Airbus Group Innovations. Rolls-Royce Research and Technology. Rolls-Royce plc 65 Buckingham Gate London SW1E 6AT United Kingdom

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1 Rolls-Royce Research and Technology In 2012, Rolls-Royce invested 919 million on research and development, two thirds of which had the objective of further improving the environmental performance of its products, in particular reducing emissions. To ensure that there is a pipeline of technology, and a balanced portfolio of research with target applications in both the near and long term Rolls-Royce has adopted 5, 10 and 20 year visions for the technology it develops. Vision 5 constitutes the low risk technology ready for application within 5 years. Vision 10 describes the next generation of technology or capability. Vision 20 describes emerging or as yet unproven technologies aimed at Rolls- Royce s future generations of products, much of which will be applied right across the product range in all sectors. A number of Vision 20 studies are currently exploring future generations of aircraft architectures that may provide significant improvements, particularly in areas of fuel burn, noise and emissions, this includes electric technologies and distributed propulsion. Rolls-Royce has also created an extensive range of partnerships and collaborations around the globe through our network of 28 University Technology Centres (UTCs). UTCs are a source of both technology and highly skilled people. The Group has also applied a similar model in creating a network of Advanced Manufacturing Research Centres to develop manufacturing capability. There are currently 6 operational facilities, the latest having opened in Crosspointe, Virginia in late These foster collaboration between companies at all stages of the supply chain, from the Original Equipment Manufacturers (OEMs) to material suppliers, measurement systems providers and tool manufacturers. Airbus Group Innovations The E-Thrust concept study is part of Airbus Group's on-going hybrid and electrical propulsion system research, which has seen the hybrid concept study for a full-scale helicopter, the successful development of a Cri-Cri ultralight modified as the world s first four-engine all-electric aerobatic aircraft, the demonstration flights of a hybrid electric motor glider for which Airbus Group Innovations developed the battery system, the flight testing of a short-range mini-unmanned aerial vehicle with an advanced fuel cell and the integration of a piston diesel engine into the TANAN UAV as well as the concept study of a hybrid-electric propulsion system for this rotorcraft. Airbus Group Innovations is the corporate network of research centres of Airbus Group. A highly skilled workforce of more than 800 is operating the laboratories that guarantee Airbus Group technical innovation potential with a focus on the longterm. The structure of the network and the teams within Airbus Group Innovations are organised in global and transnational Technical Capabilities Centres: Composites technologies Metallic technologies and surface engineering Vehicle integration industrial and support processes Electronics, communications and intelligent systems Systems engineering, information technology and applied mathematics Energy and propulsion Design and Projects Airbus Group BD&MA 05/14 EN Airbus Group. All rights reserved. Rolls-Royce plc 65 Buckingham Gate London SW1E 6AT United Kingdom Airbus Group Airbus Group Innovations UK Filton, Bristol BS99 7AR United Kingdom

2 E-Thrust Electrical distributed propulsion system concept for lower fuel consumption, fewer emissions and less noise

3 The Vision and Perspective of an Electrical Distributed Propulsion System econcept a future vision Airbus and Airbus Group Innovations, along with other industry players like Rolls-Royce and Siemens, are exploring different avenues to find innovative solutions to the challenges the aviation industry is facing in the future. They are investigating one such avenue for a 2050 timeframe a hybrid/electrical distributed propulsion system as an intermediate but necessary step towards fully electric propulsion for airliners. Airbus, in its role as integrator, has taken its concept plane a vision of aviation in the future and used it to create the econcept, a visualisation of the architecture and configuration of what an aircraft of the future could look like powered by hybrid/electrical distributed propulsion. The DEAP project (represented by the initial E-Thrust configuration) is bringing the technologies, while Airbus is giving its expertise as an integrator providing regular inputs and feedback on the technology developments. Innovative propulsion system concepts for future air vehicle applications are being developed by Airbus Group Innovations, the corporate research and technology network of Airbus Group, and by Rolls-Royce, a global provider of integrated power systems and services to the civil aerospace, defence aerospace, marine and energy markets. Results of their research activities support Airbus Group divisions in leveraging innovation solutions to further improve the efficiency and environmental performance of commercial aviation. Airbus Group Innovations and Rolls-Royce, with Cranfield University as a partner, are jointly engaged in the Distributed Electrical Aerospace Propulsion (DEAP) project, which is co-funded by the Technology Strategy Board (TSB) in the United Kingdom. The DEAP project researches key innovative technologies that will enable improved fuel economy and reduced exhaust gas and noise emissions for future aircraft designs by incorporating a Distributed Propulsion (DP) system architecture. These efforts are part of the aerospace industry s research to support its ambitious environmental protection goals as spelled out in the European Commission s roadmap report called Flightpath 2050 Europe s Vision for Aviation. This report sets the targets of reducing aircraft CO 2 emissions by 75%, along with reductions of nitrous oxides (NOx) by 90% and noise levels by 65%, compared to standards in the year 2000.

4 E-Thrust 03 Achieving these goals requires significant performance improvements in engine technology, systems architecture and engine/airframe integration to enable radically more efficient propulsion systems. Finding viable solutions requires the pioneering of unconventional aircraft and propulsion system concepts. In this perspective, propulsion technologies are continuously being improved through developments in the fields of energy storage and conversion, in electrical motors, novel combustion cycles, ultra-high bypass ratio configurations, along with hybrid electric/thermodynamic and fully electric systems. The configuration with three fans on either side of the fuselage represents an initial starting point for future optimisations, with the optimum number of fans to be determined in trade-off studies in the DEAP project. The Distributed Electrical Aerospace Propulsion (DEAP) Project The Benefits of a Distributed Propulsion System Architecture With its experience in gas turbine and gas power unit design, as well as in electric propulsion systems, Rolls-Royce has for some time been a research partner of Airbus Group in the fields of energy management and simulation, electrical machines and superconductivity, and propulsion system integration. Since 2012, Airbus Group Innovations and Rolls- Royce, with Cranfield University as a partner (and some testing subcontracted to Cambridge University), are jointly engaged in the DEAP project, which researches key innovative technologies for distributed propulsion systems. Compared to engines on existing commercial airliners, such a system will require a much higher level of integration with the airframe design than that of today s aircraft. For the E-Thrust concept, distributed propulsion means that several electrically-powered fans are distributed in clusters along the wing span, with one advanced gas power unit providing the electrical power for six fans and for the re-charging of the energy storage. The E-Thrust concept can be described as a serial hybrid propulsion system. This configuration represents an initial starting point for future optimisations, with the optimum number of fans to be determined in trade-off studies in the DEAP project. Initial study results by Airbus indicate that a single large gas power unit has advantages over two or more smaller gas power units. This will give a noise reduction and allows the filtering of particles in the long exhaust duct at the back of the engine. The DEAP project aims to deliver a preferred electrical DP system for future aircraft that may provide a breakthrough and a significant contribution to mitigating the environmental impact of the projected increase of air traffic. Rolls-Royce will develop an optimum electrical system propulsion plant, taking into consideration speed range, max speed, number of fan motors, efficiency, etc.; while Airbus Group Innovations (the DEAP project leader) will design the electrical system and work with Airbus to optimise the integration of the propulsion system in the airframe. The hybrid DP architecture offers the possibility of improving overall efficiency by allowing the separate optimisation of the thermal efficiency of the gas power unit (producing electrical power) and the propulsive efficiency of the fans (producing thrust). The hybrid concept makes it possible to down-size the gas power unit and to optimize it for cruise. The additional power required for take-off will be provided by the electric energy storage.

5 Flight Profile Energy Management Cruise In the cruise phase, the gas power unit will provide the cruise power and the power to recharge the energy storage system. In the unlikely event of a failure of the gas power unit, power from the energy storage is available to continue the flight to a safe landing. Take-off and & Climb Power comes from the gas power unit and from the energy storage system to provide the peak power needed during the take-off and climb phase. The energy storage system will be sized to ensure a safe take-off and landing should the gas power unit fail during this phase. A fundamental aspect of optimising the propulsive efficiency is to increase the bypass ratio beyond values of 12 achieved by today s most efficient podded turbofans. For the DP concept, the bypass ratio must be termed effective bypass ratio, because the fan airstreams and the core airstream are physically separated. With DP, values of over 20 in effective bypass ratios appear achievable, which would lead to significant reductions in fuel consumption and emissions. Having a number of small, low-power fans integrated in the airframe instead of a few large wing-mounted turbofans is also expected to reduce the total propulsion system noise. In addition to improving the propulsive efficiency, DP offers a greater flexibility for the overall aircraft design that could result in reduced structural weight and aerodynamic drag, for example, by relaxed engine-out design constraints leading to a smaller vertical tail plane, by being able to better distribute the weight of the propulsion system components and by reenergising the momentum losses in the boundary layers that grow over the wing and fuselage causing a wake (Boundary Layer Ingestion, BLI). For the power levels in the megawatt range that are required in an electrical distributed propulsion network, a new high-voltage superconducting electrical system has to be designed and validated to stringent requirements in terms of efficiency. Such a system must aim to reduce heat being generated due to alternating current losses in the superconducting wires, which are enclosed in cables and surrounded by cryogenic fluid, so that they are kept at a constant cryogenic temperature for their best performance. Minimizing such losses is crucial, as extracting 1 Watt of heat using a cryocooler at 20K (-252 C) to ambient temperature requires 60 Watts of electrical power. An additional efficiency gain appears possible if this boundary layer is ingested and accelerated by the fans, because it can reduce the aircraft s wake and hence its drag. However, the implementation of a boundary-layer ingesting system means that the airflow into the fans is not uniform; to realize the potential benefits, the turbo-machinery and in particular, the fan blades must be able to withstand the associated unsteady conditions due to the distorted intake flow. The design of the Rolls-Royce fans is currently being developed in collaboration with its University Technology Centre in Cambridge, and is specifically optimised to deliver the best performance in the distorted flow conditions that are experienced in a BLI configuration; its design is supported by computer analysis as well as reduced-scale testing and measurements.

6 E-Thrust 05 Descent/Gliding In the initial descent phase, no power is provided to the fans, and the gas power unit will be switched off. The aircraft will be a glider and the energy storage system will provide the power for the aircraft s on-board systems. Descent/Windmilling During the second phase of the descent, the fans will be windmilling and produce electrical power to top-up the charge in the energy storage system. Landing For the landing phase, the gas power unit is re-started and provides power at a low level for the propulsion system. This is a safety feature to cover a hypothetical loss of power from the energy storage system during this phase. Enabling Technologies Superconductivity: A key enabling technology for the DP (hybrid/distributed propulsion) concept is using superconductivity in the cables, generators and motors for the transfer of electrical power from the gas power unit and energy storage to the fans. Superconductivity is a quantum mechanical phenomenon of exactly zero electrical resistance, which occurs in certain materials when they are cooled below a critical temperature. It allows the electrical system components to be much smaller, lighter and more efficient compared to conventional copper- and aluminium-based technology. The necessary cooling can be achieved either by supplying cryogenic fluids (for example: liquid hydrogen, liquid helium or liquid nitrogen) from a reservoir, or by producing the necessary cold temperatures using a cryocooler a technology used today in space applications (for example a turbo-brayton cryocooler made by Air Liquide for ESA) or in MRI systems. A sideby-side comparison of copper and superconducting wires demonstrates the vast size and weight differences possible with this technology. Magnesium DiBoride (MgB 2 ) superconducting wires are made by Columbus Superconductors and used today, for example, in MRI scanners). Energy Storage: Scientists expect new generations of energy storage systems to exceed energy densities of 1,000 Wh/kg (Watt hours per kilogram) within the next two decades, more than doubling today s best performance. Lithium-air batteries are the most promising solution for the E-Thrust concept s energy storage requirements. They have a higher energy density than lithiumion batteries because of the lighter cathode, along with the fact that oxygen is freely available in the environment. Lithium-air batteries are currently under development and are not yet commercially available. The E-Thrust concept is based on the assumption that the required level of energy density can be achieved within the 25-year timeframe envisioned for the DP concept to mature.

7 06 E-Thrust Distributed Fan Propulsion System The distributed fan propulsion system provides thrust for the aircraft, replacing conventional turbofan engines. The large fan diameter and weight of conventional turbofans limits where they can be located on an airframe usually under the wing. Their location does not enable advanced aerodynamic efficiency techniques to be used, whereas having a number of electrically-driven fans that are integrated into the airframe allows for a more aerodynamic overall design. During descent, the energy-efficient distributed fans are turned by the airstream and, like wind turbines, they generate electrical energy which can be stored. Wake Re-energising Fan As the aircraft flies through the air, it leaves a wake behind it resulting in drag. The embedded wake re-energising fan is designed to capture the wake energy by re-accelerating the complex wake. By re-energising the wake, the overall aircraft drag is reduced. The concept uses advanced lightweight composite fan blades that are designed to maximise overall propulsive efficiency whilst minimising the weight of the propulsion system. To achieve an integrated distributed fan propulsion system design that matches the overall airframe requirements, three key innovative components are required: A wake re-energising fan Structural stator vanes that pass electrical power and cryogenic coolant A hub-mounted totally superconducting electrical machine

8 E-Thrust 07 Structural Stator Vanes By having an embedded propulsion system, the conventional turbofan mounting structure is no longer required thereby saving weight and drag. The stator section is carefully designed to provide a row of aerodynamic and structural stator vanes behind the fan recovering thrust from the swirling air. The length of the distributed fan, propulsion system has been designed to be much shorter than that of a conventional turbofan so that the centre of gravity is located about the structural stator vanes. In addition, some of the stator vanes are designed to accommodate the internal routing of the superconducting cables to the hub-mounted superconducting electrical machine. Exploded view showing the hub-mounted totally superconducting machine Hub-Mounted Totally Superconducting Machine The innovative hub-mounted totally superconducting electrical machine drives the wake re-energising fan. Rolls-Royce and Airbus Group Innovations, with Magnifye Ltd and Cambridge University as partners, are engaged in a Programmable Alternating current Superconducting Machine (PSAM) project. The PSAM project researches an innovative programmable superconducting rotor and innovative AC superconducting stator. This work is supported in part by the UK Technology Strategy Board. The superconducting stator generates a powerful electromagnetic field that rotates around the circumference at a speed directly related to the frequency of the electrical supply. The superconducting machine replaces the copper and iron stator structure of a conventional machine. It is a much more powerful, lighter and low-loss design incorporating roundwire high temperature superconducting coils embedded within a lightweight epoxy structure. Electromagnetic torque is created by effectively aligning the rotor s magnetic field with the field generated electromagnetically within the stator. The superconducting rotor magnetic field is generated through the use of bulk superconducting magnets in a puck form. A superconducting magnetic puck of this size can, when fully magnetised, generate extremely high magnetic fields with laboratory testing demonstrating 17 Tesla a magnetic field capable of easily levitating a family car. The magnetic pucks are innovatively magnetised in-situ by the stator to create a permanent magnet field that can be programmed to deliver different field strengths thereby improving controllability. The superconducting machine design is bi-directional in that it is equally efficient at driving the wake re-energising fan to provide aircraft thrust or being driven by the fan rotating in the airstream to generate electrical power, which can then be stored within the airframe.