#AMRG Presents: Summary of "A holistic review... of research on aircraft design concepts and consideration for advanced air mobility"

What?

Advanced Air Mobility (AAM) is a collaborative vision by NASA, regulatory agencies, and industry leaders to establish a reliable air transportation ecosystem for safe and efficient movement of people and cargo. This paper presents a comprehensive review of various aircraft designs, including propulsion system designs and architectures, for different AAM aircraft applications and state-of-the-art air traffic management, cybersecurity, and infrastructure strategies. The aircraft designs are categorized into core groups, including lift + cruise, tilt-wing, tiltrotor, multirotor, and rotorcraft, and analyzed through evaluation lenses to identify strengths, weaknesses, and gaps in design considerations. The paper also suggests directions for future research in AAM aircraft and ecosystem development, recommending a more in-depth, quantitative analysis and consideration of these evaluation lenses at the design and development stage.

Who?

Lukas Kiesewetter, Bhupendra Khandelwal, & Krishna Shah - University of Alabama, Department of Mechanical Engineering

Paramvir Singh - National Institute of Technology Agartala - Mechanical Engineering Department

Sudarshan Kumar - Indian Institute of Technology Bombay, Department of Aerospace Engineering

Kazi Shakib & Mizanur Rahman - University of Alabama, Department of Civil, Construction, & Environmental Engineering

Where?

Progress in Aerospace Studies - Find the full article HERE.

Summary

Urban Air Mobility (UAM) is a growing trend in the global transportation landscape in light of the fact that over half of the world's population resides in urban areas. AAM technologies offer various use cases, including transporting people and goods, air ambulance services, emergency supply delivery, organ transportation, and search and rescue operations. Advancements in AAM propulsion systems, such as eVTOLs and eSTOLs, have improved fuel efficiency, noise emissions, and safety features. However, UAM implementation faces challenges such as regulatory restrictions, infrastructure availability, air traffic management, environmental concerns, and community acceptability.

The review categorized vehicle design approaches for AAM applications based on rotor configuration and propulsion system architecture. The review focused on a holistic analysis and comparison of AAM vehicles and their ecosystem, addressing various aspects of design for sustainable and responsible growth. The review highlights the strengths, weaknesses, and gaps in research pertaining to specific evaluation lenses.

The majority of proposed AAM mission profiles are less than 100 nautical miles and provide service for up to nine passengers. The review also considered the regulation and certification process associated with AAM, highlighting gaps in design considerations and the need for more detailed analysis in all areas of AAM design.

The paper displayed a graphic of estimated AAM component readiness over the next thirty years (shown below).

The AAM industry has developed various rotor configurations, including electric, hybrid electric, and internal combustion engine propulsion architectures. Hybrid-electric fuel cell and combustion propulsion systems demand less power due to efficiency differences. All-electric propulsion often provides the highest energy efficiency, while hydrogen fuel cell technology needs more advancement. More research is needed to improve energy efficiency and gross power demand of hybrid-electric combustion and hybrid-electric fuel cell systems.

The choice of rotor configuration significantly impacts the performance of AAM vehicles. Fixed-wing approaches offer speed and design efficiency advantages over rotary-wing approaches. Studies have found that fixed-wing AAM vehicles require 60% less power during cruise and 60% more power during VTOL compared to rotary-wing counterparts. Multi-rotors have the greatest hover efficiency but do not match the aerodynamic performance of other configurations for missions of greater time spent during cruise. Tiltrotors will likely maximize performance for longer-range missions in potential intercity applications due to high lift-to-drag ratios. The AAM Reality Index ranked aircraft feasibility based on funding, team, technology readiness, certification progression, and manufacturing ability.

The study also provided details on the design, operation, and management of AAM infrastructure, focusing on factors such as rotor configuration, propulsion system type, range, and passenger capacity. A feasible and sustainable AAM design, operation, and management require a holistic understanding of the relationship between aircraft design configuration, traffic demand, air space availability, land use pattern, and allowable noise requirement. AAM infrastructure can be categorized into three classes: vertihub, vertiport, and vertistop, with optimal locations based on factors such as air traffic demand, land use pattern, charging options, aircraft design, energy station positioning, noise, and weather conditions. The image below compares costs of existing helicopters to those of AAM vehicle designs.

The images below compare the costs of the various AAM aircraft configurations.

The FAA has "providers of services" functions to support operations planning, flight intent sharing, strategic and tactical deconfliction, airspace management functions, and off-nominal operations under FAA established rules and regulation for air traffic management (ATM). To minimize noise, manufacturers must consider noise reduction approaches and vehicle configurations and fleet characteristics.

Although UAM aircraft manufacturers have repeatedly claimed the limited noise footprints of their vehicles, there has still be some concern about how low-flying eVTOLs could generate more noise than expected. Thus noise reduction technologies for insulating buildings as well as others have been planned into the adoption of AAM in many cases. The use of innovative technologies and vehicle safety is crucial for the safe operation of AAM, as vehicles will fly at significantly lower cruise altitudes.

AAM vehicles face various safety considerations, including weather response, hazard mitigation tools, and cybersecurity. Weather conditions can affect AAM operations, with regions like the Pacific Coast and Florida being favorable. To ensure reliable AAM service, operators should use mixed fleets, improve weather prediction systems, and develop proper thermal management systems.

Cybersecurity is crucial for maintaining trust, safety, and reliability in AAM operations. AAM systems face numerous threats, including eavesdropping, GPS spoofing, distributed denial of service (DDoS), and illegal intrusions on air traffic control (ATC) communication. The National Institute of Standards and Technology (NIST) emphasizes the importance of cybersecurity in detecting and counteracting attacks on AAM vehicles, infrastructures, and air traffic controllers. Key strategies include identifying attackers, securing communication channels, implementing standardized protocols, and using lightweight encryption techniques.

The study presented a framework for enabling UAVs and AAM aircraft to navigate in GPS-denied environments, combining localization algorithms like Simultaneous Localization and Mapping (SLAM) with Partially Observable Markov Decision Processes (POMDP). The framework aims to guide UAVs to navigate GPS-specific cyberattacks safely, avoiding collisions while exploring and creating occupancy maps.

The environmental impact of the AAM ecosystem is analyzed using academic literature, with future research focusing on hydrogen and sustainable aviation fuels, interdisciplinary convergence research, and community acceptability and user acceptance. This study reviewed and analyzed AAM aircraft designs and their ecosystem, focusing on rotor configuration and propulsion architecture. It identifies a lack of convergence in design due to lack of rigorous quantitative analysis and holistic evaluation.

Comments

The study indicates an absence of convergence in vehicle design attributed to insufficient rigorous quantitative analysis and comprehensive review. Rotor-wing configurations are optimal for brief urban operations owing to their hovering efficacy, whilst fixed-wing designs are superior for extended suburban or regional applications. Lift + cruise and tiltrotor systems are preferred for their simplicity and efficiency when cruising. The technological feasibility of lift + cruise, tiltrotor, and multi-rotor designs is bolstered by funding and developmental trends, whereas rotorcraft and tilt-wing configurations necessitate additional study and development. Hybrid-electric systems provide the potential for optimizing performance and efficiency, albeit with heightened environmental impact and noise emissions. Electric designs have become favored for their simplicity. The AAM ecosystem and operations are essential variables, necessitating a comprehensive understanding of elements such as aviation traffic demand, land use patterns, noise regulations, and meteorological conditions. With this said, the estimated dates shown are more pessimistic than much of what is being reported in the news. Essential for robust and reliable operation are advanced decision support tools, onboard sensing technologies, navigational enhancements, and noise reduction techniques.

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