Aerospace, Volume 12, Issue 1 (January 2025) – 33 articles

The 1–2 seat helicopters have developed considerably in recent years. They have a maximum take-off weight of 250 to 750 kg. Most of these helicopters have been converted into unmanned versions. Typically, such UAV models retain the rotor system, power plant, transmission, and empennage of the manned versions. For this reason, statistics and design methods for small manned helicopters are also applied to unmanned versions. The existing methods for selecting helicopter parameters in the preliminary design phase are based on statistical data for heavier-class helicopters. However, the lightest weight class helicopters differ significantly from their heavier counterparts. The analysis shows that the results of parameter selection at the preliminary design stage have an error rate of between 11 and 30%. The main reason for this difference is a scale factor. In this paper, a method for determining helicopter tail unit parameters at the preliminary design stage is presented. The proposed relationships for the horizontal stabilizer, fin, tail boom, and tail rotor parameters are based on an analysis of statistical data from 36 rotorcraft and the author’s design experience. In particular, the article presents the relationships between the geometric parameters of the empennage and tail rotor from other helicopter data. The relationships presented also allow the mass of the tail unit to be determined. Full article

In this work, we focused on the characterization of closed-cell Al foams and aluminum honeycomb panels, in particular their energy absorption capacity under conditions of static compressive stress. Through experimental tests, the specific energy absorbed by different samples was evaluated: in the honeycomb panels the mechanical behavior was analyzed both for large assemblies and for structures with a reduced number of cells, and the effect of the number of cells was studied too. Furthermore, for larger structures, the specific energy absorbed was calculated from stress–strain compressive graphs. For the closed-cell Al foams, manufactured in the laboratory using the powder compaction method with different percentages of SiC and TiH₂ and characterized by different relative densities, the specific energy absorbed was evaluated too. The experimental results showed that the specific energy absorbed by the Al honeycomb was always higher than that of the different types of closed-cell foams. However, when selecting the material for each specific application, it is necessary to take into account numerous parameters such as the relative density, absorbed energy, peak stress, plateau stress, plateau extension, densification strain and so on. Consequently, the overall performance must be evaluated from time to time based on the type of application in which the best compromise between strength, stiffness and lightness can be achieved. Full article

Aircraft safety is the aviation industry’s primary concern. Inspections must be conducted before each flight to ensure the integrity of the aircraft. To meet the increasing demand for engineers, a system capable of detecting surface defects on aircraft was designed to reduce the workload of the inspection process. The system utilizes the real-time object detection capabilities of the you only look once-version 9 (YOLO v9) algorithm, combined with imagery captured from an unmanned aerial vehicle (UAV)-based aerial platform. This results in a system capable of detecting defects such as cracks and dents on the aircraft’s surface, even in areas that are difficult to reach, such as the upper surfaces of the wings or the higher parts of the fuselage. With the introduction of a Real-Time Messaging Protocol (RTMP) server, the results can be monitored via artificial intelligence (AI) and Internet of Things (IoT) devices in real time for further evaluation. The experimental results confirmed an effective recognition of defects, with a mean average precision ([email protected]) of 0.842 for all classes, the highest score being 0.938 for dents and the lowest value 0.733 for the paint-off class. This study demonstrates the potential for developing image detection technology with AI for the aviation industry. Full article

Motion control of modern and advanced aircraft has to be provided under conditions of incomplete and inaccurate knowledge of their parameters and characteristics, possible flight modes, and environmental influences. In addition, various abnormal situations may occur during flight, in particular, equipment failures and structural damage. These circumstances cause the problem of a rapid adjustment of the used control laws so that the control system can adapt to the mentioned changes. However, most adaptive control schemes have a model of the control object, which plays a crucial role in adjusting the control law. That is, it is required to solve also the identification problem for dynamical systems. We propose an approach to solving the above-mentioned problems based on artificial neural networks (ANNs) and hybrid technologies. In the class of traditional neural network technologies, we use recurrent neural networks of the NARX type, which allow us to obtain black-box models for controlled dynamical systems. It is shown that in a number of cases, in particular, for control objects with complicated dynamic properties, this approach turns out to be inefficient. One of the possible alternatives to this approach, investigated in the paper, consists of the transition to hybrid neural network models of the gray box type. These are semi-empirical models that combine in the resulting network structure both empirical data on the behavior of an object and theoretical knowledge about its nature. They allow solving with high accuracy the problems inaccessible by the level of complexity for ANN models of the black-box type. However, the process of forming such models requires a very large consumption of computational resources. For this reason, the paper considers another variant of the hybrid ANN model. In it, the hybrid model consists not of the combination of empirical and theoretical elements, resulting in a recurrent network of a special kind, but of the combination of elements of feedforward networks and recurrent networks. Such a variant opens up the possibility of involving deep learning technology in the construction of motion models for controlled systems. As a result of this study, data were obtained that allow us to evaluate the effectiveness of two variants of hybrid neural networks, which can be used to solve problems of modeling, identification, and control of aircraft. The capabilities and limitations of these variants are demonstrated on several examples. Namely, on the example of the problem of aircraft longitudinal angular motion, the possibilities of modeling the motion using the NARX network as applied to a supersonic transport aircraft (SST) are first considered. It is shown that under complicated operating conditions this network does not always provide acceptable modeling accuracy. Further, the same problem, but applied to a maneuverable aircraft, as a more complex object of modeling and identification, is solved using both a NARX network (black box) and a semi-empirical model (gray box). The significant advantage of the gray box model over the black box one is shown. The capabilities of the hybrid model realizing deep learning technologies are demonstrated by forming a model of the control object (SST) and neurocontroller on the example of the MRAC adaptive control scheme. The efficiency of the obtained solution is illustrated by comparing the response of the control object with a failure situation (a decrease in the efficiency of longitudinal control by 50%) with and without adaptation. Full article

In the space environment, the elastic vibrations of satellite solar panels are caused by various factors that disturb satellite missions. Therefore, we propose a multi-layered high-damping yoke structure based on a passive control method. To optimize the proposed yoke structure, we performed a free vibration test on various multi-layered blade specimens and designed a yoke structure with the maximum damping performance based on the test results. This high-damping yoke structure was mounted on a dummy solar panel with flexible mode (0.79 Hz) and basic characteristic tests were performed to validate the effectiveness of the solar panel vibration suppression. The test results demonstrated that the proposed multi-layered high-damping yoke is effective in suppressing the vibrations of the first and second modes. In addition, a thermal vacuum test was performed to investigate the delamination between multi-layered structures, and the test results proved the applicability of the proposed yoke structure in an actual space environment. Full article

Seaplane operations connect remote areas, promote tourism, and provide unique transportation solutions. After many years of preparations, commercial seaplane operations on a network of 100 water airports and 200 waterways in Greece are about to commence. The network can serve the needs of 1.6 million permanent residents of the Greek islands, the inhabitants of the mainland, and over 35 million annual tourists. This paper aims to conduct a PESTLE (Political, Economic, Social, Technological, Legal, and Environmental) analysis to identify the factors that have delayed operations and those that will affect the success of future operations. As such, 26 factors are examined. It was found that the Greek debt crisis and the COVID-19 pandemic were impediments to operations. The potential of using electric seaplanes is discussed. Recent developments in using drone inspection capabilities for aviation safety are examined. Management strategies for the Etesian winds and other environmental issues are presented. Overall, seaplane operations have enormous potential, while the Greek economic recovery provides favorable conditions for completing the project. The critical issue determining success is executing a multi-faceted business model to ensure seaplane operations’ financial viability. The network can act in synergy with other modes of transportation to help achieve social cohesion, improve tourism services, and foster economic development. Full article

Regarding the dynamic magnification effect of structure stiffness on the gust analysis of civil aircraft, the following three methods are presented: rigid modes analysis, secondary processing based on elastic modes, and analysis with enlarged stiffness. These methods provide consistent gust load and address the challenge of extracting internal gust loads of rigid aircraft. The coupling resonant effects of the inertial force, the aerodynamic force, and the gust-induced aerodynamic force at different frequencies are examined. The response of flexible aircraft is nonlinearly related to frequency. It exhibits a significant increase in the inertial force and the aerodynamic force at higher frequencies, while a quasi-rigid response at very low frequencies shows the importance of sufficient analysis time. In addition, compared with rigid aircraft, flexible aircraft experiences a delay in the occurrence of extreme gust loads with the delay interval proportional to the frequency. The maximum gust load of flexible aircraft under a certain range of frequencies exceeds that of rigid aircraft, although this is not necessarily the case at the specific frequency. The dynamic magnification factor is 1.25 for the model in this study, which is almost constant and reaches its maximum value together with the gust loads when the frequency coincides with the frequency of the first bending mode. Full article

Understanding rock hardness on extraterrestrial planets offers valuable insights into planetary geological evolution. Rock hardness correlates with morphological parameters, which can be extracted from navigation images, bypassing the time and cost of rock sampling and return. This research proposes a machine-learning approach to predict extraterrestrial rock hardness using morphological features. A custom dataset of 1496 rock images, including granite, limestone, basalt, and sandstone, was created. Ten features, such as roundness, elongation, convexity, and Lab color values, were extracted for prediction. A foundational model combining Random Forest (RF) and Support Vector Regression (SVR) was trained through cross-validation. The output of this model was used as the input for a meta-model, undergoing linear fitting to predict Mohs hardness, forming the Meta-Random Forest and Support Vector Regression (MRFSVR) model. The model achieved an R² of 0.8219, an MSE of 0.2514, and a mean absolute error of 0.2431 during validation. Meteorite samples were used to validate the MRFSVR model’s predictions. The model is used to predict the hardness distribution of extraterrestrial rocks using images from the Tianwen-1 Mars Rover Navigation and Terrain Camera (NaTeCam) and a simulated lunar rock dataset from an open-source website. The results demonstrate the method’s potential for enhancing extraterrestrial exploration. Full article

The axial compressor is crucial for heavy-duty gas turbines, with its aerodynamic performance directly affecting efficiency. The current trend in the development of these compressors is to increase the stage load and efficiency, thereby achieving a higher pressure ratio with fewer stages. The aerodynamic characteristics of a 1.5-stage axial compressor from a 300 MW F-class heavy gas turbine at three different rotation speeds (100%, 90%, and 80%) were studied. Specifically, the distribution of the inlet Mach number, shock wave structures, isentropic Mach number of blade surface, and blade surface separation flow characteristics under three typical working conditions, at the near stall (NS) point, maximum efficiency (ME) point, and near choke point (NC), were discussed. The results indicate that at 80% rotational speed, 70~100% spanwise of the compressor rotor blade is operated under the transonic zone. Meanwhile, at 100% rotational speed, almost all the spanwise of the compressor rotor blade is operated under the transonic zone. Furthermore, compared to the detached shock wave observed under the NS condition, the normal passage shock wave observed under the NC condition exhibits more significant changes in shock intensity and shock pattern. Full article

It is very easy for a small lunar rover to slip on the regolith of the lunar surface and become stuck. Previous studies have quantitatively evaluated the effects of wheel geometry, such as elliptical or eccentric wheels, on the performance of a rover when climbing up slopes. These studies reported that the rovers were able to run on a 30-degree slope made of silica sand. In this study, a small rover was designed and created, and running tests were conducted using lunar soil simulant and silica sand to predict its performance on the lunar surface. The effects of soil differences on the performance of the rover were clarified through the running tests and the measurement of reaction force on the lug. Although the rover exhibited a greater slip ratio on the lunar soil simulant than on the silica sand, the rover with eccentric wheels was able to climb up to a 30-degree angle on the lunar soil simulant. The results for the sinkage measurement of the rover showed that the eccentric wheels prevented sinkage with their up-and-down motion, enabling the rover to climb steep slopes. Furthermore, the tests for measuring the reaction force on the lug indicated that the density change in the lunar soil simulant did not provide sufficient reaction force, and that the running performance on the lunar soil simulant was lower than that on the silica sand. Full article

Besides the fact that civil and military aerospace are governed by the same physics and design fundamentals, differences exist between the initial and continued airworthiness criteria for these two aviation fields. Whereas civil aerospace is highly regulated by national and international organizations, the military is mainly governed by national regulations or, in multinational projects, by agreed-upon regulations. A trend exists towards the homogenization of rules in both fields; however, due to national security interests, these are generally agreed upon on a case-by-case basis. This review aims to provide an overview of the processes employed for initial and continued airworthiness of civil and military aviation, focusing on the similitudes and differences. Full article

To reasonably divide the types of flow units along the latticework subchannel, one must prepare for the establishment of a one-dimensional fluid network model of the latticework in the middle region of the turbine blade. The characteristics of the flow structure along the latticework subchannel were studied by numerical simulation. The effects of rib angle (15–45°), the ratio of rib width to rib spacing (0.3–1.0), and inlet Reynolds umber (21,000–80,000) on the flow structure along the subchannel are summarized. The results indicated that the ratio of rib width to rib spacing and inlet Reynolds number had no effect on the distribution position of each flow unit in the subchannel. The change of rib angle did not change the flow structure type along the subchannel. The longitudinal vortex was mainly formed by one turning vortex and two detached vortices. The narrowing of the turning channel will cause the turning vortex to induce a secondary longitudinal vortex. There were five kinds of flow structures along the subchannel: transverse vortex zone (entrance of the inlet section), uniform flow zone (inlet section), longitudinal vortex generation zone (turning channel section), longitudinal vortex zone (turning channel section), and longitudinal vortex free development zone (outlet section). This finding provides support for the selection of empirical formulas for each module in the one-dimensional modeling of subchannels. Finally, the boundary prediction equations of each flow structure in the subchannel were established, and the average prediction error was less than 10%. The rationality of the flow structure division along the latticework subchannel was improved, and the modeling efficiency of the latticework one-dimensional model was optimized. Full article

The study of the design of emergency trajectories of air vehicles is one of the key elements in improving airspace safety for air vehicles. The aim is to lighten pilots’ workload, offering quick and effective solutions. However, almost all flight optimizers proposed in the literature still need to be completed when it comes to resolving emergency contexts, which presents a significant disadvantage to the advancement of scientific research. This resolution is based on the following problems: (a) finding paths free of obstacles, (b) ensuring their flight capacity, and finally, (c) calculating trajectories optimizing several criteria with a calculation time constraint (a few minutes). This document analyzes the safety landing problem and proposes an architecture that effectively reduces complexity and ensures solvability within a reasonable computational time. This architectural framework is designed to be adaptable, allowing for testing several algorithms to provide a quick overview of their strengths and weaknesses in this context. The primary aim of these tests is to benchmark the computational time of the overall architecture, ensuring that this adaptable framework is fully capable of handling the problem’s complexity. It is important to note that the algorithms chosen address only a simplified version of the problem. The initial results are promising in terms of time response and the potential to enhance the representativeness and complexity of the problem. The next phase of our research will focus on striking the right balance between complexity, representativity, and computational time, aiming to impact emergency response significantly. Full article

Adhesion-based space climbing robots, with their flexibility and multi-functional capabilities, are seen as a promising candidate for in-orbit maintenance. However, challenges such as uncertain adhesion establishment, unexpected detachment, and body motion unsteadiness in microgravity environments persist. To address these issues, this paper proposes a coordinated force–position compliance control method that integrates novel adhesion establishment and rotational detachment strategies, integrated into the gait schedule for a space climbing robot. By monitoring the foot-end reaction forces in real time, the proposed method establishes adhesion without risking damaging the spacecraft exterior, and smooth detachment is achieved by rotating the foot joint instead of direct pulling. These strategies are dedicated to reducing unnecessary control actions and, accordingly, the required adhesion forces in all feet, reducing the possibility of unexpected detachment. Climbing experiments have been conducted in a suspension-based gravity compensation system to examine the merits of the proposed method. The experimental results demonstrate that the proposed rotational detaching method decreases the required pulling force by 65.5% compared to direct pulling, thus greatly reducing the disturbance introduced to the robot body and other supporting legs. When stepping on an obstacle, the compliant control method is shown to reduce unnecessarily aggressive control actions and result in a reduction in relevant normal and shear adhesion forces in the supporting legs by 44.8% and 35.1%, respectively, compared to a PID controller. Full article

The Global Navigation Satellite System (GNSS) provides critical positioning, navigation, and timing (PNT) services worldwide, enabling a wide range of applications from everyday use to advanced scientific and military operations. The importance of Low Earth Orbit (LEO) PNT systems lies in their ability to enhance the GNSS by implementing signals in additional frequency bands, offering increased signal strength, reduced latency, and improved accuracy and coverage, particularly in challenging environments such as urban canyons or polar regions, thereby addressing the limitations of the traditional Medium Earth Orbit (MEO) GNSS. This paper details the system engineering of a novel CubeSat-based multi-regional PNT system tailored for deployment in LEO. The proposed system leverages on a miniaturized CubeSat-compatible PNT payload that includes a chip-scale atomic clock (CSAC) and relies on MEO GNSS technologies to deliver positioning and timing information across multiple regions. The findings indicate that the proposed CubeSat-based PNT system offers a viable solution for enhancing global navigation and timing services, with potential commercial and scientific applications. This work contributes to the growing body of knowledge on LEO-based PNT systems and lays the groundwork for future research and development in this rapidly evolving field. Full article

The Chang’e-6 mission achieved the first successful sample collection and return from the Moon’s far side. Accurate alignment detection of the primary packaging container is critical for the success of this mission, as it ensures proper retrieval of lunar soil. To address challenges such as complex backgrounds, uneven lighting, and reflective surfaces, this paper introduces an alignment detection method that integrates YOLO object recognition, Devernay subpixel edge detection, and the RANSAC fitting algorithm. By employing both linear and elliptical fitting techniques, the method accurately determines the median line of the primary packaging container, ensuring precise alignment detection. The effectiveness of this approach is demonstrated by an average alignment distance of 0.28 mm with a standard deviation of 0.03 mm in lunar surface images, underscoring its accuracy and reliability. Full article

Plasma synthetic jet (PSJ) is widely employed in flow control due to its advantages of zero-mass and fast-response. A novel measurement method for high-frequency dynamic drag variation was adopted in a Mach 8 wind tunnel experiment, demonstrating that the opposing PSJ can achieve a maximum drag reduction of 40.27% and an average drag reduction of 13.25% within one discharge cycle. Subsequently, the numerical method was verified in detail and the effects of different discharge energies and nozzle diameters on the drag reduction characteristics of the opposing PSJ were studied. The results show that an increase in discharge energy is beneficial for the drag reduction characteristics of the opposing PSJ, although the efficiency remains relatively low. In contrast, increasing the nozzle diameter enhances the average drag reduction but significantly reduces the duration of effective control. The drag reduction mechanism of the opposing PSJ can be attributed to the combined effects of pushing the strong bow shock away to form a weaker oblique shock, followed by the reattachment of the shock downstream. Full article

The 5G frequency band is extremely close to the operating frequency band of radio altimeters (RAs), so an in-depth study of the possible interference of 5G’s key parameters on RAs is especially necessary to ensure aviation safety. In this paper, the interference magnitude of 5G waveforms on an altimeter was measured by simulating the Adjacent Channel Leakage Power Ratio (ACLR) values for different sub-carrier spacing (SCS) and channel bandwidth configurations. Furthermore, interference injection experiments on simulated 5G signals and the interference thresholds of a frequency-modulated continuous wave (FMCW) altimeter were compared to experiments on the effects of the different configurations of 5G SCSs, channel bandwidths, and center frequency points. The interference thresholds of this FMCW altimeter were found to be in the range of 1 dBm to 6 dBm and −4 dBm to 0 dBm under the interference of 5G signals at the center frequency points of 3.7 GHz and 3.9 GHz. These results provided a certain reference for the engineering judgement margin of the interference thresholds. Full article

An analytical method is introduced to assess the susceptibility of radio altimeter (RA) receivers to adjacent-band fifth-generation (5G) signal interference and to quantify its impact on RA performance. The power-series method is employed to analyze the intermediate frequency (IF) signal gain compression effect of 5G signal interference on RA receivers. A behavioral-level simulation model of the RA receiver’s radio frequency (RF) front-end is constructed based on the advanced design system (ADS), and a 5G signal injection simulation is performed. The simulation results indicate that 5G signals can induce nonlinear effects in the RF front-end circuit of the RA, leading to IF signal gain compression, thereby affecting the subsequent signal processing of RA receivers. The interference effect on the RA receiver is influenced by factors such as the power and frequency of the 5G interference signal. To investigate this, an interference injection test was conducted on a specific RA receiver to validate the aforementioned interference mechanisms. The test results indicate that when the average power of the injected 5G signal at a frequency of 4000 MHz reaches −16 dBm, the IF signal power is significantly reduced. As the power of the 5G signal increases, this nonlinear effect becomes more pronounced. Furthermore, the height error ratio significantly increases, with consistent trends observed across different test frequencies. The interference threshold for the RA is lower when the signal frequency is closer to the RA operational signal frequency. Our research results demonstrate the efficacy of this method, providing a reference basis for studies on interference mechanisms and the evaluation of interference effects related to RA receivers within the electromagnetic environment of 5G signals. Full article

Continuously rotating gimbals for scanning purposes are widely used in space applications. For high-precision gimbals, it is essential to lock the gimbal before launch and unlock it on orbit. This kind of gimbal puts forward the need for hold down release mechanisms that are able to clear the gap between the rotating and fixed parts at release. Existing technologies either lack the function of gap avoidance after separation or rely more or less on the elastic deformation of the structure or limited spring forces for unlocking, which are either unreliable or complicated. To address this problem, this paper presents the design of a novel non-pyrotechnic heavy-load hold down release mechanism (HDRM) based on shape memory alloy actuator. The proposed HDRM is shock-free and capable of clearing an axial gap of 8 mm for safe rotating at release. The structure and operational principle of the proposed design are straightforward. Detailed tests show the proposed HDRM may withstand a maximum external force of 50 KN with relatively high stiffness under 15 KN of preload, indicating a better performance than existing products. The HDRM demonstrates its promising usage as an alternative to traditional pyrotechnic and non-pyrotechnic HDRMs. Full article

This study addresses an under-represented topic in turbojets’ design—the characterizing of this type of engine as an entity subject to automatic control. This study’s subject is a medium-size turbojet, improved with a water injection system for thrust augmentation, and evaluated as a controlled object. The method of coolant injection in the compressor and/or in the combustion chamber of the aviation engine has been intensively studied and applied for the temporary increase in thrust. After a period of abandonment, the method seems to be returning in a version that also produces a reduction in pollutant emissions. Starting from determining turbojet performances on the test rig and establishing the equations that define the turbojet as a system, the mathematical model for both versions (basic and with a water injection) was issued. In order to correlate the basic engine operation with the water injection, a version of control architecture was designed, containing two controllers (for engine’s speed and for the injected water flow rate). An embedded control system was described by its mathematical model; based on its equations, its block diagram with transfer functions was issued. The system’s quality was evaluated by performing studies that concern the turbojet’s main parameters (speed and combustor temperature) and time behavior (system response at step input), which led to some results and conclusions regarding how the water injection changed the properties of the engine as a controlled object: the engine has become slower with bigger static errors for the studied parameters (affecting the stabilization at their values imposed by the new operating regime). The proposed method, based on the characterization of the engine as a controlled object (with and without coolant injection), can be very useful as a method of predicting the behavior of any turbojet when the addition of coolant injection system is desired; obviously, the appropriate modeling of both the turbojet and the injection system is necessary. Full article

This review paper identifies key stability and control screening parameters needed to design low-risk, general-purpose high-speed aircraft. These derive from MIL-STD-8785C, MIL-STD-1797, and older AGARD reports, and are suitable for assessing conceptual high-speed vehicles. We demonstrate their applicability using published ground test, computation, and flight test data from the Bell X-2, North American X-15, Martin X-24A, Northrop HL-10, Lockheed Blackbird (YF-12/SR-71), and North American XB-70 as well as the Rockwell Space Shuttle Orbiter. The relative success of the X-15 and Blackbird and the performance limitations of the others indicate the need to scrutinize lateral-directional stability at the preliminary design phase. Our work reveals the need for strong bare-airframe static directional stability to obtain favorable flying qualities. Full article

This paper proposes a new model of collaborative filtering that introduces a user difference factor to address the issue of less pronounced similarity performance in traditional algorithms. The algorithm is applied to the recommendation of pilots’ core competency behavior indicators to support pilots’ daily training arrangements, improve their core competencies, and ensure civil aviation flight safety. Firstly, based on traditional collaborative filtering methods, a user difference factor is introduced to improve the Pearson similarity calculation model. Secondly, the advantages and disadvantages of collaborative filtering recommendation models were evaluated using various methods such as average absolute error, accuracy, recall, and diversity. Finally, the new model is applied to the recommendation of PLM core competency behavior indicators, providing a recommendation list of different pilot behavior indicators to support their rehabilitation or enhanced training plans and arrangements. The calculation results show that the new model of collaborative filtering demonstrates better advantages, not only reducing the MAE value, but also improving the accuracy, recall, and diversity of the calculation results, providing effective guidance and theoretical support for pilots’ flight training and safe flight. Full article

This article aims to highlight the importance of including quantitative measurements when conducting flow visualization tests, such as those performed in towing tanks, within fluid mechanics analysis. It investigates the possibility of measuring velocity fields with an economically accessible technique compared to other techniques that require large financial investments, such as traditional PIV. The development of a MATLAB R2024b code based on image recognition and the use of 3D-printed tracer particles is proposed. Code workflow and how to make a correct selection of the processing parameters and its activity are explained and demonstrated on artificial images, generated by a computer, as well as real images, obtained in a 2D-test in the tank, achieving an accuracy, in absolute values, of 95%. However, the proposed velocimetry system currently has one important limitation, the impossibility of distinguishing between particles in different planes, which limits the study to two-dimensional tests. Then, the opportunity to include this technique in the study of more complex tests requires further investigation. Full article

This paper investigates the best control method of the lowest specific fuel consumption (SFC) to reduce the specific fuel consumption of the triple-bypass variable cycle engine. Specific fuel consumption is the ratio of fuel flow to thrust. First, the Kriging model of the engine near the supersonic cruise and subsonic cruise state points was extracted using the component-level model of the triple-bypass variable cycle engine, and the PSM was obtained close to the steady-state point. The contribution of each control variable to the engine’s specific fuel consumption was computed using the PSM and, at the same time, due to the linear characteristics of the PSM, it was easy to deal with various constrained linear optimization problems, and the steady-state points with the smallest specific fuel consumption under the constraints could be obtained through the linear optimization algorithm; however, the surge margin and pre-turbine temperature of the optimized point were limited in the optimization process, the method of direct switching inevitably brought the problem of overshoot of the controlled quantity, and the actual controlled quantity could still exceed the safe operation boundary of the engine in the process of change. Moreover, the performance optimization control itself is premised on sacrificing the surge margin of the engine, and its operating boundary is closer to the surge line, so the limitation protection problem in the transition state cannot be ignored in the process of performance optimization control. In this paper, a multivariable steady-state controller was designed based on Model Predictive Control (MPC) to meet the needs of engine optimization control mode switching. The simulation results of the supersonic cruise mode show that the minimum fuel consumption control can reduce the fuel consumption of the engine by 2.6% while the thrust remains constant. Full article

Air compressors play an important role in energy, mining, civil engineering, and transportation engineering. However, the abnormal vibration and noise of air compressors may pose a serious threat to the structural stability and smooth operation of these types of engineering equipment. To address the broadband noise and vibration problems of a new oil-free piston air compressor, we developed a hybrid optimization method that combines experimental testing, theoretical evaluation, and numerical simulation. Firstly, we conduct noise experiment testing, identify the frequency band of aerodynamic noise using a coherence analysis method, and design orthogonal experiments to further optimize pipeline noise. Then, the vibration characteristics were discussed from both theoretical and simulation perspectives. The dynamic balance has been redesigned on the spindle counterweight plate to reduce the force on the bearings, and a multi-body dynamics model has been constructed to demonstrate the effectiveness of the optimization. Subsequently, a finite element model of the compressor housing was established to analyze the radiation noise characteristics. Finally, three weak points in the structure were selected as key objects, and the structural stiffness was increased to improve vibration stability. The simulation results of radiated noise show that the proposed design scheme can effectively reduce vibration and noise, with a maximum noise reduction rate of 7.45%. Full article

Cavity flows have a wide range of low-speed applications (M≤0.3), such as aircraft wheel wells, ground transportations, and pipelines. They induce strong flow oscillations which can substantially increase noise, drag, vibration, and lead to structural fatigue. In the current study, a steady jet was forced from the cavity trailing edge with different momentum fluxes (J = 0.11 kg/m·s², 0.44 kg/m·s², and 0.96 kg/m·s²). The aim of this study was to investigate the impact of the steady jet on the time-averaged flow field and the cavity separated shear layer oscillations for an open cavity with a length-to-depth ratio of L/D=4 at Reθ=1.28×103. Particle image velocimetry, surface oil flow visualisation, constant temperature anemometry, and pressure measurements were performed. The study found that increasing the jet momentum flux caused a significant increase in thickness and deflection of the cavity separated shear layer. Due to the counterflow interaction between the jet and cavity separated shear layer, the growth rate (dδω/dx) of the cavity separated shear layer increased significantly from 0.193 for the no-jet case to 0.273 for the J = 0.96 kg/m·s² case. As a result, the return flow rate increased, causing the separation point on the cavity floor to shift upstream from x/L≈0.2 for the no-jet case to x/L≈0.1 for the J = 0.96 kg/m·s² case. Furthermore, increasing the jet momentum flux increased the broadband level of the cavity separated shear layer oscillations. Full article

Body-mounted solar panels are extensively utilized in satellite construction due to their simple structure and robust vibration resistance. The quantity and arrangement of support points on the body-mounted solar panel significantly affect its natural frequency. Thus, the design of these support points is a crucial aspect of the design process for body-mounted solar panels. This study presents a method for determining the support points of body-mounted solar panels, enabling rapid and precise identification of the quantity and positioning of these points based on the stated natural frequency in the design. First, a new algorithm is proposed, based on the finite element method, to optimize the positioning of support points on the body-mounted solar panel without the need for remeshing. Utilizing this algorithm, the distinct impacts of support point positioning and stiffness on the natural frequency of the solar panel are investigated, and the practical principles are proposed for quickly and accurately identifying the optimal locations of support points to maximize the natural frequency of the solar panel, given a predetermined number of support points. Subsequently, based on Courant–Fischer’s theorem, a method to ascertain the least quantity of support points through two modal analyses is presented. By integrating the aforementioned principles and method, a two-step procedure for identifying the quantity and positioning of support points is developed. Ultimately, the proposed two-step procedure is implemented in the design of the solar panel of the Jilin-1XXX satellite. The modal test reveals that the natural frequency of the solar panel surpasses the design index criteria, hence validating the efficacy and feasibility of the optimal design technique for the support points of the body-mounted solar panel presented in this study. Full article

The aim of the present work is the improvement of a free-wake model for the analysis of a small-scale two-bladed propeller in hover. The simulations are carried out using a BEM approach implemented in the medium-fidelity solver RAMSYS. An acoustic validation is also performed using the developed tool ACO-FWH. The work proves that even mild discrepancies in the propeller geometry must be accounted for as their influence is not negligible, especially on the aeroacoustics of the propeller. In particular, the proper modeling of the blades enables the correct identification of the sub-harmonics of the SPL spectra. An optimization procedure based on the application of the evolutionary Genetic Algorithm is followed to identify the values of the parameters describing the dissipative and diffusive properties in the Bhagwat–Leishman vortex core model, an upgraded version of the classical Lamb–Oseen one. On average, this approach enabled the further improvement of the accuracy of the numerical model in terms of acoustic signature evaluation with respect to the one obtained by only modeling blade dissimilarities. The results obtained demonstrate the promising capabilities of a fine-tuned free-wake medium-fidelity approach to simulate the aerodynamic and acoustic details of a small-scale propeller in hover, provided the accurate geometrical modeling of the propeller and the selection of suitable parameters to be used in the wake modeling. Full article

Lunar in situ resource utilization is a core goal in lunar exploration, with accurate lunar rock pose estimation being essential. To address the challenges posed by the lack of texture features and extreme lighting conditions, this study proposes the Simulation-YOLO-Hourglass-Transformer (SYHT) method. The method enhances accuracy and robustness in complex lunar environments, demonstrating strong adaptability and excellent performance, particularly in conditions of extreme lighting and scarce texture. This approach provides valuable insights for object pose estimation in lunar exploration tasks and lays the foundation for lunar resource development. First, the YOLO-Hourglass-Transformer (YHT) network is used to extract keypoint information from each rock and generate the corresponding 3D pose. Then, a lunar surface imaging physics simulation model is employed to generate simulated lunar rock data for testing the method. The experimental results show that the SYHT method performs exceptionally well on simulated lunar rock data, achieving a mean per-joint position error (MPJPE) of 37.93 mm and a percentage of correct keypoints (PCK) of 99.94%, significantly outperforming existing methods. Finally, transfer learning experiments on real-world datasets validate its strong generalization capability, highlighting its effectiveness for lunar rock pose estimation in both simulated and real lunar environments. Full article