteristics of the problem could be exploited to contain the computational cost.
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Open AccessTechnical Note
Overview of the Flight Dynamics Subsystem for Korea Pathfinder Lunar Orbiter Mission
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, , , , , and
Aerospace 2021, 8(8), 222; https://doi.org/10.3390/aerospace8080222 - 10 Aug 2021
Abstract
Korea’s first lunar mission, the Korea Pathfinder Lunar Orbiter (KPLO), aims to launch in mid-2022 via the Space-X Falcon-9 launch vehicle. For the successful flight operation of KPLO, the Korea Aerospace Research Institute (KARI) has designed and developed the Flight Dynamics Subsystem (FDS).
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Korea’s first lunar mission, the Korea Pathfinder Lunar Orbiter (KPLO), aims to launch in mid-2022 via the Space-X Falcon-9 launch vehicle. For the successful flight operation of KPLO, the Korea Aerospace Research Institute (KARI) has designed and developed the Flight Dynamics Subsystem (FDS). FDS is one of the subsystems in the KPLO Deep-Space Ground System (KDGS), which is responsible for the overall flight dynamics-related operation. FDS is currently successfully implemented and meets all of the requirements derived from the critical design phases. The current work addresses the design and implementation results for the KPLO FDS. Starting from overviews on KPLO payloads, bus systems, and mission trajectory characteristics, a review on KDGS is also treated briefly. Details on the design philosophy, unique characteristics, and functionalities of all six different modules nested inside the FDS with its Graphical User Interface (GUI) design are discussed. Moreover, efforts currently devoted to the flight operation preparation of the KPLO are summarized, including many collaborative works between KARI and the National Aeronautics and Space Administration (NASA) teams.
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(This article belongs to the Section Astronautics & Space Science)
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A Parametric Study on the Aeroelasticity of Flared Hinge Folding Wingtips
Aerospace 2021, 8(8), 221; https://doi.org/10.3390/aerospace8080221 - 10 Aug 2021
Abstract
This paper presents a parametric study on the aeroelasticity of cantilever wings equipped with Flared Hinge Folding Wingtips (FHFWTs). The finite element method is utilized to develop a computational, low-fidelity aeroelastic model. The wing structure is modelled using Euler–Bernoulli beam elements, and unsteady
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This paper presents a parametric study on the aeroelasticity of cantilever wings equipped with Flared Hinge Folding Wingtips (FHFWTs). The finite element method is utilized to develop a computational, low-fidelity aeroelastic model. The wing structure is modelled using Euler–Bernoulli beam elements, and unsteady Theodorsen’s aerodynamic strip Theory is used for aerodynamic load predictions. The PK method is used to estimate the aeroelastic boundaries. The model is validated using three rectangular, cantilever wings whose properties are available in literature. Then, a rectangular, cantilever wing is used to study the effect of folding wingtips on the aeroelastic response and stability boundaries. Two scenarios are considered for the aeroelastic analysis. In the first scenario, the baseline, rectangular wing is split into inboard and outboard segments connected by a flared hinge that allows the outboard segment to fold. In the second scenario, a folding wingtip is added to the baseline wing. For both scenarios, the influence of fold angle, hinge-line angle (flare angle), hinge stiffness, tip mass and geometry are assessed. In addition, the load alleviation capability of FHFWT is evaluated when the wing encounters discrete (1-cosine) gusts. Finally, the hinge is assumed to exhibit cubic nonlinear behavior in torsion, and the effect of nonlinearity on the aeroelastic response is assessed and analyzed for three different cases.
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(This article belongs to the Special Issue Aeroelasticity, Volume III)
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Open AccessTechnical Note
Design, Production and Evaluation of 3D-Printed Mold Geometries for a Hybrid Rocket Engine
Aerospace 2021, 8(8), 220; https://doi.org/10.3390/aerospace8080220 - 08 Aug 2021
Abstract
The feasibility of 3D-printed molds for complex solid fuel block geometries of hybrid rocket engines is investigated. Additively produced molds offer more degrees of freedom in designing an optimized but easy to manufacture mold. The solid fuel used for this demonstration was hydroxyl-terminated
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The feasibility of 3D-printed molds for complex solid fuel block geometries of hybrid rocket engines is investigated. Additively produced molds offer more degrees of freedom in designing an optimized but easy to manufacture mold. The solid fuel used for this demonstration was hydroxyl-terminated polybutadiene (HTPB). Polyvinyl alcohol (PVA) was chosen as the mold material due to its good dissolving characteristics. It is shown that conventional and complex geometries can be produced reliably with the presented methods. In addition to the manufacturing process, this article presents several engine tests with different fuel grain geometries, including a short overview of the test bed, the engine and first tests.
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(This article belongs to the Special Issue Hybrid Rocket(Volume II))
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Behavior of Sliding Angle as Function of Temperature Difference between Droplet and Superhydrophobic Coating for Aircraft Ice Protection Systems
Aerospace 2021, 8(8), 219; https://doi.org/10.3390/aerospace8080219 - 08 Aug 2021
Abstract
A hybrid anti-/de-icing system combining a superhydrophobic coating and an electrothermal heater is an area of active research for aircraft icing prevention. The heater increases the temperature of the interaction surface between impinging droplets and an aircraft surface. One scientific question that has
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A hybrid anti-/de-icing system combining a superhydrophobic coating and an electrothermal heater is an area of active research for aircraft icing prevention. The heater increases the temperature of the interaction surface between impinging droplets and an aircraft surface. One scientific question that has not been studied in great detail is whether the temperatures of the droplet and the surface or the temperature difference between the two dominate the anti-/de-icing performance. Herein, this scientific question is experimentally studied based on the mobility of a water droplet over a superhydrophobic coating. The mobility is characterized by the sliding angle between the droplet and the coating surface. It was found that the temperature difference between the droplet and the coating surface has a higher impact on the sliding angle than their individual temperatures.
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(This article belongs to the Special Issue Deicing and Anti-Icing of Aircraft (Volume II))
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Open AccessArticle
Wrapping Deployment Simulation Analysis of Leaf-Inspired Membrane Structures
Aerospace 2021, 8(8), 218; https://doi.org/10.3390/aerospace8080218 - 08 Aug 2021
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Deployable membrane structures have received wide attention in many engineering applications, such as the military, aerospace, and aviation. Their properties of light weight and high storage ratio meet the requirements for aerospace exactly. In this paper, the wrapping deployment of membrane structures inspired
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Deployable membrane structures have received wide attention in many engineering applications, such as the military, aerospace, and aviation. Their properties of light weight and high storage ratio meet the requirements for aerospace exactly. In this paper, the wrapping deployment of membrane structures inspired by leaves are simulation-analyzed for prospective improvement. Three leaf-inspired patterns are investigated and discussed from the corresponding paper-craft design principles and deployment process perspectives. The deployment performance evaluation system according to the factors effecting working performance including maximum stress, driving force, maximum strain energy, smoothness index, and maximum folding height is established based on the results of the simulation analysis. Then, a comparison between the three patterns is carried out based on the deployment performance evaluation system. Moreover, it is found that adding creases reduces the folded height but the development performance gets worse. There is a balance between the folding ratio and development performance when the additional creases are added. The results can provide useful suggestions for designing wrapping deployment structures.
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Open AccessTechnical Note
Acquisition of Swept Aerodynamic Data by the Consecutive Changing of Wing Model Configuration in a Wind Tunnel Test Using Remote Feedback Control
Aerospace 2021, 8(8), 217; https://doi.org/10.3390/aerospace8080217 - 07 Aug 2021
Abstract
This study conducted wind tunnel tests with consecutive deflection angle changes on a three-dimensional (3D) wing with a control surface to procure aerodynamic data by sweeping the deflection angle. Configuration changes of a wind tunnel test model, such as changing the deflection angle
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This study conducted wind tunnel tests with consecutive deflection angle changes on a three-dimensional (3D) wing with a control surface to procure aerodynamic data by sweeping the deflection angle. Configuration changes of a wind tunnel test model, such as changing the deflection angle of control surfaces, are usually performed manually with the ventilation suspended. Hence, the number of configurations that can be implemented within a confined test period is restricted; the aerodynamic data gained are discrete values. To accomplish continuous angular modulation would dramatically improve the ability by sweeping through the aerodynamic data in wind tunnel tests, enhancing the test system as a tool for discussing complex physical phenomena. Thus, this study created a compact remote feedback control system using optical measurement to continuously obtain high-precision aerodynamic data without stopping the wind tunnel, eliminating human operation. In particular, this study targets a 3D wing wind tunnel model with a control surface, which is more challenging to fabricate, miniaturizing the system in a model. The system consequently attained consecutive aerodynamic data multiple times under numerous configurations, which had been impracticable to reach in the past, within a wind tunnel test period of several days, thereby dramatically increasing the testing capability. The reproducibility was quantitatively verified by comparing the multiple data for the identical configurations. Furthermore, the reliability was demonstrated using discrete data obtained by conventional stepwise deflection angle adjustments. Eventually, the system was able to grasp physical phenomena involving hysteresis.
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(This article belongs to the Section Aeronautics)
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