Page 46 - European Energy Innovation - winter 2019 publication
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46 Winter 2019 European Energy Innovation
ELECTRIC FLIGHT
Electric flight
for a more sustainable aviation
By Andreas Strohmayer, Professor for Aircraft Design at University of Stuttgart
AIR TRANSPORT AND THE increase efficiency with reduced or high-density energy storage, which
ENVIRONMENT eliminated in-flight emissions and is converted into electricity by
In response to the Paris Agreement less community noise, providing at generators; battery systems may
the European Commission has set the same time viable operating costs provide additional energy during
ambitious goals to have a climate and increased reliability. certain flight phases. Finally, fuel-cell
neutral aviation system by 2050. systems convert chemical energy
The evolutionary improvement of WHICH ROUTE TO TAKE TO from the fuel, which is typically
conventional airframe and aircraft ELECTRIC FLIGHT? liquid or gaseous hydrogen, to
systems technologies has achieved In conventional fuel-based electric power in a relatively cold
tremendous enhancements over propulsion concepts, the ‘power electrochemical reaction.
the past decades and will continue plant’ combines the transformation
to contribute to this target. But of chemical energy stored in the EACH ROUTE HAS ITS CHALLENGES
a significant gap will remain that fuel to mechanical power, and While the Solar Impulse 2 has
has to be closed with more radical propulsion via the production of impressively demonstrated what can
approaches, if targets are to be met thrust by accelerating air-mass flow be technologically achieved, solar
that take into account the predicted with propellers or fans, driven by powered flight will not find its way
growth rates in air transport. Since the shaft power. Additional thrust to air transport due to an extremely
aviation today is undoubtedly the may be generated by the recovery of unfavourable ratio of surface
only viable transport mode for thermodynamic energy in the exhaust required for solar cells to useful
distances beyond about 1,000km, gases. payload. Battery-powered systems
this growth cannot be constrained can be highly efficient as no energy
without jeopardising the ability of In electric flight, the conversion from conversion is involved, but their major
the world citizens to move and chemical energy stored in fuel can be drawback is the low specific energy,
interact. Mobility restrictions could locally separated from the propulsor. i.e. the amount of energy that can be
easily promote Orwellian conditions, Furthermore, electric motors can stored per unit of battery mass. For
a situation definitely to be avoided be installed at unconventional a given aircraft mass, constrained by
in a global and open society. In places on the airframe due to their lift capability and structural strength,
order to close the emissions relatively small size. For energy only a limited amount of batteries
gap, full-electric and hybrid- storage a variety of concepts are can be installed, thereby restricting
electric propulsion technologies under evaluation: solar-powered the flight distance compared to fuel
are promising candidates for the systems convert the sunlight energy based propulsion systems. To some
required fundamental innovation in in the using a photovoltaic process extent hybrid-electric systems can
the aviation system. The integration to electricity that drives the motor. compensate this disadvantage, but
of an electric propulsion system in In full-electric systems the energy is only at the cost of higher systems
an airframe specifically designed stored in batteries. Hybrid-electric complexity and lower efficiency
for this purpose has the potential to propulsion systems keep fuels as compared to an all-electric power
train. Hydrogen powered fuel cell
Student project 'Seagull' – all-electric systems can take advantage of the
commuter aircraft fuel’s high specific energy density,
but the integration of hydrogen tanks
becomes too voluminous in the case
of gaseous hydrogen, or too heavy for
liquid hydrogen. Unfortunately aircraft
performance is extremely sensitive to
both of these factors.
In addition to these limitations, all
