FUTUR E A I RCR A FT
OCTOBER 2019 049
Work is ongoing to regulate the new
types of aircraft under development.
With supersonic jets, which will
basically rely on more powerful
versions of engines that are already
certifiable, the certification issue
is primarily about overland noise
from sonic booms. The FAA is thus
developing rules for supersonic flight
testing in US airspace, and for their
certification and acceptable noise
levels over land. Up to now, US law has
banned overland supersonic flight.
Meanwhile, EVTOLs are small
and slow enough to fit into existing
certification categories, but the rules
still need to be tailored because they
were designed for piston-powered
fixed-wing aircraft. On 2 July 2019,
EASA published special conditions for
operating hybrid and eVTOL aircraft
with maximum take-off masses up
to 3,175kg (7,000 lb). EASA is working
with the industry to develop technical
requirements for eVTOL certification.
The FAA’s rule that encompasses
eVTOL is Part 23, and it underwent
changes in 2016 and 2017 to allow
innovations such as hybrid propulsion,
but policy development is still ongoing.
FAR LEFT: THE AERION AS2’S
CABIN WILL ACCOMMODATE
LEFT AND BELOW: THE PLAN IS FOR
THE PAL-V FLYING CAR TO ENTER
SERVICE IN 2021
Ehang and Volocopter are now seeking certification
and entry into service for their eVTOLs. Ehang is
working with an Austrian company to mass produce its
two-passenger 216 Autonomous Aerial Vehicle, which
it presented in April 2019.
The 216 is designed to fly at low altitudes, controlled
by a ground station. Passengers will use a touchscreen to
select a destination. The vehicle’s 16 rotors are positioned
around its base, where the battery is located. A one-hour
charge will power the 216 for a 30-minute flight and a
range of 18.9 nautical miles (35km). The vehicle’s top
speed is 70kts (130km/h).
Ehang was not available for comment, but online
pictures show the 216’s interior featuring two seats
(with seatbelts), walls covered in a beige fabric, and a
touchscreen console. There are no manual flight controls.
Meanwhile, Volocopter’s VoloCity air taxi has 18 small
rotors and carries a passenger and a pilot, plus hand
Ongoing research – including
by the EU and NASA – aims
to develop hybrid and allelectric
systems. Rolls-Royce is also
making moves – in June 2019
the company announced it
was buying Siemens’ electric
propulsion business and in
July 2019, Rolls-Royce
a hybrid-electric propulsion
partnership with Brandenburg
Electrical power for
conventional aircraft is
generated by the turbofan’s
integrated drive generator and
it produces alternating current.
These generator systems have
a constant speed drive that
allows the generator to turn
at a constant speed, like a
dynamo does, irrespective
of the jet engine’s axle’s
rotations per minute.
A conventional jet engine
produces enough electrical
power for cockpit and cabin
systems, and hybrid propulsion
can do the same.
There are two types of hybrid
propulsion – serial and parallel.
In the latter, a conventional
turbine generates electricity
in the normal way, which then
powers electric turbofans,
known as propulsors, as well
as onboard systems. With the
serial version, the fuel-burning
turbine charges a battery that
then powers the propulsors.
The all-electric aircraft uses
a battery to power propellers
or propulsors and the onboard
systems. European and US
studies have concluded that
an airliner would need a
power supply with current
driven by thousands of
volts, while a business jet
will need hundreds of volts.
The more power drawn
by onboard systems such
as environmental control,
satcom and entertainment,
the less there is available for
propulsion, and thus range.