A major challenge for aircraft fuel cell propulsion systems is to ensure that the air properties on the cathode side remain within a narrow, suitable envelope throughout the flight. The components must maintain almost constant temperature, pressure and humidity levels under widely varying ambient conditions. The choice of components must take into account the aviation-specific requirements for weight and waste heat. In this numerical study, we investigate a novel cathode air supply system for a hydrogen fuel cell propulsion system which replaces the state-of-the-art electrical components used to drive the compressor in the cathode air supply system with a hydrogen-fuelled micro gas turbine. Previous studies have shown the potential of waste heat and overall cathode gas path size reduction but the off-design performance of such system is yet to be investigated. Hence, based on realistic regional aircraft flight missions and realistic atmospheric conditions, we investigate the off-design performance of the propulsion system. Therefore, a constant mass flow algorithm along cathode and gas turbine gas paths is developed and presented. Next, earth observation data are used to determine realistic boundary conditions and air contamination. Based on these data, the possible contaminant ingestion of the fuel cell is evaluated to allow for future sizing of filters for robust operation. Furthermore, the effects of realistic ambient conditions on the thermodynamic cycle yield important information about necessary revisions of the cycle design point.

The use of polymer electrolyte membrane fuel cells (PEMFC) to generate propulsion power for future aircraft represents a promising approach to reduce carbon emissions caused by the aviation sector. The design of a PEMFC system requires a detailed consideration of the individual subsystems, such as the air supply and thermal management system. These subsystems have a significant impact on performance, parasitic power requirements, and system mass. For this reason, a comprehensive system analysis is required to evaluate the effects on aircraft performance for the entire flight mission. In Part I of this two-part paper, an initial design workflow is presented, focusing on the design point selection and the design of the turbo components and thermal management. The first objective of this part, Part II, is the integration of the components designed previously into the overall system calculation to cover interdependencies. For this purpose, the off-design performance of the air supply compressor, turbine, and thermal management is considered for a flight mission analysis on a standard and hot day scenario. Thereby, the effects on the propulsion power demand of the aircraft due to component masses, parasitic powers, and additional drag caused by the ram air heat exchanger are taken into account. The overall design process is iterative, as updated aircraft power demand affects the boundary conditions for the component design. The second objective of this study is to evaluate the influences and sensitivities of different operating strategies, power densities, as well as heat exchanger pressure losses on key system parameters such as fuel consumption, waste heat, and system mass. In addition, a weighted mission-specific efficiency is defined in order to facilitate a fast, yet application-oriented assessment of turbo component designs.

Hydrogen fuel-cell-powered all-electric aircraft are promising for decarbonizing short-range aviation, but the substantial low-temperature waste heat demands a compact thermal management system (TMS). This study presents a methodological framework for the integrated co-design of the TMS and powertrain using multi-objective optimization and holistic mission-level analysis to identify optimal TMS designs and operating strategies. Changes in TMS net drag translate into changes in required aircraft thrust, while changes in powertrain, TMS, and fuel mass affect the available payload under a constant maximum take-off mass assumption. This iterative process yields performance metrics across TMS cooling architectures (parallel or series), heat exchanger mass-drag characteristics, coolant temperature targets (50, 70, or 90 degrees C), and installation objectives (minimizing mass or ram-air duct length). The optimal design is a parallel cooling architecture that balances mass-specific heat rejection of 4.77 kW kg-1 at hot-day take-off with drag-specific heat rejection of 1.29 kW N-1 at standard-day cruise. A reduction in coolant temperature at standard-day missions entails no significant performance penalties and could improve the efficiency of electrical components. A shorter ram-air duct significantly decreases the available payload by 630 kg but may facilitate nacelle integration. The findings underscore that holistic TMS-powertrain co-design and optimization is essential for rigorous design of sustainable all-electric aircraft.

The development of novel propulsion systems is essential to achieve the zero-emissions goals in aviation. One promising approach is the electrification of aircraft engines using hydrogen-based polymer electrolyte membrane fuel cells (PEMFC). In addition to the fuel cell stack, the propulsion system includes several subsystems, which determine the mass and volume and thus the feasibility of the architecture. A key subsystem is the cathode air supply, which preconditions the air for efficient and reliable operation. The compressor work required to pressurize the air has a significant impact on the power requirements, efficiency, and mass of the overall system. In addition, the operating range of the compressor influences the possible operating strategy of the fuel cell system. Another crucial subsystem of PEMFC-aircraft is the thermal management system, which manages the heat rejection of all heat sources. The paper is organized into two parts. In this part, Part I, a design approach for the air supply system and its components is presented. The objective is to apply the design method to a reference medium-range aircraft with a variable number of cathode air supply systems. This is an important decision point that influences both the design of the individual components of the cathode air supply system and the aircraft design, and thus the performance during the entire flight mission. The design points and boundary conditions are derived from an overall system simulation. Based on this, the compressor, turbine, and thermal management system are designed for the identified design points.

Purpose The purpose of this study was to increase knowledge of digital service innovation in servitisation by extending design principles and proposing an innovation process design for smart product-service systems (PSS) development. Furthermore, the study addresses the alignment of multiple stakeholders in the development of smart PSS, thereby bridging the gap between theory and practice. Design/methodology/approach A qualitative 17-month action design research approach was taken. This study designed an innovation process for smart PSS development. For this, different development streams were synchronised and multiple stakeholder perspectives were integrated. Drawing on the socio-technical systems perspective as theoretical lens, the authors utilised knowledge in the field of digital service innovation and servitisation. In multiple iterations, the authors, together with practitioners, explored how best to synchronise different smart PSS development activities to ensure subsequent operations of the system. Findings The findings of the longitudinal study conducted with the manufacturing firm uvex propose a hybrid stage-gate innovation process design for smart PSS development. An evaluation with several international academics and practitioners enhances the rigour of the innovative approach. Originality/value The findings contribute to the literature on digital service innovation and servitisation by applying a rarely used socio-technical perspective to innovation process design for smart PSS development. The longitudinal approach over 17 months in a qualitative action design research setting adds to the knowledge base with novel insights from practitioners’ problems.

Aircraft icing poses a significant safety risk, making the replication of atmospheric icing conditions in a laboratory environment essential. Current ice generation methods for preliminary testing of ice protection systems primarily rely on silicon molds for static ice and icing wind tunnels for impact ice. However, due to the different freezing processes, static and impact ice differ, limiting the relevance of preliminary tests. This paper introduces a novel ice printer as a simplified method to generate impact ice on a small scale comparable to that produced in icing wind tunnels. For validation, ice specimens generated with the ice printer are compared to those from an icing wind tunnel and silicone molds. The comparison is based on optical properties, density, and adhesion strength measured via centrifuge testing. Results show that the ice printer can reproduce a range of icing conditions similar to those generated in icing wind tunnels, in terms of density and adhesion strength. The static ice specimens generated with silicon molds show similar density but slightly higher adhesion strength. Based on these findings, the ice generated with the printer can be classified as impact ice. Additionally, this novel method offers high reproducibility and significantly improves cost and time efficiency compared to traditional icing wind tunnels.

Um dem Klimawandel zu begegnen, ist u. a. ein Umstieg von Fahrzeugen mit Verbrennungsmotoren auf E-Fahrzeuge geboten. Konsequenterweise ist in Deutschland eine stark zunehmende Anzahl von E-Fahrzeugen zu beobachten. In diesem Zusammenhang stellt sich die Frage, ob und - wenn ja - wie sich diese Entwicklung auf Brandrisiken in Parkgaragen auswirkt. Antworten auf diese Frage gibt ein Forschungsprojekt unter Federfuhrung des Instituts fur Stahlbau der Leibniz Universitat Hannover in Kooperation mit dem iBMB, Fachgebiet Brandschutz, der TU Braunschweig. Konkret ging es darum, wie sich die unterschiedlichen Brandszenarien von E-Fahrzeugen im Vergleich zu Fahrzeugen mit Verbrennungsmotoren auf das Tragverhalten von Stahl- und Stahlverbundkonstruktionen in offenen, oberirdischen Parkhausern auswirken. In diesem Beitrag wird die methodische Vorgehensweise zur Bewertung des Brandrisikos auf Basis einer Zuverlassigkeitsanalyse fur die Tragstrukturen dieser Parkgaragen erlautert. Mittels der Zuverlassigkeitsanalyse wird an exemplarischen Brandszenarien fur einen Verbundtrager die Vorgehensweise zur Bewertung des Brandrisikos dargestellt. Im Ergebnis kann aus der Brandrisikoanalyse abgeleitet werden, dass Brandszenarien mit E-Fahrzeugen keine hoheren Risiken als herkommliche Fahrzeuge mit Verbrennungsmotoren bergen und das gebotene Sicherheitsniveau erfullen. Fire risk analysis of electric vehicles and internal combustion vehicles in open car parks: part 2: fire safety and reliability analysisIn order to counteract climate change, it is necessary to switch from vehicles with combustion engines to electric vehicles. Consequently, an increasing number of electric vehicles can be observed in Germany. In this context, the question arises whether and if how this development influences the fire risks in open car parks. Answers to this question are the subject of a research project under the leadership of the Institute of Steel Construction of Leibniz University Hannover in cooperation with the iBMB, Division of Fire Safety, of TU Braunschweig. In particular, the project is investigating the influence of a fire scenarios with electric vehicles compared to vehicles with combustion engines on the load-bearing behaviour structure of an open car park. In this paper, the methodological approach to evaluate the fire risk based on a reliability analysis for the load-bearing structure of these car parks is explained. By means of the reliability analysis, the fire risk assessment procedure is illustrated for the composite beam using exemplary fire scenarios. As a result, it can be concluded from the fire risk analysis that fire scenarios with electric vehicles do not have a higher fire risk than conventional vehicles with combustion engines and fulfil the required safety level.

Folding wingtips address the challenges posed by high-aspect-ratio wings, such as airport conformity and increased wing root bending moment. Actuated adaptive wingtips extend the functionalities of folding wingtips by using a stiffness-adaptive aeroelastic hinge that is actively adjustable in flight. The objective of this paper is the aeroelastic analysis of a wing equipped with an adaptive-stiffness hinge. While the structural design of the wingtip actuator based on pressure-actuated cellular structures (PACS) was developed in a previous study, in this study the authors verify the concept of actuated adaptive wingtips through aeroelastic analysis. This study shows that the investigated PACS actuator, structurally designed from glass-fiber-reinforced plastic, is capable of bearing the loads acting on the wingtips of a Cessna Citation X. The adaptive-stiffness hinge, positioned between 86.7 and 91.2% of the semispan, reduces the wing root bending moment by up to 7.8% in a 2.5[Formula: see text] maneuver load case, while keeping the wing straight in cruise. A further increase in load alleviation potential can be achieved in the future by extending the actuator’s operating envelope and thus increasing its load-bearing capacity. The functional verification of the actuated adaptive wingtip concept by means of aeroelastic analysis forms the basis for the manufacturing and testing of a functional prototype.

Folding wingtips address the challenges of high aspect ratio wings, such as airport conformity, increased wing root bending moment, and reduced aircraft maneuverability. The functionalities of free-flapping folding wingtips can be extended with multifunctional wingtip actuators that allow for active adjustment of the wingtip's cant angle and hinge stiffness. The objective of this paper is the identification of governing factors influencing the adaptive-stiffness characteristics of pneumatic rotary actuators. The authors experimentally determine the characteristics of such a commercially available pneumatic rotary actuator and formulate analytical equations for actuator moment and stiffness as well as the wingtip's natural frequencies. The actuator characteristics can be accurately described by an isobaric or adiabatic process, depending on the pneumatic setup. The pneumatic actuator exhibits zero stiffness in a pressure-regulated mode, whereas targeted adjustment of the actuator stiffness is possible by shutting off the mass flow into the actuator chambers. The formulated equations allow a detailed design of multifunctional wingtip actuators for application in highly efficient high aspect ratio aircraft. The findings of this study can be transferred to hydraulic rotary actuators, which would be required to achieve the necessary load-bearing capacity for application in larger transport aircraft.

To operate small and medium-sized helicopters even under critical icing conditions, new deicing technologies are necessary because the existing heating solutions cannot be economically downscaled without drastically reducing the helicopters’ payload. Therefore, this paper investigates the potential of a low-frequency electromechanical deicing (EMDI) system for an actual fiber composite helicopter structure and its combination with an ice detection system that uses the EMDI components for ice detection. The primary objective of this study is the design of the deicing system for a given helicopter structure and its evaluation under realistic icing conditions. Experimental and numerical modal analyses are used to analyze the vibration behavior of the structure and to select favorable positions and phase relations for the actuators. To determine the performance of the EMDI system, experimental deicing tests were performed in a deicing test facility that is able to generate realistic icing conditions. The EMDI system can cause delaminations and cracks in glaze ice layers and partially remove the ice on the test object. The results show that there is an upper and lower limit for ice thickness at which the system is effective. Therefore, the system needs to be combined with an ice detection system that is capable of measuring the ice thickness on the surface of the structure. Using the piezoelectric actuators of the EMDI, this can be achieved by monitoring their impedance changes, which is experimentally proven for different ice thicknesses and different temperatures on a carbon fiber composite plate. The findings of this study support the idea of a combined ice detection and deicing system using the same hardware components. Integrating an autonomous control system, local icing phenomena on a rotorcraft structure can be detected and consequently, ice accretion can be removed with low energy consumption.

To unlock the potential of natural laminar flow aircraft wings, novel structural designs are necessary for the wing leading edge and its attachment. Those designs may not impinge on operability and maintenance of the aircraft. This paper presents a leading edge and attachment design for the natural laminar flow environment as well as the testing of this design on a large-scale ground -based demonstrator. The leading edge design is numerically verified by considering operational loads. For operational viability, the replacement of damaged leading edges without alterations to the spare part is desirable. In a series of tests, such interchange trials are made with two 2.3 m full complexity leading edge segments and the aerodynamic step height at the interface of leading edge and wing cover is assessed in both ground and cruise deformation. The leading edge design and its attachment concept were proven to support natural laminar flow step height requirements even under global part deformations of a multi -material structure under thermal loading both numerically and experimentally. Interchangeability of the leading edge is demonstrated with very low mean variation in step height between different installations.

This paper investigates the cathode air supply system of a medium-range fuel cell-powered aircraft. The main focus is on determining a suitable system architecture. Based on the literature, promising humidification and cooling strategies for cathode gas preconditioning are identified and evaluated. System configurations with membrane and spray humidification as well as intercooling between compressor stages and wet compression are calculated using a thermodynamic cycle calculation model. By analysing the design parameter spaces of the cathode air supply systems, the different configurations are compared in terms of their influence on key system parameters such as specific fuel and parasitic power consumption or heat exchanger size to find the most promising architecture. Further, the operating limits of the systems at different operating pressures and temperatures are determined. The second area of focus is the identification of a suitable system design point. It is discussed that the most critical operating points of the individual components are located at different flight conditions. Therefore, off-design performance is taken into account in order to design the entire system. A model based on the constant mass flow method is introduced to calculate steady state operating points for the system using membrane humidification. It can be seen that the turbo components have their design point at top of climb operating point, while the heat exchanger has to be designed for the maximum waste heat at take-off and the humidifier for the most critical operating point in terms of membrane water content at cruise.

Modern aircraft designs with high aspect ratio wings pose challenges in accurately determining vibrational modes due to the increased flexibility of their wings. To accurately represent the large deformations occurring during flight in experimental modal analysis, actuators of low stiffness are needed, leading to the exploration of quasi-zero-stiffness vibration isolators. Such vibration isolators, combining positive and negative stiffness elements, lack the adaptability needed for varying wing load conditions. This study explores bellow-type soft pneumatic actuators, fabricated using 3D printing for iterative design and parameter studies, as a potential solution. Initial experiments and simulations focused on the actuator stiffness for different geometric parameters and pressures. While simulations suggested that the occurrence of zero stiffness was primarily influenced by geometric parameters like the radius-to-height ratio, experimental results did not align with these findings, revealing discrepancies due to unmodeled boundary conditions. This misalignment highlighted the challenges in achieving the desired zero-stiffness characteristic in practical applications. In conclusion, This study reveals that current bellow-type actuators fall short of the near-zero stiffness required for accurate modal analysis in flexible aircraft structures. Despite promising simulation results, experimental discrepancies highlight the need for improved designs and testing methods. Future research, potentially exploring rolling lobe actuators and refining 3D printing techniques, remains crucial in the ongoing quest for an ideal actuator in this domain.

Shape-morphing structures based on pressure actuation promise efficiency gains and performance improve-ments in aeronautics, but require complex three-dimensional geometries. The compliance of these morphing structures originates from local areas of reduced wall thickness. However, the required high wall thickness ratios are challenging for integral fabrication from high-performance fiber-reinforced plastics, which are demanded to achieve high load-bearing capacity. This study investigates different woven flexure hinges made from a hybrid yarn of glass fibers and the polyamide PA6 for application in pressure-actuated cellular structures. The flexure hinges are mechanically characterized under pure axial and pure bending loading in a tensile and a column bending test method specifically derived for flexure hinges. The specimen quality is further assessed by permeability testing, optical microscopy, and thermogravimetric analysis. This study shows that the stiffness of anisotropic flexure hinges can be determined in simple mechanical tests without the need for complex modeling of reinforcing fibers or consideration of manufacturing-specific effects. The mechanical properties of a double-layer hinge configuration are superior to those of a single-layer configuration, whereas integrating additively manufactured PA6 inlays into the woven preform offers an effective approach for achieving high wall thickness ratios. The most promising hinge configuration is selected for the integral fabrication of the aeronautical morphing structure, which consists of multiple pressurized cells.

Due to climate changes and environmental considerations, the current transportation changes to modern vehicles with different vehicles models and engine types. Especially vehicles with alternative types of drive, such as electrical vehicles, are increasing. This raises the question of whether modern vehicles, such as electric vehicles, lead to an increased fire risk as well as an increased heat release rate (HRR). In this article, a new fire design approach for modern vehicles is presented to evaluate the fire risk of electric vehicles compared to vehicles with combustion engines with respect to the fire resistance of the structural elements in open car parks. For this purpose, HRRs of different vehicles are analyzed and an approximated approach for modern vehicles is derived. The methodology can be used for performance‐based design, where the HRR plays a fundamental role. Furthermore, modeling approaches of the vehicle dimensions are presented, which are based on statistical data of the German Federal Motor Transport Authority. The vehicle dimensions are used to determine the fire spread time between vehicles using a parameter study. Based on the statistical data analyses and the parameter studies, this article provides a new fire design approach for modern vehicles in fire.

Aufgrund steigender Online-Konkurrenz, zunehmenden Kostendrucks und omnikanaler Customer JourneysCustomer Journeys versucht der stationäre Handel durch den Einsatz innovativer Technologien neue Mehrwerte für Kunden zu bieten. In diesem Zusammenhang wird der Einsatz von Servicerobotern am Point of SalePoint of Sale (POS) ebenso kontrovers wie erwartungsvoll diskutiert, die Akzeptanz der Kunden ist dabei eine entscheidende Voraussetzung. Studienergebnisse zeigen, dass der unmittelbar wahrgenommene Nutzen des Serviceroboters für die langfristige Nutzungsabsicht entscheidend ist. Während sich die wissenschaftliche Forschung bislang überwiegend darauf konzentriert, die Haltung von Kunden und Verkaufsmitarbeitern gegenüber Servicerobotern zu verstehen oder einzelne Anwendungsfälle von Servicerobotern zu validieren, bleibt für einen zielgerichteten Einsatz von Servicerobotern offen, für welche expliziten Tätigkeiten ServiceroboterServiceroboter am POS geeignet erscheinen. Im Rahmen einer explorativen Interviewstudie wurden zwölf Handelsexperten und zwölf Experten aus dem Bereich Servicerobotik zu Einsatzmöglichkeiten von Servicerobotern am Point of Sale befragt. In Anlehnung an die Task-Technology-Fit-Theorie wurden relevante Tätigkeiten und Fähigkeiten von Frontstage-Mitarbeitern mit den gängigen technischen Leistungsmerkmalen von am Markt erhältlichen Servicerobotern abgeglichen und deren Relevanz für das Verkaufsgespräch gewichtet. Die Ergebnisse des Abgleichs wurden entlang der fünf Phasen eines Verkaufsgesprächs strukturiert. Basierend darauf wurden die Erkenntnisse in eine Weboberfläche überführt, welche Wissenschaftler und Praktiker für eine erste schnelle Indikation über die Einsatzmöglichkeiten von Servicerobotern am POS nutzen können.

Service robots (SR) have the potential to revitalise value creation in brick-and-mortar retailing. While both the competitive and evolving nature of the retailing industry as well as customers and FLE have obtained substantial coverage in academic literature, the managerial angle towards SR in organisational frontlines has rarely been addressed in service research. This qualitative exploratory interview study explores retail managers' perceptions of SR in organisational frontlines. Building on 28 in-depth interviews with retail managers, three dimensions of predisposing factors (impact on the functional, relational and organisational level), as well as two aggregated dimensions of managerial coping strategies (transforming FLE and work routines) were identified. Further, the findings reveal that retail managers perceive inherent difficulties in balancing the needs of customers and FLE when it comes to effective SR implementation.

The design of compliant mechanisms requires detailed knowledge about the stiffness properties of their flexible segments. However, there are no standardized test methods for flexure hinges, and therefore the influence of manufacturing-specific effects, such as anisotropy, on the stiffness properties cannot be quantified. This paper presents novel test methods for variable cross-section flexure hinges subjected to large deformations and pure bending loading, which determine the bending stiffness of flexure hinges over their entire deflection range using a universal testing machine. The novel test methods for flexure hinges are based on the tensile test, the four-point bending test (FPBT), and the column bending test (CBT). These test methods were initially formulated for constant cross-section specimens, but are adapted in this study to examine variable cross-section specimens. The derived test methods are validated by using isotropic materials with well-known properties and by comparing the calculated deflections with deflections measured by means of image processing. The deflection validation shows that the adapted CBT (aCBT) is accurate over the entire deflection range, achieving curvature of up to κ =0.40 mm^-1 , whereas the maximum curvature in the adapted FPBT (aFPBT) is limited by the test methodology to about κ =0.15 mm^-1 . At small strains, the flexural modulus determined in the aCBT and aFPBT agrees well with the Young’s modulus determined in the tensile test, as would be expected for isotropic materials. The aCBT proves to be a suitable test method for flexure hinges at large deflections, whereas the stiffness characterization at small deflections can be performed with both the aCBT and the aFPBT. The presented test methods validated on isotropic materials form the basis for characterizing anisotropic flexure hinges with geometry-dependent stiffness properties.