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    Sound Perception Study of Auralized Novel Propeller Design for Future Electrical Air Mobility Platforms
    (AIAA, 2024) Aalmoes, R. ; Knepper, K.M. ; Sieben, N.R. ; Haan, W. de ; Margalida, G. ; Sinnige, T.
    To reduce climate impact of aviation, it is imperative to consider to introduce aircraft based on electrical engines. These electrical aircraft replace jet engines by propeller-driven propulsion systems, making the propeller the dominant noise source. A quieter and more efficient propeller blade design may generate a different noise signature, justifying a perception study to assess overall noise impact. In this study, a novel designed propeller “S2PROP” is compared with a baseline propeller “XPROP”. Both blades were measured in an aeroacoustic wind-tunnel, and wind-tunnel measurements of tonal and broadband noise were used as an input to generate fly-over sound samples of an aircraft equipped with these propellers. Atmospheric absorption, the secondary ground reflection path and Doppler effect were considered in creating a synthesized flyover sound. A noise simulator with virtual reality glasses and headphones was used to simulate both a visual and audible flyover procedure for participants of the perception study. Although a noise reduction is attained at the highest sound level around 600Hz for the S2PROP, it also generates higher broadband sounds at higher frequencies, resulting in finding no significant differences in perceived loudness or annoyance in the study between the two propeller designs.
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    Hybrid inspection method using 3 dimensional scanning, lock-in thermography and laser shearography
    (NDTnet, 2024) Jansen, H.P. ; Platenkamp, D.J. ; Hwang, J.S.
    The proportion of composite materials (such as CFRP) to the metal used on the modern aircrafts is rising, imposing different kind of failure modes. Since the composite structures are known to be sensitive to the impact loading, there is need for means to assess the sub-surface damage in the structure rapidly. Royal Netherlands Aerospace Centre NLR has an extensive track record on contactless non-destructive inspection (NDI) methods based on optical sensors, such as 3D surface scanning, lock-in thermography and laser shearography. The combination of these methods (multi-domain inspection) enables us to assess the structural integrity of an aircraft outer surface in a short time, reducing inspection costs and the “down time” of the aircraft. Recently, NLR is working towards a 3D oriented mesh environment of an object, enhanced with NDI data, providing sub-surface damage information. By automatically stitching the 3D object images, it is possible to expand this method for a complete scan of an aircraft surface. Furthermore, the thermographic and shearography imaging information has been integrated into the 3D surface accounting for the image distortion from the different measurement angles. In this paper, the results from the various studies will be presented involving integration of the 2D measurements with the 3D scan mesh. Keywords: Thermography, Shearography, 3D scanning, Data fusion
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    An Assessment of STPA as Applied to the Scaled Flight Demonstrator Test Program
    (SFTE, 2024) MacCafferty, J.P. ; Bumgardner, W.R.
    Systems Theoretic Process Analysis (STPA) is a methodology for system development and safety assessment which builds on the System-Theoretic Accident Model and Processes (STAMP) causality model which approaches safety as a dynamic control problem. The STPA methodology addresses system analysis and safety assessment for systems that involve complex human interactions and high degrees of coupling. The purpose of this paper is to demonstrate the application of STPA to the remotely piloted Scaled Flight Demonstrator (SFD) aircraft test program, and assess the effectiveness for test planning and risk assessment relative to the traditional Test Hazards Analysis (THA) process. The SFD aircraft is a 1:8.5 scaled model of the Airbus A320 which has been modified into a distributed electric propulsion (DEP) configuration. The aircraft was developed in collaboration with members of the Clean Sky 2 program: The Royal Netherlands Aerospace Centre (NLR), Technische Universiteit Delft (TU Delft), The Office national d'études et de recherches aérospatiales (ONERA), Centro Italiano Ricerche Aerospaziali (CIRA), Airbus, and Orange Aerospace. This effort identifies multiple benefits for flight testers when applying STPA to a highly complex system, including: increased knowledge of the system under test, forced collaboration between the test team and system experts, and identification of risks and mitigations that may otherwise be missed. The team also identifies some drawbacks to applying STPA, including: the time investment required to learn and apply the process, and the challenge in identifying specific hardware or software failure modes. Lessons learned and recommendations are presented to help other flight test professionals determine how and when STPA can best be applied to their programs in the future.
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    Robustness Levels of Critical Infrastructures Against Global Navigation Satellite System Signal Disturbances
    (MDPI, 2023) Bos, A. ; Snijders, M. ; Zevenbergen, A. ; Drost, K. ; Zelle, H.D. ; Hoeven, B. van der
    Resilience against signal disturbances is an important characteristic of GNSS-based PNT solutions. In particular, for critical infrastructures, failure to provide correct PNT information in these domains may have a major societal impact. The Resilience Framework by the Department of Homeland Security (DHS) provides a set of requirements and guidelines to design a PNT solution of a certain level of resilience. Over the lifetime of the applications, it will be of prime importance to assess the resilience of the PNT solutions on a regular basis. Given how often GNSS-based solutions are being applied, partly automating the assessment process will be needed to make this task feasible. To automate the generative process, a machine-readable structure with well-established meaning is required. In this work, the use of fault trees as a formal system to encode the resilience framework is investigated.
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    Evaluating the climate impact of aviation emission scenarios towards the Paris agreement including COVID-19 effects
    (Springer Nature, 2022) Grewe, V. ; Rao, A.G. ; Gronstedt, T. ; Xisto, C. ; Linke, F. ; Melkert, J. ; Middel, J. ; Ohlenforst, B.A. ; Blakley, S. ; Christie, S. ; Matthes, S. ; Dahlmann, C.
    Aviation is an important contributor to the global economy, satisfying society’s mobility needs. It contributes to climate change through CO2 and non-CO2 effects, including contrail-cirrus and ozone formation. There is currently significant interest in policies, regulations and research aiming to reduce aviation’s climate impact. Here we model the effect of these measures on global warming and perform a bottom-up analysis of potential technical improvements, challenging the assumptions of the targets for the sector with a number of scenarios up to 2100. We show that although the emissions targets for aviation are in line with the overall goals of the Paris Agreement, there is a high likelihood that the climate impact of aviation will not meet these goals. Our assessment includes feasible technological advancements and the availability of sustainable aviation fuels. This conclusion is robust for several COVID-19 recovery scenarios, including changes in travel behaviour.