Asrel Aerospace Research Letters Latest Issue

Model Reference Adaptive Controllers (MRAC) are widely used control designs suitable for systems with unmodeled dynamics or parameter uncertainties. The primary goal in MRAC design is to minimize or eliminate the error between the selected reference model and the system to be controlled. While the controller reduces the error over time, smooth tracking of the reference model at all times is also desired. Therefore, the convergence rate to the reference model response, directly linked to the adaptation rate, is crucial when designing the adaptation rule. Conventional adaptation rule designs may struggle with large or rapid tracking error changes unless the adaptation rate is set to very high values. In some cases, a priori knowledge of the system’s dynamics may be required, as even high adaptation rates may not guarantee success without such information. Additionally, compatibility between system dynamics and reference model dynamics can significantly enhance adaptation success and tracking performance. In this study, the reference model is designed as a nonlinear system, more suitable for the nature of the physical system being controlled compared to classical methods. The research investigates the impact of the adaptation rate variable, a key factor in the adaptation rule, on a physical system controlled with an MRAC designed using a nonlinear reference model. A three-degree-of-freedom helicopter system is simulated to evaluate the proposed MRAC design. Comparisons are made across two axes for helicopter position control. Each MRAC configuration is tested with identical variables, except for the adaptation rate, to assess how well the reference system is followed under different adaptation rules.

Satellites have had a major impact on the world since the mid-20th century. The launch of the first artificial satellite, Sputnik 1, by the Soviet Union in 1957 marked the beginning of the space age for humanity. This development paved the way for satellite technologies to be used in a wide range of applications, from communications and military applications to environmental monitoring and scientific research. Today, satellites play a critical role in many strategic areas, from national security to economic development. In this era of increasing global competition, leadership in satellite technologies offers an important opportunity for countries to strengthen their position in the international arena. In this context, Turkey is attracting attention with its investments in satellite technologies and is on its way to becoming a regional power. This article comprehensively examines Turkey's satellite efforts from the perspective of SWOT analysis. Turkey has gained many economic, scientific and strategic advantages with its investments in space technologies and developments in this field. Satellite technologies have strengthened the country's global position in many areas such as communication, environmental monitoring and military applications. Turkey's achievements have been especially thanks to the satellites developed within the framework of its indigenous production and national space program. The Göktürk and TÜRKSAT projects have been important steps in demonstrating Turkey's capacity to develop independent satellites. However, there are also some weaknesses that Turkey faces in its satellite efforts. Limited investments in R&D activities, foreign dependence on critical technologies and lack of qualified human resources are the main factors that make the sustainability of satellite projects difficult. This may limit Turkey's competitiveness in an environment where satellite technologies are rapidly developing. On the other hand, international cooperation and indigenous satellite projects offer great opportunities for Turkey. In particular, the potential to gain a greater foothold in the global satellite market could help Turkey realize economic and strategic gains. However, to capitalize on these opportunities, the threats posed by global competition and economic uncertainties need to be carefully managed. In conclusion, this SWOT analysis assesses the current state of Turkey's satellite activities and provides a strategic guide for future steps.

This study focuses on the conceptual and detailed design of a multi-purpose Vertical Take-Off and Landing (VTOL) Unmanned Aerial Vehicle (UAV) capable of operating in rugged terrains. Recent advancements in VTOL technology have significantly increased the demand for aircraft with reduced space requirements and versatile capabilities across sectors such as agriculture, logistics, and defense. VTOL aircraft, with their ability to efficiently alter operational payloads, are now used in various applications, including ammunition delivery, agricultural spraying, search and rescue, and firefighting. Thanks to their hybrid configurations, VTOL UAVs provide critical operational advantages, such as the ability to take off and land in confined spaces, hover during operations, and transition into horizontal flight mode. The UAV designed in this study has been optimized for challenging missions with a cruise speed of 20 m/s, a maximum altitude range of 100-500 meters, and a payload capacity of 0.5 kg. Configurable with various mission equipment, the UAV supports operations like data collection, cargo transport, and surveillance. The aerodynamic and structural features, including the NACA 4412 airfoil, inverted V-tail configuration, and modular components, were carefully selected to enhance performance. Analytical tools like XFLR5 and OpenVSP validated the aerodynamic parameters, while SolidWorks was used for modeling. The analyses confirmed that the UAV meets flight stability and performance requirements. This UAV provides a cost-effective, high-performance, and reliable solution for both defense and commercial applications. Its modular design allows easy adaptation to diverse mission scenarios. Ultimately, this study presents innovative approaches to enhance the operational potential of VTOL aircraft and offers practical solutions for various scenarios.

Air cargo companies discovered new business dynamics in response to the increased demands during the pandemic. The demand that continued in the post-pandemic period has also enabled them to redefine their goals for the newly developed business processes. The business visions related to these goals could also be decisive for the organizational values of the cargo companies. In the literature of strategic management, organizational values are needed for employees to share the vision, which is defined as the desired future position or dream. Organizational values are the most important component of corporate culture. In this regard, organizational values will play an important role in creating a conducive environment for achieving the vision. In this study, the vision statements and organizational value statements of four businesses licensed in the air cargo operation class by the General Directorate of Civil Aviation, which only engage in cargo transportation, were examined. The vision and organizational value statements obtained from the official websites of the businesses were subjected to content analysis. In the content analysis, the statements were coded and summarized into categories, and then themes representing these categories were created. After the vision and organizational value themes for the sector as a whole were identified, the commonalities for each business were determined, and a chi-square test was conducted. According to the chi-square test result, businesses in the air cargo sector are not statistically significantly different from the overall sector in terms of the content of their vision and organizational value statements. The themes of vision statements are mostly also present in organizational value statements. Vision themes include globalization, customer, partner, sustainability, quality, leader, special flexible solutions, innovation, growth, competition, and professionalism. Some of the organizational value themes are honesty, fairness, customer focus, respect for people, innovation, teamwork, leadership, performance, and globalization. The research is the first study in the literature to examine the relationship between vision statements and organizational values in Turkish air cargo companies, and it revealed that the companies examined were not significantly different at the sector level. Corporate managers must closely monitor the process of dynamically creating organizational values in order to realize the vision

This paper provides a comparative analysis of methods for cloud classification and cloud mask generation using multispectral remote sensing data. It evaluates the performance of traditional threshold-based techniques alongside advanced machine learning methods, focusing on Multilayer Perceptrons (MLP) and Convolutional Neural Networks (CS-CNN). MLP, with its feedforward neural network architecture, is highlighted as an effective approach for pixel-level classifications due to its accuracy and simplicity. However, its inability to directly utilize spatial context limits its performance in complex scenarios. In contrast, CS-CNN stands out as an innovative method that integrates both spatial and spectral information, delivering high-accuracy segmentation without requiring predefined feature extraction. The study also explores the contribution of specific spectral bands in cloud detection and classification using multispectral satellite data. Visible bands, such as 0.6 μm and 0.8 μm, are instrumental in determining aerosol scattering and surface-cloud contrast. The 1.6 μm near-infrared band effectively distinguishes snow, ice, and water clouds, while the 3.9 μm infrared band is crucial for detecting low clouds. Thin cloud temperatures are measured using the 6.2 μm water vapor band, whereas the 10.8 μm infrared band is vital for identifying surface and cloud-top temperatures, volcanic ash, and cirrus clouds. The results demonstrate that CS-CNN outperforms traditional threshold-based methods and the EUMETSAT cloud mask algorithm (CLM). While MLP achieves an accuracy of 88.96% and CLM reaches 86.10%, CS-CNN's ability to incorporate contextual information yields even higher accuracy and flexibility. This makes CS-CNN particularly effective in scenarios where spatial context is critical. The study underscores the potential of machine learning-based approaches in remote sensing applications, positioning CS-CNN as a powerful tool for cloud detection and classification. These findings highlight the significant role of advanced algorithms in enhancing the accuracy and efficiency of remote sensing tasks.

In this study, the free vibration behavior of a sandwich plate with a re-entrant auxetic core layer placed between two functionally graded (FG) composite surface layers are analyzed. Both analytical and numerical methods are employed under various boundary conditions to investigate the free vibration response of the three-layer sandwich structure. The FG layers are modeled using a silicon nitride (〖Si〗_3 N_4)-nickel (Ni) ceramic-metal matrix, selected for its superior thermal and mechanical properties. The material properties of the re-entrant auxetic core and FG surface plates are considered temperature-dependent, allowing for a realistic representation of environmental effects. The effective material properties of the FG plates are defined using a power-law distribution, enabling a gradual variation in composition through the plate’s thickness. Hamilton's principle is applied to derive the governing equations of motion for the sandwich plate, ensuring an accurate theoretical foundation. To analyze the free vibration response, the Finite Element Method (FEM) and Navier method are utilized. FEM offers flexibility for various boundary conditions (BCs), while the Navier method provides a precise analytical solution for plates with uniform conditions. Simulations explore the effects of temperature changes, the power-law index, and the auxetic core’s geometric parameters on the plate’s vibration behavior. The results from the analytical and numerical methods show excellent agreement, confirming the validity of the approaches used. The findings reveal that temperature variations significantly influence the natural frequencies due to changes in material stiffness. Additionally, the power-law index impacts the stiffness distribution, while the auxetic core geometry, such as cell angles and dimensions, plays a key role in modifying the plate's rigidity and free vibration response. This study concludes that by optimizing these parameters, the vibration performance of sandwich plates can be enhanced for specific operating conditions. The findings are expected to provide valuable insights for designing advanced structures in areas such as aerospace, automotive and marine industries.

High entropy alloys (HEAs) have emerged as a prominent class of innovative engineering materials and are attracting increasing interest across various industries. In the aerospace industry, these alloys possess unique potential due to their ability to meet both strength and lightweight requirements. Offering superior mechanical, thermal, and chemical properties compared to conventional alloys, HEAs are therefore considered promising materials for modern aerospace applications. In this study, CoCrFeNiMox (x=0, 0.2, 0.4 at. %) HEA were produced using the vacuum arc melting method. The structural and mechanical properties of the produced HEAs were characterized using X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Vickers hardness test, compression test, and nanoindentation test. According to the results, a face centered cubic (FCC) matrix structure forms, and the lattice parameter increases with Mo addition. Microstructural investigations revealed that even the addition of 2 at. % Mo causes significant changes in the microstructure, leading to the formation of a dendritic structure. When Mo addition is increased to 4 at. %, Mo-Cr-rich regions were observed in the interdendritic regions. The hardness values were determined as 184 HV, 195 HV, and 214 HV for Mo contents of 0, 2, and 4 at. %, respectively, while the yield strengths obtained from compression tests were measured as 206 MPa, 254 MPa, and 287 MPa. Nanoindentation tests identified high hardness values (~7.9 GPa) in Cr-Mo rich regions, confirming that Mo enhances the strength of alloy through solid solution hardening and segregation mechanisms. The findings demonstrate that the addition of Mo to CoCrFeNi alloy increases strength while maintaining the ductility of the structure through solid solution strengthening and minor secondary phase precipitations. These results highlight that HEAs are strong candidates for aerospace applications, where mechanical strength and microstructural properties are critically important.