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The challenges
and benefits of the
electrification of aircraft
Author
James Domone
Senior Engineer
June 2018
No more blue-sky thinking: how and why the aviation sector
is moving towards cleaner, greener skies
Author
James Domone
Senior Engineer, Atkins
About us
SNC-Lavalin’s Atkins business is one of the world’s
most respected design, engineering and project
management consultancies. Together, SNC-Lavalin, a
global fully integrated professional services and project
management company, and Atkins help our clients
plan, design and enable major capital projects, and
provide expert consultancy that covers the full
lifecycle of projects.
With a strong, proven heritage in aerospace design and
consultancy services, we have worked on some of the
industry’s biggest projects. Including: Airbus’ A380,
A400M and Single Aisle aircraft, and with Marshall
Aerospace and Defence Group, Bombardier, BAE
Systems, Rolls-Royce and the Royal Air Force.
3
Each day we see the electric car industry
growing apace. In the UK, hybrid and electric
cars are becoming a more common sight on
our roads, as are electric charging points in
car parks. Their price is falling, too. Railway
electrification is on the renewal agenda across
the UK, because it offers better performance
and protection of the environment than diesel
trains, as well as reducing noise pollution for
people living along busy train lines. So, when will
other forms of transport, like shipping, and air
travel, join them?
There’s no doubt that aircraft emissions cause
pollution. The European Union says direct
emissions from aviation account for about
three per cent of the EU’s total greenhouse
gas emissions, and more than two per cent of
global emissions. Figures suggest that if current
technology isn’t advanced, then CO2 output from
aircraft will likely increase by two and a half
times. This is due mostly to the growing middle
classes of China, India, and African and South
American countries, who increasingly want to
fly. Even when offset by countries seeking to
reduce CO2 output, that still means an overall
global rise of CO2 emissions from aircraft of
somewhere in the region of five per cent.
But that’s only part of the story. Increased
aircraft operations activity in or around where
an airport is located also produces emissions
that degrade the air quality. The risk comes
from the production of nitrous oxides, NOX, fine
The earth’s climate is changing and our behaviour
must also change. That means moving towards
cleaner, more efficient, forms of transport.
As road and rail travel shift towards electric,
is now the time for aviation to join them?
particulate matter, PM2.5, and ozone, O3. This
is documented widely by scientific evidence;
and as a serious risk to public health it must be
tackled. The other complaint from residents
near airports is noise. More recent aircraft
designs have reduced noise levels, but there are
still improvements needed.
Anyone taking a return trip from London to New
York today will generate roughly the same level
of emissions as it takes to heat the average
European household for a whole year. By
introducing electric battery powered aircraft, the
potential exists for charging the batteries using
power generated via more sustainable means
– such as nuclear, wind, hydro, solar and tidal
generation. However, if non-sustainable means
of power generation for battery charging are
used, then at least potentially harmful emissions
are released away from areas with denser
populations and the upper atmosphere.
There’s also the economic argument. Reducing
the quantity of fuel needed reduces the costs
of operating an aircraft. This will become more
apparent over time if the predicted reduced
availability of oil materialises and drives costs
ever higher.
So, there’s the target for cleaner air travel: the
reduction of CO2, NOX, PM2.5 and O3 emissions,
noise and fuel costs. But how can we achieve
this when faced with so many technological
challenges?
Introduction
The challenges and benefits of the electrification of aircraft
4
Going beyond the plateau
Through years of refining and optimising
aircraft design, many feel that we’ve reached a
plateau in terms of aircraft performance when
it comes to fuel efficiency and aiming for lower
emissions. If we look to battery power, like the
car industry has, how can we square the circle,
and reconcile the fact that batteries are heavy,
and planes need to fly? The role of engineering
is about finding solutions and solving problems,
and to find new and better ways of doing
things. To that end, new technologies are
emerging, and their prototypes are starting
to be tested.
So, what does that mean for those of us in the
industry? It means making sure, if you’re a
company involved with the maintenance, repair
and overhaul of aircraft, or you manufacture
equipment, or operate an airline or airport,
that you must prepare for disruption – but also
position yourself to exploit the opportunities
that cleaner, greener air travel will bring to
the industry.
Unquestionably, there is a united sense of
purpose across the European aviation sector
to move towards greener solutions that will
have proven efficiency and performance
and become less reliant on fossil fuels. One
example is ACARE, the Advisory Council
for Aeronautics Research in Europe, which
launched in 2001 and has set itself some
challenging environmental goals through its
Flightpath 2050 initiative which it is seeking
to achieve through joint research projects,
by the year 2050. ACARE’s members include
industry giants Airbus and Rolls-Royce, and its
goals range from achieving a seventy-five per
cent reduction in CO2 emissions per passenger
to ensuring all aircraft are designed and
manufactured to be recyclable.
Average fuel burn for new jet aircraft, 1960-2010.* Large reductions in fuel burn are seen from 1960
up to the 1990s; however, since then any decrease has been modest, despite the development
costs of new aircraft continuing to rise.
Fuel burn at specified range (1960+100)
1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010
25
50
75
100
Seat-km
1960s
1970s
1980s
1990s
Post-2000
*www.theicct.org/blogs/staff/overturning-conventional-wisdom-aircraft-efficiency-trends
The challenges and benefits of the electrification of aircraft
5
While it’s still early days, key research and
development in this area is preparing for
take-off, as major players in the aviation
sector start to roll-out prototypes and test
concepts. Finding an alternative to kerosene,
and identifying a sustainable power source,
suggests electric power is the first answer.
As such, aircraft programmes such as the
Airbus A350 and Boeing 787 have increasingly
used batteries to power on-board systems.
The 787 also exhibits greater use of electric
power from engine installed generators. This
approach is described as the ‘more-electric
aircraft’. Future progression to electric
propulsion is increasingly being proposed; first,
by considering a hybrid option with energy still
provided by hydrocarbon fuel but powering
electric propulsion – then, progressing to a fully
electric system with batteries providing the
energy. In which case, we would start to see
reductions in emissions even at the earliest,
hybrid, stage, with further gains from a move
to full electric systems.
1952
de Havilland
Comet – first
commercial
jet airliner
1973
Brditschka HB-3
– first full-sized,
manned aircraft
to be solely
electrically powered
1998
NASA Pathfinder
Plus sets
altitude record
2016
Solar Impulse
2 completes
circumnavigation
of the globe
2018
E Fan X, Zunum,
Wright Electric
all working on
new projects
2030s
In-service for
hybrid electric
airliners?
2040s +
All electric
airliners?
History of electric innovation in aerospace
The challenges and benefits of the electrification of aircraft
6
‘UK-built hybrid electric plane flying by 2020’
In 2017, The Guardian reported that Rolls-
Royce has joined the race to develop ‘electric
passenger jets’ and how Rolls-Royce claims its
collaboration with Airbus and Siemens on their
E-Fan X project could result in a partly UK-built
hybrid electric plane flying by 2020.
“Manufacturers will convert a short-
haul passenger jet, paving the way to
making commercial air travel running
partly on electricity a reality.”
Also, the report says, “engineers involved in the
E-Fan X project said the technology could mean
cleaner, quieter and cheaper journeys. They
also raised the prospect of radically changing
aircraft and airport design, allowing air travel to
supplant rail for many more intercity journeys.”
Also quoted in the article was Carolyn McCall,
EasyJet’s former chief executive,
who said it was
“a matter of when, not if, a short-
haul electric plane will fly.”
And later, in April 2018, Siemens announced:
“The world’s first flying serial-hybrid aircraft
landed its maiden flight at Matkópuszta airfield
in Hungary, powered by a Siemens propulsion
system. This hybrid Magnus eFusion is
equipped with a Siemens SP55D electric motor
and a FlyEco diesel engine to allow for silent
take-off and landing with an extended range.
The complete propulsion system including a
new generator, inverters and control systems
has been developed by Siemens eAircraft and
is expected to provide meaningful insights into
the application of hybrid-electric systems for
aircraft during future operation.”
www.theguardian.com/business/2017/dec/28/electric-passenger-jet-revolution-looms-e-fan-x-air-taxis-hybrid-planes
The challenges and benefits of the electrification of aircraft
7
Powerful, yet lightweight
The key phrase here is ‘complete propulsion
system’. In technical terms, the challenge that
E-Fan X and other projects of its kind that
are also in the pipeline – such as the Magnus
eFusion, Zunum Aero and Wright Electric – are
faced with the question of power to weight
ratios; a fully electric system requires batteries
with greater energy densities than those
currently available that are fully reliable and
have a long life.
Predictions of when appropriate batteries might
be available for all-electric larger aircraft, and
even the specific technologies that will be
used, vary widely – and historical judgement,
combined with the current understanding of
aircraft development cycles, suggest such
batteries won’t be available until at least the
late 2030s. Full-integration with an aircraft and
potential in-service dates would likely stretch
further into the 2040s.
Turboshaft
Fuel
Generator
Power
electronics
Electric
Bus
Motor(s)
Aircraft systems
Battery
Turboshaft
Fuel
Battery
Generator
Electric
Bus
Motor(s)
Aircraft systems
Power
electronics
Battery
Electric
Bus
Motor(s)
Aircraft systems
Power
electronics
Turboshaft
Fuel
Generator
Power
electronics
Electric
Bus
Motor(s)
Aircraft systems
Battery
Turboshaft
Fuel
Battery
Generator
Electric
Bus
Motor(s)
Aircraft systems
Power
electronics
Battery
Electric
Bus
Motor(s)
Aircraft systems
Power
electronics
Turboshaft
Fuel
Generator
Power
electronics
Electric
Bus
Motor(s)
Aircraft systems
Battery
Turboshaft
Fuel
Battery
Generator
Electric
Bus
Motor(s)
Aircraft systems
Power
electronics
Battery
Electric
Bus
Motor(s)
Aircraft systems
Power
electronics
MORE
ELECTRIC
HYBRID
FULL
HYBRID
ALL
ELECTRIC
Three potential system architectures are shown with a progression from the ‘More Electric – Hybrid’ to ‘Full Hybrid’
to ‘All Electric’. There are varying development needs for each system component and a large integration
challenge for the complete systems. While other proposals for hybrid systems exist,
those presented here are considered the most feasible at present.
The challenges and benefits of the electrification of aircraft
8
A hybrid-powered solution is much more likely
to be available sooner. This could deliver real
benefit through reduced emissions. It would
also allow for the development of electric
propulsion motors and power electronics so
that these would be ready for the switch to
full electric operation. Let’s look at the system
level integration of a hybrid-powered solution
within an aircraft.
The gas turbine and the electrical generator,
which are existing and understood solutions,
are put together. Jet fuel – kerosene,
which could include biofuels for further
environmental benefit – powers the gas
turbine, which drives the electrical generator.
A new power electronics system is likely to be
required to then transfer this electrical energy
to new electric motors to provide thrust. A
‘More Electric-Hybrid’ system could extend
the use of batteries to power all remaining
systems on the aircraft. A ‘Full Hybrid’ solution
would combine the power available from the
generator and batteries to power all aircraft
systems, with each means of energy supply
augmenting the other in different ratios during
different flight phases. Both architectures can
collectively be described as hybrid solutions,
with a high likelihood that prototype testing
will enable the jump straight to the Full Hybrid
solution with electrical energy being combined
from both sources to power all systems. So,
where does the emission reduction come from
if kerosene is still providing the energy?
In this case, when we consider how the
aircraft’s flight will be affected by a variety
of different thrust requirements that are
needed for take-off, climb and cruise, as well
as different air flows coming onto the aircraft,
changes in altitude, and varying aircraft
design – the current generation of gas turbine
engines are designed to operate in all these
conditions, but do not function with optimal
efficiency in all cases. In a hybrid solution, the
gas turbine could be kept relatively isolated
from those shifting conditions, so that its only
job is to power a generator and it can run at an
optimised, single speed. Then, in turn, it would
power an electrical generator that drives the
conversion systems needed to give
electrical energy.
A risk to this approach would be the reliance
on unproven power distribution systems and
high power electric motors – but this is one of
the issues being addressed through prototype
development, such as with the Airbus E-Fan
X, which does so initially by switching one, of
four, engines to be powered in this way. This
system could then be developed by changing
the energy source from a kerosene powered
gas turbine and generator to the use of
batteries in an ‘All Electric’ system. If suitable
battery technology does not emerge, the
system also presents the option of switching
the kerosene for hydrogen. This is not without
its own challenges, including the supporting
infrastructure, but moves towards the same
goal of (harmful) emission free flight, with
water vapour as the by-product. With an
‘All Electric’ system, the initial conversion
electronics may then need to be adjusted
from the hybrid solutions, but the propulsive
element of the system wouldn’t have to
be changed.
The challenges and benefits of the electrification of aircraft
9
A 50kg electric motor
Siemens has already developed a new type
of electric motor that, with a weight of just
fifty kilograms, delivers a continuous output
of about two hundred and sixty kilowatts
– five times more than comparable weight
systems – using a hybrid-electric propulsion
system. While this is pushing at boundaries, it’s
important to remain realistic: two hundred and
sixty kilowatts is a small amount compared to
what’s needed to power a commercial aircraft
– anything from two to fifty megawatts. But
the company says it is determined to establish
hybrid-electric propulsion systems for aircraft
as a future area of business, in its ongoing drive
to get the weight down – so this without doubt
marks a significant step forward.
But can enough power be generated through
improved technology, bearing in mind the size
of existing jet engines, to power planes to fly
at acceptable speeds, and at an acceptable
overall weight? And what about safety
considerations with electrical systems, such
as wiring routes, redundancy considerations,
electrical interference – or faults – and the
thermal environment from heat generated
by batteries.
Longer, thinner wings
One key aspect of design here is in the
distribution of the energy supply system.
Aeroplane wings are tuned to withstand
aerodynamic and mass loads – today, they
carry distributed jet fuel – but what could
be the effects on wings if they have to carry
batteries, instead of fuel? One possible answer
could result in a very positive side-effect.
Currently, jet fuel in the wings depletes as
the flight continues, and the structure of the
wing accounts for that. Batteries could help
in a future wing because they’d be a fixed
mass throughout the flight; and adding their
mass into the wing could help with aeroelastic
tailoring. That means there’s a possibility
of tuning the wings to make them more
aerodynamically efficient by allowing them to
become longer and thinner.
While, historically, this type of shift in design
would have made a jet-fuelled aircraft more
prone to ‘flutter’ – a physical phenomenon
whereby a build-up of wing oscillations can
break them away from the main structure
– with the strategically-placed, immovable,
batteries on thinner wings, a more efficient,
aerodynamic shape could emerge that
won’t succumb to flutter and improves
aerodynamics. The change to an electrical
system could also enable distributed
propulsion allowing radically different
aircraft configurations.
The challenges and benefits of the electrification of aircraft
10
The challenge
of reducing
airframe mass
Next, what about weight? Let’s say we reach
the hybrid system. The full propulsion and
electrical system, combining all the technical
operation equipment inside the aircraft, would
almost certainly become heavier than the
current systems it replaces. Also, the aircraft
will land at a higher proportion of the take-off
weight compared to today’s aircraft, due to
the batteries. Some estimates suggest that
to compensate for these effects we’d need to
reduce the airframe mass by around twenty
per cent. The potential reductions required for
a full electric system are greater still.
This would be a huge challenge. Structurally,
today’s aeroplanes have reached a plateau:
a large effort is required for minimal mass
reductions. That means the next step must
be in advancing materials science and asking
how much the physical properties of structural
materials might be pushed. We must look at
the full capabilities of future metallic alloys
and fibre reinforced plastics.
Funding future flight
A further important point to consider is funding,
and the importance of co-ordinated effort to
ensure a collaborative, knowledge-sharing
approach that leads to conformity in standards
and the emergence of the best solutions. The
good news is, as a major player in aerospace
Research & Development, the UK is engaged in
extensive research networks and partnerships,
and bids into numerous funding bodies – from
university grant funding to industry-level
consortia – working on developing the future
technologies of air travel.
Such bodies include the Engineering and
Physical Sciences Research Council (EPSRC)
and the Aerospace Technology Institute (ATI),
which was established as a collaboration
between government and industry to create
the UK’s aerospace technology strategy
through £3.9 billion of investment. Another
is the Air Transportation Systems Lab*,
which collaborates on research projects with
universities in the UK and overseas.
Further, Airbus’ BLADE and Safran’s Contra-
Rotating Open Rotor engine are just two
examples of very many projects backed by the
EU’s €4 billion Clean Sky initiative, a ‘research
powerhouse for greener aircraft’ which is
the largest European research programme
developing innovative, cutting-edge technology
aimed at reducing aeroplane gas emissions
and noise levels.
*www.atslab.org
The challenges and benefits of the electrification of aircraft
11
The view from
the ground
The sheer size and breadth of these
funding pools certainly suggests a financial
confidence in developing future cleaner air
travel, but that’s just one part of the overall
story. Maintenance, repair and overhaul
companies should also be alive to the
potential opportunities in, and far-reaching
consequences of, the new world of air travel
from another position: services on the ground.
What kind of physical infrastructure will
we need to support this game-changing
technology? From supporting spare battery
capacity to locating recharging points? How
long between flights will it take for batteries
to be changed, or charged? Will flight times
be dramatically affected? What happens when
flights are diverted?
Could greener air travel lead to an expansion of
essential support locations across the world?
And, could quieter planes in our skies mean
more runways are built to connect-up our
major cities? And what about the important
issues of safety, and instilling confidence in
flying passengers about the new technology,
where combustible fuel is taken out of the
equation, but new technology is put in? And
what kind of air travel will take priority? Large
civil aircraft, on-demand air taxis, or
commuter traffic?
Fasten your seatbelts,
there may
be turbulence
The challenge of integration is, arguably, the
biggest challenge of all. How will all the new
technology integrate with legacy systems,
design, and infrastructure? When engineers
and designers have the new technologies
refined and ready for flight, how does the
industry then support in-service operation?
And, as an aviation company, what will your
business model need to look like over the
next five, ten or twenty years, when that time
comes? When is the optimal time to start
thinking about how to integrate your business
model strategically with this major shift in
aircraft architecture and supply chain?
Because, alongside understanding the
technological barriers and breakthroughs –
while it may be fifteen or twenty years away,
change of this nature will be, without doubt,
disruptive right across our industry, and that
isn’t a lot of time when you consider how
long new aircraft developments can take.
But disruption also brings opportunity: and
forward-looking companies will need to take
the time to understand and map-out what’s on
the horizon, and pinpoint where activity
can connect.
As that green-sky future moves closer,
forward-looking companies will also need
to seek professional support in terms of
traditional aviation engineering knowledge and
integration capability, as well as support from
business consulting and change management
experts. Atkins is in a great position to help
with the transition to green aviation, and across
many different aspects. We are involved in
developing cutting-edge vehicle engineering
as well as aircraft design and systems
analysis. There is going to be both turbulence
and enormous opportunities ahead as the
electrification of aircraft slowly becomes a
reality, so it’s important to be prepared, to
ensure a smooth flight.
About the author
James Domone
Senior Engineer
James Domone is a senior engineer in aerospace
design, security and technology for Atkins, a member
of the SNC-Lavalin Group that is working to transform
aerospace engineering for faster design, reduced
downtime, and lower costs.
© Atkins Limited except where stated otherwise.
www.atkinsglobal.com/aerospace
Transforming aerospace engineering,
for faster design, reduced downtime
and lower costs.
Image sources
Pg 4:
https://www.quartoknows.com/blog/quartodrives/the-de-havilland-comet
https://en.wikipedia.org/wiki/Brditschka_HB-3#/media/File:HB_Brditschka_HB_23_2400-1.JPG
https://upload.wikimedia.org/wikipedia/commons/6/68/Pathfinder_Plus_solar_aircraft_over_Hawaii.jpg
https://mfgtalkradio.com/solar-power-continues-impress-solar-impulse-2-crosses-pacific/
https://upload.wikimedia.org/wikipedia/en/f/f9/E-FanX-3D-graphic.jpg
https://upload.wikimedia.org/wikipedia/en/f/f0/Zunum-midsize-airplane.jpg
https://upload.wikimedia.org/wikipedia/en/a/a6/Easyjet_-_Wright_electric_concept.png
Pg 5:
www.theguardian.com/business/2017/dec/28/electric-passenger-jet-revolution-looms-e-fan -x-air-taxis-hybrid-planes
Pg 8:
www.siemens.com/press
