Urban Air Mobility: The Future of Flight
Engineering the Future of Transportation
Image Source: designprojects/stock.adobe.com
By Brandon Lewis for Mouser Electronics
Published October 2, 2024
Flying cars have been a symbol of futurism for decades. Now, small cargo drones and passenger vehicles are finally taking flight. This article explores emerging applications for urban air mobility (UAM) and the battery, motor, and navigation technology powering short-distance electronic flight.
What Is Urban Air Mobility?
UAM involves short-distance, low-altitude flights in urban and suburban areas. While traditional helicopters can fill this role, UAM typically refers to highly automated aircraft—particularly electric vertical takeoff and landing (eVTOL) aircraft and unmanned aerial vehicles (UAVs, also known as drones).
UAM is expected to become operational in some cities around 2025, with an initial focus on piloted aircraft for passenger transport and drone deliveries.[1] Other potential applications include emergency services, public safety, and traffic monitoring.
A key benefit of UAM is that it uses open airspace rather than overloaded ground vehicle infrastructure, creating faster, more efficient transportation possibilities.[2] Instead of sitting in traffic, flying vehicles can take a direct route to wherever they need to go. Because these vehicles rely on electric propulsion rather than combustion engines, they also represent a compelling option for reducing emissions.[3]
However, UAM requires powerful batteries, better motors, and sophisticated navigation systems to achieve these goals.
Lighter, Denser, More Resilient Batteries
Battery technology remains one of the most significant barriers to the proliferation of UAM technology.
Challenges and Requirements
To achieve useful range and payloads, UAM vehicles require batteries with an energy density of around 400Wh/kg at the cell level—but existing batteries top out at around 300Wh/kg.[4] Longevity is also a problem: Batteries can lose up to 45 percent of their capacity after just a single year of use.[5]
UAMs will also be subject to stringent aircraft safety regulations imposing battery requirements that significantly reduce energy density. Therefore, engineers must consider how to prevent thermal runaway while also ensuring high performance.
Designers will also need to boost peak performance. To provide the necessary power for vertical takeoff and landing, UAM batteries must deliver high discharge rates. They will also need to maintain performance across the different temperatures and atmospheric conditions likely to be encountered during flight.
Arguably, the greatest challenge of all is cost. For UAMs to be economically viable, battery costs must decrease significantly. In addition to advancements in battery chemistry, UAM batteries may require new materials and manufacturing techniques.
Emerging Battery Technologies and Innovations
Researchers and designers are approaching these challenges in several ways. One promising avenue is the development of solid-state batteries. Unlike traditional lithium-ion batteries, which use liquid electrolytes, solid-state batteries utilize a solid electrolyte. This can increase energy density and reduce the risk of thermal runaway. Companies like Toyota and QuantumScape are leading the charge in developing solid-state batteries, aiming to commercialize their technology by the late 2020s.[6], [7]
Another approach is to integrate hybrid energy systems that combine batteries with fuel cells. Fuel cells can provide continuous power over longer durations, complementing the high power output of batteries needed for takeoff and landing. This hybrid approach could extend the operational range of UAM vehicles while maintaining the benefits of electric propulsion. Companies like Hyundai are exploring hydrogen fuel cell technology for their future UAM vehicles.[8]
The successful development and deployment of UAM technology will require collaboration between battery manufacturers, UAM developers, and regulatory bodies. Initiatives like the European Battery Alliance aim to accelerate advancements in battery technology through collaborative research and development efforts.[9]
Scalable, Modular, Efficient Electric Motors
Rather than noisy, high-emission combustion engines, eVTOL aircraft will likely rely on a distributed electric propulsion architecture. In this scheme, each vehicle will be equipped with multiple small propellers that are considerably quieter and more efficient than traditional propellers.[10]
As with battery technology, however, electric motor technology must overcome several technological obstacles to be viable for widespread proliferation. To maximize aircraft efficiency and range, motors must be lightweight and deliver high power output with sufficient torque for vertical takeoff and landing.
Complicating matters further, motors must provide this torque without producing excessive noise. After all, no one wants to hear the equivalent of multiple helicopters passing overhead numerous times per day.
Motors That Can Go the Distance
Effective thermal management is critical for maintaining the performance and safety of electric motors in UAM applications. Traditional air-cooling methods may not suffice in extreme climates, prompting the need for more advanced cooling technologies. Liquid cooling systems, phase-change materials, and heat pipes are being investigated to provide more efficient thermal management.[11]
Motors will need to be able to withstand frequent use cycles with long operational lifespans to keep maintenance costs manageable. They must also integrate seamlessly with control and power distribution systems for optimal performance. To extend flight range and reduce energy consumption, these motors must be compatible with high-voltage systems, allowing them to deliver increased power with reduced current.
These features will all need to be incorporated into motors designed to the exacting safety standards of the aviation industry, with multiple fail-safes and redundancies to mitigate the risk of motor failure. Safety specifications aside, cost efficiency will also necessitate scalable, modular motor designs that allow motors to adapt quickly to multiple aircraft configurations and power requirements.
Advances in Motor Architecture
Electric motor modularity is another critical factor in the scalability and adaptability of UAM vehicles. Modular designs allow users to replace and upgrade motors quickly, reducing maintenance downtime and costs. This approach also enables manufacturers to customize motor configurations based on specific aircraft requirements, enhancing the versatility of UAM solutions.[12]
Developing new materials is also driving significant improvements in electric motor performance. Lightweight, high-strength materials, such as carbon fiber composites and advanced alloys, are being used to construct motor components, reducing overall weight and increasing efficiency. Additionally, advances in magnetic materials and winding technologies are enhancing electric motors' power density and thermal performance. Researchers at institutions like the Massachusetts Institute of Technology (MIT) are at the forefront of exploring these new materials, aiming to push the boundaries of what is possible with electric propulsion.[13]
These advances are not limited to the academic domain. Companies such as Rolls-Royce are already developing innovations that address these challenges, exploring materials and motor design advancements. One way the company is differentiating itself is through its engine architecture. It is a pioneer in developing transverse flux motors with unforced air cooling.[14] Not only does this help the company’s motors achieve high torque-to-weight ratios, but it also enables considerably more efficient thermal management.
Smarter Navigation
Self-driving ground vehicles have already been on the road for several years. Unfortunately, one thing holding them back from widespread commercial use is the absence of an AI system powerful enough to account for the unpredictability of human drivers.[15]
At least in the short term, this will likely not be much of a concern for UAM. The relevant airspace is uncluttered, making it an ideal environment for autonomous technology. To some extent, air taxis could even serve as an ongoing testbed to help companies perfect ground-based autonomous vehicles.
GPS Alone Is Not Enough
However, considerable hurdles remain. For one, UAM requires positioning with accuracy and reliability far beyond the capabilities of current global navigation satellite system (GNSS) technology.
As noted in a report by Robert Tenny and Todd E. Humphreys from the University of Texas at Austin, "It is not enough for a UAM [position, velocity, and timing (PVT)] solution to offer decimeter-accurate positioning with 99 percent availability, or even 99.9 percent availability. UAM will demand that its navigation systems offer decimeter-accurate positioning with integrity risk on the order of 10-7 for a meter-level alert limit and availability [well above] 99.9 percent."[16]
Navigation systems will also need to be hardened against and designed to address the multipath and signal blockage conditions frequently encountered within urban environments. In other words, they must be operable even during a GNSS outage. This includes the capacity to operate reliably even in extreme weather conditions that might interfere with functionality.
Manufacturers will need a deep-layered navigation approach that uses advanced sensor fusion algorithms to combine data from GNSS, inertial sensors, terrestrial radio navigation, optical sensors, inertial measurement units (IMUs), and radar—especially to support self-flying vehicles. Advanced computer vision techniques will also be necessary to support navigation, particularly in high-density environments [17]
Transition to Autonomy
Autonomous capabilities such as collision avoidance, autonomous takeoff, and landing are also crucial. While training humans to operate this new generation of UAM may be feasible, keeping them entirely self-flying is arguably safer in the long term, mainly as skies grow more congested. Otherwise, we're likely to encounter the same problems we must deal with on the ground—namely, that human drivers are often careless.
As with land-based autonomous vehicles, cybersecurity will remain an ongoing concern. UAM systems must incorporate robust protection against passive interference and spoofing, jamming, and other types of cyberattacks.
Fortunately, navigation is arguably the area in which our technology is furthest along. Companies like Honeywell are already developing integrated solutions that blend avionics, navigation, flight control, fly-by-wire systems, and advanced radar technology. Recent developments in artificial intelligence will also prove invaluable for UAM navigation, enabling more sophisticated sensor fusion, better real-time decision-making, and more novel approaches to urban-specific navigational challenges.
What Comes Next?
According to Rolls-Royce, the immediate future is likely to primarily involve fixed-route air taxis to ferry customers between dedicated vertiports.[18] For example, instead of taking a ground-based bus from an airport to a city’s downtown core, one could catch an air taxi. Megacities such as Tokyo, Beijing, Los Angeles, and New York are likely to be the first beneficiaries of the technology. In fact, helicopters are already used for transportation in these cities.
Infrastructure will be the next major challenge facing UAM once batteries, motors, and navigation systems reach the necessary level of sophistication. Manufacturers and cities will need to work together to understand the power needs of this new vehicle class and air traffic control and maintenance.
Conclusion
Only a few decades ago, the idea of mass-produced flying cars seemed almost absurd. It's nearly daunting to think that we could now be only a few years away from them becoming a reality. Companies within the aerospace and automotive sectors are hard at work creating the first generation of urban air mobility vehicles.
The future of urban transportation is nearly here. Soon, the sky really will be the limit.
Sources
[1]https://www.easa.europa.eu/en/what-is-uam
[2]https://www.rolls-royce.com/media/our-stories/discover/2024/propulsion-technology-to-unlock-urban-air-mobilitys-full-potential.aspx
[3]https://www.assemblymag.com/articles/96879-assembling-the-future-of-urban-air-mobility
[4]https://physicsworld.com/a/lithium-ion-batteries-break-energy-density-record/
[5]https://eepower.com/tech-insights/the-impact-of-battery-performance-on-urban-air-mobility/
[6]https://www.businesswire.com/news/home/20240711282094/en/PowerCo-and-QuantumScape-Announce-Landmark-Agreement-to-Industrialize-Solid-State-Batteries
[7]https://electrek.co/2024/01/11/toyota-solid-state-ev-battery-plans-750-mi-range/
[8]https://www.hyundai.news/eu/articles/press-releases/hyundai-reveals-vision-for-hydrogen-energy-and-software-solutions-at-ces-2024.html
[9]https://single-market-economy.ec.europa.eu/industry/industrial-alliances/european-battery-alliance_en
[10]https://www.clean-aviation.eu/ciclop-casts-an-eye-on-distributed-propulsion
[11]https://www.sae.org/publications/technical-papers/content/2024-26-0468/
[12]https://www.rolls-royce.com/media/our-stories/discover/2024/propulsion-technology-to-unlock-urban-air-mobilitys-full-potential.aspx
[13]https://news.mit.edu/2023/megawatt-motor-could-help-electrify-aviation-0608
[14]https://www.rolls-royce.com/media/our-stories/discover/2023/powering-urban-air-mobility.aspx
[15]https://www.idtechex.com/en/research-article/the-biggest-challenge-for-autonomous-vehicles/25011
[16]https://radionavlab.ae.utexas.edu/wp-content/uploads/2022/10/tenny_tight_coupling.pdf
[17]https://www.researchgate.net/publication/376618069_Vision-Based_Navigation_for_Urban_Air_Mobility_A_Survey
[18]https://www.rolls-royce.com/media/our-stories/discover/2023/powering-urban-air-mobility.aspx