E-Thrust_EN

Airbus Group InnovationsThe 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 worlds 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 long-

term. 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

Rolls-Royce Research and TechnologyIn 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-

Royces 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 2012. 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.

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Rolls-Royce plc65 Buckingham GateLondon SW1E 6AT United Kingdom

Airbus GroupAirbus Group Innovations UKFilton, Bristol BS99 7ARUnited Kingdom

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

The Vision and PersPecTiVe of an elecTrical disTribuTed ProPulsion sysTem

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.

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.

These efforts are part of the aerospace industrys research

to support its ambitious environmental protection goals as

spelled out in the European Commissions roadmap report

called Flightpath 2050 Europes Vision for Aviation.

This report sets the targets of reducing aircraft CO2 emissions

by 75%, along with reductions of nitrous oxides (NOx) by

90% and noise levels by 65%, compared to standards in the

year 2000.

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.

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.

03E-Thrust

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 disTribuTed elecTrical aerosPace ProPulsion (deaP) ProjecTWith 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 todays aircraft.

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 benefiTs of a disTribuTed ProPulsion sysTem archiTecTureFor 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 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.

A fundamental aspect of optimising the propulsive efficiency is

to increase the bypass ratio beyond values of 12 achieved

by todays 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 re-

energising the momentum losses in the boundary layers that

grow over the wing and fuselage causing a wake (Boundary

Layer Ingestion, BLI).

An additional efficiency gain appears possible if this boundary

layer is ingested and accelerated by the fans, because

it can reduce the aircrafts 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.

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.

flighT Profile energy managemenT

Take-off and & ClimbPower 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.

CruiseIn 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.

05E-Thrust

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 side-

by-side comparison of copper and superconducting wires

demonstrates the vast size and weight differences possible

with this technology. Magnesium DiBoride (MgB2)

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

todays best performance. Lithium-air batteries are the most

promising solution for the E-Thrust concepts energy storage

requirements. They have a higher energy density than lithium-

ion 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.

Descent/GlidingIn 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 aircrafts on-board systems.

Descent/WindmillingDuring 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.

LandingFor 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.

E-Thrust06

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.

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

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.

disTribuTed fan ProPulsion sysTem

07E-Thrust

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.

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 electro-

magnetic 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 round-

wire high temperature superconducting coils embedded within

a lightweight epoxy structure.

Electromagnetic torque is created by effectively aligning

the rotors magnetic field with the field generated electro-

magnetically 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.

Exploded view showing the hub-mounted totally superconducting machine