<abstract>
<title style='display:none'>Abstract</title>
In-service non-destructive inspection (NDI) is a very important part of the aircraft maintenance program that minimizes aircraft breakdowns due to the fracture of critical components. The eddy current (EC) NDI method is one of the most applicable methods for this purpose, due to its high sensitivity to fatigue cracks and corrosion damage in the main structural materials. In this paper, selective double differential type EC probes characterized by the enhanced possibility of detecting subsurface cracks initiated by fatigue or stress corrosion phenomena are presented. For different applications, a family of double differential type EC probes was developed with different sizes (from 5 to 33 mm) and different spatial resolutions. These types of probes are characterized by different operational frequencies in a wide frequency range (from 0.2 kHz to 1.0 MHz), high penetration depth and unique sensitivity to subsurface defects of different types (like elongated fatigue cracks or local corrosive pitting), and a high level of specific noise suppression concerned with the scanning inspection procedures. The EC probes proposed were investigated as effective tools for characteristic aircraft applications concerned with subsurface defect detection in multilayer structures, such as the detection of cracks in the second layer of a riveted two-layer structure or cracks initiated on the side surface of a multilayer structure with the suppression of the reinforcing hoop influence; the detection of subsurface defects in arc welding with a rough surface; the detection of cracks through repair patches fabricated from aluminum alloy or carbon fiber reinforced plastic, etc. These techniques create remarkable possibilities for the well-timed detection of dangerous damage without disassembling the aircraft structure or removing protective coating.
</abstract>

Eddy Current Techniques for Detecting Hidden Subsurface Defects in Multilayer Aircraft Structures

<abstract>
<title style='display:none'>Abstract</title>
This paper describes the recent theoretical and experimental research by the Netherlands Organisation for Applied Scientific Research (TNO) into green replacements for hydrazine, hydrazine derivatives and nitrogen tetroxide, as propellants for in-space propulsion. The goal of the study was to identify propellants that are capable of outperforming the current propellants for space propulsion and are significantly less hazardous for humans and the environment. Two types of propellants were investigated, being monopropellants and bipropellants. The first section of the paper discusses the propellant selection. Nitromethane was found to be the most promising monopropellant. As bipropellant, a combination of hydrogen peroxide (HP) and ethanol was selected, where the ethanol is rendered hypergolic with hydrogen peroxide. The second part of the paper describes the experimental verification of these propellants by means of engine testing. Initiation of the decomposition of nitromethane was found to be problematic, hypergolic ignition of the hydrogen peroxide and ethanol bipropellant however was successfully demonstrated.
</abstract>

Green Propulsion Research at TNO the Netherlands

<abstract>
<title style='display:none'>Abstract</title>
This paper presents a concept of a small scale liquid-propellant rocket engine designed in AGH Space Systems for sounding rocket. During preliminary design of thermal aspects various ways of cooling were evaluated and described. Possible issues and design approaches for ablative, radiation and regenerative cooling are raised. The authors describe available solutions. Regenerative cooling is especially concerned as it is most popular solution in bi-liquid engines, in which alcohol fuel acts as coolant and is preheated before it reaches combustion chamber. To estimate a possible temperature distribution - and thus an applicability of such a system in the engine - a mathematical model of heat transfer was developed. Unique element of said engine is its oxidizer - nitrous oxide, which have been rarely used to date. Comparison between typical LOX bi-liquids is given and major differences that affect cooling arrangement are discussed. The authors compared different combinations of coolants, fuel/oxidizer ratios etc. to optimize the temperature distribution which is a key factor for the engine performance.
</abstract>

Preliminary Design Analysis of Regenerative Cooling for N2O/Alcohol Small Scale Liquid Rocket Engine

<abstract>
<title style='display:none'>Abstract</title>
The increasing level of urbanisation and traffic congestion promotes the concept of urban air mobility (UAM), which has become a thriving topic in engineering and neighbouring disciplines. the development of a suitable ground-based infrastructure is necessary to supply these innovative vehicles, which mainly includes networks of take-off and landing sites, facilities for maintenance, energy supply, and navigation and communication capabilities. Further requirements comprise robust business and operating models for emerging service providers and regulatory frameworks, particularly regarding safety, liability and noise emissions. the objective of this study is to provide an overview of the current results and developments in the field of UAM ground-based infrastructure by conducting a systematic literature review (SLr) and to identify the most relevant research gaps in the field. For the systematic literature analysis, our search string contains vertiports and the equivalents, UAM and equivalents, and search phrases for the individual domains. In the final analysis 64 articles were included, finding a strong focus on simulations and vertiport networks, while specific case studies and related aspects like automated MrO and urban planning appear less frequently. therefore, this article provides insights for a more holistic perspective on challenges and necessities of future UAM.
</abstract>

A Systematic Review of Ground-Based Infrastructure for the Innovative Urban Air Mobility

<abstract>
<title style='display:none'>Abstract</title>
Satellites are used for navigation, communication, oceanography, astronomy, etc.. Satellites come in a diversity of sizes and forms. Depending on the satellite’s mission, different subsystems are used. These subsystems are installed inside a housing to protect them from the space environment. This housing, which is also known as the satellite primary structure or mechanical structure, is made of durable materials that can endure severe conditions during launch and in the orbit. The optimisation of satellite mass is crucial right now since satellites are losing mass every day to reduce the cost of manufacturing and launching. This review first introduces an overview of the satellite classifications and subsystems. Then, the different types of mechanical load analysis the satellite subjects itself to are demonstrated. The advanced approaches for promoting the performance of the mechanical structures of satellites are explored, with a spotlight on the effect of the optimisation parameters of isogrid and honeycomb sandwich structures on the mechanical performance of the satellite primary structure. The assembly, integration and testing (AIT) of the small satellite are briefly presented. Finally, the important potential designs to improve the mechanical performance of the satellite primary structure and the challenges of further research are summarised.
</abstract>

Basic Principles and Mechanical Considerations of Satellites: A Short Review

<abstract>
<title style='display:none'>Abstract</title>
The article describes participation of Mi-2 helicopters in both military and civilian operations at sea. Although the multipurpose Mi-2 rotorcraft were not designed to operate in the harsh environment over the sea, they became - in the second half of the 1960s and in the 1970s - a standard type performing a wide array of tasks at sea. Modern turboshaft engines, a favorable weight-to-power ratio and a dual engine configuration were all factors enabling safe flight over the sea, at considerable distances from land. The specialized Mi-2RM variant designed by WSK PZL Świdnik provided the Naval Aviation with an opportunity to establish, in the 1st half of the 1970s, a unique marine air rescue system. The last Mi-2RM used for rescue missions was decommissioned as late as in 2010, although at that stage it was only used for aircrew training purposes. The Navy was also using the Mi-2Ch variant tasked with creating smokescreens to conceal vessels and port facilities. General purpose variants of the helicopter were used to transport people and goods. They also performed well during patrolling missions and while identifying various types of contamination.
As far as civilian use of the helicopters is concerned, Mi-2 versions equipped with special purpose on-board systems supported scientists in the exploration of the Antarctica at two stations of the Polish Academy of Science. The Maritime Authority in Gdynia was also using its own Mi-2 helicopter for over 30 years - until 2015 - for patrolling the Gdańsk and Puck Bays and waters around the Hel Peninsula. The missions were focusing primarily on detecting potential contamination of the coastal areas.
In the former Soviet Union, civilian Mi-2 variants were (and still are) standard equipment of deep sea icebreakers operating in the Arctic and around the North Pole. The machines are mainly used for safety purposes, as well as for transporting scientists and groups of extreme tourists. Approximately a dozen Mi-2 purchased from Russia in the mid-1990s, in turn, were used by the Aviation Force of the Mexican Navy. Unfortunately, no further details regarding their use are available.
</abstract>

Mi-2 Helicopters Operating at Sea

<abstract>
<title style='display:none'>ABSTRACT</title>
The methodology of efficiency analysis of turbulent flow modification by making permeable sections in the streamlined wing surface with the aim to reduce aerodynamic drag is the principal subject of the presented research. The numerical analysis of the effect of laterally and longitudinally located permeable sections on boundary-layer properties showed the following flow features: (1) the most effective place for permeable surface is an upwind side of the wing; (2) multi-sectional blowing can simply be organised as non-uniform (especially in the case of laterally arranged permeable sections) that brings additional flexibility to change the blowing intensity depending on flight mode and, first of all, on angle of attack; and (3) arrays of longitudinal permeable sections allow to intensify turbulent vortical structures exchange in the lateral direction and improve flow stability to stall. Moreover, due to creating the regular anisotropy of the boundary layer in the lateral direction, this modified blowing technique can potentially have some synergistic properties, which can give the additional benefit. All these effects are too delicate and their experimental study cannot be performed with the use of directed measurements of aerodynamic forces. The comparison of the obtained flow properties with the corresponding experimental data demonstrates an appropriate level of agreement.
</abstract>

Various Blowing-Suction Schemes for Manipulating Turbulent Boundary Layers

<abstract>
<title style='display:none'>ABSTRACT</title>
This article presents the results of the analysis of approaches to designing a mobile vacuum system ‘METAMORPHOSIS’ for simulation of space environment, which could help provide services of testing space objects at the request of the customers at a place and time acceptable to them, which allows saving time and assets in the development of space objects, their elements, including satellites. As a result of the conducted analysis, methodological approaches to the determination of the structure of the vacuum system were undertaken. To avoid unanticipated issues and to validate computer-driven modelling, testing in a space simulation chamber is an important part of the quality-assurance process. Spacecraft and their components must withstand extreme temperatures and pressure to travel outside the Earth’s atmosphere. Space simulation testing involves the use of a thermal vacuum chamber to replicate the conditions experienced in space.
</abstract>

Calculation and Design of the Main Equipment for Mobile Space Simulation System

<abstract>
<title style='display:none'>ABSTRACT</title>
The article describes the problem of controlling an aircraft control when performing a landing on a curvilinear trajectory. The adoption of a curvilinear approach trajectory allows reducing the impact of air traffic on the areas adjacent to the airport. Performing the correct approach on the curvilinear path requires support. For the correct execution of the landing manoeuvre on the curvilinear track, it is necessary to establish reference points so that the repeatability of the manoeuvre is ensured, especially in the case of landing more than one aircraft at the same time. In the following parts, the landing control system is presented. Particularly carefully presented is the issue of performing tests of the designed control system, which in the case of the aircraft control system during the approach to landing must be extremely thoroughly verified. The test plan included both verification the correctness of the adopted control laws and their robustness to interference occurring as a result of atmospheric air streams.
</abstract>

Curvilinear Approach to Landing

<abstract>
<title style='display:none'>ABSTRACT</title>
To choose optimal place for wind turbine, you need to know two basic parameters:
<list list-type="order">
<list-item><italic>V</italic>average – the average wind throughout the year (or during the season when more electricity is needed). The total amount of kilowatt hours of electricity you will get, depends on this parameter.</list-item>
<list-item><italic>V</italic>max – the maximum possible dangerous gust of wind during a storm. The required strength depends on this parameter and hence the cost of construction.</list-item>
</list>
In order to evaluate the place itself, it is possible to combine these two parameters to only one physical parameter: <italic>VBojat</italic> – the average wind speed which is devaluated by hurricanes.
In this article, it is called: “Bojatspeed”: <inline-formula><alternatives><inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="graphic/j_tar-2024-0006_ieq_001.png"/><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mi>V</mml:mi><mml:mrow><mml:mtext>Bojat</mml:mtext></mml:mrow></mml:msub><mml:mo>=</mml:mo><mml:mfrac><mml:mrow><mml:msubsup><mml:mi>V</mml:mi><mml:mrow><mml:mtext>average</mml:mtext></mml:mrow><mml:mn>3</mml:mn></mml:msubsup></mml:mrow><mml:mrow><mml:msubsup><mml:mi>V</mml:mi><mml:mrow><mml:mi>max</mml:mi></mml:mrow><mml:mn>2</mml:mn></mml:msubsup></mml:mrow></mml:mfrac></mml:mrow></mml:math><tex-math>\[{{V}_{\text{Bojat}}}=\frac{V_{\text{average}}^{3}}{V_{\max }^{2}}\]</tex-math></alternatives></inline-formula>.
Measurements for <italic>V</italic>average must be done for at least a year, but for <italic>V</italic>max for at least ten years. They are obligatory before any decision about construction of wind turbine. And not generally in the country, but exactly in the particular place. A system of two devices for such measurements is described in this article: anemometer and brazmometer. Both are made in Latvia. They are purely mechanical and include no electronics – that is why they do not require battery or any service during many years.
</abstract>

Preliminary Analysis of Wind Parameters at the Planned Construction Sites of Wind Generators

<abstract>
<title style='display:none'>ABSTRACT</title>
This paper considers the comparative analysis of the physical and mathematical methods of the optimal operation of aviation objects’ automatic control systems, which is an urgent scientific and technical task. The paper also represents the corresponding stability criteria, depending on the operating conditions, and the influence of external factors that allows ensuring the automatic control systems’ reliable operation not only in normal circumstances, but also in the presence of probable disagreements. The scientific novelty of the research lies in developing new stability criteria by means of synthesising the influence of different factors and also the ability to ensure optimal functioning of the automatic control systems. Corresponding mathematical and computer models have been developed. The use of these models allows to determine the optimal stability criteria for control systems with parameters of a different physical nature and ensure reliable operation of electromechanical systems for general and special applications based on the current analysis. The research results are illustrated by corresponding mathematical models, engineering calculations and modelling of the optimal control limits depending on the influence of various factors. The simulation results coincide with the theoretical calculations, which indicates the consistency between the microprocessor-based and software of automatic control systems.
</abstract>

Study of Stability Criteria of Automatic Control Systems By Multiparametric Aviation Objects

<abstract>
<title style='display:none'>ABSTRACT</title>
The flap strut fairing system is made of movable construction inside, but the outer skin is made of composite material. Each day, we can face an expensive repair for movable construction and outer skin as most of the aviation companies are dealing with mechanical issues that are not solved during a long period of time or somebody misses it due to human errors. In this abstract, we will look for options for easier and faster solutions to avoid the expensive operation process.
</abstract>

Flap Strut Fairing System Expluatation and Critical Path Method Use

<abstract>
<title style='display:none'>Abstract</title>
The article presents a research conducted with the project: ‘Additive technology used in conduction with optical methods for rapid prototyping of 3D printed models’ [13]. In this article selected three different 3D printing technologies: Fused Deposition Modeling (FDM), Selective Laser Sintering (SLS) and Material Jetting (MJ). Each of them was tested paying special attention to accuracy and resolution of printed elements. Accuracy tests were conducted on the reference specimens which also showed material texture. These specimens were scanned to verified dimensional deviations of printing methods. Printing resolution was verified on a heat exchanger model which was characterized by complicated structure. The highest accuracy and printing resolution was noticed in the MJ technology, PolyJet method on the Objet Eden 260 VS printing machine and the SUP 707 water soluble support material.
</abstract>

The Accuracy and the Printing Resolution Comparison of Different 3D Printing Technologies

<abstract>
<title style='display:none'>Abstract</title>
Detonation is a promising combustion mode to improve engine performance, increase combustion efficiency, reduce emissions, and enhance thermal cycle efficiency. Over the last decade, significant progress has been made towards the applications of detonation mode in engines, such as standing detonation engine (SDE), Pulse detonation engine (PDE) and rotating detonation engine (RDE), and the understanding of the fundamental chemistry and physics processes in detonation engines via experimental and numerical studies. This article is to provide a comprehensive overview of the progress in the knowledge of rotating detonation engine from the different countries. New observations of injection, ignition, and geometry of combustor, pressure feedback, and combustion modes of RDE have been reported. These findings and advances have provided new opportunities in the development of rotating detonation for practical applications. Finally, we point out the current gaps in knowledge to indicate which areas future research should be directed at.
</abstract>

Review on the Rotating Detonation Engine and It’s Typical Problems

<abstract>
<title style='display:none'>Abstract</title>
Additive Manufacturing (AM) based on Selective Laser Sintering (SLS) and Selective Laser Melting (SLM) is relatively widely used to manufacture complex shape parts made from metallic alloys, ceramic and polymers. Although the SLM process has many advantages over the conventional machining, main disadvantages are the relatively poor surface quality and the occurrence of the material structure defect porosity.
The paper presents key problems directly related to the implementation of AM, and in particular the selection and optimization of process conditions. The first section examines the issues of dimensional accuracy, the second surface quality and porosity problem determining the mechanical properties of manufactured products.
</abstract>

Selected Problems of Additive Manufacturing Using SLS/SLM Processes

<abstract>
<title style='display:none'>Abstract</title>
Eddy current (EC) method is considered as most applicable for in-service detection of fatigue subsurface cracks initiated in aircraft multilayer structures near the rivet holes. At the same time, the successful solution of this problem is obstructed by additional noise created by defect-free rivets. All EC inspection techniques for the detection of subsurface cracks around the rivets can be classified into three main groups: 1) static mode – carried out by placing the EC probe concentrically on the rivet head; 2) rotational mode – when the EC probe is rotated around the rivet axle and 2) sliding mode – performed by the movement of EC probe along the rivet line or near it. All these approaches have some advantages and limitations. In this study, known EC techniques for the detection of cracks in multilayer aircraft structures are analyzed. New advanced EC techniques for the detection of fatigue cracks in internal layers of the riveted structures based on different types (ring, sliding, and rotational) probes are presented. The static EC method with developed low-height ring-type probe creates the possibility to detect cracks in the difficult of access areas. The possibility to estimate the length of detected cracks by a ring-type probe is shown. The proposed rotational remote field EC probe can detect as small as 1.0 mm long cracks under the button-head rivet and 2 mm thick upper skin with a high signal-to-noise ratio. Therefore, in many aircraft structures, fatigue cracks will be detected before a critical threshold achieved. New EC sliding techniques based on remote field and double differential probes were proposed for the rapid detection of cracks in internal layers of riveted aircraft structures. Remote-field EC probe for reliable detection of fatigue cracks in third and fourth layers of five-layer units was proposed. Another sliding technique based on a double differential EC probe gives the possibility to detect transverse cracks in the second layer without the rivet row area access. The main advantage of developed techniques is high inspection reliability due to the possibility to discriminate the signals created by cracks and defect-free rivets. Presented inspection procedures include the selective signal analysis in the complex plane diagram. Proposed EC inspection techniques were successfully implemented into the aircraft maintenance practice.
</abstract>

Detection of the Fatigue Cracks Initiated near the Rivet Holes by Eddy Current Inspection Techniques

<abstract>
<title style='display:none'>Abstract</title>
Aircraft, their assemblies, and units must provide high durability and reliability, and maintain mechanical and technological characteristics throughout the life span of the aircraft. Different elements of aircraft structures work under mechanical loads, over a wide temperature range, with varying degrees of exposure to corrosive environments. Aircraft structural materials have a variation in the characteristics values and require the various testing methods for their inspection.
In many NDT methods applied in aviation materials testing, signals that could be represented by a narrowband processes model are used. Known methods of their processing are focused on determining and analyzing the signals amplitude characteristics, but the information resource contained in phase characteristics is not used.
In the article, the methodology for signal processing and determining phase characteristics in the time domain are discussed. It is based on the combination of the discrete Hilbert transform and the deterministic and statistical methods of the phase measurement. There are given examples of the application of the methodology for pulsed eddy current testing of electrically conductive materials and products, ultrasonic thickness measurement of products made of materials have significant ultrasonic attenuation, the realization impulse variant of acoustic impedance flaw detection of products made of composite materials. The examples have shown that the proposed signal processing methodology enables to determine new information parameters and signal characteristics for the industry, and extend the scope of known NDT methods.
</abstract>

Advanced Signal Processing Methods for Inspection of Aircraft Structural Materials

<abstract>
<title style='display:none'>Abstract</title>
Well-timed detection of the defects (e.g., fatigue cracks and corrosive damages) in aircraft structures is the question of vital importance. Periodic in-service non-destructive inspection (NDI) is necessary to prevent expensive aircraft breakdowns during in-service life. Eddy current (EC) NDI method have many advantages for in-service aircraft inspection due to high mobility and the possibility to detect fatigue cracks without direct contact with the inspected surface (even through a protective coating without removal). Last decades some enhanced EC techniques were developed for aircraft in-service inspection in the Karpenko Physico-Mechanical Institute of National Academy of Sciences (Lviv) in collaboration with Ukrainian and foreign aircraft companies.
Proposed earlier EC efficiency coefficient was applied for the selection of the ferrite-core EC probe parameters. Investigations concerned with the crack detectability for single-coil EC probes of different sizes were carried out to improve the inspection procedures. The sensitivity of the developed single-coil EC probe was experimentally investigated. The possibility to distinguish the signals associated with detected defect and lift-off was shown. The new inspection procedure was proposed for full suppression of the noise concerned with the rivet edge influence.
The high-frequency EC flaw detector of Leotest VD 3.03 type based on self-generator mode and miniature single-coil EC probes application was developed for detection of the surface-breaking fatigue cracks. The original scheme of double-circuit self-generator with intermittent oscillations was invented and investigated. The pulse-repetition frequency of high-frequency oscillations was used as an informative parameter. The important feature of the developed self-generating scheme is the effective suppression of the lift-off influence (the changes of the clearance between the EC probe and the inspected object surface during the scanning).
Developed EC flaw detectors of Leotest VD 3.03 type and inspection procedures were successfully implemented into the maintenance practice for detection of the fatigue cracks initiated in the wing and the fuselage structures and aviation engines in many companies such as ANTONOV AIRCRAFT, Lviv State Aircraft Repair Plant, Konotop aircraft repair plant «AVIAKON», Ukrainian International Airlines, MOTOR-SICH, State Enterprise “IVCHENKO-PROGRESS”, etc.
</abstract>

Enhanced Eddy Current Techniques for Detection of Surface-Breaking Cracks in Aircraft Structures

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