Page 29 - Flight International (January 2020)

ROTORCRAFT

GARRETT REIM AMARILLO
ack in January 2019, when Bell first
unveiled its Nexus electric vertical
take-off and landing (eVTOL) aircraft, Vertical
Bthe design featured six ducted fans
and was to be powered by a hybrid-electric
architecture. But fast forward 12 months and
the aircraft has undergone a major revamp:
two ducted fans have been removed, all-
electric propulsion is now planned and the challenge
wing has been lengthened.
The new demonstrator, revealed at this
year’s Consumer Electronics Show in Las Strong demand for short-hop intra-city travel has prompted
Vegas, is called the Nexus 4EX – as in
“Electric” and “Xperimental”. Bell to switch its Nexus eVTOL to all-electric power, with
Removal of the two ducted fans will create
an aircraft with less drag that is therefore potential applications in ride sharing and public transport
more efficient in the cruise, says Bell.
Efficiency is critically important as battery
4EX will be capable of
energy density remains one of the chief limit-
carrying up to five passengers
ing factors for electric aircraft, says Scott
with a range of some 52nm
Drennan, vice-president of innovation at Bell.
Bell expects that its 4EX will be capable of
flying up to 52nm (97km) while carrying four
to five passengers, plus a pilot.
“The battery energy power densities right
now are right on the edge for a mission like
this,” says Drennan. He believes battery ener-
gy density could improve by 10-15% by the
mid-2020s, when Bell hopes the eVTOL in-
dustry will take off.
For longer flights, Bell is working on a hy-
brid-electric variant of the 4EX, which will
use a turbo-generator to charge batteries,
which will in turn power electric motors. The
hybrid-electric aircraft would have a range of
130nm and would be developed after the all-
electric vehicle.
With its change to all-electric power, Bell
dropped its former propulsion supplier,
Safran Helicopter Engines, with a replace-
ment electric motor supplier to be named in
early 2020. Bell says it is still considering Sa-
fran for hybrid propulsion.
The company says the Nexus 4EX
demonstrator will be likely to closely resem-
ble the eVTOL aircraft it eventually puts for-
ward for commercial certification; a regula-
tory hurdle it expects to clear in the latter
half of the 2020s.
“You’re not going to see it have an
electrical system, or a duct, or a rotor system
that is markedly different than what you’ll
see down the road in the certification plan,”
says Drennan.

FOCUSED ENVELOPE
Whereas traditional helicopters are designed
as utility vehicles, with broad abilities that
vary from emergency medical service, police,
or passenger transportation work, Bell
envisions its eVTOL aircraft having a much
narrower performance envelope, purely Bell

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