For UAM to Succeed, the Stars Won’t Need to Align, But a Lot of Systems Will

Researchers at the Hamburg, Germany-based German Aerospace Center, Institute of System Architectures in Aeronautics (DLR), wanted to understand how different fully electric urban air mobility (UAM) aircraft architecture might affect the overall system of systems’ (SoS’) capability. (SoS refers to a complex system composed of multiple systems that work together to achieve what can’t be accomplished alone.)

Prajwal Shiva Prakasha, Nabih Naeem, Patrick Ratei, and Björn Nagel developed an agent-based simulation study that considered differing UAM aircraft architectures, fleet combinations, technology scenarios, operational strategies and their prospective strengths and weaknesses, and consequently, their likelihood of success or failure.

The framework the DLR team developed simulated UAM fleets that operated 24/7, had non-uniform passenger demand (including deadhead flights that carry no paying passengers), varying load factors, energy consumption, and turnaround procedures.

In all, the study considered roughly 5,000 design points. The framework the team developed took into account the linkage of subsystems, aircraft systems, and a fleet-level approach. They hoped their likely operational scenarios would suggest how best to optimize individual UAM aircraft and the overall fleet in specific cities.

Efficiency or Range?

Not surprisingly, many eVTOLs in development require a tradeoff between battery efficiency and cruise range. Multirotor eVTOLs, such as the single-seat EHang 216 or the Volocopter’s two-seat VoloCity, are more energy efficient.

By comparison, Jaunt Air Mobility’s Jaunt Journey Air Taxi, attempts to offer the best of both worlds by using a compound helicopter architecture which includes a supplementary fixed wing. Among this group, you’ll also find the two-seat lift + cruise Wisk Cora, the five-seat tiltrotor Joby S4, and the seven-seat tilt-duct Lilium Jet.

The researchers hope their work will guide UAM developers and operators in how best to use their aircraft safely and profitably by taking into consideration the efficiencies of various designs and systems they deploy.

And in Conclusion…

Some of the study’s conclusions were, in fact, inconclusive. The SoS approach the team used saw “few results” that revealed an advantage in predicting aircraft design and operations. Some of the conclusions were nonlinear and weren’t discernible by an analytical method.

But, some of the study’s outcomes were useful:

• With a fleet of 30 aircraft, increasing speed from 25 m/s to 55 m/s (approximately 55 mph to 123 mph) corresponds to a doubling of the percentage passengers being able to obtain a ride within 15 minutes. Conversely, if cruise speeds were reduced by 55%, an operator would need to increase fleet size by 25% to achieve similar success rates.
• If the aircraft’s passenger capacity could be doubled, the fleet size required to achieve similar success would drop by 33%. Removing the pilot from the equation when the aircraft’s capacity has been doubled could result in a threefold increase in revenue-carrying capacity.
• Not surprisingly, higher battery capacities, which would reduce the time and frequency of charging or swapping out batteries, would lead to increased revenue possibilities for an operator. An air taxi operator might want to consider a two-phased approach: one for the near-term and another for the longer term as battery capacities increase over time. The study suggests that, for a city like Hamburg, a fleet of 30 aircraft would be optimal when the operator begins commercial operations.

Hamburg is known for its congested roads and the resulting traffic jams. But, the study’s authors advise that every city is unique.

“Vertiport locations,” they write, “should be derived based on the city[’s] topography, demand, and intermodal transport.”

The study, “Aircraft Architecture and Fleet Assessment for Urban Air Mobility Using a System of Systems Approach” published in Aerospace Science and Technology in 2022, may not offer all the answers the emerging UAM industry needs, but it certainly adds insight and direction that is already useful.