IEEE Electrification - March 2021 - 97

designs for the commuter, regional, and short-range segments,
respectively. All three cases are
based on fuel cells as the main
source for electric propulsion during cruise mode. The superior efficiency of the fuel cells causes the
energy demand to be reduced by
10, 8, and 4%, respectively. In addition, all of the concepts radically
reduce the climate impact, with
complete elimination of CO 2
emissions. To reach beyond the
smaller segments, revolutionary
aircraft designs would be needed
to make hydrogen competitive
for the medium- and long-range
categories beyond 10,000 km.
For other segments, there are
no limitations on the range. Battery electric systems are limited
to ranges up to 500-1,000 km due
to lower battery energy density.
Moreover, they have limited lifecycles and still suffer from low
gravimetric power density of 0.2-
0.5 kWh/kg, which reduces their
potential for larger airplanes.
However, they have the best
achievable climate impact since
they cause no emissions or emission-related effects.

Examples of Commercial
Hydrogen Aviation

TABLE 2. A summary of the EU case studies of different hydrogen-

powered revolutionary electric aircrafts for different segments.

Description

Commuter

Regional

Short Range

Passengers

19 PAX

80 PAX

165 PAX

Range

500 km
270 nautical miles

1,000 km
540 nautical miles

2,000 km
1,080 nautical miles

Cruise
speed

500 km/h
Mach 0.419

543 km/h
Mach 0.440

889 km/h
Mach 0.720

Propulsion

Fuel cell electric
distributed motors

Hybrid fuel cell electric
and hydrogen turbine

Efficiency

FCS: 58% peak
e-motors
PMAD: 97%

FCS: 59% peak
e-motors
PMAD: 97%

FCS: 60% peak
e-motors
PMAD: 97%

Power
density

FCS: 1.50 kW/kg
e-motors: 5 kW/kg

FCS: 1.75 kW/kg
e-motors: 5 kW/kg

FCS: 2.00 kW/kg
e-motors: 5 kW/kg

Energy
density

Battery: 0.60 kWh/kg
LH2: 2.36 kWh/L

Climate
impact
reduction

80-90% overall
100% in CO2

70-80% overall
100% in CO2

Energy
demand

-10%

-8%

-4%

Added
weight

2x LH2 tanks: 0.5 tons 2x LH2 tanks: 2 tons
+15% MTOW
+10% MTOW

Additional
cost

0-5% CASK
(10-15% less expensive than synfuel)

5-15% CASK
(10% less expensive
than synfuel)

20-30% CASK
(5-10% less expensive
than synfuel)

Entry-intoservice

<10 years

10-15 years

15 years

2x LH2 tanks: 4 tons
+14% MTOW

CASK: cost per available seat km; MTOW: maximum takeoff mass; PMAD: power management and distribution;
FCS: fuel cell system.

Hydrogen-powered aviation has,
until recently, been limited to
TABLE 3. Examples of hydrogen aviation projects.
demonstration projects and feasiProject
PAX
Range
Propellers Storage
Initiated
bility studies. Table 3 presents a
list of several hydrogen-based aviHY4
4
800-1,500 km 1
GH2
2015
ation projects that have been
HES Element One
4
500-5,000 km 14
GH2/LH2
2018
recently initiated. They all use fuel
cells as the main energy source,
Alaka'i Skai
4
640 km
6
LH2
2019
but it varies as to whether GH2 or
Apus i-2
4
1,000 km
2
GH2
2019
LH2 is employed. The concepts are
NASA CHEETA
n/a
n/a
LH2
2019
mostly made for a few passengers, but the range can be relaPipistrel E-STOL
19
n/a
n/a
2019
tively high.
ZeroAvia
10-20
6,500 km
2
GH2
2019
One of the projects is highlighted in more detail in Table 4,
Hydrogen Electric Solutions
which details the key performances of a smaller airIn hydrogen-powered aircraft, there will always be the
plane. In this example, the energy storage density of
need for a variety of electric solutions. Even though it
GH2 is about 13 times higher than the internal battery
storage buffer onboard. Moreover, the airplane is comcould be decided that the hydrogen should be burned
posed of a conventional permanent magnet motor as
directly to produce propulsion (i.e., as a modified gas turthe electric propulsor.
bine), there will always be a need for auxiliary electric

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IEEE Electrification - March 2021

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