Role of flying cars in sustainable mobility

Human-wildlife conflicts in the aerial habitat: Wind farms are just the beginning

The aerial habitat occupies an enormous three-dimensional space around Earth and is inhabited by trillions of animals. Humans have been encroaching on the aerial habitat since the time of the pyramids, but the last century ushered in unprecedented threats to aerial wildlife. Skyscrapers, jet-age transportation and recently huge wind turbines kill millions of flying animals annually and despite substantial efforts, our detection and mitigation capabilities are lagging far behind. Given the situation, our readiness to handle the impact of millions of drones buzzing through the sky carrying batteries, payloads and soon also people, is questionable at best. In radar aero-ecology, radars are used to document and analyse animal movement high above the ground, opening a hatch to ecological processes in the aerial habitat. Differentiating bats from birds, a simple task at ground level, was impossible aloft, which limited our ability to study and characterise high-altitude bat behaviour. Many high-altitude infrastructure developments around the world were thus planned and executed with no regard to possible impacts on bats and caused millions of bat fatalities. BATScan, the first automatic bat identifier for radar, demonstrates how artificial intelligence can be implemented together with ecological insight to solve basic scientific questions and minimise negative human impact on natural habitats. We demonstrate a facet of the complexity of bat aero-ecology using the Israeli BATScan database and substantiate the claim that activities taken by the wind energy industry to minimise bat mortality may prove limited and leave bats unprotected. We further discuss upcoming challenges in the face of a forthcoming transportation revolution that will change the human-aerial wildlife conflict from a conservation concern to a major human safety issue.

Critical assessment of emissions, costs, and time for last-mile goods delivery by drones versus trucks

Electric drones as an autonomous mode of transport are scaling up to transform last-mile goods delivery, raising an urgent need for assessing impacts of drone transport from a systems perspective. In this paper, we conduct systems analyses to assess the environmental, economic, and delivery time impact of large drones for delivery scenarios to pick-up centers between mid-size cities predominantly in rural areas, and deliveries within city limits compared with electric and diesel trucks. Results show that large drones have lower emissions than diesel trucks for deliveries in rural areas and that drones don't compete with electric trucks, mainly due to the high energy demand required for take-off and landing for each delivery. Furthermore, we show that electric drones are an economically more cost-effective option than road-bound transport modes such as diesel and electric trucks due to the high degree of automation, and also provide the fastest delivery times. Our analysis provides unique insights that drones can address rapid electrification and emergency applications due to low costs, high flexibility, and fast operations. However, for regulators and practitioners to realize it as an emission-friendly option it is necessary to determine the optimal size of drones, particularly for use cases in urban areas, avoid very low landings for deliveries, and have home deliveries instead of pick-up points.

Flying cars economically favor battery electric over fuel cell and internal combustion engine

Flying cars, essentially vertical takeoff and landing aircraft (VTOL), are an emerging, disruptive technology that is expected to reshape future transportation. VTOLs can be powered by battery electric, fuel cell, or internal combustion engine, which point to entirely different needs for industry expertise, research & development, supply chain, and infrastructure supports. A pre-analysis of the propulsion technology competition is crucial to avoid potential wrong directions of research, investment, and policy making efforts. In this study, we comprehensively examined the cost competitiveness of the three propulsion technologies. Here we show that battery electric has already become the lowest-cost option for below-200-km VTOL applications, covering intra-city and short-range inter-city travels. This cost advantage can be robustly strengthened in the long term under various technology development scenarios. Battery energy density improvement is the key to reducing cost. In particular, a 600 Wh/kg battery energy density provides battery electric with all-range cost advantage, and promises high return in business. Fuel cell and internal combustion engine, under certain technology development scenarios, can obtain cost advantage in long-range applications, but face intense competition from ground transportation such as high-speed rail. The findings suggest a battery-electric-prioritized VTOL development strategy, and the necessity of developing VTOL-customized high-energy-density batteries.

Anode-free Na metal batteries developed by nearly fully reversible Na plating on the Zn surface

The anode-free battery architecture has recently emerged as a promising platform for lithium and sodium metal batteries as it not only offers the highest possible energy density, but also eliminates the need for handling hazardous metal electrodes during cell manufacturing. However, such batteries usually suffer from much faster capacity decay and are much more sensitive to even trace levels of irreversible side reactions on the anode, especially for the more reactive Na metal. This work systematically investigates electrochemical interfaces for Na plating and stripping and describes the use of the Zn surface to develop nearly fully reversible Na anodes with 1.0 M NaPF₆ in a diglyme-based electrolyte. The high performance includes consistently higher than 99.9% faradaic efficiencies for a wide range of cycling currents between 0.5 and 10 mA cm^-2, much more stable interfacial resistance and nearly no formation of mossy Na after 500 cycles compared with conventional Al and Cu surfaces. This improved reversibility was further confirmed under lean electrolyte conditions with a wide range of electrolyte concentrations and cycling temperatures and can be attributed to the strong interfacial binding and intrinsic sodiophilic properties of the Zn surface with Na, which not only ensured uniform Na plating but also eliminated most side reactions that would otherwise cause electrolyte depletion. As a result, full cells assembled with Na-free Zn foil and a high capacity Na₃V₂(PO₄)₃ cathode delivered ∼90% capacity retention for 100 cycles, higher than the 73% retention of Cu foils and much higher than the 39% retention of Al foils. This work provides new approaches to enable stable cycling of anode-free batteries and contribute to their applications in practical devices.

Communications and High-Precision Positioning (CHP2): Hardware Architecture, Implementation, and Validation

Spectral congestion and modern consumer applications motivate radio technologies that efficiently cooperate with nearby users and provide several services simultaneously. We designed and implemented a joint positioning-communications system that simultaneously enables network communications, timing synchronization, and localization to a variety of airborne and ground-based platforms. This Communications and High-Precision Positioning (CHP2) system simultaneously performs communications and precise ranging (<10 cm) with a narrow band waveform (10 MHz) at a carrier frequency of 915 MHz (US ISM) or 783 MHz (EU Licensed). The ranging capability may be extended to estimate the relative position and orientation by leveraging the spatial diversity of the multiple-input, multiple-output (MIMO) platforms. CHP2 also digitally synchronizes distributed platforms with sub-nanosecond precision without support from external systems (GNSS, GPS, etc.). This performance is enabled by leveraging precise time-of-arrival (ToA) estimation techniques, a network synchronization algorithm, and the intrinsic cooperation in the joint processing chain that executes these tasks simultaneously. In this manuscript, we describe the CHP2 system architecture, hardware implementation, and in-lab and over-the-air experimental validation.

Unmanned aerial vehicles (UAVs): practical aspects, applications, open challenges, security issues, and future trends

Recently, unmanned aerial vehicles (UAVs) or drones have emerged as a ubiquitous and integral part of our society. They appear in great diversity in a multiplicity of applications for economic, commercial, leisure, military and academic purposes. The drone industry has seen a sharp uptake in the last decade as a model to manufacture and deliver convergence, offering synergy by incorporating multiple technologies. It is due to technological trends and rapid advancements in control, miniaturization, and computerization, which culminate in secure, lightweight, robust, more-accessible and cost-efficient UAVs. UAVs support implicit particularities including access to disaster-stricken zones, swift mobility, airborne missions and payload features. Despite these appealing benefits, UAVs face limitations in operability due to several critical concerns in terms of flight autonomy, path planning, battery endurance, flight time and limited payload carrying capability, as intuitively it is not recommended to load heavy objects such as batteries. As a result, the primary goal of this research is to provide insights into the potentials of UAVs, as well as their characteristics and functionality issues. This study provides a comprehensive review of UAVs, types, swarms, classifications, charging methods and regulations. Moreover, application scenarios, potential challenges and security issues are also examined. Finally, future research directions are identified to further hone the research work. We believe these insights will serve as guidelines and motivations for relevant researchers.

A New Mobility Era: Stakeholders’ Insights regarding Urban Air Mobility

Urban Air Mobility (UAM) constitutes a future aerial mobility alternative, which concerns the use of electric and autonomous aerial vehicles for transporting people throughout a planned network of vertiports. To materialize UAM, several actors of the air and urban transport ecosystem play a vital role. This paper describes the insights gathered from 32 key stakeholders around the world to present and frame the key aspects for the future implementation of UAM. The participants include representatives from the UAM industry such as airports, airlines, aviation consulting companies, academia, and authorities. The data collection encompasses various key research areas, covering topics such as UAM strengths, weaknesses, opportunities and risks, requirements for implementation, concept integration in the existing transport system, specific use cases, business models, and end-user segments. The research aims at setting up the stakeholder scene and expanding the current literature for UAM by engaging key decision makers and experts towards shaping the new mobility era. The results demonstrate that ensuring certification standards for UAM fleets and updating the current legal and regulatory framework are the main prerequisites for UAM’s realization. In addition, the usage of UAM for transporting cargo or for air ambulance services are the most mature business models for the coming decade.

A Methodology for the Comparative Analysis of Hybrid Electric and All-Electric Power Systems for Urban Air Mobility

The present investigation addresses the topic of Urban Air Mobility with particular reference to the air-taxi service with electrified power systems. A new and detailed methodology is proposed for the simplified design and energy analysis of conventional, hybrid-electric, and full-electric power systems for this application. The original contributions to the scientific literature on UAM are the detailed modeling approach, the evaluation of CO2 emissions with a Well-to-Wing approach as a function of the electricity Emission Intensity factor, and the comparison with road vehicles performing the same route in different driving conditions. The comparison demonstrates the advantages of a full electric air-taxi with today’s technology versus a hybrid-electric road taxi, especially in cases involving low emission intensity and unfavorable driving conditions (congested traffic, aggressive driving style, and high circuity factor values). In the case of 2035 technology, the comparison with a referenced fully electric road vehicle is detrimental to the air taxi but the values of Well-to-Wheel/Wing CO2 with the expected Emission Intensity of 90 g/kWe for the European Union are still quite low (67 g/km). The investigation also quantifies the negative effect of battery aging on the consumption of the air taxi and on the number of consecutive flights that can be performed without fully charging the battery.

The promise of energy-efficient battery-powered urban aircraft

Improvements in rechargeable batteries are enabling several electric urban air mobility (UAM) aircraft designs with up to 300 mi of range with payload equivalents of up to seven passengers. Novel UAM aircraft consume between 130 Wh/passenger-mi and ∼ 1,200 Wh/passenger-mi depending on the design and utilization, compared to an expected consumption of over 220 Wh/passenger-mi and 1,000 Wh/passenger-mi for terrestrial electric vehicles and combustion engine vehicles, respectively. We also find that several UAM aircraft designs are approaching technological viability with current Li-ion batteries, based on the specific power and energy, while rechargeability and lifetime performance remain uncertain. These aspects highlight the technological readiness of a new segment of transportation.

Urban Air Mobility: Projections for Air Taxis

The growing global demand for efficient and sustainable urban mobility in metropolitan areas has created innovative approaches to new modes of transportation and vehicles. Using the Delphi method, this study explored the prospective development of urban air mobility (UAM), specifically the emergence of air taxis or vertical take-off and landing (VTOLs). The two-staged study examined 25 projections regarding technological and infrastructural aspects to propose a future scenario for UAM and air taxis for the next 5–10 years. The questioned experts confirmed most of the proposed statements from both areas but were undetermined regarding certain technological aspects. Considering the crucial impacts of regulation and certification as well as consumer perception and acceptance for UAM and air taxis, further research on these topics and their correlation is suggested.

Stochastic Drift Counteraction Optimal Control of a Fuel Cell-Powered Small Unmanned Aerial Vehicle

This paper investigates optimal power management of a fuel cell hybrid small unmanned aerial vehicle (sUAV) from the perspective of endurance (time of flight) maximization in a stochastic environment. Stochastic drift counteraction optimal control is exploited to obtain an optimal policy for power management that coordinates the operation of the fuel cell and battery to maximize the expected flight time while accounting for the limits on the rate of change of fuel cell power output and the orientation dependence of fuel cell efficiency. The proposed power management strategy accounts for known statistics in transitions of propeller power and climb angle during the mission, but does not require the exact preview of their time histories. The optimal control policy is generated offline using value iterations implemented in Cython, demonstrating an order of magnitude speedup as compared to MATLAB. It is also shown that the value iterations can be further sped up using a discount factor, but at the cost of decreased performance. Simulation results for a 1.5 kg sUAV are reported that illustrate the optimal coordination between the fuel cell and the battery during aircraft maneuvers, including a turnpike in the battery state of charge (SOC) trajectory. As the fuel cell is not able to support fast changes in power output, the optimal policy is shown to charge the battery to the turnpike value if starting from a low initial SOC value. If starting from a high SOC value, the battery energy is used till a turnpike value of the SOC is reached with further discharge delayed to later in the flight. For the specific scenarios and simulated sUAV parameters considered, the results indicate the capability of up to 2.7 h of flight time.

Potential Urban Air Mobility Travel Time Savings: An Exploratory Analysis of Munich, Paris, and San Francisco

The advent of electrified, distributed propulsion in vertical take-off and landing (eVTOL) aircraft promises aerial passenger transport within, into, or out of urban areas. Urban air mobility (UAM), i.e., the on-demand concept that utilizes eVTOL aircraft, might substantially reduce travel times when compared to ground-based transportation. Trips of three, pre-existent, and calibrated agent-based transport scenarios (Munich Metropolitan Region, Île-de-France, and San Francisco Bay Area) have been routed using the UAM-extension for the multi-agent transport simulation (MATSim) to calculate congested trip travel times for each trip’s original mode—i.e., car or public transport (PT)—and UAM. The resulting travel times are compared and allow the deduction of potential UAM trip shares under varying UAM properties, such as the number of stations, total process time, and cruise flight speed. Under base-case conditions, the share of motorized trips for which UAM would reduce the travel times ranges between 3% and 13% across the three scenarios. Process times and number of stations heavily influence these potential shares, where the vast majority of UAM trips would be below 50 km in range. Compared to car usage, UAM’s (base case) travel times are estimated to be competitive beyond the range of a 50-minute car ride and are less than half as much influenced by congestion.

Constrained Urban Airspace Design for Large-Scale Drone-Based Delivery Traffic

Large-scale adoption of drone-based delivery in urban areas promise societal benefits with respect to emissions and on-ground traffic congestion, as well as potential cost savings for drone-based logistic companies. However, for this to materialise, the ability of accommodating high volumes of drone traffic in an urban airspace is one of the biggest challenges. For unconstrained airspace, it has been shown that traffic alignment and segmentation can be used to mitigate conflict probability. The current study investigates the application of these principles to a highly constrained airspace. We propose two urban airspace concepts, applying road-based analogies of two-way and one-way streets by imposing horizontal structure. Both of the airspace concepts employ heading-altitude rules to vertically segment cruising traffic according to their travel direction. These airspace configurations also feature transition altitudes to accommodate turning flights that need to decrease the flight speed in order to make safe turns at intersections. While using fast-time simulation experiments, the performance of these airspace concepts is compared and evaluated for multiple traffic demand densities in terms of safety, stability, and efficiency. The results reveal that an effective way to structure drone traffic in a constrained urban area is to have vertically segmented altitude layers with respect to travel direction as well as horizontal constraints imposed to the flow of traffic. The study also makes recommendations for areas of future research, which are aimed at supporting dynamic traffic demand patterns.

Multi-Criteria Decision Making Process in Metropolitan Transport Means Selection Based on the Sharing Mobility Idea

The article presents the idea of modeling the decision-making process in the field of the metropolitan areas transport system. Due to the increasing process of metropolization and urbanization, which is predicted to be 68.4% worldwide and 83.7% in Europe in 2050, the issue will be even more sophisticated. The problem of depletion of transport network capacity as well as the implementation of modern technology solutions forces metropolitan committees to apply tools for metropolitan passenger transport system optimization. Significantly, the policy and regulations on sustainable urban mobility management are based on the mobility demand predictions and understanding of the travel decision-making process of citizens. The scientific purpose of this article is to build a mathematical model, as a tool supporting the multi-criteria decision-making process regarding the choice of means of transport in a developing metropolis. The issue raised in this article considers the most important research areas of the metropolitan transport means selection, which includes transport safety, qualitative, financial, and ecological aspects. The model was implemented in Silesian Metropolis in Poland with a particular emphasis on sharing mobility transport means users. As a result, a ranking of sharing transport means was developed, which is a piece of significant information for planners and future investors in the development of the metropolitan transport system.