28TH INTERNATIONAL CONGRESS OF THE AERONAUTICAL SCIENCES

THE EREA VISION ON HIGH PRIORITY RESEARCH AXES TOWARDS AIR TRANSPORT SYSTEM 2050

Muriel Brunet1, Alte de Boer2, Volker Gollnick3, Steffen Loth4, Graciano Martinez5, Dennis Nieuwenhuisen6 ONERA1, NLR2, DLR3, DLR4, INTA5, NLR6 [email protected];[email protected];[email protected];[email protected]; [email protected];[email protected]

Keywords: configuration, propulsion, subsystems, automation, airport

Abstract Strategic Research and Innovation Agenda to be prepared by the Advisory Council for Aviation Europe is writing the future of its air transport research and innovation in Europe (ACARE). In in the new Strategic Research and Innovation this open context of building the future of Agenda. In this open context of building the aviation, the research centres have a key role in future of aviation, the research centres have a providing their vision independently of any key role in providing their vision independently economic interest. Therefore, the association of of any economic interest. Therefore, the the European Research Establishments in association of the European Research Aeronautics (EREA) has decided to provide to Establishments in Aeronautics (EREA) is the European commission and to the committed to provide to the European aeronautical community in general its vision on commission and to the aeronautical community the 2050 Air Transport System (ATS) and in general its vision on the 2050 air transport consequently its recommendations on high system and its recommendations on high priority research axes to be funded in order to priority research axes to be funded in order to pave the way towards 2050. pave the way towards 2050. The study briefly presented here has investigated five Following a first study providing a high level interdependent technological domains identified vision on the ATS 2050 [2], EREA has as priority and common ones to any scenarios conducted a second phase of this study on the of the future: configurations, on-board ATS 2050 in order to go more deeply in the sub-systems, propulsion systems, airport and the promising break-through technologies roadmap automation issue of the air transport system. [3]. Therefore, the study has investigated five interdependent technological domains identified in the first phase as priority and common ones 1. General Introduction to any scenarios: revolutionary aircraft Europe is preparing aviation 2050. Indeed, the configurations, on board subsystems, propulsion European Commission is preparing Horizon systems, airport and the automation issue of the 2020 through the Common Strategic Framework ATS. Programme for research and innovation that will be the next main instrument for funding 2. Challenges and objectives to reach 2050 research in Europe. The part dedicated to the transport domain and more specifically the In accordance with challenges identified in the aeronautics chapter is under preparation through Europe's Vision for Aviation [1], the EREA the Strategic Transport Technology Plan, the study investigated revolutionary ideas within the Flightpath 2050 report of the High Level Group five major technological domains of the ATS on Aviation Research [1] and finally the

1 M. BRUNET, A. DE BOER, V. GOLLNICK, S. LOTH, G. MARTINEZ, D. NIEUWENHUISEN

with regard to the following non ordered list of studies must always consider integration with objectives: different levels of the air transport system. • Environmental impact: noise, chemical The two following paragraphs highlight emissions, recycling different single aircraft technologies and some • Passenger aspects: mobility choice, promising aircraft configurations, which might affordability, comfort contribute to the Flightpath 2050 challenges. • Safety: accident rate reduction • Industrial competitiveness (design and production methodologies) 3.2. Key single technologies for innovative • Performance: Increase of transportation configurations capacity/performance 3.2.1 reduction The five domains, that are Aircraft configurations, Propulsion, On board • Increased : wingspan is the subsystems, Towards full automation? and main parameter controlling vortex- Airport are successively presented in the induced drag. Slender, high-span following chapters. (i.e. high aspect ratio) generate less vortex-induced drag, but may result in a heavier structure. Early jet 3. Aircraft configurations transports favoured wing aspect ratios of around 8. This requires stronger structures to carry the resulting bending 3.1. Shaping the future and torsional moments without increasing the structural mass. Tuning The configuration of civil aircraft has evolved spanwise lift distribution with movable little since the 1920s. Almost without exception, trailing-edge devices is promising. There passengers have been transported in a tubular could be a potential 10% fuel burn , with the at the rear and the improvement if airport terminal layouts engines mounted either under the wings, or at allowed for increased wingspan in future the rear. Although major advances in aircraft configurations, but this should and flight control systems have be balanced against increased aircraft contributed greatly to improving the mass and operational flexibility. performance of the classic configuration, the advent of new design materials and design • Wingtip Devices: the right choice of processes, along with a far better understanding wingtip device and its integration into of the aerodynamic and structural interactions the aircraft is a key research area. The that occur in different phases of flight, are aim is to maximise efficiency in cruise, driving some radical ideas for the future. where drag reduction is crucial.

Winglets are the most popular wingtip It is now therefore possible to consider some of device, and are already in used on some the enabling technologies needed for aircraft. Other designs include the wing revolutionary configurations and identify grid, wingtip sails and spiroid, as well as potential technical solutions and their the wingtip turbine, which can recover integration within the overall air transportation some of the energy losses caused by system. Since these perspectives and their vortex-dependent drag and use it to drive related technologies are closely linked, a system a generator. Wingtip devices could bring integration-oriented approach must be taken. cruise fuel savings of up to 10%. Whether they are single subsystem technologies or completely new aircraft configurations,

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• Wetted Surface Area: vertical extremely smooth surfaces presents are sized for ensuring lateral challenges. Forward-swept wings are stability, crosswind landings and beneficial for achieving natural laminar complying with one engine-inoperative flow at relatively high Mach numbers safety requirements. For modern fly-by- and can also help to prevent fuselage wire aircraft lateral stability can be boundary layers from interfering with relaxed and sizing becomes dependent the wing flow. Natural on the one-engine-out scenario. Double- laminar flow can be applied to hinged can reduce area components with slightly swept leading by as much as 15%, which might edges, such as engine . Hybrid produce a 0.5% fuel burn reduction. This laminar flow can be achieved by could be increased by passive or active embedding perforated suction panels flow control devices to further increase into the leading edges of highly-swept efficiency. wings and tail surfaces for aircraft flying faster than Mach 0.7. New structural • Turbulent Drag: technologies like morphing leading current transport aircraft achieve almost edges may enable the generation of lift fully turbulent boundary layer flow over at low speeds for take-off and landing all wetted surfaces. Although the physics with a laminar flow wing. Other design of fully turbulent flow is well options would reduce parasitic drag due understood, there are still opportunities to external roughness and wakes due to to reduce turbulent boundary layer drag. windscreen design, windscreen wipers, V-grooved riblets have shown rain rims over doors, inlet and exhaust substantial reductions in skin friction. ducts, and door handles etc. Wind-tunnel and flight testing have 3.2.2 Mass reduction indicated potential aircraft fuel burn savings of up to 2%. In-service trials • Integrated structural design: revealed premature wear of riblet films, composite materials and manufacturing however - an area of continued research. technologies allow for the design of Controlling turbulent boundary layers more integrated structures with fewer with smart Micro-Electro-Mechanical- fasteners, reducing weight. Other Devices (MEMs) on all surfaces holds advantages compared to metals include real potential. A more detailed fatigue damage resistance, corrosion understanding of unsteady turbulent resistance and thermal insulation. These substructures and how to modify these materials' drawbacks are, in general, actively to achieve drag reduction needs their sensitivity to impact, limited to be developed. Because experiments damage tolerance properties and low are very difficult to perform, pure electrical conductance. Composites aerodynamics research needs to be already represent up to 50% of the complemented by continued effort on structural weight for the most modern technologies such as high-performance commercial aircraft, such as the computing (HPC) for virtual simulations 787 and A350. of new configurations. • Aeroelastic tailoring: aircraft wings are • Laminar flow promises a potential 5% - designed such that their shape yields 10% fuel burn reduction, with the optimum lift and load distribution, but benefits increasing the longer the aircraft these values vary as the wing is is in cruise. While the aerodynamic deformed during flight. Aeroelastic principles are well understood, the tailoring can generate wing designs that production and operation of the 3 M. BRUNET, A. DE BOER, V. GOLLNICK, S. LOTH, G. MARTINEZ, D. NIEUWENHUISEN

deflect under loading in such a way as to manufactured” material details in the moderate the internal load increase. design loop. Composites are particularly useful for this type of design because, by orienting • Windowless cabin: aircraft windows in fibres in specific directions, the stiffness the passenger cabin and cockpit characteristics of the structure can be contribute to weight and drag. A radical designed to give precisely the solution to reduce weight might be deformation response to the experienced replacing the windows with lightweight loading to achieve the optimum wing low-power-consumption screens with shape. passenger-selectable views. This technology would mean that unusual • Self-healing materials: a structurally- aircraft configurations such as BWB and incorporated ability to repair damage flying wings could be considered. caused by mechanical use over time. Current research on composite materials • Thermoplastic composites: most will expand the scientific understanding carbon fibre composites contain of self-healing materials and introduce thermoset polymers (mainly epoxy) for the cradle-to-cradle concept for the matrix material. To enhance damage thermoset-based plastics and tolerance and toughness, thermoplastic composites. polymers can be used, which can be heated, melted or softened, reshaped, • Material-related structural design: life and then cooled to a final hardened cycle assessment studies of shape, making them easy to rework and environmental emissions have repair. demonstrated the benefits of structural aircraft components made from • Nano-technologies for improved lightweight Carbon Fiber Reinforced material properties: further Plastic (CFRP) in comparison to improvement of carbon fibre composites aluminium and Glass Laminate properties, in particular their brittleness Aluminium Reinforced Epoxy and fracture sensitivity, can be achieved (GLARE), expressed in fuel by nano material additives such as consumption and CO2 emissions and graphene platelets or carbon nanotubes. taking into account their “cradle-to- Strength, stiffness and resistance to grave” emissions. Besides increasing the fatigue crack propagation gains of amount of composites in the several orders of magnitude have been structure, further weight and fuel burn demonstrated. Moreover, the reduction can also be achieved by significantly improved electrical further optimising current composite conductivity of the composite materials structures in terms of cost and overcomes the need for lightning strike performance. protection systems usually achieved by copper or bronze meshes inserted in the • Unconventional fibre lay-ups / elastic laminate. tailoring: lighter composite structures 3.2.3 Interdisciplinary and integrative can be obtained through improved local technologies directional stiffness properties. This can be achieved by local elastic tailoring of • Large integrated panels' production: structures using advanced fibre composite materials and their related placement, in combination with manufacturing technologies provide advanced design, analysis and technical and economical enablers for optimisation methods, including “as- 4 THE EREA VISION ON HIGH PRIORITY RESEARCH AXES TOWARDS AIR TRANSPORT SYSTEM 2050

new aircraft configurations. Larger, rotors will improve access to city centres and integrated structural elements with offshore platforms. Finally, personal aircraft and curved shapes can be realized using supersonic transports are assessed. CFRP. Although some experience has 3.3.1 Blended Wing Body been achieved over the last 20-30 years, efficient production in terms of tooling Today's classical aircraft configurations feature and procedures remains to be developed. separate structures for providing lift (wings) and Automated fibre placement and filament carrying the payload (fuselage). This results in a winding has enabled advanced, heavier structure, additional wetted surface and economically viable manufacturing of associated viscous drag. The flying wing composite material structures, but for configuration is recognized as the most efficient one-shot composite components, the aerodynamic solution, but presents challenges in final assembly line process must be many other areas. The blended wing body adapted to composite materials, which (BWB) presents a good compromise. Its higher have less ductility and higher stiffness. structural complexity could be mitigated with development of advanced composite materials • On-Line Aircraft Health and Usage and production processes. The BWB also Monitoring: aircraft operational provides good potential for larger, more behaviour can be improved through comfortable passenger cabins and new storage efficient damage and fault detection, solutions for baggage, cargo and fuel. maintenance, and logistics. For this, real-time assessment of the composite 3.3.2 Prandtl Plane structure by integrated strain monitoring For a given wing span and lift, the Prandtl-type systems, based on networks of fibre biplane, with wings connected at the tip, optic sensors, can be applied. A better provides a theoretical induced drag reduction of understanding of structural behaviour about 20% during low-speed phases such as during flight may lead to a reduction of take off, climb, descent and landing. Such a drag losses by using strain readings to configuration might be an interesting solution adjust deformation during flight or to for short take-off and landing short-range improve the safety margins used in the aircraft with less range than today’s Airbus design process. Strain readings from A320 or . The potential benefit of critical parts of the structure could this radical change in configuration might be a monitor damage or damage growth reduction of up to 10% in fuel burn, as long as during flight. This information could be weight is not increased compared to a used to develop an integrated aircraft conventional aircraft. This concept provides health and usage monitoring system, also new solutions for engine integration. which enables the overall aircraft state to be assessed. Such a system would 3.3.3 Tilt-rotor aircraft require high reliability, intelligent sensor data gathering, sensor fusion and Tilt-rotor aircraft combine the hover advantages analysis, and the development of of with the higher-speeds of appropriate action procedures. turboprop aircraft, overcoming the problem of speed being limited by the loss of main rotor efficiency at higher forward speeds. 3.3. Promising aircraft configurations The next generation of tilt-rotors will feature a The five aircraft configurations that are partially tilted wing to improve rotor efficiency presented hereafter are considered as catalyst for at hover. A 20-passenger aircraft would have break-through: the Blended Wing Body and higher range than the BA609 at a cruise speed Prandtl wing are potential solutions for of around Mach 0.5 - close to that of modern commercial transports, while advanced tilt- turboprop aircraft. Depending on the regulatory

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situation, civil tilt-rotors would operate as commuters between medium/large cities and for offshore oil & gas plants, or long-range strategic-air reconnaissance applications. 3.3.4 Personal aircraft For personal air transport, short-range small aircraft provide the lowest emissions and easiest handling. Such aircraft would be operating along with others at lower altitudes and speeds. An aircraft with up to eight seats could be powered by an electric main engine and have all-electric systems with blown wing concept or distributed propulsion. High level of automation Fig. 1. Key technologies for innovative configurations and pilot assistance would be required. The characteristics of such aircraft are reduced acquisition cost, reduced weight, reduced fuel consumption, increased reliability, reduced support equipment, simpler maintenance, expanded flight envelope, and improved survivability. The concept requires the resolution of a number of major technology issues, however, including electromechanical actuators, environmental control and ice protection systems, and engine technology. Fig. 2. Key aircraft configurations for fostering innovation 3.3.5 Supersonic aircraft Supersonic business transport: although this type of aircraft does not pave the way towards a 4. Propulsion greener air transport, the current wave of The turbofan engines powering today’s aircraft globalization unquestionably creates a business are approaching their optimum in terms of regarding rich and busy people all around the efficiency and only major changes in aircraft world. Linking the growing business configuration and propulsion concepts will metropolises in North America as well as in bring step changes in fuel burn and emissions. Europe, Asia and South America with supersonic business aircraft could provide a While there is still plenty of scope for further more realistic business case than charter and improvements in turbofan technology, the major scheduled travel. engine manufacturers and research institutions are working on a large set of radical solutions 3.4. Recommendations on priority research for the next generation of short/medium range axes for future aircraft technologies and transports, which account for most fuel configurations consumption, and hence emissions. The attraction of major fuel savings is balanced, Recommendations on priority research axes to however, by significant challenges on noise, pave the way forward for aircraft are complexity and passenger acceptability. summarized and expressed according to research investment and respectively timeframe in Fig. 1 and aircraft type in Fig. 2. 4.1. Technologies based on classical engines

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Engine manufacturers are constantly working to would have to replace conventional improve engine efficiency. Work currently kerosene with no modifications to the focuses on raising the bypass ratio with new fan existing system. Assuming the CO2 configurations, and improving the released during combustion is balanced thermodynamic efficiency of the core. There is by that extracted from the atmosphere also much potential for improving the during cultivation through performance of aircraft piston engines. photosynthesis, CO2 emissions could be The major promising technologies to be deeply virtually eliminated. The main biofuels investigated are: under consideration are biologically- • Contrarotating open rotor obtained hydrocarbons and biohydrogen. • Contrarotating fan A third generation, based on algae, is • Intercooled sytems another possibility. The most promising • Nanotechnology state-of-the-art fuels are based on • Rotating detonation engine biomass or waste feedstock and • Pulse detonation engine hydroprocessed natural oils (plant oils or animal fats) - called hydroprocessed • Piston engine injection technology renewable jet fuels (HRJ), both certified as a 50% blend for use in aviation. These 4.2. Revolutionary technologies are quite close to compatibility with A number of evolutionary technologies are current engines in terms of energy being studied, covering all propulsion density, viscosity and temperature. All disciplines. Biofuels are amongst the most of the technical details are manageable, promising fuels in the shorter term for reducing and standardization can be achieved emissions, with hydrogen a longer term using mineral or bio-additives. There is, possibility. Electric power in various forms is however, much to be done in the field of attracting increasing interest as the necessary genetic engineering to decode and technologies mature. For specialized ultra-high- enhance biomechanisms able to deliver speed air vehicles, ramjets and scramjets are different sorts of biofuels, additives and under development. lubricants.

4.2.1 Sustainable alternative fuels • Hydrogen can be burned in a jet or internal combustion engines, or used to • Non-biofuels: innovative ideas for non- power fuel cells which generate biofuels are beginning to emerge, such electricity to drive a . The high as fuel produced from solid waste or energy content per mass unit would from industrial waste gases like fumes bring significant payload and range produced by the steel industry increases, and emissions, particularly containing carbon monoxide (e.g. 1 CO2, would be virtually eliminated. LanzaTech gas-liquid fermentation Liquid hydrogen has nearly four times process that converts CO in alcohol the volume for the same energy output which can be upgraded in hydrocarbon). as kerosene and its highly volatile nature precludes storage in the wings. Most • Biofuels: biofuels could bring reductions designs therefore store hydrogen in the of up to 15% in greenhouse gas fuselage, leading to a far bigger fuselage emissions, as well as helping to secure volume than for conventional aircraft. future fuel supplies. Engine lifetime, The performance of a hydrogen-fuelled fuelling infrastructure and fuel aircraft is therefore a trade-off between consistency considerations mean they larger wetted area (and hence drag) and lower fuel weight, and this depends on

1 http://www.lanzatech.co.nz the aircraft size. Complete redesign of 7 M. BRUNET, A. DE BOER, V. GOLLNICK, S. LOTH, G. MARTINEZ, D. NIEUWENHUISEN

the aircraft and of the global distribution • Battery power: one of the solutions to infrastructure would be necessary and powering aircraft with electric motors is hydrogen and existing infrastructures to produce the energy on the ground and would have to co-exist. Another store it in onboard batteries. For large challenge would be to develop aircraft the size and weight of the sustainable supplies from industry. batteries remains excessive. However, Liquid hydrogen at -253 degrees C for smaller aircraft electric propulsion requires heavy insulation of appears more accessible and has already infrastructure, heat exchangers to been applied successfully in the Yuneec increase fuel temperature before E430 light aircraft. Boeing has proposed combusting and a totally new aircraft combining electric propulsion and gas configuration. On an energy-for-energy turbine power on the same aircraft in its basis, liquid hydrogen is considerably SUGAR study, which could solve the more expensive than fossil fuels. issue of the large power density required for take-off. 4.2.2 Electrical propulsion

All-electric aircraft use electric motors instead • Fuel cells are becoming a viable option of internal combustion engines. Power comes to power electric motors for small from fuel cells, ultra-capacitors, power aircraft, and to generate electricity for beaming, solar cells and/or batteries. the more-electric-aircraft architecture Research is concentrating on development of increasingly present in commercial advanced technologies such as superconducting aircraft. Fuel cells are also modular and or liquid hydrogen-cooled cryogenic motors for theoretically any voltage or power can lightweight, high-performance motors. be produced by a series and/or parallel configuration of stacks of cells. • Energy-efficient storage: highly Technologies under consideration efficient energy storage devices could include the advanced proton exchange bring advances in generation, membrane (PEM) and solid oxide fuel conversion, distribution and storage. cells. The possibility of using a PEM Potential solutions include harvesting fuel cell stack providing the total power energy from vibrations, using thermo- needed by the engine and all the acoustic engines for energy conversion, auxiliary systems has been demonstrated actively controlling airflows for better in light aircraft, using commercial fuel energy distribution, and flywheel energy cell and power management storage. Energy harvesting devices can technologies, albeit with reduced speed, be used to capture the energy in climb rate, range and payload-carrying unwanted vibrations. They include capability. The major challenge is to conventional, miniaturized devices as reduce the size of the electric drive well as micro devices that use novel propulsion system (mainly fuel cell, methods of energy conversion. motor and power management system) Examples include micro heat engines, and to increase efficiency. and micro fuel cells, both of which have power densities comparable to larger- • Photovoltaic fuel cells are a promising scale power plants, as well as more technology especially for high-altitude novel devices such as micro-electro- long endurance unmanned air vehicle mechanical systems (MEMS), and small aircraft. To be competitive, piezoelectric devices, photovoltaic cells, costs need to be reduced by up to a and biologically-inspired energy factor five. At present most of the solar conversion devices. cell market is based on crystalline silicon wafers, but there is now major 8 THE EREA VISION ON HIGH PRIORITY RESEARCH AXES TOWARDS AIR TRANSPORT SYSTEM 2050

interest in thin-film solar cells with film theoretical and experimental studies on the thicknesses in the range of 1–2 μm design of two high-speed concepts, equipped which can be deposited on cheap with dual-mode airbreathing and hydrogen-fed substrates such as glass, plastic or propulsive systems, are being performed in stainless steel. The development of order to demonstrate their feasibility for long- suitably light, powerful batteries is still haul flight. several decades away. Solar-powered aircraft powered solely from the heat • Low NOX combustor ramjet: provided by the sun are being tested, but combustion of the air-hydrogen mixture clearly would not be suitable for 24-hour required for the pre-cooled LAPCAT II deployment. ramjet engine results in high levels of NOX production, with a resulting • Hybrid electric turbines would use the unacceptable effect on the ozone layer. excellent –to-weight ratio of a The thruster-combustor design is turbine engine for high-power therefore critical to the future of this requirements such as take-off and concept. Rich-burn, Quick-mix Lean- electrical power for cruise and descent. burn (RQL) combustion appears to be Cycle analysis has shown that a good promising. It involves two-stage compromise could be to install a 4MW combustion in which all of the fuel is electric motor on the low-pressure (LP) injected in the first stage, reacting with a shaft. The additional power would be fraction of the airflow and resulting in a activated during cruise to reduce the fuel-rich mixture. In the second stage the power demand on the LP turbine. A remaining air is mixed with the main simple cycle simulation shows that when flow and reacts with the remaining fuel 50% of the power required to drive the in a fuel-lean combustion process. fan is provided electrically, specific fuel consumption falls by 21%. The ratio of • MHD scramjet: a strategy for jet fuel to batteries depends on the improving supersonic combustion ramjet mission. Short-range flights would use (scramjet) performance could be based more battery power, while long-range on the Magneto-Hydro-Dynamic (MHD) missions would be mainly kerosene- bypass system. MHD scramjets promise fuelled. The required electric motor and increased combustion efficiency and battery performances are currently stability, with more compact design of unavailable, but could be within the the scramjet propulsive system. 2050 timeframe. Feasibility has still not been demonstrated, however. Combustor 4.2.3 High-speed propulsion efficiency is critical to overall thruster Research on high-speed aircraft capable of performance and there remains doubt as reducing long-range flights to between two and to whether the concept is possible four hours has been ongoing for several years. without excessive aerodynamic drag. Speeds of Mach 4 – Mach 8 are necessary, at 4.2.4 Alternative configurations altitudes from 24km – 30km, which point towards advanced high-speed airbreathing New materials and manufacturing technology engines such as ramjets and scramjets. are increasing the feasibility of new aircraft Within the European Union’s Long-Term configurations, such as the Blended Wing Body Advanced Propulsion Concepts and aircraft, opening possibilities for major Technologies (LAPCAT I and II2) project, powerplant installation improvements bringing significant reductions in fuel burn and 2 http://www.transport- emissions. research.info/web/projects/project_details.cfm?ID=37390 9 M. BRUNET, A. DE BOER, V. GOLLNICK, S. LOTH, G. MARTINEZ, D. NIEUWENHUISEN

• Embedded propulsion: distributed and would have the additional advantage of embedded propulsion places the engines improving the electrical properties of the where they can partially or totally ingest airframe as well as increasing resistance the airframe boundary layer, reducing to lightning strikes. The electrical energy drag and making the downstream flow from the solar cell paint would be of air more uniform. A BWB converted into high voltage/low intensity configuration distributes thrust pulses which would be applied inside the generation along the wingspan by using combustion chamber to increase the several embedded, or buried, small enthalpy of the gas impinging on the engines. Propulsion can come from two high-pressure turbine, increasing the or more engines. Ideally, a higher thermodynamic efficiency of the engine number, ingesting the entire boundary core. layer, would be used. Poor fan performance at the boundary layer 4.3. Recommendations on priority research indicates an optimum of three or four axes for propulsion engines and two conventionally- mounted engines. The baseline is a Recommendations on priority research axes to conventional turbofan, but with a pave the way towards 2050 propulsion are gearbox to reduce engine core size and summarized and expressed according to low-pressure turbine size. The core research investment and respectively timeframe engine is then used to mechanically inFig. 3 and aircraft type in Fig. 4. drive the three fans which, for a 300- passenger aircraft would have a diameter of 1.2m. The lower weight and noise and higher aerodynamic efficiency of this solution could produce a potential 54% fuel burn reduction, noise levels 46 EPNdB below ICAO Stage 4 and NOX emissions 81% below CAEP 6. Economically, small engines have lower development, production and maintenance costs. Also, because the necessary thrust would be achieved with

a number of equally-sized small engines Fig. 3. Roadmap towards 2050 propulsion it might be expected that only a few small engine types would need to be developed, which would open the production and maintenance markets to a wider, more competitive market.

• Solar energy to improve combustion: the BWB configuration offers an opportunity to cover the upper wing surfaces with photovoltaic elements. A technology breakthrough would be solar cell paint, and some concepts have already been developed and demonstrated. Such a layer, applied to the carbon fibre materials from which the wing would almost certainly be built, Fig. 4. Key innovations versus research investment

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5. On board subsystems safety (integrity, reliability, availability) and robustness Aircraft subsystems provide functions for the • Revolutionary energy technologies: crew, passengers, aircraft and air traffic Revolutionary new ways of supplying management system. Because they involve energy to the aircraft will require on many fields of expertise and technology, a full board subsystems technology in many list of potential solutions for the subsystems of areas. Apart from reducing the energy 2050 is likely to be incomplete. Research which consumption or environmental footprint can realistically contribute to the 2050 goals of individual systems and of the will therefore be characterized more by complete aircraft, areas of interest evolution than by revolution. include: efficient, power-dense and The term “subsystem” is mainly related to one recyclable energy storage systems, or several interacting electric, electronic and energy generation and energy electro-mechanical on board equipments which control/management. support “system” functions or pneumatic/hydraulic equipment related to on • Advanced health monitoring and board actuation systems. prognotics: reduction in aircraft life cycle costs, and that of on board The study was based on top-down and bottom- systems, can be achieved by improved up approaches: maintenance, supported by aircraft • Top-down approach: high level goals health-monitoring systems. These enable analysis and investigation of the needs long-term scheduled maintenance to be within the other domains of this study; replaced by on-condition-based • Bottom-up approach: existing aircraft maintenance. systems analysis aiming at any possibilities for radical improvements. • Meta-systems: the ever-increasing 5.1. Top-down approach complexity of systems and functions brings a need for research into effective The main areas for the development of on board and reliable meta-systems which process subsystems that have been identified are the and interpret the data of many systems at following ones: a higher level. A combined for manned and • All-weather all-time flight: systems unmanned aircraft can be foreseen, which support the pilot, or in unmanned which shares decisions between the vehicles, the autonomous flight navigation system and the ground management system, to fly in all- operator. weather conditions at all times require on board presentation of meteorological • Systems engineering: methods, data and the technologies necessary for processes and tools: development and enhanced and synthetic vision to support certification of new aircraft subsystems flight in low-visibility conditions. involves meeting safety and reliability requirements, calling for methods, • Data-links: a large increase in high- processes and tools relevant to systems speed data link usage is foreseen, which engineering rather than technology will require on board subsystems development. The development of technology. Important aspects are the sophisticated tools supporting the increasingly stringent requirements on development process will be as important as the development of new technologies. 11 M. BRUNET, A. DE BOER, V. GOLLNICK, S. LOTH, G. MARTINEZ, D. NIEUWENHUISEN

Technologies alone are not enough. In parallel, system engineering methods and tools have to • Standardization and modularization: be developed in order to apply those for technology development in general, technologies in the aeronautical environment. open systems and standards are important building blocks that allow Further to the main areas of research defined modularization. Here, a role is seen within the top-down approach, an overview of especially for research institutes because research topics defined following the bottom-up of their independency. While approach is proposed below within a non- standardization is not in itself expected ordered list: to be useful as a stand-alone research • Reconfigurable communication systems topic, each topic should have • Adaptive communication systems standardization as a goal. • Conformal antennae • Enhanced and Synthetic Vision Systems • Adaptive, reconfigurable, multi- • Vision-based UAV and auto- purpose hardware: one of the landing challenges will therefore be to enable • Fuel cells for basic hardware to be reconfigurable, so • Powerline data communication in that it can implement different functions, aircraft depending on the flight phase. For non- • Wireless in-aircraft data communication safety-critical equipment, the weight and volume of dedicated electronic equipment will be replaced by basic, 6. Towards full automation? “general-purpose” electronic boards. The ever more complex air transport system 5.2. Bottom-up approach facing more and more ambitious goals is naturally evolving towards automation. From the bottom-up perspective, the Whatever the degree of automation, the air development of a new aircraft subsystem has to transport system will continue to comply with satisfy safety and reliability criteria if it is to its key performance areas: service level, achieve certification. Such requirements call for environment, safety and security, increased methods, processes and tools relevant to capacity, airline cost, flexibility and systems engineering rather than to technology predictability. The aim here is to define the development. biggest challenges in the path towards a high The development of sophisticated tools level of automation. Although this may lead to supporting the phases of a development process full automation at some points, full automation - design, verification, testing, etc - will be as is not a goal on its own. Automation is merely a important as the development of new means to improve the above performance areas. technologies. The applicability of new A highly automated air transport system is technologies will be conditioned by the based on three pillars: the 4-dimension contract, availability of processes and methods to certify automated air traffic management and the related equipment. As an example, there is automated aircraft. the possible use of artificial intelligence to Enabling technologies paving the way towards achieve for full autonomy. Nowadays, functions full automation are already being studied, but using artificial intelligence cannot be certified many are still at low operational levels. because of their unpredictability. If we do not Naturally, the shift towards full automation will elaborate new ways to state the reliability, and not happen overnight, but will rather be an consequently the safety, of such new paradigms, evolution in which more and more tasks are technologies based on them will no be useable. executed by automated systems.

12 THE EREA VISION ON HIGH PRIORITY RESEARCH AXES TOWARDS AIR TRANSPORT SYSTEM 2050

6.1. Developing realistic models data-mining algorithms are needed to support data extraction and selection. Creating sufficiently realistic models for research is a major challenge as systems become 6.4. Sensor fusion more complex and interactive. The biggest challenge lies in testing the interaction between Current onboard and offboard sensors provide a elements of the system. New modelling wealth of information. Often this information is techniques and methods to validate models will (partially) overlapping. Sensor fusion aims to be necessary to build the air traffic management combine the various sensor information sources (ATM) system of the future. Standardized to provide a single, optimized, view of the models that allow coherent and comparable world. For the future, innovative sensor fusion testing at different sites would be a major step in algorithms need to be developed which are ATM simulation. As different models could be extremely tolerant of any system failure. compared more easily, the development cycle of Situational awareness must be guaranteed in all new techniques could benefit as decisions about weathers conditions, all times. the most promising techniques become much Innovative sources of data will be created which easier. offer accurate weather forecasting before and during the flight. New Synthetic Aperture Radar 6.2. Human-machine interface technologies, molecular/optical air data sensors and multiple magnetometers for advanced The main challenge in designing a next attitude determination will have to be generation human-machine interface (HMI) for developed. Such technologies will enable fully ATM is deciding which information not to automated operations with low cost, weight and present. As the potential amount of information size. However, more onboard computational will be huge, only information that is necessary power will be required for real-time for next-generation controllers to execute their implementation tasks should be presented. Advanced monitoring tools will be necessary to verify if the planning 6.5. 4-dimension contract is properly executed. In case a problem arises that cannot be solved by the automated tools, The 4-dimension (4D) ATM contract is the the ATM manager will need to be brought in the central operational concept enabling the global loop by presenting the right information such optimization of air traffic management. It that he can make a deliberate decision provides the framework for automatic handling of the flight management of all air traffic 6.3. Interoperability and data collection, participants by a central ATM system ensuring data mining safe separation and optimization of all flights, according to global performance criteria. The path towards full automation puts high A 4D contract can be represented as a time demands on the timely availability of the right dimension moving along with a three- data in the right place at the right time. As the dimensional airspace tube assigned to each current ATM system consists of a huge number aircraft by the ATM system and/or negotiated of incompatible systems, interoperability is a by the aircraft themselves. All aircraft must stay major challenge. Systems will need to be within their assigned 4D volumes (i.e. respect interconnected and data should be shared and their contracts) for the entire duration of the made available among stakeholders using flight. As long as they do so, they are standardized protocols and formats. guaranteed conflict-free trajectories and the As more and more systems become entire air traffic system is globally optimised to interconnected, it is important to be able to the extent of the capability of the central system. locate and extract the right information. New All 4D contracts are generated by the central ATM system (strategic planning). Each contract

13 M. BRUNET, A. DE BOER, V. GOLLNICK, S. LOTH, G. MARTINEZ, D. NIEUWENHUISEN

is issued for the entire flight, including ground air transport system 2050 are summarized in the operations, and is conflict-free in relation to all roadmap below (Fig. 5). other contracts. The aircraft are in charge of executing their contracts and the ground system monitors them. Under certain circumstances, such as emergencies or off-nominal situations, the contract can be updated on-board the aircraft (dynamic planning). The implementation of a 4D contract-based ATM system will bring significant improvements to ground and on-board systems, both on technology and conceptual levels. However, the 4D contract robustness against ATM uncertainties is still to be quantified.

6.6. Emergency handling Fig. 5. Key research axes toward automation Today, flight procedures are subdivided into normal, abnormal, and emergency situations. 7. 2050 Airport In a highly automated environment, systems should contain built-in rules to handle abnormal The airport of 2050 must be driven by the dual and emergency situations. Statistics indicate for requirements for increased capacity and more than half of all aircraft accidents as reason improved efficiency while being customer human error, so it is reasonable to ask whether orientated [1]. Airport location, layout and the system itself or the responsible human-in- equipment will take into account environmental the-loop manager should respond to abnormal concerns as well as passenger comfort. Airports situations. must also function with the highest possible Aviation systems are usually designed as levels of safety. human-assistance systems which provide advisories to the operator. In the future, fully 7.1. General concept of the 2050 airport automated systems will decide and execute actions, and the operator will have a managing The following are seen as critical elements: and supervising task. If an error occurs, the • Air traffic management will be related to human will be able to intervene to solve a network of airports rather than local problems the system is not able to solve. and individual airports; A high level of automation will enable more • Landside and airside components need systems to be operated with fewer humans (i.e to be re-thought and intermodal means single pilot cockpit, Single European Sky), of transport described. although this will reduce the situational The airports of 2050 will be integrated into a awareness of an operator for a particular network of air, ground and even water transport emergency. If humans are supposed to handle that will enhance capacity and make these situations, it is essential to identify how transportation more efficient. The airport the operator should focus on it in an efficient network will be mainly composed of hubs and safe way. connected to secondary airports that will provide services to a greater number of users 6.7. Recommendations on priority research and operators. By 2050, the Single European axes towards automation Sky (SES) four-dimensional (4D) air traffic management system will have been fully Recommendations on priority research axes to implemented. It will be important to provide pave the way towards future highly automated airport networks with the capability to

14 THE EREA VISION ON HIGH PRIORITY RESEARCH AXES TOWARDS AIR TRANSPORT SYSTEM 2050 coordinate/ manage ground operations with 4D will have been fully implemented. It will be airborne operations. important to provide airport networks with the capability to coordinate and manage ground Within this timeframe, several scenarios can be operations with 4D airborne operations. envisaged: • Commercial aircraft to or from hubs. An integral element of the airport of the future Passengers have access to airports using is the handling of information and the the intermodal transport system; collaboration of all involved stakeholders. Total • Personal transport systems to or from Airport Management (TAM) will be expanded, secondary dedicated airports connected the role of operators changing from tactical to with the home by air-rail transportation; pre-tactical and from specialized controlling • Hub and secondary airports connected, functions to multi-system management. enabling passengers using personal aircraft to reach the hub and transfer to In the short term, the airside will take advantage commercial aircraft. of improvements resulting from the SES Connections between hubs and secondary programme and will evolve towards higher airports will be possible by means of efficient automation. The airport infrastructure will and environmentally friendly public transport, include revolutionary architecture adapted to but will also include an optimised network for any new aircraft configuration and propulsion private transportation that will enable the mode (i.e blended wing body and new fuels, efficient, safe use of personal ground transport. such as hydrogen or biofuels). Ships may be used to connect secondary airports, depending on their location. As capacity of the current airport systems is often a limiting factor, new approaches are Air transport will include current-configuration made to tackle these. Completely new runway aircraft, plus other actors such as personal air layouts and locations (remote at sea, large transportation vehicles or aircraft with surfaces enabling operations from any direction) passengers pre-loaded into standard fuselage or new operational procedures (formation boxes. In addition, different types of runways as flying, multiple approach paths) are possible well as take-off and landing assistance systems solutions. will be available to provide services for conventional take-off and landing aircraft, To achieve the goals of reductions of emissions short-take off and landing air vehicles or ground operations are tending to use electrical convertible vehicles. energy for ground movement of aircraft (autonomous and automated taxi systems Airport networks should be designed to connected to the aircraft) and all ground accommodate them all. handling equipment. Interconnections within this network will be provided by multimodal transport, including 7.3. A passenger-oriented airport high-speed trains for the national or The 2050 airport will use new technologies to international network, trains, subways, make passengers’ stay in the airport as short and tramways or suburban trains at regional airports, comfortable as possible. One of the most electric ground vehicles, environmentally important challenges will be achieving public friendly ships or even air-buses. confidence in automation, although this will demand significant advances in technology. 7.2. 2050 Airport operations Automation will mean that users are informed By 2050, the Single European Sky (SES) four- about the current status of their journey and dimensional (4D) air traffic management system alternative options, periodically or on demand. Information points will be distributed around

15 M. BRUNET, A. DE BOER, V. GOLLNICK, S. LOTH, G. MARTINEZ, D. NIEUWENHUISEN

the terminals and interactive devices embedded reliable services for the passenger and luggage. in transport systems so that passengers can Automatic subway trains and/or tramways access travel information at any time using should be considered instead of buses. smart phones or interactive panels/screens situated along the intermodal transport network. In the door-to-door approach, the airport landside is enlarged or redefined: 7.4. The airport as the heart of • Railway stations are part of an extended intermodality ‘landside’ • The journey starts anywhere in the A major goal for the future intermodal transport public zone system is to reduce dependence on the • Security checks and luggage automobile as the major mode of ground registration/deposit are done in the transportation and increase use of public railway station, on board a train or in transport, especially in the case of the future air dedicated points in a city transport system (Fig. 6). • Quick & easy checking using, for example, biometry Underground railway stations built below • Luggage transportation from home to the terminals reduce the need for private cars as terminal/plane (or door to door) is well as limiting the environmental footprint. available Intermodality can be envisaged at several levels, The subway or railroad serves all the from local public transport to international terminals/gates: long walks are no longer connections: needed to reach any point in the airport • City centres and suburban areas have to (especially with underground terminals) be accessible using the tramway or subway connecting with railway stations located on the airport landside • At regional level, connections to a high- speed train is a strong advantage for an airport’s attractiveness if it is rapid and serves the nearby cities • For national / international connections - Integration of airports within a regional/national railway network or other future modes of public transport - National railway stations at airports must be part of the landside, where Fig. 6. The 2050 airport as the heart of intermodality the passenger journey starts with passenger check-in and luggage deposit 8. Conclusion - High-speed train connections to The EREA vision on 2050 air transport system connect regional megacities aims at giving recommendations on priority - Connections between regional research axes to be carried out in Europe during airports to major hubs with high- the next decades if we want to pave the way speed train as an alternative to short- towards an ambitious future system as haul air services, releasing slots and advocated by the European Union. This vision relieving airport congestion does not pretend to predict the future; it rather provides keys to build our future. The airport landside should provide inter- terminal shuttles to provide convenient, fast and 16 THE EREA VISION ON HIGH PRIORITY RESEARCH AXES TOWARDS AIR TRANSPORT SYSTEM 2050

Acknowledgment This study, co-funded by EREA, involves seven national public research establishments in Europe: CIRA, DLR, INCAS, ILOT, INTA, NLR and ONERA, respectively from Italy, Germany, Romania, Poland, Spain, the Netherlands and France. This study, briefly summarized here, gathers knowledge and expertise of almost 50 researchers and engineers. It is worth noting that detailed technical reports on the five domains, aircraft configuration, propulsion, on board subsystems, automation and airport, are available upon request to the authors.

References

[1] European Union Flightpath 2050 - Europe's Vision for Aviation. EUR 098 EN, 2011. [2] EREA EREA vision for the future – Towards the future generation of air transport system. 2010. [3] EREA From Air Transport System 2050 vision to Planning for Research and Innovation. 2012.

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