Tech Briefs Magazine - July 2022 - 12

Sustainable Technology
Right: The energy cost of the two-seat Pipistrel
aircraft per hour is at 0.9 € while a conventional
Cessna two-seat aircraft C152 commonly used for
training is approximately $34 (pre-Ukraine war
estimate), which is equivalent to 34X that of the
Pipistrel Alpha Electro. (Image: Pipistrel)
Left: The Pipistrel two-seat " Velis Electro " is the world's
first EA to receive a Type Certificate from EASA in June
2020. (Image: Pipistrel)
Shift Toward Electric
Aviation has witnessed the shift toward " more electric aircraft "
(MEA) since the introduction of Boeing's 787 in 2011.
For the traditional airplane, power is extracted from the engines
in two ways to power other airplane systems. First, the
generators are driven by engines to create electricity (e.g., to
power avionics system). Second, a
pneumatic system " bleeds " air off the
engines to power other systems (e.g.,
hydraulics). The B787's MEA approach
uses electric instead of the
pneumatic system and provides much
more efficient power generation and
distribution for use and reduces systems
weight, including the adoption
of a higher capacity electric energy
storage system (ESS).
The evolutionary change toward
MEA for large transport aircraft, such
as the B787, is a very slow process.
However, the significant technology
development and adoption of ground electric vehicles (EV) in
the last decade has made the EA more feasible. In addition to
the relevant technological advances, the economy of scale and
new supply base growth have driven down the component systems
cost tremendously. These potentially common component
systems include, e.g., electric motors and inverters, which
when operating together in an EA are defined as the " electric
engine " [4]
the conventional " fuel system. "
Key Challenges and Opportunities
Today's state-of-the-art commercial lithium batteries are ~50X
heavier than aviation fuel. Even accounting for the much lower
losses through an e-engine leaves a ~25X net energy weight disadvantage.
However, an e-engine weighs a lot less than a combustion
engine. ARPA-e's ASCEND project seeks to extend this
12
advantage leading to 12 kW/kg for an e-engine compared to a
MW-class gas turbine at ~3 kW/kg,[5]
or 4X the power-to-weight
" If we want to reduce
climate change,
performance. In addition, there is a rapid development in solid-state
batteries (SSB), which will reach 4X higher energy density
and power density, substantially surpassing the performance,
safety, and processing limitations of Li-ion batteries.
It is estimated that these SSBs will
become commercially available in
2030s in the EV and aircraft market
respectively.[6]
Some eVTOLs, (hydecarbonizing
aviation is
a must - electric aviation
needs to be an important
part of the solution. "
brid) eCTOLs, and eSTOLs, such as
Ampaire's 9-seat Eco Caravan and
Outlander with compelling emission
reduction and meaningful range
performance of up to 500+ miles,
are already on the horizon to enter
into service by 2025.
The hydrogen fuel cell is another
ESS. It is an electrochemical device
that converts hydrogen directly into
electricity supply for the e-engine
while releasing heat and water. Boeing's hybrid-electric and fuel-cell
demonstrator flew in 2007 for approximately 20 minutes
on energy from the fuel cell ESS. However, Boeing " does not
envision that fuel cells will ever provide primary power for large
commercial airplanes. " [7]
The second key challenge is unique to the aerospace indus(e-engine)
and ESS (battery or fuel cell) instead of
try, as it is a highly regulated industry for an important reason,
safety. All of the new (and retrofit) EAs must be type certified
for air worthiness by regulatory bodies, including FAA
and EASA. With over 200 projects of new EAs going to the
regulatory bodies for certification, the regulators will have
not only a resource issue but also knowledge and experience
issue, which is necessary to address the gaps of existing standards
and rules.
The Pipistrel two-seat " Velis Electro " is the world's first EA to
receive a Type Certificate from EASA in June 2020, approved
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