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The Eagle Flight Research Center (EFRC) continues to push
the edge of technology in the emerging area of Urban Air
Mobility (UAM). For a number of years, the center has been
working on independent threads of technology that have turned
out to be the pillars, the fundamentals, of UAM. For years,
the focus area of the Eagle Flight Research Center (EFRC)
has been ight controls and autonomy, Unmanned Aerial
Systems (UAS), alternative propulsion including electried
propulsion and FAA certication. All of these technologies
have now converged to allow for the rapid advancement of the
understanding of the UAM design space.
The “Trojan Horse” for the conuence of all of these
technologies has been electried propulsion which is either
fully electric aircraft propulsion or hybrid electric propulsion.
Electric propulsion was seen, early on, as a technology that
could lower emissions, lower direct operating costs and
enhance safety. In Europe, there was a movement to y
electric aircraft and design commercial aircraft with this
technology. The crux of electric propulsion implies non-
traditional methods of controlling the propulsion system;
y-by-wire. Conventional methods of control make little sense
in the realm of electried propulsion. Thus, in the enthusiasm
wave for electric propulsion, the ability to certify modern
aircraft controls was baked into the new regulatory landscape.
The embrace of automation then drew in the third generation
technology Unmanned Aerial Vehicles (UAV). It is becoming
accepted that UAV or UAS may be either manned or unmanned
which is clearly strange since “unmanned” is the main part of
a title. However, once the vehicle is autonomous, whether it
is manned or unmanned is irrelevant. Now, the research into
unmanned vehicle is spilling over into the people transportation
sectors. An example of this is UAS Trafc Management
(UTM). This was stood up by NASA as a method of separating
and controlling UAVs. Now that manned autonomous aircraft
are behaving like their unmanned counterparts, the UAV
technology has also been folded into Urban Air Mobility. As
seen, the UAM market has brought together three independent
columns of research, i.e. controls, UAVs, and electried
propulsion into a single thread by leveraging the desire for
electried propulsion, the “Trojan Horse.”
Electric propulsion is the second major disruption in aircraft
propulsion after the jet engine. Similar to the step to the jet
age there are early congurations that we are all comforted
seeing that look like the airplanes we know. However, like the
evolution of the jet the real advantage of electried propulsion
is not replacing an existing engine in an existing airframe,
but rather the design of an airframe that takes advantage
of the unique characteristics of the electried propulsion.
This dichotomy has led to two emerging paths in electried
propulsion: thin haul and Urban Air Mobility. Thin haul is
the idea that electric propulsion can take an existing short
range commuter aircraft and reduce the emissions and direct
operating cost much in the same way as a hybrid or fully
electric plug-in car. This category of electric airplane designs
looks much like the aircraft we have known for years. The
reason that this is a “thin haul” is because it was understood
early on that the limitations of a battery powered aircraft
where signicant. Early battery powered aircraft would be
small, slow, and range challenged. It is thin on every aspect.
This category emerged rst because it does not require much
imagination to envision this class of aircraft. This will be
a viable class of aircraft when the weight of batteries comes
down. This class of aircraft is in the future, because current
state-of-the-art battery technology does not support it. It is
clear to all aircraft designers that in aircraft design weight is
king. Right now the equivalent weight of energy of batteries
is 70 times greater than aviation fuel. When one considers
that the propulsion system of an electric aircraft is signicantly
more efcient, this drops to 20:1. The good news is that
batteries get better every day and gas does not. So, we can
predict using the average advancement of battery specic
energy the likely year of viability of thin haul. Using these
predictions this should happen this century but not this decade.
The other branch of electried propulsion is not as obvious
as thin haul. This obscurity is due to the novel nature of
the technology: a technology that is only possible through
electried propulsion. For thin haul it was discussed that
minimizing emissions and direct operating costs were the
motivation. The path that really takes advantage of the novel
aspects of electried propulsion is enabling missions that
are not possible with conventional propulsion; they are only
possible with this new technology. Also, when discussing
direct operating cost and emissions, something funny happens.
You may be comparing the UAM aircraft, not to another
aircraft but to a car or truck. This opens the control volume of
what is “good” to a different level. In future aircraft design
classes it may be necessary to analyze surface transportation as
the competitor to your design. It is interesting to note that the
division between thin haul and UAM also falls along the lines
of top level hybrid electric architectures. Thin haul designs will
likely employ parallel hybrid architectures whereas UAM will
deploy serial generators. As the entire design space is yet to
be understood, the state-of-the-art technology actually supports
UAM architectures and business models with thin haul will
have to wait for the advancement of battery technology.
There is, however, one question that has not yet been addressed
here. What is the mission of the UAM that cannot be own
by existing aircraft or helicopters? What does electried
propulsion enable that allows for the urban air mode of travel?
The answer is simple: noise. The public is unlikely
Eagle Flight Research Center - Urban Air Mobility (UAM)
(Dr. Richard Anderson)