dream
actually envisages simpler parallel hybrid systems
entering the aviation market fi rst, developing a serial
hybrid system of this kind, where the turbine is used
purely to generate electric power for the motor, enabled
the engineering team to get to grips with a greater range
of challenges. “You learn everything from doing a serial
hybrid and you solve far more of the challenges so we can
step back to parallel hybrid having worked though all of
the challenges.”
As well as reducing emissions, she added that a serial
hybrid confi guration also opens up some interesting
longer-term opportunities to fundamentally redesign
aircraft. “Because you’re not trying to install huge gas
turbines under the wing of an aircraft, and electric fans
are not as hot as gas turbines, closer integration between
the aircraft and the engine is more possible.” This could
lead, for instance, to aircraft with smaller wings that are
be er suited to operating from smaller airfi elds; thereby
creating opportunities to reshape transport networks.
Ge ing to that point, however, is a monumental
challenge, and - said Armesmith - an order of magnitude
more diffi cult than developing the kind of hybrid
technology now widely used in the automotive sector.
“It’s really about weight,” she said. “The energy density
of ba eries is not really comparable to kerosene.
When Rolls-Royce and
Airbus jointly announced
the cancellation of their
E-Fan X hybrid electric
aircraft project at the end
of April it seemed fair
to ask whether this was
an early sign of the aerospace sector
abandoning its much-touted low carbon
ambitions in the face of a Covid-19
induced ba le for survival.
But as Rolls-Royce engineer
Riona Armesmith, who heads up the
company’s hybrid electric projects, told
The Engineer, whilst the experimental
aircraft may not be taking the skies as
planned, the technologies developed
and lessons learned through the
initiative have positioned the UK fi rm at
the forefront of a fi eld that remains key
to the sector’s future.
E-Fan X was originally launched in
2017 as part of a drive to explore how
new technology could help reduce
emissions and ensure that the
sector can continue to
grow whilst meeting a
host of increasingly
demanding
environmental
targets.
27 June 2020 / www.theengineer.co.uk
Whilst a number
of smaller electric
aircraft have been
developed – including
the two-seater Airbus
E-Fan - the aim of E-Fan X
was to explore the application of
hybrid electric technology to a larger
passenger aircraft by developing a
fl ying test-bed demonstrator aboard a
100-seater Bae 146 short-haul airliner.
The project would have seen one of
the aircraft’s four existing turbofans
(LF-507 engines) replaced by a 2MW
electric motor driven fan as part of
a serial hybrid propulsion system.
This was to be powered by a 2.5MW
generator, consisting of a gas turbine
and associated 3000V power electronics
system, housed in the fuselage of the
aircraft. The aircraft’s remaining three
engines would operate as normal,
thereby enabling the team to test the
hybrid system without relying on it to
stay in the air.
Armesmith said that whist she
We will be in a
great position whenever
anyone is ready to
create a hybrid electric
demonstratoR vehicle
The project
would have seen
a serial hybrid
propulsion system
installed on a
fl ying test-bed
demonstrator
Also, if you’re replacing a mechanical system (a gas
turbine which drives a fan) with a fan which is driven
by a motor which is fed by cables, power electronics,
switches, and then into a generator and into another
set of power electronics and into a gas turbine, you’re
adding a lot more complexity into that system.”
Whilst the system won’t now fl y as intended, Rolls-
Royce plans to complete ground-tests of an integrated
system later this year. Meanwhile, a number of key
technological milestones have already been reached.
On the Airbus side, the company has carried out
extensive wind tunnel testing on scale models of the
aircraft as well high power ba ery system testing at
facilities in France. And whilst its E-Fan X activities have
come to an end, Airbus CTO Grazia Vi adini recently
confi rmed that technologies developed through the
project are already feeding into research at the fi rm’s
E-Aircraft System Test House, a facility originally set up
as part of E-Fan X.
Meanwhile Rolls Royce has already carried
/www.theengineer.co.uk