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    Fluid selection for space thermal control systems
    ( 2014) Gerner, H.J. van ; Benthem, R.C. van ; Es, J. van ; Schwaller, D. ; Lapensée, S.
    The selection of a suitable fluid is one of the first and most important steps for the design of a thermal control system. For example, for a heat pipe it is important to use a fluid with a high surface tension and heat of evaporation, and a low viscosity. These characteristics can be combined in a ‘figure of Merit’. This figure of Merit is used to pre-select a number of fluids, after which these fluids are further investigated for material compatibility, safety, radiation hardness etc. This systematic approach results in the selection of the most favourable fluid for each application. In this paper, the fluid selections for heat pumps and pumped loops (both single- and two-phase) are discussed. It is explained for instance why CO2 is used in the thermal control system of AMS02 (which was launched with the space shuttle in May 2011 and subsequently mounted on the International Space Station). Also discussed is the selection of Galden HT80 for ESA’s single-phase Mechanically Pumped Fluid Loop (MPFL) and the selection of isopentane for an ESA Heat Pump application.
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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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    Transient modelling of pumped two-phase cooling systems: Comparison between experiment and simulation
    (46th International Conference on Environmental Systems, 2016) Gerner, H.J. van ; Braaksma, N.
    Two-phase pumped cooling systems are applied when it is required to maintain a very stable temperature in a system, for example in the AMS02, which was launched with a space shuttle (in May 2011) and subsequently mounted on the International Space Station. However, a two-phase pumped cooling system can show complex transient behavior in response to heat load variations. For example, when the heat load is increased, a large volume of vapor is suddenly created, which results in a liquid flow into the accumulator and an increase in the pressure drop. This will result in variations in the temperature in the system, which are undesired. It is necessary to calculate these temperature variations before an application is being built. For this reason, a software tool for transient two-phase systems has been developed by NLR. This tool numerically solves the one-dimensional time-dependent compressible Navier-Stokes equations, and includes the thermal masses of all the components. The tool has been used for different projects, and the numerical results show an excellent agreement with experiments. In this paper, several pumped two-phase cooling systems are discussed, and a comparison between simulations and experiments is presented.
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    The Risk Observatory: Developing an Aviation Safety Information Sharing Platform in Europe
    (Macrothink Institute, 2016-12) Verstraeten, J. ; Baren, G.B. van ; Wever, R.
    In Europe the accident rate in commercial aviation has stagnated at around 40 accidents per ten million flights: forty times higher than Europe’s ambition. Currently safety management is done per organisation, focusing on an organisation’s own domain. European research institutions and the aviation sector have joined their expertise in the EU-funded Future Sky Safety Programme. One project within the programme aims to enable inter-organisation and inter-domain safety management. The four year project will deliver a tool, the Risk Observatory, which acquires safety data and translates it into actionable safety information. In the first year, more than 20 European stakeholder organisations have been consulted to express their needs for a Risk Observatory. The resulting requirements have been used to develop an early prototype: mock-ups of dashboards and a user interface. The Risk Observatory has four main elements. (1) Tracking of safety performance indicators distilled from input safety data. (2) Trend diagrams and visualisations of accident risk. Risk models will be developed to translate the input data into accident risk. The risk models also allow (3) assessment of the effects of mitigation measures. There is added value in sharing qualitative safety knowledge, such as identified hazards, therefore, (4) a searchable repository is included. The early prototype is successfully used to validate and further specify the requirements. The need for inter-organisation and inter-domain safety data dissemination was confirmed by the stakeholders. In the coming years the project will develop a fully functional prototype risk observatory, risk models and a business model.
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    Braking Capabilities on Flooded Runways: Flight Test Results Obtained with a Business Jet
    (AIAA, 2017) Es, G.W.H. van
    Statistics show that the likelihood of a runway excursion during takeoff or landing is much higher on flooded runways than on dry runways. Extreme loss of tyre braking can occur during rejected takeoffs and landings on flooded runways. As a result the stopping distance increases significantly and could exceed the available runway length. Most research in the past has focused on the braking capabilities of aircraft on wet runways instead of flooded runways. Most of the knowledge of aircraft braking performance on flooded runways was gained with older aircraft designs. This knowledge is still used to determine the takeoff and landing performance of today’s modern aircraft. During the development of the European Action Plan for the Prevention of Runway Excursions it was recognised that current aircraft designs may act differently when braking on water flooded runways from aircraft tested earlier, due to new tyres and anti-skid system designs. Also the water depths during these earlier tests were often just above the wet-flooded runway threshold. Flight tests with more modern aircraft designs were therefore scheduled as part of a research project under EU’s Horizon 2020 Research and Innovation Programme. This paper summarises the flight tests conducted with a Cessna Citation II aircraft on a flooded runway. Unbraked and braked tests were conducted in a specially constructed water pond at different ground speeds. Numerous parameters were recorded during each test run including accelerations, speeds, engine performance, etc. From the test data, effective braking friction for different grounds speeds were derived, contamination drag levels were established, and insight into the hydroplaning characteristics under unbraked and braked conditions were obtained.
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    Transient Modelling of Pumped Two-Phase Cooling Systems: Comparison between experiment and simulation with R134a
    ( 2017) Gerner, H.J. van ; Bolder, R. ; Es, J. van
    Two-phase pumped cooling systems are applied when it is required to maintain a very stable temperature in a system, for example in the AMS02, which was launched with a space shuttle (in May 2011) and subsequently mounted on the International Space Station. However, a two-phase pumped cooling system can show complex transient behavior in response to heat load variations. For example, when the heat load is increased, a large volume of vapor is suddenly created, which results in a liquid flow into the accumulator and an increase in the pressure drop. This will result in variations in the temperature in the system, which are undesired. It is necessary to calculate these temperature variations before an application is being built. For this reason, a software tool for transient two-phase systems has been developed by NLR. This tool numerically solves the one-dimensional time-dependent compressible Navier-Stokes equations, and includes the thermal inertia of all the components. In this paper, the numerical results from the model are compared to experimental results obtained with the NLR two-phase test facility with R134a as refrigerant.
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    Stopping performance flight test on a flooded runway
    (Society of Experimental Test Pilots, 2017-07) Tump, R.S. ; Mulder, T.J.
    One of the identified solutions for runway excursions is the research into the “Impact of fluid contaminants of varying depth on aircraft stopping performance”. For this, NLR has carried out water-pond flight testing with the NLR/TUD Cessna Citation research aircraft to assess braking performance of modern aircraft and tyres on water covered runways. Airbus Military performed the same test using an A400M. Both tests took place using the water-pond facility of NLR. Aircraft operating on runways that are contaminated by standing water or slush (> 3 mm, up to the AFM limit) are significantly affected in take-off and landing performance. Most data available today is bases on test carried out in the 60s and 70s of the last century. Improved aircraft braking systems and tires were only tested at small scale in recent years.
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    NLR’s experience with flight testing on wet and flooded runways
    (Society of Flight Test Engineers, 2017-09) Es, G.W.H. van ; Koks, P.
    Braking performance of aircraft is affected whenever a runway is wet or flooded. Aircraft manufacturers do wet runway braking tests during the certification of a civil transport aircraft. These are normally limited to tests on smooth runways. Additional tests are sometimes conducted on wet grooved or porous friction course runways when the manufacturer seeks for additional stopping performance credit for such runways. Braking tests on flooded runways are not conducted during certification. In the past such tests have been conducted in research programmes on runway friction. The Netherlands Aerospace Centre NLR has conducted braking tests on a highly textured runway under wet and flooded conditions. The wet runway tests were conducted to demonstrate an equivalent performance of the test surface with grooved and porous friction course runways under wet conditions. The flooded tests were conducted as part of an European Research project on the prevention of runway excursions. All tests were conducted in the autumn of 2016 at a former Air Force base in the Netherlands (Twente Airport). This paper discusses in detail the preparation, logistics, and execution of the flight tests conducted with NLR’s Cessna Citation test aircraft. The use of large water trucks to wet the runway and the construction of a water pond to conduct the flooded runway tests is discussed in detail. Difficulties encounter during the preparation and execution of the flight tests are briefed and finally lessons learned are shared with the reader.
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    A clustered and surrogate-based MDA use case for MDO scenarios in AGILE project
    (AIAA, 2018) Lefebre, T. ; Bartoli, N. ; Dubreuil, S. ; Panzeri, M. ; Lombardi, R. ; Lammen, W.F. ; Mengmeng, Z. ; Gent, I. van ; Ciampa, P.D.
    In this paper methodological investigations regarding an innovative Multidisciplinary Design and Optimization (MDO) approach for conceptual aircraft design are presented. These research activities are part of the ongoing EU-funded research project AGILE. The next generation of aircraft MDO processes is developed in AGILE, which targets significant reductions in aircraft development cost and time to market, leading to cheaper and greener aircraft solutions. The paper introduces the AGILE project structure and recalls the achievements of the first year of activities where a reference distributed MDO system has been formulated, deployed and applied to the design and optimization of a reference conventional aircraft configuration. Then, investigations conducted in the second year are presented, all aiming at making the complex optimization workflows easier to handle, characterized by a high degree of discipline interdependencies, multi-level processes and multi-partner collaborative engineering activities. The paper focuses on an innovative approach in which knowledge-based engineering and collaborative engineering techniques are used to handle a complex aircraft design workflow. Surrogate models replacing clusters of analysis disciplines have been developed and applied to make workflow execution more efficient. The paper details the different steps of the developed approach to set up and operate this test case, involving a team of aircraft design and surrogate modelling specialists, and taking advantage of the AGILE MDO framework. To validate the approach, different executable workflows were generated automatically and used to efficiently compare different MDO formulations. The use of surrogate models for clusters of design competences have been proved to be efficient approach not only to decrease the computational time but also to benchmark different MDO formulations on a complex optimization problem.
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    Testing of high heat flux 3D printed aluminium evaporators
    ( 2018) Gerner, H.J. van ; Smit, M. de ; Helvoort, D. van ; Es, J. van
    The amount of waste heat that is generated in electronic components in aerospace application is increasing because of higher electrical power demands. As a result, conventional cooling methods are not able to maintain the electronic component below its maximum temperature. For this reason, a two-phase Mechanically Pumped Fluid Loop is being developed for high-power electronic components in a commercial aerospace application. These electronic components generate a heat load of 722 W on a 3.8 cm x 3.8 cm surface, resulting in a heat flux of 50 W/cm2. Tests with 8 different evaporator samples were carried out to determine the heat transfer coefficients and pressure drop and to select the optimal evaporator sample that is further developed in the detail design phase of the project. The tests show that the 3D printed aluminium evaporators are able to keep the heat source well below its maximum temperature.
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    Water-filled heat pipes for CubeSat thermal control
    (IOP Publishing, 2018) Gerner, H.J. van ; Brouwer, H. ; Groot, Z. de ; Guo, J.
    Currently, the amount of electrical power that is available for CubeSat's is very small and for this reason, simple thermal conductance through the frame of the CubeSat is sufficient for most CubeSat missions. However, deployable solar panels have been developed recently and peak powers up to 40W can now be generated. This higher generated electrical power results in more waste heat and potentially too high temperatures inside the CubeSat. For this reason, the use of water-filled heat pipes is studied, since these are cheap, widely commercially available, and can be bent in the desired shape. Both the condenser and evaporator thermal resistance and the total heat transfer capacity of these heat pipes have been measured for a wide range of temperatures with a unique automated setup that uses Peltier elements to control the temperature. Furthermore, the heat pipes have been subjected to multiple freeze/thaw cycles and start-ups from a frozen state. After these successful tests, a heat pipe was integrated in a CubeSat and tests were carried out in several orientations. The tests show that commercially available water-filled heat pipes are suitable for CubeSat thermal control.
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    Low-Frequency Analysis of Multiconductor Transmission Lines for Crosstalk Design Rules
    (IEEE, 2018-09-18) Lansink Rotgerink, Jesper ; Schippers, Harmen ; Leferink, Frank
    For early risk assessment in the design of cabling in an aircraft, as well as cable bundle optimization, efficient crosstalk estimations, and dependency of crosstalk with respect to designable parameters are required. A low-frequency technique for analyzing crosstalk in multiconductor transmission lines is presented. The result of this analysis is a closed-form expression for crosstalk in a specific cabling configuration. The technique has been validated via measurements and is used in two examples comprising two wire pairs close to a ground plane and in free space. Low-frequency closed-form expressions for near-end crosstalk are derived for both situations, which directly relate any designable parameter to crosstalk levels. Moreover, these expressions clearly show differences between the cases with and without a ground plane. Specifically, with the ground plane, the decrease in crosstalk when doubling the separation distance is 24 dB for pairs close to the ground, while it is 12 dB in free space. The closed-form expressions are utilized to create an overview of sensitivities of crosstalk to all designable parameters for both configurations. Finally, the low-frequency approximations of the chain parameters are applied to more complex nonuniform transmission lines, yielding more than 20 times faster computations when compared with complete MTL simulations.
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    Learning curve: interpreting the results of four years of safety culture surveys
    (Flight Safety Foundation, 2018-12) Kirwan, B. ; Reader, T. ; Parand, A. ; Kennedy, R. ; Bieder, C. ; Balk, A.
    Safety culture is seen as a pillar of aviation safety and is a cornerstone in both the International Civil Aviation Organization’s and the European Aviation Safety Agency’s (EASA’s) safety management system (SMS) models. But what does this mean in practical terms? For aviation organizations, is there something credible, tangible and manageable they can work with, or is this simply meant to be an inspirational goal?
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    Soap bubbles for large-scale PIV in industrial wind tunnels
    (Universität der Bundeswehr München, 2019) Engler Faleiros, D. ; Tuinstra, Marthijn ; van Rooijen, Bart D. ; Scarano, F. ; Sciacchitano, A.
    This work evaluates the use of helium-filled soap bubbles (HFSB) for Particle Image Velocimetry (PIV) measurements at high Reynolds numbers (up to 3.2 million) in aeronautics. The measurements are performed in the Low Speed Tunnel (LST) of the German-Dutch Wind Tunnels (DNW) using a high-lift airfoil in close-to-stall conditions up to 70 m/s. Experiments using Di-ethylhexyl- sebacat (DEHS) particles are performed for a comparison of the two seeding techniques. The signal to noise ratio of HFSB images was two orders of magnitude larger than that of DEHS, which strongly reduced the unwanted effects of background reflections and light intensity spatial variations, compared to DEHS particle images. The mean velocity field obtained with HFSB exhibits differences typically within 1% of the free stream velocity, when compared to DEHS measurements.
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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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    Lightweight Two-Phase Pumped Cooling System with aluminium components produced with Additive Manufacturing
    ( 2019) Gerner, H.J. van ; Smit, M.J. de ; Es, J. van ; Migneau, M.
    The amount of waste heat that is generated in electronic components in aerospace application is increasing because of higher electrical power demands. As a result, conventional cooling methods are not able to maintain the electronic component below its maximum temperature. For this reason, a two-phase Mechanically Pumped Fluid Loop has been developed for high-power electronic components in a commercial aerospace application. These electronic components generate a waste heat of 1200 W that is divided over several hotspots while the temperature gradient over the component has to be kept to a minimum. The developed cooling system uses R245fa as refrigerant and is made from aluminum components produced with additive manufacturing. The use of this novel production technique results in an unprecedented low system mass (2.5 kg) and small system dimensions. Measurements show that the system has an excellent thermal performance and is able to cool 2400W.
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    Breadboard Testing of a HiPeR Inflatable Radiator (HiPeR INFRA)
    (49th International Conference on Environmental Systems, 2019) Groot, T. de ; Schwieters, B. ; Benthem, R.C. van ; Pauw, A. ; Es, J. van
    With a twenty times higher thermal conductivity per unit mass than aluminium, pyrolytic graphite (PG) offers great potential in the application to spacecraft thermal control systems. Over the last years, Airbus Defence and Space Netherlands (Airbus DS NL) has been developing thermal control applications for this material. The patented High Performance Radiator (HiPeR) uses the PG to efficiently spread the heat from a heat source over a large radiative area. Recently, Airbus DS NL and the Royal Netherlands Aerospace Centre (NLR) have been working on a HiPeR Inflatable Radiator (INFRA) application. This concept consists of a HiPeR radiator and a single phase fluid loop. Flexible tubing enables the radiator to be rolled up to a small stowed volume. Once in orbit, the system pressure is increased, triggering the radiator to unroll and maintain its shape over the mission lifetime. Heat is supplied via the same fluid tube that gives the radiator its shape, making use of a dedicated mini-pump. To validate the functional design, a breadboard model has been made. Deployment and thermal performance have been tested successfully. Based on the measured data, the thermal performance of an INFRA system operating at a 45 °C root temperature in a space environment with a sink temperature of -270 °C would be approximately 300-325 W/m2, corresponding to a radiator efficiency of approximately 60%. This performance is deemed to be competitive, especially considering the mass-to-power (expected <10 kg / kW after a design iteration) and small stowed volume of such a system. Additionally, a small-scale breadboard test of protection measures against micro-meteoroids and orbital debris (MMOD) has yielded promising results. The revised design includes MMOD shielding in the form of bi-stable metal strips with a resulting probability of no penetration of the kapton fluid tubing of 0,9 over a lifetime of 15 years.
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    Wind tunnel flutter testing on a highly flexible wing for aeroelastic validation in the transonic regime within the HMAE1 project
    ( 2019-06) Govers, Yves ; Mai, Holger ; Arnold, Juergen ; Dillinger, Johannes K.S. ; Pereira, Allan K.A. ; Breviglieri Jr., Carlos ; Takara, Edgard K. ; Correa, Manoela S. ; Mello, Olympio A.F. ; Marques, Rodrigo F.A. ; Geurts, E.G.M. ; Creemers, R.J.C. ; Timmermans, H.S. ; Habing, R. ; Kapteijn, K.
    The aircraft manufacturer Embraer, the German Aerospace Center (DLR), the Netherlands Aerospace Centre (NLR) and German–Dutch Wind Tunnels (DNW) have tested an innovative highly flexible wing within an aeroelastic wind tunnel experiment in the transonic regime. The HMAE1 project was initiated by Embraer to test its numerical predictions for wing flutter under excessive wing deformations in the transonic regime. A highly elastic fiberglass wingbody pylon nacelle wind tunnel model (see Figure 1), which is able to deform extensively, was constructed for the experiment. The model was instrumented with a large number of pressure orifices, strain gauges, stereo pattern recognition (SPR) markers and accelerometers. The wing was tested from Ma = 0.4 to Ma = 0.9 for different angles of attack and stagnation pressures. The static and dynamic behavior of the wing model was monitored and a new method to analyze its eigenfrequencies and damping ratios was used. In the past, the large amounts of data acquired during such experiments could only be evaluated with a time lag. An efficient method developed by DLR now allows performing the data analysis in real time [1, 2]. As a result, it was possible during the test to identify exactly which safety margins remained before the onset of flutter and the resulting possible destruction of the model.
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    Design and validation of a numerical high aspect ratio aeroelastic wind tunnel model (HMAE1)
    ( 2019-06) Timmermans, H.S. ; Tongeren, J.H. van ; Geurts, E.G.M. ; Marques, R.F.A. ; Correa, M.S. ; Waitz, S.
    The aircraft manufacturer Embraer, the German Aerospace Center (DLR), the Netherlands Aerospace Centre (NLR) and German–Dutch Wind Tunnels (DNW) have tested an innovative highly flexible wing within an aeroelastic wind tunnel experiment in the transonic regime. The HMAE1 project was initiated by Embraer to test its numerical predictions for wing flutter under excessive wing deformations in the transonic regime. A highly elastic fiberglass wing-body pylon nacelle wind tunnel model, which is able to deform extensively, was constructed for the experiment. The model was instrumented with a large number of pressure orifices, strain gauges, stereo pattern recognition markers and accelerometers. The wing was tested from M = 0.4 till M = 0.9 for different angles of attack and stagnation pressure. The HMAE1 model was tested in two different test campaigns in which the Mach number was increased. This paper will focus on the first test campaign of the HMAE1 project in which the windtunnel model is tested up to M = 0.7 and will describe the development of the physical numerical structural dynamic MSC Nastran model representing the manufactured windtunnel model in order to perform numerical aeroelastic analyses.
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    A Large-Scale European Union Study of Aircrew Fatigue During Long Night and Disruptive Duties
    (Aerospace Medical Association, 2020) Dijk, H. van ; Maij, A. ; Sallinen, M. ; Aeschbach, D. ; Akerstedt, T.
    We examined aircrew fatigue during the following flight duty periods (FDPs) mentioned in the European Union (EU) Flight Time Limitations (FTLs): night FDPs longer than 10 h and FDPs typical of disruptive schedules (early starts, late finishes, and nights). An alternative way of classifying night FDPs was also examined to reveal possible subcategories that warrant special attention.