flightglobal.com 28 January-3 February 2020 | Flight International | 31
BELL NEXUS 4EX
Shutterstockarrangements of digital flight controls.
For cost and safety reasons, Bell is aiming
to ultimately make its eVTOL aircraft fully au-
tonomous. This would save operators the cost
of a pilot, one of the most expensive parts of
flying a helicopter. Also, there are simply not
enough pilots currently, or capacity to train
more of them, to fly the hundreds or thou-
sands of eVTOL aircraft within the cities of
the future that Bell envisions.
Moreover, Bell believes fully automated
flight controls would allow it to operate at a
higher flight frequency, avoiding human error
and fatigue problems.
In the light of two recent Boeing 737 Max
crashes caused by that airliner’s automated
flight controls – the Maneuvering Character-
istics Augmentation System (MCAS) – Bell
is quick to explain its belief that designing an
automated eVTOL from scratch is safer than
bolting automation on to a manned aircraft.
“By starting with the understanding that
it’s going to be fully autonomous from the
beginning you have a different mental
starting point than when you iterate to
something over time,” says Michael Thacker,
Bell’s executive vice-president for technolo-
gy and innovation.
While investigations into the two 737 Max
crashes remain ongoing, flightcrews’ efforts
to understand and correct the behaviourfocused on moving passengers as efficiently
as possible from point to point.
The Nexus 4EX is to have a maximum gross
take-off weight of about 3,200kg (7,050lb) and a
cruise speed of 130kt (241km/h).
Based on conversations and surveys of po-
tential customers and stakeholders, such as
ride-share companies, as well as city, state
and national governments, the company esti-
mates flights on average would be 13-22nm
in length.
Each aircraft is likely to operate for 2,000h
per year, the company says.
Bell believes hundreds to thousands of
eVTOL aircraft would be needed within a
city to significantly change traffic patterns on
the roads.
The company declines to say how many
aircraft would be required to reach profitabil-
ity, noting its analysis is ongoing, but it
expects that eVTOL aircraft would be pri-
marily used for faster ride-share, public
transportation and cost-sensitive traditional
helicopter applications.
At least in the beginning, Bell does not ex-
pect eVTOL aircraft to stimulate travel demand
- in other words, trips people would not take if
they did not have access to the speed and range
of the aircraft. Rather, early users will likely fly
out of curiosity or as an experiment. Gradually,
the company expects the aircraft to become a
more established feature of business and
personal travel, says Drennan.
PREDICTING UPTAKE
Bell says it is forecasting demand using traffic,
mobility and mobile phone databases,
examining how different factors such as
passenger load, weather, digital infrastructure
and eVTOL airport loading patterns might
affect usage.
Predicting aircraft usage will be key to man-
aging the battery charge levels and life-cycles
of a fleet of eVTOL aircraft, says Drennan.
“State of charge at any given moment in the
life – and really the operating day – affects the
next flight available because of time of re-
charge required and the life of the battery,” he
says. “Therefore, it is imperative to smartly
manage fleet operations and battery system
operations by mixing flight distances to opti-
mise operational cadence and battery life for
our customers.”
The Nexus 4EX’s batteries are to be sup-
plied by Electric Power Systems. Algorithms
within that company’s battery management
system will be used to monitor battery tem-
perature, current, voltage, discharge and
charge rates.
Bell is aiming to build an eVTOL aircraft
that has fully autonomous flight controls.
However, to initially gain public trust and
US Federal Aviation Administration (FAA)
certification, will have a pilot or “mission
manager” on board as a back-up.
Indeed, because eVTOL aircraft are so
novel Bell is taking the opportunity to rethink
many aspects of the aircraft’s flight controls,
including removing the helicopter’s tradition-
al collective and cyclic sticks and foot pedals.“When you’re talking about fly-by-wire it
just doesn’t make sense anymore to make peo-
ple move their feet, move their hands and wig-
gle their ears all in unison to make this thing
fly,” says Drennan. “A fly-by-wire aircraft can
have control laws that can take into account in-
tention [and] mission. And, if we integrate that
in the right way we will take a great step right
through the piloted piece to the autonomous.”
Using its Future Flight Controls simulator,
the airframer says it has studied how more
than 6,000 participants, including profes-
sional helicopter pilots, but also a wide
variety of amateurs, interact with different ❯❯Helicopters provide some urban transport, but volume operations will require automation“It is imperative to smartly
manage fleet operations and
battery system operations by
mixing flight distances”
Scott Drennan
Vice-president of innovation, Bell