Analysis of Spatio-Temporal Airspace Sector Interdependencies: Capacity-on-Demand Potential Solutions
Flow Field Reconstruction of 2D Hypersonic Inlets Based on a Variational Autoencoder
Condition-Based Maintenance in Aviation: Challenges and Opportunities

Journal Description

Aerospace

Aerospace is a peer-reviewed, open access journal of aeronautics and astronautics published monthly online by MDPI. The European Aeronautics Science Network (EASN), and the ECATS International Association are affiliated with Aerospace and their members receive a discount on the article processing charges.

Open Access— free for readers, with article processing charges (APC) paid by authors or their institutions.
High Visibility: indexed within Scopus, SCIE (Web of Science), Inspec, and other databases.
Journal Rank: JCR - Q1 (Engineering, Aerospace) / CiteScore - Q2 (Aerospace Engineering)
Rapid Publication: manuscripts are peer-reviewed and a first decision is provided to authors approximately 22.3 days after submission; acceptance to publication is undertaken in 2.7 days (median values for papers published in this journal in the second half of 2023).
Recognition of Reviewers: reviewers who provide timely, thorough peer-review reports receive vouchers entitling them to a discount on the APC of their next publication in any MDPI journal, in appreciation of the work done.
Companion journal: Astronomy.

Impact Factor: 2.6 (2022); 5-Year Impact Factor: 2.6 (2022)

Imprint Information Journal Flyer Open Access ISSN: 2226-4310

Latest Articles

53 pages, 13613 KiB

Open AccessArticle

Flight-Data-Based High-Fidelity System Identification of DJI M600 Pro Hexacopter

Péter Bauer

and

Mihály Nagy

Aerospace 2024, 11(1), 79; https://doi.org/10.3390/aerospace11010079 - 15 Jan 2024

Abstract

Research and industrial application can require custom high-level controllers for industrial drones. Thus, this paper presents the high-fidelity dynamic and control model identification of the DJI M600 Pro hexacopter. This is a widely used multicopter in the research and industrial community due to its high payload capability and reliability. To support these communities, the focus of control model identification was on the exploration and implementation of DJI Onboard Software Development Kit (OSDK) functionalities, also including some unconventional special modes. Thus, the resulting model can be controlled with the same OSDK functionalities as the real drone, making control development and application time effective. First, the hardware and software structure of the additional DJI M600 onboard system are introduced. Then, the postulated dynamic and control system models are shown. Next, real flight test campaigns generating data for system identification are presented. Then, the mass and inertial properties are estimated for TB47S and TB48S battery sets and the custom Forerunner UAV payload. Dynamic system model identification includes the aerodynamic effects and considers hover, vertical, and horizontal forces together with static horizontal wind components and finally the rotational moments and dynamics. The control system components were identified following the structure of OSDK, including vertical, horizontal, and yaw loops. After identification, the model was validated and refined based on an unused flight test and software-in-the-loop simulation data. The simulation is provided by DJI and was also compared to real flight results. This comparison showed that the DJI simulation covers the dynamics of the real drone well, but it requires being connected to the drone and needs the controllers onboard to be implemented in advance, which limits applicability and increases development time. This was another motivation to introduce a standalone simulation in Matlab Simulink, which covers all the important modes of OSDK control and can be run solely in Matlab without any hardware support. The constructed model will be published for the benefit of the research and industrial community. Full article

► Show Figures

Figure 1

14 pages, 3811 KiB

Open AccessArticle

Prediction of Hourly Airport Operational Throughput with a Multi-Branch Convolutional Neural Network

Huang Feng

and

Yu Zhang

Aerospace 2024, 11(1), 78; https://doi.org/10.3390/aerospace11010078 - 15 Jan 2024

Abstract

Extensive research in predicting annual passenger throughput has been conducted, aiming at providing decision support for airport construction, aircraft procurement, resource management, flight scheduling, etc. However, how airport operational throughput is affected by convective weather in the vicinity of the airport and how to predict short-term airport operational throughput have not been well studied. Convective weather near the airport could make arrivals miss their positions in the arrival stream and reduce airfield efficiency in terms of the utilization of runway capacities. This research leverages the learning-based method (MB-ResNet model) to predict airport hourly throughput and takes Hartsfield–Jackson Atlanta International Airport (ATL) as the case study to demonstrate the developed method. To indicate convective weather, this research uses Rapid Refresh model (RAP) data from the National Oceanic and Atmospheric Administration (NOAA). Although it is a comprehensive and powerful weather data product, RAP has not been widely used in aviation research. This study demonstrated that RAP data, after being carefully decoded, cleaned, and pre-processed, can play a significant role in explaining airfield efficiency variation. Applying machine learning/deep learning in air traffic management is an area worthy of the attention of aviation researchers. Such advanced artificial intelligence techniques can make use of big data from the aviation sector and improve the predictability of the national airspace system and, consequently, operational efficiency. The short-term airport operational throughput predicted in this study can be used by air traffic controllers and airport managers for the allocations of resources at airports to improve airport operations. Full article

(This article belongs to the Special Issue Advances in Air Traffic and Airspace Control and Management (2nd Edition))

► Show Figures

Figure 1

18 pages, 7275 KiB

Open AccessArticle

Comparative Study of Soft In-Plane and Stiff In-Plane Tiltrotor Blade Aerodynamics in Conversion Flight, Using CFD-CSD Coupling Approach

and

Aerospace 2024, 11(1), 77; https://doi.org/10.3390/aerospace11010077 - 15 Jan 2024

Abstract

Tiltrotors permit aircrafts to operate vertically with lift, yet convert to ordinary forward flight with thrust. The challenge is to design a tiltrotor blade yielding maximum lift and thrust that converts smoothly without losing integrity or efficiency. The two types of blades, soft in-plane and stiff in-plane—the designation depending on the value of the blade’s natural lag frequency—exhibit different structural responses under the same flight conditions, differently affecting the aerodynamics of the blades, especially in the complex aerodynamic environment of conversion flight where the aerodynamic differences are significant. This phase of flight is not deeply researched, nor is the analytical coupling method much used. To study the influence of blade type on aerodynamics during conversion, models suitable for the conversion flight simulation are established for the application of coupled computational fluid dynamics and computational structural dynamics (CFD-CSD) methods. Each method is implemented with well-accepted techniques (the Unsteady Reynolds-Averaged Navier–Stokes (URANS) equations, the Reverse Overset Assembly Technique (ROAT), and the Timoshenko beam model. To improve the solving efficiency, a loose coupling strategy is used in constructing the two-way coupled model. The XV-15 tiltrotor is used for verification. The aeroelastic simulation of soft in-plane and stiff in-plane blades in conversion flight indicates an impactful role on the modal shapes, with a significant difference in the third flap modal shapes for the XV-15 rotor. However, the effect on aerodynamic performance is relatively small. In the first half of the flight conversion, the thrust of stiff in-plane blades is larger than that of soft in-plane blades, but in the last half, the influence of structural characteristics on aerodynamic performance is negligible and the thrust of the blades tends to be equal. Full article

(This article belongs to the Special Issue Applied Aeroelasticity and Fluid-Structure Interaction)

► Show Figures

Figure 1

18 pages, 21772 KiB

Open AccessArticle

Flow Characteristics of Liquid Jet in Transverse Shear Crossflow

and

Aerospace 2024, 11(1), 76; https://doi.org/10.3390/aerospace11010076 - 13 Jan 2024

Abstract

The numerical simulation method was used to investigate the deflection and deformation process of a circular lubricating oil jet in transverse shear airflow. The numerical model was compared and validated against the experimental data. The physical parameters of Mobil jet Oil II were utilized in this simulation with the nozzle diameter ranging from 0.5 to 2.5 mm, the maximum liquid/gas momentum ratios varying from 10.35 to 165.50, and the injection angle ranging from 0 to 30° in the opposite airflow direction. The results show that an increase in the nozzle diameter decreases the degree of jet deflection. The higher airflow velocity causes more fluctuations in the oil-jet trajectory, while the higher oil-injection velocity reduces fluctuations in the trajectory. The parabolic curve equations were used to derive the trajectory equations for the jet column’s pre-disintegration under both vertical incidence and a small angle of reverse airflow. The nozzle diameter and maximum oil/air momentum ratio were used to obtain a formula for the trajectory curve of the lubricating oil. Additionally, a formula for fitting the trajectory curve of oil injected in the opposite airflow direction regarding the injection angle was developed. Full article

(This article belongs to the Special Issue Jet Flows)

► Show Figures

Figure 1

51 pages, 6383 KiB

Open AccessArticle

Aerodynamic Instabilities in High-Speed Air Intakes and Their Role in Propulsion System Integration

Aristia L. Philippou

Pavlos K. Zachos

and

David G. MacManus

Aerospace 2024, 11(1), 75; https://doi.org/10.3390/aerospace11010075 - 12 Jan 2024

Abstract

High-speed air intakes often exhibit intricate flow patterns, with a specific type of flow instability known as ‘buzz’, characterized by unsteady shock oscillations at the inlet. This paper presents a comprehensive review of prior research, focused on unraveling the mechanisms that trigger buzz and its implications for engine stability and performance. The literature survey delves into studies concerning complex-shaped diffusers and isolators, offering a thorough examination of flow aerodynamics in unstable environments. Furthermore, this paper provides an overview of contemporary techniques for mitigating flow instability through both active and passive flow control methods. These techniques encompass boundary layer bleeding, the application of vortex generators, and strategies involving mass injection and energy deposition. The study concludes by discussing future prospects in the domain of engine-intake aerodynamic compatibility. This work serves as a valuable resource for researchers and engineers striving to address and understand the complexities of high-speed air induction systems. Full article

(This article belongs to the Special Issue Vortex Flow Phenomena and Physics of Aerospace Engineering Applications)

► Show Figures

Figure 1

16 pages, 1279 KiB

Open AccessArticle

Autonomous Shape Decision Making of Morphing Aircraft with Improved Reinforcement Learning

and

Aerospace 2024, 11(1), 74; https://doi.org/10.3390/aerospace11010074 - 12 Jan 2024

Abstract

The autonomous shape decision-making problem of a morphing aircraft (MA) with a variable wingspan and sweep angle is studied in this paper. Considering the continuity of state space and action space, a more practical autonomous decision-making algorithm framework of MA is designed based on the deep deterministic policy gradient (DDPG) algorithm. Furthermore, the DDPG with a task classifier (DDPGwTC) algorithm is proposed in combination with the long short-term memory (LSTM) network to improve the convergence speed of the algorithm. The simulation results show that the shape decision-making algorithm based on the DDPGwTC enables MA to adopt the optimal morphing strategy in different task environments with higher autonomy and environmental adaptability, which verifies the effectiveness of the proposed algorithm. Full article

(This article belongs to the Special Issue Cross-Domain Intelligent Flight Vehicle Design)

► Show Figures

Figure 1

16 pages, 2721 KiB

Open AccessArticle

Enhancing Planetary Exploration through Digital Twins: A Tool for Virtual Prototyping and HUMS Design

and

Giuseppe Francesco De Luca

Aerospace 2024, 11(1), 73; https://doi.org/10.3390/aerospace11010073 - 12 Jan 2024

Abstract

In recent times, the demand for resilient space rovers has surged, which has been driven by the amplified exploration of celestial bodies such as the Moon and Mars. Recognising the limitations of direct human intervention in such environments, these rovers have gained a great deal of importance. Our proposal introduces a digital twin for space exploration rovers that seamlessly integrates intricate geometric, kinematic, and dynamic models, along with sensor and control systems. It faithfully emulates genuine real-world scenarios, providing an authentic testing ground for rover prototypes and the development of damage detection algorithms. Its flexibility in replicating diverse terrains, environmental conditions, and operational scenarios significantly expedites rover development. The digital twin serves as a valuable tool in the perfecting of damage detection systems, allowing engineers to efficiently craft diagnostic algorithms. This innovative approach not only conserves valuable resources but also ensures the robustness of space mission systems, thus enhancing the overall success and safety of planetary exploration endeavours. Full article

(This article belongs to the Special Issue Space Systems Preliminary Design)

► Show Figures

Figure 1

21 pages, 15263 KiB

Open AccessArticle

Evaluation of Mixing Effect on Coupled Heat Release and Transfer Performance of a Novel Segregated Solid Rocket Motor

and

Aerospace 2024, 11(1), 72; https://doi.org/10.3390/aerospace11010072 - 12 Jan 2024

Abstract

The effect of mixing on coupled heat release and transfer performance of a novel segregated solid motor is numerically evaluated with a transient two-dimensional combustion model. The results show that vortex structures are formed and evolved in the combustion chamber. Quantitative calculation of the mixing effect shows the inhomogeneous distribution of oxidant and fuel species. The well-mixing area is located in a narrow belt-like coupled combustion region near the burning surface of the propellant. Heat transfer coefficient decreases greatly due to lower combustion reaction rate and enlarged flow channel area. Heat transfer coefficients near the two ends of the propellant grain are higher than other parts due to the influence of vortex mixing. Raising the inlet mass flow rate leads to enhanced mixing and heat transfer, which results in a lower temperature and regression rate of the propellant with combustion time. Temperature and oxidation rates of H₂ and CO are unevenly distributed in the boundary layer of coupled combustion. Increasing the mass flux of inlet oxidizer gas leads to a higher combustion heat release rate. Therefore, the gas-phase temperature increases significantly. The heat release rate reaches the maximum near the ends of the propellant grain, where vortex mixing strengthens the coupled combustion process in the motor. Full article

(This article belongs to the Special Issue Space Propulsion: Advances and Challenges)

► Show Figures

Figure 1

16 pages, 2542 KiB

Open AccessArticle

Switching Logic for a Direct Hybrid Electric Powertrain

and

Aerospace 2024, 11(1), 71; https://doi.org/10.3390/aerospace11010071 - 12 Jan 2024

Abstract

Hybrid electric aircraft with a powertrain based on fuel cells and batteries can reduce climate-active emissions in aviation. In a direct hybrid powertrain, the fuel cell and the battery are connected in parallel, without a DC/DC converter balancing their voltage levels. Switches make it possible to select different operational modes (fuel cell only, hybrid or battery charging) depending on the power demand during different flight phases. To exploit the high specific energy of hydrogen, the system should change from Hybrid Mode during take-off to Fuel Cell Mode in cruise. During descent, the battery can be charged if Charging Mode is selected. To avoid voltage and current peaks and consequent damage to components when switching between modes, certain conditions must be fulfilled. Those switching conditions were defined, and switching procedures for changing from one mode to the other during flight were developed and tested in a lab system. In a direct hybrid, the system voltage depends on the required power. When switching from Hybrid Mode to Fuel Cell Mode, a short reduction in power of 65% is necessary for the examined system to meet the switching requirements. It is also shown how this power loss can be reduced to 25% by distributed propulsion with a second powertrain or even eliminated by a change in the hybrid ratio. Full article

(This article belongs to the Special Issue Electric Power Systems and Components for All-Electric Aircraft)

► Show Figures

Figure 1

26 pages, 16984 KiB

Open AccessArticle

Aircraft Upset Recovery Strategy and Pilot Assistance System Based on Reinforcement Learning

and

Aerospace 2024, 11(1), 70; https://doi.org/10.3390/aerospace11010070 - 11 Jan 2024

Abstract

The upset state is an unexpected flight state, which is characterized by an unintentional deviation from normal operating parameters. It is difficult for the pilot to recover the aircraft from the upset state accurately and quickly. In this paper, an upset recovery strategy and pilot assistance system (PAS) based on reinforcement learning is proposed. The man–machine closed-loop system was established and the upset state, such as a high angle of attack and large attitude angle, was induced. The upset recovery problem was transformed into a sequential decision problem, and the Markov decision model of upset recovery was established by taking the deflection change of the control surface as the action. The proximal policy optimization (PPO) algorithm was selected for the strategy training. The adaptive pilot model and the reinforcement learning method proposed in this paper were used to make the aircraft recover from the upset state. Based on the correspondence between the flight state, the recovery method, and the recovery result, the aircraft upset recovery safety envelopes were formed, and the four-level upset recovery PAS with alarm warning, coordinated control, and autonomous recovery modes was constructed. The results of the digital virtual flight simulation and ground flight test show that compared with a traditional single pilot, the aircraft upset recovery strategy, the upset recovery safety envelopes, and the PAS established in this study could reduce the handling burden of the pilot and improve the success rate and effect of upset recovery. This research has certain theoretical reference values for flight safety and pilot training. Full article

► Show Figures

Figure 1

14 pages, 4218 KiB

Open AccessArticle

Design and Validation of a Photoelectric Current Measuring Unit for Lunar Daytime Simulation Chamber

and

Aerospace 2024, 11(1), 69; https://doi.org/10.3390/aerospace11010069 - 11 Jan 2024

Abstract

Charging of the lunar surface induced by solar radiation can potentially threaten in situ resource utilization. Associated issues include dust adhesion and material degradation. Photoelectric currents are the primary cause of surface charging. This work reports on the development of a unit capable of measuring photoelectric currents in a vacuum chamber, which can simulate surface charging under conditions similar to those on the moon in daytime. The main components of the unit are a mesh grid, a photocathode specimen, and a ring collector. Photoelectric currents from an aluminum sample were measured by adjusting the electric potential of these components, and the impact of the electric potential of each component is discussed. Calculating the expected electric current within the experimental setup allowed validation of the current measurements: the measured and calculated values agreed well with an error of ~5.5%. Finally, the photoelectric currents for various metals (aluminum, nickel, and copper) were measured using the same experimental setup. The results showed consistent measurement of photoelectric current values across all metals. This study offers insights into the development of units for measuring photoelectric current and methodologies to validate their results. Full article

► Show Figures

Figure 1

35 pages, 20484 KiB

Open AccessArticle

Testing Structural Elements under Multiaxial Loading: A Numerical Model of the Bench to Understand and Predict Complex Boundary Conditions

and

Aerospace 2024, 11(1), 68; https://doi.org/10.3390/aerospace11010068 - 10 Jan 2024

Abstract

Airworthiness certification requires proof of structure strength, which is performed generally through a building block approach. To achieve this, representative intermediate-scale experiments generated by test benches are, in general, needed, in addition to material characterization on a coupons scale and structure testing on a large scale. The VERTEX test bench can generate the combined loading of tension/compression-shear-pressure on structural elements and was modelled with Finite Elements to perform virtual testing, representative of its intermediate-scale specificity. The numerous bolted joints of the bench were modelled and their behavior was identified in previous tests, so the model could quantitatively estimate the transfer function of the bench, which is the relationship between the displacements imposed by the jacks and the resulting loads on a given sample. The VERTEX model was identified to represent load shapes and amplitudes based on a training set and was later confronted by a validation set of tests of tension and shear. A model with ideal boundary conditions was also developed for a comparison, but it failed to predict some load shape specificities and did not give any indication of the loading amplitude. Application cases of the developed model are shown to assess a range of virtual testing possibilities. Full article

(This article belongs to the Section Aeronautics)

► Show Figures

Figure 1

19 pages, 8265 KiB

Open AccessArticle

Contribution of Different Parameters on Film Cooling Efficiency Based on the Improved Orthogonal Experiment Method

and

Aerospace 2024, 11(1), 67; https://doi.org/10.3390/aerospace11010067 - 10 Jan 2024

Abstract

The use of film cooling technology is one of the most effective ways to minimize the damage to wall materials caused by the high-temperature environment in a ramjet. Optimization of the design to achieve the highest film cooling efficiency on the hot wall is the focus of current research. Due to the large number of parameters affecting the film cooling efficiency and the interactions between them, an improved orthogonal design-of-experiments method is chosen to investigate the contribution of different parameters. Flat plate film cooling and transverse groove film cooling are simulated numerically. The results indicated that the contribution of each parameter is ranked as hole spacing (S/D) > incidence angle > blowing ratio for flat plate film cooling; hole spacing > transverse groove depth > blowing ratio > incidence angle for transverse groove film cooling. The film cooling efficiency is inversely proportional to the size of the flow field area affected by the vortex ring and directly proportional to the size of the vortex intensity. Transverse groove film cooling forms a more complete film in most cases, which is better than flat plate film cooling. Within the scope of this study, a complete film at S/D > 2.0 cannot be generated on the flat plate, which should not be used in ramjet. Full article

(This article belongs to the Special Issue Recent Advances in Ramjets)

► Show Figures

Figure 1

23 pages, 6629 KiB

Open AccessArticle

Parameter Tuning of a Vapor Cycle System for a Surveillance Aircraft

Adelia Darlene Drego

Daniel Andersson

and

Ingo Staack

Aerospace 2024, 11(1), 66; https://doi.org/10.3390/aerospace11010066 - 10 Jan 2024

Abstract

Surveillance aircraft perform long-duration missions (>eight hours) that include detection and identification of objects on the ground, the water, or in the air. They have surveillance systems that require large amounts of cooling power (typically 10 s of kW) for long durations. For aircraft application, vapor cycle systems (VCS) are emerging as a more efficient alternative to conventional cooling systems. In this study, a two-part method was applied to a cooling system with a VCS that can be installed on a surveillance aircraft. The first part focused on a parameter tuning study set-up and demonstrated how after identifying the operating conditions, constraints, and requirements, the only cooling system parameter available for tuning was the VCS compressor speed. The second part focused on a modelling and solving strategy for the cooling system and showed how the capacity of an aircraft cooling system was impacted by tuning the VCS compressor speed (Hz) for a surveillance system heat flow rate from 10 kW to 70 kW. The results from this study can be used to design a control strategy for the compressor. In a broader perspective, the two-part method and the results analysis presented can serve as a preliminary method for aircraft VCS control optimization studies. Full article

(This article belongs to the Section Aeronautics)

► Show Figures

Figure 1

15 pages, 4271 KiB

Open AccessArticle

Structural Flexibility Effect on Spaceborne Solar Observation System’s Micro-Vibration Response

and

Aerospace 2024, 11(1), 65; https://doi.org/10.3390/aerospace11010065 - 10 Jan 2024

Abstract

The spaceborne solar observation system is crucial for the study of space phenomena such as solar flares, which requires high tracking accuracy. This study presents a coupling model that integrates mechanical, electrical, and control models to investigate the structural flexibility effect on the micro-vibration response. We established a rigid–flexible model using mechanical parts. We considered the influence of flexible features while studying the dynamic responses in its operation. The state-space equations of the system showed that modal frequency, damping, and modal participation factors played significant roles. We derived transfer functions using the Laplace transform of the coupling models to better understand this mechanism, and Simulink models were thereby established. We simulated the acceleration responses of the rigid–flexible and rigid models under angle tracking modes, and the results showed significant differences. We also simulated the acceleration responses of the models under various control frequencies, and the optimal control frequency was thus obtained. Finally, we performed experiments, and the results indicated that the rigid–flexible model could better predict the motion and acceleration responses for the spaceborne solar observation system. This study provides valuable information for understanding the role of flexible features in space performance high-tracking accuracy instruments and for micro-vibration suppression research. Full article

► Show Figures

Figure 1

21 pages, 20314 KiB

Open AccessArticle

Robust Design Optimization of Supersonic Biplane Airfoil Using Efficient Uncertainty Analysis Method for Discontinuous Problem

Kyohei Hanazaki

and

Wataru Yamazaki

Aerospace 2024, 11(1), 64; https://doi.org/10.3390/aerospace11010064 - 09 Jan 2024

Abstract

Busemann’s supersonic biplane airfoil can reduce wave drag through shock interactions at its designed freestream Mach number. However, a choking phenomenon occurs with a decrease in the freestream Mach number, and the drag coefficient increases significantly, resulting in an aerodynamic problem with a discontinuous change in the performance function. In this study, an uncertainty analysis method, the divided inexpensive Monte Carlo simulation (IMCS), is proposed to solve discontinuous problems efficiently and is applied to Busemann’s biplane airfoil. In the divided IMCS, the discontinuity point is determined using a simple sampling method. The uncertainty input space is divided at the detected discontinuity point, and a surrogate model is constructed for each space. Uncertainty analysis was performed using the constructed surrogate models, and the results of the divided IMCS showed qualitative agreement with those of the conventional Monte Carlo simulation, which is the most straightforward uncertainty analysis method. Moreover, the divided IMCS significantly reduced the computational cost of the uncertainty analysis. A robust design optimization of the supersonic biplane airfoil was performed using the divided IMCS, yielding more robust designs than Busemann’s biplane airfoil. The usefulness of the divided IMCS for uncertainty analysis of discontinuous problems was confirmed. Full article

(This article belongs to the Special Issue Research and Development of Supersonic Aircraft)

► Show Figures

Graphical abstract

11 pages, 2639 KiB

Open AccessArticle

Study of Starting Performance of a Series Hybrid Aero Propulsion System

and

Aerospace 2024, 11(1), 63; https://doi.org/10.3390/aerospace11010063 - 09 Jan 2024

Abstract

Combined with the development trend of high speed generators and the high voltage of DC microgrids in high-power series hybrid aero propulsion system, a set of hybrid systems with a power of 200 kW, voltage of 540 V, and speed of 21,000 r/min is established in this article. Ground starting tests were conducted, focusing on the analysis of the coupling characteristics between the engine, generator and motors/propellers during the starting process, and further facilitated the optimization of the strategy of starting control. Firstly, the starting process of the series hybrid aero propulsion system mainly consists of four stages: the turboshaft engine is started, the gas turbine speed is increased, the controlled rectification intervenes, and the electric propeller is activated. The recommended definition of the idle state of the 200 kW hybrid propulsion system in this paper is as follows: power turbine speed N_P = 10,500 rpm, grid system voltage U_DC = 540 V, and the minimum stable power state of the electric motor P_M = 150 W. Furthermore, experiments reveal that during the starting process, the resistance value and the rectification strategy, respectively, affect the steady-state and dynamic characteristics of the power turbine speed. By comparing multiple sets of experiments and utilizing data fitting software for optimal design, the results indicate that, based on the starting strategy of no-load protection and two-step controlled rectification, the total duration of the optimized starting process is shortened by 64.7%, and the gas turbine speed is reduced by 22.7% compared to the pre-optimized state. The starting control sequence is clearer, and the optimization effect is significant. Full article

► Show Figures

Figure 1

16 pages, 26466 KiB

Open AccessArticle

Robust Flight Tether for In-Orbit Demonstrations of Coulomb Drag Propulsion

and

Aerospace 2024, 11(1), 62; https://doi.org/10.3390/aerospace11010062 - 09 Jan 2024

Abstract

A new method of producing robust multi-wire tethers for Coulomb drag applications was developed. The multi-wire structure required for redundancy against the micrometeoroid flux of the space environment is realised through the method of wire twist bonding traditionally used for chicken wire. In the case of the Coulomb drag tether, the diameter of the individual wires is 50 μm, which introduces the main technological challenge. To manufacture the tether, a manually driven tether machine was designed and built. Two multi-wire tethers for Coulomb drag applications were produced for two in-orbit demonstrations of the FORESAIL-1 and ESTCube-2 CubeSat missions. The flight tethers were both 60 m long as produced, clearly demonstrating beyond the level of proof of concept the applicability of both the method and the manually driven tether machine. Altogether, 6480 twist bonds were produced without a single wire cut. In this paper, the requirements for the tether are listed and justified. The production method is reviewed, and the 4-wire tether produced is evaluated against the requirements. Finally, the test procedures of the tether are described, and on the basis of the results, it is concluded that the tether can tolerate a tension of 14 g without the twist bonds slipping or the tether structure collectively collapsing. Furthermore, the tether can be reeled from the production reel to the flight reel, which simplifies the final integration of the tether reeling system with the Coulomb drag propulsion device. Full article

(This article belongs to the Special Issue Advances in CubeSat Sails and Tethers)

► Show Figures

Figure 1

24 pages, 13172 KiB

Open AccessArticle

Design and Machining of a Spherical Shell Rotor for a Magnetically Levitated Momentum Ball

and

Aerospace 2024, 11(1), 61; https://doi.org/10.3390/aerospace11010061 - 09 Jan 2024

Abstract

Ball-shell rotors with non-standard shapes, non-uniform conductive coatings, and eccentric masses machined by conventional processes constrain the improvement of levitation and torque accuracy of magnetically levitated momentum balls. This paper focuses on the machining method of multilayer ball-shell rotors to develop a ball-shell rotor with a standard shape and uniform conductive coating, which can improve the levitation and torque accuracy of magnetically levitated momentum balls. In this paper, a machining method for multi-coated ball-shell rotors is proposed. The machining process combining hemispherical surface and workpiece is adopted, and the whole sphere is assembled by threading, which effectively reduces the machining error. The influence of the cutting depth and feed rate of the tool on the cutting force of the ball shell was analyzed through the cutting force model. The effect of cutting force on the deformation of the ball shell was analyzed by the finite element method. The superiority of the machining method was verified by measuring the dimensions of the ball shell with a coordinate measuring machine. Compared with the traditional machining process and assembly method, the proposed ball-shell rotor machining method effectively improves the dimensional accuracy, reduces the center of mass to center of mass deviation, and ensures the levitation accuracy and output torque accuracy of the magnetically levitated momentum ball. Measurement results show that the diameter values of the pure iron ball shell are between 98.694 and 98.707 mm with a machining error of ±0.007 mm, and the diameter values of the spray-painted ball shell are between 99.490 and 99.510 mm with a machining error of ±0.01 mm. The machining static equilibrium of the pure iron ball shell and the spray-painted ball shell is good by the static equilibrium test method. Full article

► Show Figures

Figure 1

14 pages, 6086 KiB

Open AccessArticle

Experimental Study on Hypersonic Double-Wedge Induced Flow Based on Plasma Active Actuation Array

and

Aerospace 2024, 11(1), 60; https://doi.org/10.3390/aerospace11010060 - 09 Jan 2024

Abstract

The double-wedge configuration is a typical characteristic shape of the rudder surface of high-speed aircraft. The impact of the shock wave/boundary layer interaction and the shock wave/shock wave interaction resulting from the double wedge on aircraft aerodynamics cannot be ignored. The aerodynamic performance of the aircraft would be seriously affected. Accordingly, to reduce the wave drag, and to relieve the thermal load and pressure load, flow control is required for the shock wave/shock wave interaction and the shock wave/boundary layer interaction induced by the double-wedge configuration. In this paper, double-wedge shock wave/shock wave interaction is controlled by a high-energy surface arc discharge array and observed by high-speed schlieren flow field measurement at Mach 8. The 30-channel discharge array is set on the primary wedge plane, and actuation is generated. Hypersonic V shock wave/shock wave interaction is effectively controlled by the shock wave array induced by the high-energy surface arc discharge array, which makes the shock wave/shock wave interaction structure disappear or intermittent. The potential control mechanism is to reduce strong shock wave interaction by transforming the type of shock wave interaction. Therefore, the ability of plasma array actuation to control complex shock wave/shock wave interaction is verified, which provides a new method for hypersonic shock wave/shock wave interaction control. Full article

(This article belongs to the Special Issue Shock-Dominated Flow)

► Show Figures

Figure 1

Journal Menu

Journal Browser

► Journal Browser

Highly Accessed Articles

Latest Books

More Books and Reprints...

E-Mail Alert

News

2 January 2024
MDPI Insights: The CEO's Letter #7 - Nobel Laureates Entrust MDPI with Their Research

30 November 2023
MDPI Insights: The CEO's Letter #6 - MDPI Spain Summit and ResearchGate

21 November 2023
769 Editorial Board Members of MDPI Journals Achieve Highly Cited Researcher Recognition in 2023

More News & Announcements...

Topics

Propose a Topic

Topic in Aerospace, Applied Sciences, Automation, Drones, Remote Sensing, Sensors

Target Tracking, Guidance, and Navigation for Autonomous Systems Topic Editors: Won-Sang Ra, Shaoming He, Ivan Masmitja
Deadline: 20 February 2024

Topic in Aerospace, Applied Sciences, Catalysts, Energies, Mathematics

Theoretical, Numerical and Experimental Studies on Clean Energy and Combustion Topic Editors: Pedro Resende, Mohsen Ayoobi, Alexandre M. Afonso
Deadline: 31 March 2024

Topic in Aerospace, Drones, Inventions, Materials, Sensors, Polymers, Applied Sciences, Energies

Innovation and Inventions in Aerospace and UAV Applications Topic Editors: Andrzej Łukaszewicz, Mohamed Thariq Hameed Sultan, Quang Ha, Wojciech Giernacki, Leszek Ambroziak, Wojciech Tarasiuk, Andriy Holovatyy
Deadline: 31 August 2024

Topic in Aerospace, Applied Sciences, Batteries, Energies, JMSE, Machines, Mathematics, Sensors

Uncertainty Quantification in Design, Manufacturing and Maintenance of Complex Systems Topic Editors: Chen Jiang, Zhenzhong Chen, Xiaoke Li, Xiwen Cai, Zan Yang
Deadline: 30 September 2024

Conferences

Announce Your Conference

More Conferences...

Special Issues

Propose a Special Issue

Special Issue in Aerospace

Structural Dynamics and Control (2nd Edition) Guest Editor: Hekmat Alighanbari
Deadline: 20 January 2024

Special Issue in Aerospace

Machine Learning for Aeronautics Guest Editor: Olivia J. Pinon Fischer
Deadline: 31 January 2024

Special Issue in Aerospace

Advances in Entry, Descent, and Landing (EDL) for Planetary Exploration Guest Editor: Alessandro Zavoli
Deadline: 9 February 2024

Special Issue in Aerospace

Deicing and Anti-Icing of Aircraft (Volume III) Guest Editors: Hirotaka Sakaue, Xiaobin Shen
Deadline: 29 February 2024

More Special Issues

Topical Collections

Topical Collection in Aerospace

Avionic Systems Collection Editors: Carlos Insaurralde, Francesco Dell’Olio

Topical Collection in Aerospace

Latest Advancements in Aeronautics and Astronautics from Beihang University Collection Editors: Daochun Li, Ting Li, Weizong Wang, Xiaoqiang Li, Zhenxun Gao, Zhihua Wang, Lizhan Bai, Zhan Tu

Topical Collection in Aerospace

Space Systems Dynamics Collection Editors: Mikhail Ovchinnikov, Dmitry Roldugin

Topical Collection in Aerospace

Unmanned Aerial Systems Collection Editors: David Anderson, Javaan Chahl, Michael Wing

Journal Description

Aerospace

Latest Articles

Journal Menu

Journal Browser

Highly Accessed Articles

Latest Books

E-Mail Alert

News

Topics

Conferences

Special Issues

Topical Collections

Further Information

Guidelines

MDPI Initiatives

Follow MDPI