Flight International – 11 June 2019

ightglobal.com 11-17 June 2019 | Flight International | 67

PARIS

Electric flight

Passenger Air Vehicle could

feature in aerial ride-sharing

service as early as 2023

Bell Nexus on display at the

2019 CES technology show

Boeing

Bell

have been made besides directing “focus of ef-
fort” while granting access to the vast resourc-
es of its new parent company. Since the acqu-
sition, Aurora designs have evolved into the
PAV; with Boeing engineers in January the
team reached a milestone with a hovering test
flight. Aurora and Boeing would not give up-
dates about the next challenge, which will be
to make the transition from vertical to forward
flight – a step that had been difficult for such
aircraft during past decades before advances

in distributed electric propulsion simplified

the process.

Electric propulsion offers “system simplic-

ity” because an electric motor has fewer mov-

ing parts and the potential for a longer lifes-

pan than a thermal engine reliant on a heavy

fuel tank, Kunz says.

All manufacturers developing electric or

hybrid aircraft will have to prove their safety

to both regulators and the flying public, but

eVTOL aircraft have several factors in their

favour. “To fly you need to be relatively light,”

Kunz says, so aircraft like the PAV will require

less battery power than larger, heavier hybrid

or fully electric commercial aircraft.

Energy is also less challenging for eVTOL

aircraft because many designs intend for them

to be flown on short trips – the PAV’s range is

43nm (80km); shorter than the distance cov-

ered by the average regional aircraft flight.

Through its partnership with Uber, Boeing

aims to market the PAV for aerial ride-sharing

flights to ferry people between pre-set landing

pads in cities and suburbs through an Uber

Air mobile application. If the US Federal Avi-

ation Administration certificates VTOL air-

craft, Uber aims to start passenger flights in

2023, in Los Angeles and Dallas/Fort Worth.

Electric aircraft designed for cargo trans-

port such as Boeing’s CAV have “a lower risk

profile because you are not carrying passen-

gers”, says Kunz – although he stresses: “That

doesn’t diminish the need for safety on those

platforms because they are relatively large.”

COMMON CHALLENGES

Dozens of companies have concepts for some

type of VTOL product for cargo or passenger

flight, including larger hybrid electric designs

assisted by a fuel tank pending advancements

in battery technology, according to a Vertical

Flight Society database.

Boeing and its competitors face the same

difficulties over how to make electric propul-

sion safe, affordable and socially acceptable.

A wide range of industries have chosen lithi-

um-ion as their preferred battery type, but in-

tegrating batteries for aircraft propulsion re-

quires different technology than is used to

power smartphones or electric cars.

Mining materials for lithium-ion is not en-

vironmentally friendly and those batteries

have a risk of overheating or even starting fires

if they are not packaged safely. In spite of this,

“lithium-ion is the best we have right now”,

says Herve Blanc, Safran’s general manager of

electric power.

Kunz agrees that battery technology is “on

a trajectory that is sustainable” but barring an

unforeseen change at the chemistry level, im-

provement will be more of a “slow creep”.

Boeing and Safran each invest in compa-

nies innovating battery chemistry and share

information with the rest of the industry to

contribute to the common quest for stronger,

safer, longer-lasting batteries. Safran invests

in OXIS Energy, an Oxfordshire, England-

based designer of lithium-sulfur cells; Boe-

ing is a partner in California company Cu-

berg, which is trying to improve energy

storage and reduce the volatility of lithium-

ion units.

TRADE SECRETS

Some technology is a more closely guarded

secret. Battery management concepts, to in-

tegrate storage with aircraft power systems,

including software to monitor the power

supply, is a prime example.

While “there is no free lunch” and energy

for batteries must come from somewhere,

Kunz says shifting power generation from an

aircraft to ground infrastructure could be

more efficient and environmentally friendly

as powerplants become more renewable. Bat-

teries also have the potential to reduce waste

because they can be used “multiple times in

multiple places” across their life cycle,

whether by recharging them for different air-

craft or by selling them to other industries on

“a used battery market”, says Kunz.

Safran is also part of a VTOL project, the

Bell-built Nexus, which would be among the

aircraft Uber would include in its air taxi eco-

system.

Smaller electrical aircraft such as VTOL

types are stepping-stones “to validate and de-

velop the next generation of technology for

bigger platforms”, Blanc says. Safran is de-

signing turboshaft-based hybrid electric pro-

pulsion to power the six propellers of the

Nexus, which, unlike the PAV, would be as-

sisted by a gas turbine.

“We are working on a number of projects

that have not been disclosed,” Blanc says, but

Safran will also showcase numerous electric

propulsion technologies at Le Bourget, in-

cluding electric motors, generators and power

management systems. ■