Electric Vertical Takeoff Research Articles

Battery cycle life assessment for a lift+cruise electric vertical takeoff and landing transporter drone

Advanced Air Mobility (AAM) is a new future concept of air transportation to move people and cargo effectively and safely between places that are under or not served by different transportation modes. Transporter drone is one of the potential vehicles envisaged to fulfill this future AAM needs. One of the key challenges and crucial components in enabling successful transporter drone flight is the batteries used as they have limited usage cycle lifespan that affects the system airworthiness significantly. Hence to ensure continuous airworthiness of the platform, it is vital to know or predict the battery State of Health (SOH) and cycle life accurately. This paper describes a systematic approach on battery cycle life assessment through experimental battery usage cycle test for a lift+cruise transporter drone using realistic operating flight profile. Analysis on the battery cycle test data collected provides useful battery health and usage cycle lifespan information for system preventive and predictive maintenance in maintaining its airworthiness. Battery SOH estimation was done using linear predictive models with the collected battery cycle data while battery cycle life model was formulated using a double exponential parametric regression model. The battery cycle data collected is made publicly available for the community.

A new method to perform lithium-ion battery pack fault diagnostics – Part 3: Adaptation for fast charging

Electric Vertical Take-Off and Landing (eVTOL) aircraft are expected to become ubiquitous in the future Urban Air Mobility (UAM) landscape. Several eVTOL aircraft propelled using Lithium-ion batteries are under development. However, despite the early spotlight, the manufacturers need to ensure safe long-term operation of the vehicles including strict checks on battery-related hazards. On the other hand, fast charging of eVTOL batteries is crucial to enable multiple flights per day and justify the economics of UAM. This work is aimed at contextualising battery safety for eVTOL through the modification of a battery fault diagnosis algorithm for fast charging. The algorithm was developed in Parts 1 and 2 of the paper to use the charging cycle data for detecting disconnection faults but tested only for low charging currents. This paper adapts the algorithm for fast charging through a novel technique termed as Partial Incremental Capacity (PIC). The PIC method was developed using experiments at single cell and supercell level before integrating it into the algorithm. Finally, the fault detection ability of the adapted algorithm was validated using a real-life eVTOL battery module. Thus, the updated version of the algorithm facilitates fault diagnosis while charging fast, making it ideal for implementation in eVTOL.

A novel heat pipe bipolar plate for proton exchange membrane fuel cells

The proton exchange membrane fuel cell (PEMFC) system is appealing for electric vertical takeoff and landing vehicles, but its power density needs to be improved for practical applications. Ultra-thin flat heat pipes (UTFHP) have potential to improve the power density of PEMFC system by reducing the complexity of thermal management subsystem, but the large stack volume have hindered their wider adoption. This paper proposes a novel design of heat pipe bipolar plates (HPBP) to reduce the volume of heat pipe cooled stack. A three-dimensional numerical model has been developed for analyzing and comparing the performance of the PEMFCs with HPBP and UTFHP. Compared to the UTFHP, the HPBP could significantly reduce the stack volume while maintaining comparable maximum heat load. It can also significantly reduce the maximum temperature and improve the temperature uniformity over the cathode catalyst layer middle plane. The operating range and the peak power density of the PEMFC cooled by HPBP are larger than that cooled by UTFHP. We also performed system-level evaluations and found that the PEMFC system with HPBP cooling exhibits 22% and 36% higher gravimetric and volumetric power densities than that with conventional liquid cooling, respectively.

Analysis of cost-efficient urban air mobility systems: Optimization of operational and configurational fleet decisions

With the introduction of low-noise and low-emission electric vertical take-off and landing vehicles, passenger air transportation in urban areas is becoming increasingly important. Previous studies have designed vehicle concepts based on reference mission profiles, however, without considering strategic decisions about fleet operations, such as charging infrastructure, range and battery capacity. Comprehensive cost analyses for urban air mobility fleets have been largely neglected. In this paper, we develop an optimization model to analyze the cost-efficient operation of urban air mobility systems. Strategic decisions on vehicle concepts, battery capacity, and charging infrastructure are incorporated and evaluated using a total cost of ownership approach. We consider state-of-the-art modeling approaches, including vehicle-specific parameters, for accurate calculation of energy consumption. The optimization model is applied to the multi-agent transport simulation MATSim in a case study of the Ruhr (Germany) scenario to evaluate key parameter variations.The study results indicate the feasibility of an urban air mobility system in the study region with trip costs ranging from 27 US-$ to 46 US-$ per requested trip, depending on the scenario settings. Based on parameter variations, we find that a high cruising speed has a detrimental effect on the total cost. A medium charging power level is sufficient and energy costs account for only a moderate share. The latter is in contrast to previous research results, but can be attributed to the more detailed modeling approach of vehicle-specific parameters. We propose a cost incentive system as the ground handling time of the vehicles outweighs the recharging and flight time. The overall results provide a promising basis for model extensions.

Introducing an efficiency index to evaluate eVTOL designs

The evolution of electric vertical takeoff and landing (eVTOL) aircraft as part of the Advanced Air Mobility initiative will affect our society and the environment in fundamental ways. Technological forecasting suggests that commercial services are fast emerging to transform urban and regional air mobility for people and cargo. However, the complexities of diverse design choices pose a challenge for potential adopters or service providers because there are no objective and simple means to compare designs based on the available set of performance specifications. This analysis defines an aeronautically informed propulsion efficiency index (PEX) to compare the performance of eVTOL designs. Range, payload ratio, and aspect ratio are the minimum set of independent parameters needed to compute a PEX that can distinguish among eVTOL designs. The distribution of the PEX and the range are lognormal in the design space. There is no association between PEX values and the mainstream eVTOL architecture types or the aircraft weight class. A multilinear regression showed that the three independent parameters explained >90 % of the PEX distribution in the present design space.

Worst-Case Analysis of Complex Nonlinear Flight Control Designs Using Deep Q-Learning

With the objective of exposing hidden design deficiencies in complex nonlinear systems, this paper presents the use of reinforcement learning techniques for application in flight control law development and testing. Following the idea of worst-case testing, a deep Q-network agent is trained to identify input sequences that lead to detrimental system behavior. Because the analysis is based directly on the repeated interaction between the agent and the investigated system, no model simplifications are required, making the presented method applicable to highly complex systems. The capability of the learning-based worst-case analysis is demonstrated for the speed protection function of the hover flight control law of an electric vertical takeoff and landing (eVTOL) aircraft. The analysis discovers possible piloted maneuvers that violate the implemented protection algorithm. A root cause analysis of the emerging behavior reveals the neglect of an important flight mechanical coupling term in the design of the protection algorithm and ultimately leads to the revision and improvement of the controller. This demonstrates the benefits of the presented testing method for the design, verification, and validation of complex systems. The application to a high-fidelity system used for control law development of an actual eVTOL prototype currently under construction demonstrates the relevance of the method beyond academia.

BattX: An equivalent circuit model for lithium-ion batteries over broad current ranges

Advanced battery management is as important for lithium-ion battery systems as the brain is for the human body. Its performance is based on the use of fast and accurate battery models. However, the mainstream equivalent circuit models and electrochemical models have yet to meet this need well, due to their struggle with either predictive accuracy or computational complexity. This problem has acquired urgency as some emerging battery applications running across broad current ranges, e.g., electric vertical take-off and landing aircraft, can hardly find usable models from the literature. Motivated to address this problem, we develop an innovative model in this study. Called BattX, the model is an equivalent circuit model that draws comparisons to a single particle model with electrolyte and thermal dynamics, thus combining their respective merits to be computationally efficient, accurate, and physically interpretable. The model design pivots on leveraging multiple circuits to approximate major electrochemical and physical processes in charging/discharging. Given the model, we develop a multipronged approach to design experiments and identify its parameters in groups from experimental data. Experimental validation proves that the BattX model is capable of accurate voltage prediction for charging/discharging across low to high C-rates.

An Efficient and Robust Sizing Method for eVTOL Aircraft Configurations in Conceptual Design

This paper presents the development of a robust sizing method to efficiently estimate and compare key performance parameters in the conceptual design stage for the two main classes of fully electric vertical take-off and landing (eVTOL) aircraft, the powered lift and wingless aircraft types. The paper investigates hybrids of classical root-finding methods: the bisection, fixed-point and Newton-Rapson methods for use in eVTOL aircraft sizing. The improved convergence efficiency of the hybrid methods is at least 70% faster than the standard methods. This improved efficiency is significant for complex sizing problems. The developed sizing method is used to investigate the comparative performance of the wingless and powered lift eVTOL aircraft types for varying mission lengths. For a generic air taxi mission with a payload of 400 kg, the powered lift type demonstrates its mass efficiency when sized for missions above 10 km in range. However, the simpler architecture of the wingless eVTOL aircraft type makes it preferable for missions below 10 km in range when considering energy efficiency. The results of the sizing study were compared against a selection of eVTOL aircraft data. The results showed a good agreement between the estimated aircraft mass using the proposed sizing method and published eVTOL aircraft data.

Annoyance of helicopter-like sounds in urban background noise

Scenarios of urban air mobility see electric vertical take-off and landing aircraft (eVTOLs) operating within cities. Rotorcraft sounds are typically characterised by short bursts of noise, although eVTOLs offer more opportunities for a quieter sound design. We asked participants to compare the annoyance of a reference sequence of bursts of noise with a burst duration of 20 ms with that of a test sequence for which the burst duration was 1 or 5 ms. There were 20 bursts/s. A two-interval, two-alternative forced-choice task and a 1-up/1-down procedure was used. Both sequences were played in background noise that had either the same root-mean-square (RMS) level as the sequence of bursts or 10 dB less. The results were similar to those for loudness: On average, sequences with 1-ms bursts needed 6-7 dB less RMS level to sound equally annoying as the 20-ms bursts, and sequences with 5-ms bursts needed 3 dB less. This suggests that psychoacoustic annoyance is mainly explained by loudness and that the RMS level is an insufficient descriptor. Compared between the two background noise levels, the level difference for equal annoyance between short and 20-ms bursts was 1.5 dB larger in the louder background, which was statistically significant.

System Identification Approach for eVTOL Aircraft Demonstrated Using Simulated Flight Data

This paper describes a system identification method for electric vertical takeoff and landing (eVTOL) aircraft. The approach merges fixed-wing and rotary-wing modeling techniques with new strategies to develop a modeling method for eVTOL vehicles using flight-test data. The eVTOL aircraft system identification approach is demonstrated through application to the NASA Langley Aerodrome No. 8 tandem tilt-wing, distributed electric propulsion aircraft using a high-fidelity flight dynamics simulation. Orthogonal phase-optimized multisine inputs are applied to each control surface and propulsor at numerous flight conditions throughout the flight envelope to collect informative flight data. An aero-propulsive model is identified at each flight condition using the equation-error method in the frequency domain. The local model parameters are then blended to create a global model across the nominal flight envelope. The identified models are shown to provide a good fit to modeling data with good prediction capability. The methodology is developed with a discussion of unique eVTOL vehicle aerodynamic characteristics and practical strategies intended to inform future flight-based system identification efforts for eVTOL aircraft.

X-TEAM D2D Project: Designing and Validating a Concept of Operations for Door-To-Door Multimodal Transport

The project X-TEAM D2D (extended ATM for door-to-door travel) has been funded by SESAR JU in the framework of the research activities devoted to the investigation of integration of Air Traffic Management (ATM) and aviation into a wider transport system able to support the implementation of the door-to-door (D2D) travel concept. The project defines a concept for the seamless integration of ATM and Air Transport into an intermodal network, including other available transportation means, such as surface and waterways, to contribute to the 4 h door-to-door connectivity targeted by the European Commission in the ACARE SRIA FlightPath 2050 goals. In particular, the project focused on the design of a concept of operations for urban and extended urban (up to regional) integrated mobility, taking into account the evolution of transportation and passengers service scenarios for the next decades, according to baseline (2025), intermediate (2035) and final target (2050) time horizons. The designed ConOps encompassed both the transportation platforms integration concepts and the innovative seamless Mobility as a Service, integrating emerging technologies, such as Urban Air Mobility (e.g., electric vertical take-off and landing vehicles) and new mobility forms (e.g., micromobility vehicles) into the intermodal traffic network, including Air Traffic Management (ATM) and Unmanned Traffic Management (UTM). The developed concept has been evaluated against existing KPAs and KPIs, implementing both qualitative and quantitative performance assessment approaches, while also considering specific performance metrics related to transport integration efficiency from the passenger point of view, being the proposed solution designed to be centered around the passenger needs. The aim of this paper is to provide a description of the activities carried out in the project and to present at high level the related outcomes.

Prognostics for Lithium-ion batteries for electric Vertical Take-off and Landing aircraft using data-driven machine learning

The health management of batteries is a key enabler for the adoption of Electric Vertical Take-off and Landing vehicles (eVTOLs). Currently, few studies consider the health management of eVTOL batteries. One distinct characteristic of batteries for eVTOLs is that the discharge rates are significantly larger during take-off and landing, compared with the battery discharge rates needed for automotives. Such discharge protocols are expected to impact the long-run health of batteries. This paper proposes a data-driven machine learning framework to estimate the state-of-health and remaining-useful-lifetime of eVTOL batteries under varying flight conditions and taking into account the entire flight profile of the eVTOLs. Three main features are considered for the assessment of the health of the batteries: charge, discharge and temperature. The importance of these features is also quantified. Considering battery charging before flight, a selection of missions for state-of-health and remaining-useful-lifetime prediction is performed. The results show that indeed, discharge-related features have the highest importance when predicting battery state-of-health and remaining-useful-lifetime. Using several machine learning algorithms, it is shown that the battery state-of-health and remaining-useful-life are well estimated using Random Forest regression and Extreme Gradient Boosting, respectively.

Flight Performance with Respect to Rotor Rotation Directions of Multirotor Aircraft

A multirotor electric vertical takeoff and landing (EVTOL) aircraft is specialized for intracity point-to-point urban air mobility services due to its advantages of efficient hover performance, high gust resistance, and relatively low noise. Because of its multiple rotors, rotor–rotor interference inevitably affects flight performance, mainly depending on inter-rotor distance and rotor rotation directions. It is assumed that there exists an optimal rotation direction for a given lot of multiple rotors. In this study, the aim is to investigate rotor–rotor interference for various rotation directions and the resulting flight performance. We propose a concept of rotor rotation direction that achieves the desirable flight performance in forward flight. The concept is called front-retreating/rear-advancing (FRRA), in which the retreating side of the front rotor and the advancing side of the rear rotor are aligned in a straight line. To this end, a multidisciplinary flight simulation framework was developed to predict the flight performance of a general multirotor EVTOL aircraft. It was found that the FRRA concept minimizes thrust loss due to rotor–rotor interference in high-speed forward flight. For a generic mission profile, the rotation direction set by the FRRA concept reduces the battery energy consumption by 7% in comparison to the rotation direction of unfavorable rotor–rotor interference in operation.

Preliminary Concept of Urban Air Mobility Traffic Rules

Driven by recent technological breakthroughs, the electric vertical take-off and landing (eVTOL) aircraft has gained considerable attention. The widespread demand for eVTOL aircraft can be attributed to their potential use in the commercialisation of urban air mobility (UAM) in low-altitude urban airspaces. However, the urban low-altitude airspace environment is complex. UAM has a high traffic density and the eVTOL aircraft specifications are not uniform. Particularly in commercial scenarios, controlling eVTOL aircraft and ensuring safety in UAMs are the two major problems that should be addressed in future studies. The design of reasonable traffic rules is a potential solution; hence, we organised a UAM traffic rule system and proposed several alternative UAM traffic rules from three perspectives: a single eVTOL aircraft, a certain route, and key control areas. In addition, we validated these traffic rules using multi-rotor and fixed-wing eVTOL aircraft. The results show that designing reasonable traffic rules can facilitate attaining the primary objectives of commercialisation of UAM.

Rapid Blade Shape Optimization for Contra-Rotating Propellers for eVTOL Aircraft Considering the Aerodynamic Interference

The rising interest in the evolvability of electric vertical takeoff and landing (eVTOL) promises substantial potential in the field of urban air mobility (UAM). Challenges in energy storage density and geometry restriction both emphasize the propeller efficiency for endurance and takeoff weight, whereas the contra-rotating propellers (CRP) advantage is balancing high thrust and efficiency over a single propeller. The aim of this paper is twofold: (i) to present a novel rapid CRP blade shape optimization framework and (ii) to study the impact of the dual propellers revolution speed allocations on the overall CRP power efficiency. The core of the framework is the blade element momentum theory (BEMT)-based blade shape optimization considering the wake effect of the upper propeller by the rotational CFD (computational fluid dynamics) actuator-disc simulation method. The results show that for the same thrust, the optimized CRP at the equal revolution speed is superior to the original (upper-lower-identical) one by 5.9% in thrust-to-power ratio. The overall efficiency can be additionally lifted by 5.3% when the dual propellers share similar torques. By excluding the integral propeller CFD simulation and empirical parameters estimation, the framework enables the swift obtaining of an optimized CRP scheme while maintaining robustness as well.

Flight simulation from takeoff to yawing of eVTOL airplane with coaxial propellers by fluid-rigid body interaction

In this study, we adopt a coupled fluid-rigid body simulation using the moving computational domain method and multi-axis sliding mesh method for the takeoff, hovering, and yawing flight of an electric vertical takeoff and landing aircraft (eVTOL). The aircraft model has four pairs of coaxial propellers, and the computational domain is divided into three domains to move the aircraft and eight propeller domains to rotate the propellers. As a result, we clarify the behavior and aerodynamic force of the aircraft when the input values are determined by the automatic control. The results in the flow field also show that the downwash spreads in a crisscross pattern on the ground, the wind reaches different ranges on the ground depending on the flight altitude, and that the coaxial propeller causes an asymmetry in the velocity field during yawing. Consequently, we conclude that this method is effective for the flight simulation of an eVTOL.

Finally, an eVTOL You Can Buy Soonish: Opener's BlackFly is the first of a radical new class of automated ultralight fliers

If electric vertical takeoff and landing aircraft do manage to revolutionize transportation, the date of 5 October 2011, may live on in aviation lore. That was the day when a retired mechanical engineer named Marcus Leng flew a home-built eVTOL across his front yard in Warkworth, Ont., Canada, startling his wife and several of his friends.

A reference model to visualize and deepen discussions on emergency medical services electric vertical takeoff and landing aircraft

A reference model to visualize and deepen discussions on emergency medical services electric vertical takeoff and landing aircraft

Economic and emission reduction benefits of the implementation of eVTOL aircraft with bi-directional flow as storage systems in islands and case study for Canary Islands

This research paper presents a novel approach for cost-benefit analysis for the bi-directional functionality of eVTOL (Electric Vertical Take-Off and Landing) aircraft charging. eVTOL aircrafts represents an emerging aviation market that seeks to revolutionize mobility, both intra-city and inter-city, through an air transportation system for passengers based on safety, efficiency and accessibility on demand. In this research, an optimization based on genetic algorithms has been used to find the number of eVTOL vehicles which makes vehicle-to-grid services profitable for each of the electrical systems considered. This research discusses the impact that vehicle-to-grid eVTOL aircraft would cause, changing the current demand curve peaks and the economic benefits for eVTOL end users, power plant companies and system operator. The results show that there is an increase in the penetration of renewable energy sources, causing a reduction of approximately 4.6% in global emissions. In addition, the benefits obtained by the stakeholders considered in the system is greater than zero. The methodology considered in this research offers a new perspective for electrical systems to predict the demand of eVTOL aircraft, in specific territories, such as in the presented case study in the Archipelago of Canary Islands.

Airports and the rise of eVTOL

A new form of aircraft — electric Vertical Take-off and Landing (eVTOL) — holds the potential to upend the transportation industry. Some eVTOLs are crosses between a helicopter and a traditional aeroplane, combining the vertical take-off of helicopters with the horizontal flight of aeroplanes. Others take on a more drone-like appearance. They are the next wave in aviation innovation and are expected to be flying as soon as 2025. As with any new and evolving industry, there are a myriad of questions to be answered. Here we discuss the advent of the eVTOL industry, why airports should be paying attention, and the impacts this new form of transportation may have on airports and their functions, including eVTOL-specific energy, aviation, regulation, emergency and infrastructure needs.