Electric Distributed Propulsion for Small Business Aircraft – A Concept-Plane

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Electric Distributed Propulsion for Small Business Aircraft – A  Concept-Plane


application/pdf Electric Distributed Propulsion for Small Business Aircraft – A Concept-Plane Jean Hermetz, P. Choy, O. Atinault, Thierry Lefebvre, Peter Schmollgruber, Michael Ridel, B. Paluch, C. Do
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Electric Distributed Propulsion for Small Business Aircraft – A  Concept-Plane



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Electric Distributed Propulsion for Small Business Aircraft – A Concept-Plane J. Hermetz (1), P. Choy (3), O. Atinault (3), Thierry Lefebvre (1), Peter Schmollgruber (1), M. Ridel (1), B. Paluch (2), C. Doll (1), D. Donjat (1), A. Guigon (3), Claude le Tallec (3), Olivier Dessornes (3), 1 : ONERA, The French Aerospace Lab, Toulouse, France carsten.doll@onera.fr, david.donjat@onera.fr, jean.hermetz@onera.fr, Thierry.Lefebvre@onera.fr, michael.ridel@onera.fr, Peter.Schmollgruber@onera.fr, 2 : ONERA, The French Aerospace Lab, Lille, France, bernard.paluch@onera.fr 3 : ONERA, The French Aerospace Lab, Paris, France, antoine.guigon@onera.fr, olivier.atinault@onera.fr, philippe.choy@onera.fr, Olivier.Dessornes@onera.fr, claude.le_tallec@onera.fr Electric propulsion for aircraft begins to be effective in the field of leisure aviation mainly for initial training. However, some challenges appear when performance-level needs to be increased to address more demanding application such as business travel even for small passenger capacity. Based on its expertise in all disciplines of aviation design, and in the following of projects dedicated to future Air Transport System, Onera started exploratory studies, a few years ago, to investigate potential new technologies and concepts that could participate in answering societal need for On-Demand Mobility [1]. The resulting concept-planes illustrate some possible assembly of such key-technologies which will serve as basis for future research aiming at demonstrating both performance potential and feasibility of the most relevant technologies. Introduction and context Environmental considerations, in term of noise as well as pollutant emissions, in addition to the potential reduction of carbon-based natural resources, lead to investigate the use of electric propulsion for transportation. All-Electric powered cars are now in use, as well as hybrid cars aiming at reducing fuel consumption in coherence with the above observation. Electric propulsion for aircraft arises in the field of leisure aviation and promised performance of several prototypes suggest that some light two-seat electric- powered aircraft could be in-service in the coming years for initial training. Generally based on a pragmatic approach, several manufacturers are investigating the possibility to substitute, on an existing airframe, piston engine(s) for a LiPo or Li-Ion battery powered electric motor with a conventional propeller, connected to an Electronic Control Unit (ECU). Performance, such as take-off distance, climb and cruise speed appear to be adequate for very light aircraft having a rather short range and low cruise speed, but a strong challenge appears when trying to extend the range beyond one hour of flight (excluding reserves): due to the energy density of such batteries, their mass increases rapidly leading to redesign the aircraft, larger and heavier, reducing the expected economic viability. Similarly to what is on in the automotive sector, an alternative solution to extend range with a limited weight penalty consists in integrating a range- extender based on the association of a piston-engine and an electric generator, used mainly during cruise phase. That remains efficient, although complex, but doesn’t fulfil the main objective: to be independent from any carbon-based energy for flying. In order to contribute to the growth of this emerging market by investigating some potential solutions coping with the main issues of electric propulsion for aircraft, Onera decided to start an expert-based exploratory study, done in association with CEAtech. This expert-group concluded that there is a potential for all-electric powered airplane for civil transportation based on the association of several key-technologies integrated in a new airframe configuration using distributed propulsion, in addition to some changes in operational use [1,2]. Above mentioned breakthrough technologies concerns: • Aerodynamics of distributed propulsion, • Command and control through the association of multi-motors and control surfaces, • Energy supplying, storage and hybrid capabilities, • Modular architecture and in-flight reconfiguration capabilities of the overall electric propulsion system, • Electric Ducted Fan (EDF), • Improved multidisciplinary design and optimization capabilities. Concept-planes overview As these conclusions are potentially applicable from light to regional aircraft, a first pre-design exercise has been done in order to illustrate the potential of such innovations in a first application-case based on the recent results of the UE funded PPlane project [3] dedicated to Personal Plane. The need for a 4 to 6 seats small business aircraft, operated from downtown or close to urban area, able to cover ranges from 400 to 500 km in about two hours at low cruise altitude (up to 3000 m AMSL), has emerged from this project, with some requirements in term of automation in order to be used by everybody without specific skills and qualification. Two 14.5 m-span wing concept-planes (Fig. 1, Fig. 2) have been designed using an integrated approach, compliant with CS-23 main rules. Two sets of twenty 10 kW-Electric Ducted Fan (EDF) are distributed along the inner part of the wing, either on the leading edge or on the trailing edge. Distributed propulsion promises dramatic increases in aerodynamic and propulsive efficiency [4], and potentially noise reduction. Fig. 1: Three-surface concept-plane with distributed EDF at the wing trailing edge Fig. 2: High-wing concept-plane with distributed EDF along the wing leading edge As an electric motor remains efficient whatever its dimensions, a high propulsive efficiency is expected and depends more on the design of the electric ducted fan used. The wing flow management, thanks to EDF distribution and location, increases lift at very low speed w/o flaps or slats, and contributes to controlling the plane (Fig. 3). Higher control authority and safety levels are therefore anticipated, through the use of fly-by-wire controls. In addition, EDFs use various rotation speeds and directions in order to reduce perceived noise by spreading out noise energy on a wide frequency spectrum. Fig. 3 – Distributed probulsion based on co-located EDF 500 kWh energy is supplied by a set of PEMFC 1,2 combined with a small battery pack used mainly during more power-demanding flight phases or emergency situations. Hydrogen is stored in a same number of high-pressure (700 bar) tanks in composite materials (Fig. 4). Fig. 4 – Schematic internal arrangement of fuel cells and hydrogen tanks For safety reasons, each fuel cells unit supplies energy to 2x2 EDF in order to maintain symmetrical thrust in case of failure (Fig. 5). Electric architecture is safety-driven designed and intelligent energy management is fully integrated with flight control as power-trains act both for propulsion and control [5]. Fig. 5 – Schematic view of the electric architecture In the vicinity of electric components, primary structure uses metal parts – which participate in electric network as well as helping maintaining thermic stability. Others parts of the airframe would 1 Polymer Exchange Membrane Fuel Cell 2 Thanks to CEAtech data be made with composite materials. That comes from a trade-off between several design criteria regarding thermic flow control, electric conductivity, EMC behaviour and lightning protection, as well as aiming to reach the lightest airframe. Finally, key-technologies selected and illustrated in this first conceptual design step result from a multidisciplinary approach in order to find the best trade-off regarding design objectives and technical or operational constraints. Conclusions and next steps As we assume that future technologies could reach a certain level of performance that lead to the expected viability of such electric-powered planes, they need to be further investigated in order to increase knowledge, improve modelling and therefore consolidate proposed concepts. Facing this challenge, Onera recently decided to focus effort on two of the key-technologies mentioned: distributed propulsion and its effects on aerodynamics and control, and controllability of such planes using unconventional, distributed and heterogeneous actuators. In addition to their central role played in the overall efficiency of all-electric powered aircraft, they also contribute to increase safety and robustness of such vehicles. This is essential to answer the on-demand mobility market. In that way, Onera is going to participate in the future of aviation, with a first step dedicated to small transport aircraft, but with the will to continue developing these potential breakthrough technologies for their future use on larger planes. References 1 Rapport de synthèse du Groupe de Travail Études Prospectives “GTEP12”, Onera – CEAtech, Septembre 2013 2 "Conceptual Feasibility Study for A Fully Electrically Powered Regional Transport Aircraft", C. Döll¹, B. Paluch¹, A. Guigon¹, D. Fraboulet; CEA Tech, France; ¹ONERA – The French Aerospace Lab, France, 29th Congress of the International Council of the Aeronautical Sciences ICAS, Saint Petersburg, Russia, 7-12 September, 2014. 3 PPlane projet - http://www.pplane-project.org and http://www.onera.fr/en/zoominthelab/after-velib- planelib-pplane 4 "Drag Reduction Through Distributed Electric Propulsion", Alex M. Stoll_and JoeBen Bevirty (Joby Aviation, Santa Cruz, California, 95060) ,Mark D. MoorectricDistributedPropulsionez,William J. Fredericksx, and Nicholas K. Borer (NASA Langley Research Center, Hampton, Virginia, 23681), Aviation Technology, Integration, and Operations Conference, 16-20 June 2014, Atlanta, Georgia 5 A Concept Plane using electric distributed propulsion - Evaluation of advanced power architecture, M. Ridel et al; MEA 2015 More Electric Aircraft conference, 04-05 February 2015, Toulouse, France