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    A challenging high-end data acquisition system in a harsh wind tunnel environment at high rotational speed
    (3AF, 2023) Bardet, S.M. ; Zutphen, W.J.C.M. van ; Fontaine, F.M. ; Faasse, P.R.
    NLR developed an advanced, high-performance data acquisition system for a generic engine test rig. The test rig is intended for wind tunnel use. The RDAS and MDAS subsystems are bespoke developments, supporting a total of 120 rotating and almost 700 stationary measurement channels. All measurements are made under harsh environmental conditions: wide temperature range and high vibration levels. The rotating section tolerates rotation up to 16,000 rpm.
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    A Crosstalk Sensitivity Analysis on Bundles of Twisted Wire Pairs
    (IEEE, 2018) Lansink Rotgerink, J.H.G.J. ; Leferink, F.
    Uncertainties in the geometry of complex cable bundles highly complicate crosstalk predictions. A change in for instance the position or the twist rate of individual cables in a bundle might have an impact on crosstalk levels. Application of sensitivity analyses can indicate which model parameters are most sensitive, and in which cabling configurations. In this paper, the efficient Stochastic Reduced Order Models (SROM) method is used to perform such a sensitivity analysis. It is applied to two cable bundles with two and seven twisted wire pairs, respectively. Monte Carlo simulations are performed to determine the accuracy of the SROM method. The sensitivity of parameters like inter-pair and intra-pair separation distance and the twist rate is determined in two different cases. Moreover, the effects of bundle twist and cable meandering to parameter sensitivities is investigated.
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    A Framework for Integrity Monitoring for Positioning through Graph-based SLAM Optimization
    (MDPI, 2025) Bekkers, S.M. ; Engwerda, H.J.A.
    As satellite navigation show vulnerabilities in specific circumstances such as urban canyons or jamming and spoofing situations, additional sensors such as cameras may be incorporated on the platform. Despite advancements in the robotics and computer vision community, which have lead to increasingly accurate Simultaneous Localisation and Mapping (SLAM) positioning solutions, visual navigation has its own vulnerabilities. It remains therefore of critical importance for many applications to study the integrity of fused navigation algorithms and their components, which is done less for SLAM than for satellite navigation. In this paper, a framework for integrity monitoring (IM) of a visual SLAM algorithm is proposed. A sensor-level IM scheme analyses feature reprojection errors. It is demonstrated that in dynamic environments multiple hypotheses can be generated from different subsets of feature measurements. Additionally, the factor graph-based framework employs a fusion-level IM scheme which deals with these multiple hypotheses and selects the most probable one by calculating the sum of weighted measurement residuals. These concepts are applied to scenarios from real and simulated experiments in order to demonstrate applicability.
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    A Heat Pump for Space Applications
    ( 2015) Gerner, H.J. van ; Donk, G. van ; Pauw, A. ; Es, J. van ; Lapensée, S.
    In commercial communication satellites, waste heat (5-10kW) has to be radiated into space by radiators. These radiators determine the size of the spacecraft, and a further increase in radiator size (and therefore spacecraft size) to increase the heat rejection capacity is not practical. A heat pump can be used to raise the radiator temperature above the temperature of the equipment, which results in a higher heat rejecting capacity without increasing the size of the radiators. A heat pump also provides the opportunity to use East/West radiators, which become almost as effective as North/South radiators when the temperature is elevated to 100°C. The heat pump works with the vapour compression cycle and requires a compressor. However, commercially available compressors have a high mass (40 kg for 10kW cooling capacity), cause excessive vibrations, and are intended for much lower temperatures (maximum 65°C) than what is required for the space heat pump application (100°C). Dedicated aerospace compressors have been developed with a lower mass (19 kg) and for higher temperatures, but these compressors have a lower efficiency. For this reason, an electrically-driven, high-speed (200,000 RPM), centrifugal compressor system has been developed in a project funded by the European Space Agency (ESA). This novel 3-stage compressor system has a mass of just 2 kg and a higher efficiency than existing aerospace compressors. The compressor system has been incorporated in a heat pump demonstrator, which uses isopentane (R601a) as refrigerant. Due to the exposure of isopentane to radiation in a space application, other substances will form. However, a literature study shows that the amounts of the formed substances are so small, that no significant influence on the performance of the heat pump is expected. Tests were carried out with the heat pump, and at the target setting (saturation temperature of 45°C at the evaporator, 100°C at the condenser, and a payload heat input of 5 kW), the measured COP is 2.3, which is higher than the original requirement of 2.
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    A Literature Review and Proposal Towards the Futher Integration of Haptics in Aviation
    (Springer, 2024) Lange, R.D. de
    Flight simulator training is essential for aircraft pilots to learn and maintain the ability to fly specific aircraft for both commercial and defence purposes. With recent advances in extended reality, the implementation thereof has made its way into proposed simulated flight training protocols. In conjunction to the advent of extended reality, research into the use of haptics or the sense of touch within VEs has accelerated. A few challenges persist within simulation training including training effectiveness, level of immersiveness, and the manageable exposure duration per training run. Extended reality experiences face similar challenges. The field of haptics might provide solutions for these challenges. Thus, this paper reviews the state-of-the-art of haptics, current challenges, and possible future applications within aviation simulation and training. It is found that research with respect to the integration of haptics in aviation training and simulation is not yet mature. A lot of potential exists for research into the improvement of training effectiveness, performance and immersiveness within extended reality based simulation for flight training and maintenance engineering purposes via haptics. Based thereupon future work is suggested to look into 1) decreasing simulator sickness by simulating and synchronizing expected real life perturbations within flight simulation via haptic wearables 2) simulating a sense of physical flight within a static simulator set-up by leveraging self-motion 3) enabling physical interaction of aircraft parts digital twins for improving extended reality based maintenance engineering performance by utilizing haptic wearables.
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    A Review on Education and Training Needs for Military Space Operations
    (NTSA, 2024) Caso, S. ; Tanis, T.P. ; Kleef, A.J.P. van
    Space is a dynamic and rapidly evolving domain, driven by the increased engagement across the commercial, scientific, governmental and military sectors. Particularly, operations in low Earth orbit (LEO), medium Earth orbit (MEO) and geostationary Earth orbit (GEO) play a vital role in sustaining infrastructures for daily on-Earth activities, e.g., global positioning system (GPS) and 5G. In 2019, a significant milestone was reached with the adoption of NATO’s Space Policy, officially recognizing space as a distinct operational domain alongside land, air, sea and cyberspace. This integration positioned space capabilities as an integral part to military strategies, supplying vital information for secure operations. Due to the growing dependency of space infrastructures, military personnel must be trained to be able to effectively operate space assets and to be prepared for hostile or environmental calamities. This paper conducted a state-of-the-art analysis of military training needs in the realm of space. A literature review was made, encompassing the current scientific literature in space training, with the latest topics from several space agendas outlined by relevant organizations and countries. In addition, interviews were conducted, complemented by surveys, in order to identify the current training gaps and areas for improvement. The findings identified several research gaps and needs related to training and education tools, with a specific emphasis on the Space Situational Awareness (SSA) and Space Traffic Management (STM) topics. These recommendations were particularly addressed to the recognizing and mitigating of potential calamities, a concern heightened by the dense presence of satellites in the Earth's orbit. Additionally, a training gap was identified within the use of satellite images for Intelligence, Surveillance & Reconnaissance (ISR) activities. These activities play a vital role in supporting military operations with their decision-making processes, by improving situational awareness on land, in air, and at sea. Finally, suggestions were made regarding the use of the latest technological tools.
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    A systematic literature review of low-cost 3D mapping solutions
    (Elsevier, 2025) Balado Frias, J. ; Garozzo, R. ; Winiwarter, L. ; Tilon, S.M.
    In "low-cost" solutions, ensuring economic accessibility and democratizing the availability of emerging technologies stand as pivotal considerations. This study undertakes a systematic literature review of low-cost 3D mapping solutions. Leveraging SCOPUS as the primary database, a comprehensive bibliometric analysis encompassing 1380 publications was conducted, subsequently narrowing the focus to 87 recent publications for detailed review. This research endeavors to delineate the defining characteristics of low-cost systems, elucidate their principal applications and preferred platforms, assess accessibility level, gauge the extent of innovation in both hardware and software development, explore the contributions of Deep Learning and data fusion, evaluate the consideration of data quality, and examine the contemporary relevance of photogrammetry within low-cost context. The findings demonstrate that many authors subjectively use the term low-cost to highlight qualities of a technology, methodology or sensor, but challenges arise from data quality comparisons with high-cost systems.
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    Acoustic Lucky Imaging for microphone phased arrays
    (Elsevier, 2023) Biesheuvel, J. ; Tuinstra, M. ; Santana, L.D. de ; Venner, C.H.
    Acoustic imaging methods are used to detect and quantify aerodynamic noise sources in aeroacoustic experiments. In wind tunnels with an open jet test section the sound wave propagating from an aeroacoustic source to a microphone array is distorted by the shear layer in the propagation path. The velocity fluctuations caused by the turbulence in the shear layer continuously alter the propagation time between source and observer causing reduction of the coherence between two microphone signals. The reduction in coherence is stochastic and dependents on the relative position between source and microphone. This leads to blurred acoustic source images with reduced peak Sound Pressure Level. This paper presents the Acoustic Lucky Imaging methodology, based on a methodology in astronomy to correct for image distortion due to turbulence present in Earth’s atmosphere. Furthermore, a model for coherence loss is derived to explain the loss of acoustic image resolution and allow for a-priori estimates on acoustic image blurring. The methodology is applied to an acoustic data set obtained in the open jet of a large industrial wind tunnel. It is shown that the presented methodology can restore a loss of 6 dB peak Sound Pressure Level by 3 dB and increase the resolution of the acoustic image at 8 kHz, a wind tunnel speed of 34 m s−1, and a shear layer thickness of ~1 m.
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    Addressing Non-Uniqueness in GuidedWave Tomography for Limited-View Corrosion Mapping
    (MDPI, 2026) Hassefras E. ; Volker, A.W.F. ; Verweij, M.
    Guided wave tomography has proven to be an effective method for detecting pipeline corrosion, providing both location and quantitive estimates of wall thickness loss. However, the limited view geometry of source–receiver pairs on pipes leads to a significantly ill-posed problem. In practical terms, this means that the wall thickness measurements become unreliable, as small errors or noise in the data can result in large inaccuracies in the reconstructed thickness profile. To address the non-uniqueness inherent in Full Waveform Inversion (FWI) for guided wave tomography, we explore a joint inversion framework that combines multiple guided wave modes: specifically 𝐴0 , 𝑆0 , and 𝑆𝐻1 . These modes have different sensitivities to wall thickness variations in pipelines, and by jointly inverting them, we aim to enhance the overall information content available to the inversion process. By deriving statistical measures of solution precision and accuracy through sampling-based analysis, we quantify the reliability of inversion outcomes under different mode-frequency configurations. These measures offer practical guidance for selecting suitable combinations in future experiments, helping to mitigate non-uniqueness without altering the sensor layout. This insight supports more informed system design choices for corrosion monitoring applications.
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    Adhesive bond thickness inversion using through transmission data
    (BINDT, 2025) Volker, A.W.F. ; Jansen, H.P.
    Bonded metal panels are frequently used in aircraft structures. Non-destructive inspections are performed to ensure the integrity of these panels. A commonly applied method is through transmission ultrasonic inspection. Due to the layered structure of these panels, the transmission response is strongly frequency dependent and consists of a series of resonance peaks. Even a small thickness variation in the bondline causes a strong imprint in C-scan images. This imprint is generally considered as an undesired output, complicating the interpretation of the inspection. Bondline thickness variations may affect the mechanical properties of the panel. As the imprint contains information about the actual thickness of each individual bondline, this data could be utilized to assess the mechanical properties of the bonded structure. This resonance pattern can be calculated using a simple 1D-transmission model. An inversion scheme has been developed to determine the local bondline thickness of each individual bondline from transmission data. The uniqueness of the solution is studied for panels with three bondlines. The approach has been evaluated on aluminium bonded panels with one and three bondlines. Using the estimated bondline thicknesses and the thickness of the individual aluminium panels the total panel thickness can be calculated, which shows good agreement with reference measurements.
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    Advanced landing gear fibre Bragg grating sensing and monitoring system
    ( 2022) Grooteman, F.P. ; Goutagny, R. ; Davies, C. ; Leest, T. van ; Platt, I. ; Symons, J.
    In this paper an advanced optical-based landing gear load sensing and monitoring system is presented. The system measures strains using fibre Bragg grating sensor that are converted into loads and torque at the landing gear wheels and provides this data for use by the aircraft systems for integration with aircraft health monitoring, hard landing detection, flight management, flight controls and ground controls. A complete sensing system was developed in the European Union Clean Sky 2 Joint Technology Initiative Advanced Landing Gear Sensing and Monitoring (ALGeSMo), described herein. This involved: the integration of optical fibres into a composite structure, the development of an optical harness (cabling and connectors) meeting aircraft installation requirements, the readout of the optical fibre sensors with state-of-the-art miniature optoelectronics and the processing and communication of the data. Apart from specific tests on the various components, a bespoke test rig was developed to rigorously test the whole sensing and monitoring system on an A320 main landing gear slider tube to validate the performance of the system. The system-level tests performed on the test rig showed a very good correlation with applied actuator loads and additional conventional strain and temperature sensors. It demonstrates that loads along all three axis of the landing gear and the torque about the wheel axle can be accurately measured. Tests performed at cold and elevated temperatures, however, revealed that the generally applied one-dimensional temperature compensation equation is not accurate enough for this application, due to the non-uniform non-stationary temperature field. The ALGeSMo research activities have advanced the state of the art in several key areas for the deployment of optical sensing systems for safety-critical applications, such as integration of optical fibres into composite material, robust optical connections, avionic-compliant optical interrogator and landing gear load measurement up to technology readiness level technology readiness level 5.
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    Advanced models for the transfer impedance of metal braids in cable harnesses
    (IEEE, 2018) Verpoorte, J. ; Schippers, H. ; Lansink Rotgerink, J.H.G.J.
    Since the development of the model for transfer impedance of metal braids by E.F. Vance, a large number of authors have tried to improve this model in order to make it more accurate and more reliable. The improvements were based on a more accurate physical or electromagnetic description, or on empirical data of a large number of transfer impedance measurements. This paper provides an overview of the specific models for diffusion, hole inductance and braid inductance. In addition to the general overview, a preferred combination of models for the calculation of transfer impedance is presented.
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    Advanced RAIM and Local Effects Models for Rail, Maritime and UAVs Sectors
    (MDPI, 2025) De Toro De Murga, J. ; Fidalgo, J. ; Domínguez, E. ; Sanz, C. ; Moreno, G. ; Buendia, F. ; Labrador, E. ; Mistrapau, F. ; Clopot, R. ; Cezón, A. ; Snijders, M. ; Engwerda, H.J.A. ; Casals Sadlier, J. ; Damy, S. ; Sgammini, M.
    Advanced Receiver Autonomous Integrity Monitoring (ARAIM) represents an advancement over RAIM, designed to utilize dual-frequency and multi-constellation technologies. Originally developed for aviation, the European Commission (EC) is now exploring its broader application. This paper examines the adaptation of ARAIM for rail, maritime, and Unmanned Aerial Vehicles (UAVs) sectors. It briefly discusses aspects of the integrity concept, including architecture and user algorithms while the main focus is on characterizing local error models for local effects using real data campaigns. Keywords: ARAIM; integrity; local errors; rail; maritime; UAVs
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    Advanced Receiver Autonomous Integrity Monitoring (ARAIM) for Unmanned Aerial Vehicles
    (MDPI, 2023) Snijders, M. ; Engwerda, H.J.A. ; Fidalgo, J. ; Dominguiz, E. ; Moreno, G. ; Duque, J.P. ; Martinez, J. ; Martini, I. ; Sgammini, M. ; Boyero, J.P.
    Advanced Receiver Autonomous Integrity Monitoring (ARAIM) is an evolution of the currently used aviation-focused Global Navigation Satellite System integrity service, Receiver Autonomous Integrity Monitoring (RAIM). Where RAIM supports only lateral navigation, with its adaptations including multiple frequencies and constellations, and with the use of Integrity Support Messages (ISMs), ARAIM also supports vertical guidance. Although these techniques were designed to serve the aviation community, ARAIM could be used in a wide range of applications, especially safety-critical applications. With further evolutions, ARAIM could also be extended to cover more demanding applications in various sectors. This work reports the outcomes of the study of the applicability of ARAIM for the Unmanned Aerial Vehicle (UAV) sector. Keywords: integrity; ARAIM; GNSS; UAV; HAS; sensor fusion
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    Advancing safety in organisations: application via the Luton Safety stack
    (MATEC Web of Conferences, 2019) Smeltink, J. ; Stroeve, S. ; Kirwan, B.
    Controlling and improving safety in organisations is achieved using a Safety Management System (SMS). Notwithstanding the variety of components considered in SMS standards, including human factors and safety culture, safety management systems are sometimes observed by those at the ‘sharp end’ as being bureaucratic, distinct from actual operations, and being too focused on the prevention of deviations from procedures, rather than on the effective support of safety in the real operational context. The soft parts of advancing safety in organisations, such as the multitude of interrelations and the informal aspects in an organisation that influence safety, are only considered to a limited extent in traditional safety management systems. The research in Future Sky Safety Project 5 (FSS P5) focused on improving these human-related, informal organisational aspects. Since every organisation is unique, in the operations it conducts, its history, and its organisational culture, there cannot be a one-size-fits-all standard for advancing safety in organisations. Rather, this needs to be based on the organisation at hand, leading to tailored solutions. This has been applied to a safety culture assessment and enhancement approach applied for six key organisations at London Luton Airport, and the approach has become known as the Luton Safety Stack. The six organisations decided to share the detailed results of their individual safety culture assessments. They formed a group that holds quarterly meetings, which always include a workshop element. From this approach, the organisations were stimulated to develop harmonised procedures for all ground-handling operators at Luton, and for each operation, creating a simple one-page procedure with diagrams, to keep it simple and safe. The Luton Safety Stack shows that when organisations share a place, such as at an airport, they need the opportunity to meet to discuss both potential safety threats, and opportunities to advance safety, because even through organisations are interdependent, safety issues in one organisation often have implications for others.
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    Aeroacoustic Prediction of Overwing Propulsion at Incidence
    (AIAA, 2025) Dekker, H.N.J. ; Tuinstra, M. ; Ragni, D.
    The premise of over-the-wing mounted rotors is that a favorable aerodynamic effect is achieved by interaction with the lifting wing, which also acts as noise shield. A physics-based low-order model is proposed that accounts for aerodynamic interactions in the prediction of the aeroacoustic footprint of the installed rotor. The nonuniform inflow of the rotor disk is modeled by an analytical description of the inviscid potential effects of the wing’s circulation, given as a function of the blade sectional coordinates. Furthermore, the ingestion of the separated boundary layer is considered at large angles of attack. The related steady inflow distortion serves as input to an aeroacoustic noise prediction chain that computes the unsteady loading on the blades and the resulting tonal noise emission by helicoidal surface theory. The model is validated by measurements from a single over-the-wing mounted rotor for a wide range of angle of attack, advance ratios, and rotor positions over the wing’s chord. The predictions and experimental data show an equivalent increase in the tonal components relative to the isolated rotor, and a minimization of the tonal noise for a midchord rotor position, for emission directions around the rotor disk plane over the wing’s suction side.
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    Aerodynamic Interactions of Side-by-Side Rotors in Ground Proximity
    (AIAA, 2022) Dekker, H.N.J. ; Ragni, D. ; Baars, W.J. ; Scarano, F. ; Tuinstra, M.
    An experimental investigation is conducted to study the aerodynamic behavior of a two-rotor system in ground proximity. The counter-rotating rotors are placed side-by-side in the hovering condition. The time-averaged and unsteady flow behavior is studied when the rotor-to-rotor lateral distance and the distance between the rotors and the ground are varied. The experiments are performed using three-dimensional large-scale volumetric velocimetry with helium-filled soap bubbles as tracers, tracked by the particle motion analysis technique “Shake-The-Box.” The mean velocity field reveals the wake deflection due to the ground plane and the formation of toroidal-shape regions of separated flow below each rotor. The interaction of the wall jets formed by slipstream deflection results in a separation line with the flow emerging from the wall in a fountain-like pattern. Regimes of flow re-ingestion occur when the rotors are sufficiently far apart. The flowfield exhibits the tendency toward asymmetric states, during which the fountain flow column and the domain of re-ingestion shift closer to one of the rotors. A generic classification of flow regimes is proposed in relation to the behavior of two rotors in ground effect.
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    Aeropropulsive Performance Modeling of Over-the-Wing Propulsion at Incidence
    (AIAA, 2025) Dekker, H.N.J. ; Tuinstra, M. ; Baars, W.J. ; Scarano, F. ; Ragni, D.
    A semi-analytical model is proposed that incorporates aerodynamic interactions between the rotor- and wing-induced flowfields. Predictions are validated through experiments performed with an array of five rotors above an airfoil, where the angle of attack, advance ratio, and chordwise rotor position are varied. At moderate angles of attack, the propulsive thrust is reduced due to the acceleration induced by the wing’s circulation. Around the stall angle of the isolated wing, the rotors re-energize the boundary layer when operated in low-thrust conditions. By increasing the thrust, a pronounced region of reverse flow between the rotors and wing adversely affects the leading-edge separation delay over the wing that occurs for lower thrust settings. However, in this condition, the wing–rotor-array system exhibits increased thrust compared to the attached flow condition due to the rotors ingesting low-momentum flow. In addition, the rotor-induced flow over the wing augments suction, while the pressure side is subjected to a pressure increase, ascribed to flow entrainment from the rotors. After comparison with the experimental observations, it is confirmed that the model predictions accurately describe the lift and thrust performance trends, aside from a discrepancy in the lift force when the rotors are operated in low-thrust conditions.
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    Aircraft Level Thermal Management Analysis for Early Design Stages of Future Aircraft: Integration of Systems and Compartments into an Interacting Generic Approach
    (MDPI, 2025) Muijden, J. van ; Aalbers, V.J.E.
    For future commercial aircraft having hybrid electric drivetrains, the impact of electrical power generation and distribution on heat production and required heat rejection is of a larger magnitude than for conventional aircraft. The thermal management system (TMS) to control component and compartment temperatures may require dedicated solutions. The impact of TMS on top-level aircraft requirements (TLARs), e.g., weight and drag penalties, should become clear in the early stages of design for integration in the configuration. To assess this impact, a generic approach is presented to support aircraft level thermal management analysis and design based on global aircraft parameters.
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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.