Against the backdrop of the rapidly growing low-altitude economy and urban air mobility (UAM), electric vertical takeoff and landing (eVTOL) aircraft have undoubtedly emerged as the most eye-catching “new species.” Compared to traditional helicopters, eVTOLs offer advantages such as zero emissions, low noise, and a high degree of automation, making them a key solution for future urban transportation. However, one of the biggest challenges to making eVTOLs truly take to the skies and operate safely is battery performance and safety. A study jointly published by the University of Warwick and Vertical Aerospace provides a new solution to this problem. They propose a novel testing method for battery power capability, specifically targeting the landing phase of eVTOLs, and introduce a more scientifically grounded definition of the “lower limit of battery reserve energy.” This is not only a technical innovation but also a lifeline for flight safety, ensuring that aircraft have sufficient power for emergency landings.
- Why Is the Landing Phase the Most Critical?
A typical eVTOL flight mission consists of three phases: takeoff, cruise, and landing. Among these, takeoff and landing place the highest power demands on the battery. Research shows that for composite-wing eVTOL aircraft, the discharge rate during cruise is close to 1C, while during takeoff and landing, it can exceed 3C. This means the battery must not only have sufficient energy reserves but also be capable of delivering high power output in short periods. Under existing industry standards, batteries typically reserve a certain amount of “backup power” as a safeguard for emergencies. However, there has been a lack of effective experimental validation for scientifically defining the lower limit of this backup range. An overly conservative approach wastes valuable range, while an overly aggressive one may lead to voltage drops, insufficient power, and ultimately, compromised flight safety.
- A Novel Power Testing Method: Closer to Real-World Flight Conditions
Traditional battery power testing methods, such as the Hybrid Pulse Power Characterization (HPPC) test, are typically conducted at fixed states of charge (SoC). This makes it difficult to simulate the complex conditions during actual landing, where the battery operates at low charge levels while delivering high power output. This study proposes a new testing protocol:◎ Apply prolonged constant-power discharge pulses to batteries under varying temperatures (20°C, 25°C, 40°C) and different aging conditions (calendar aging, electrochemical cycle aging);◎ Directly measure whether the battery can complete the pulse and record the minimum SoC value at completion;
◎ Generate a three-dimensional characteristic map that correlates temperature, power, duration, and the minimum achievable SoC.
This characteristic map can indicate how much charge the battery must retain under specific operating conditions to ensure a reliable landing without failure.
power capability characteristic maps of a calendar aged cells and cycle aged cells - Experimental Findings: The Impact of Battery Aging Has Been Underestimated
The results indicate that batteries aged through calendar aging can achieve a minimum SoC as low as 6%–14% for safe landing, whereas those aged through cyclic aging require 8%–27% of charge retention to ensure a successful landing. In other words, failing to account for battery aging may lead to overly optimistic estimates of reserve energy, significantly underestimating operational risks. For instance, if a cyclically aged battery is operated under standards designed for new batteries, the aircraft might continue flying at 14% SoC, while in reality, at least 27% is required to complete landing safely.This underscores a key point emphasized in the paper: Battery Health Management (BHM) must dynamically track the aging state. Otherwise, the “reserve energy” safety buffer becomes effectively meaningless.
- Model vs. Characteristic Map: Which Is More Reliable?
In addition to experimental work, the research team developed a second-order equivalent circuit model (2RC ECM) and parameterized it using experimental data. Comparative analysis revealed:◎ The characteristic map based on empirical data demonstrated higher accuracy in the vast majority of cases, with a maximum average error of only approximately 3%–7.5%;
◎ While the model achieved comparable accuracy under certain conditions, it often exhibited significant deviations in low state-of-charge (SoC) regions.
These findings indicate that the empirical characteristic map is more suitable for engineering applications, particularly as a safety reference within eVTOL battery management systems (BMS). Although the modeling approach offers certain advantages in terms of real-time performance and computational efficiency, it requires further optimization before it can independently assume a critical decision-making role.
- Implications for the Industry
The significance of this study lies not only in proposing a novel experimental method but also in reshaping our understanding of eVTOL battery safety margins:◎ The lower limit of reserve energy must account for aging effects; otherwise, risks become unmanageable.
◎ The characteristic map provides an intuitive safety boundary for BMS, contributing to enhanced flight safety.
◎ Power capability testing should align closely with mission profiles, particularly during critical phases such as landing.
In the future, if integrated with big data and online monitoring, this method could evolve into a dynamic safety assessment system, providing real-time guidance for eVTOL operations.
- Future Outlook.
The research team highlights that future work should focus on:
◎ Extending this methodology to the battery pack level, considering cell-to-cell consistency issues;
◎ Developing rapid prediction algorithms to enable real-time application in BMS;
◎ Establishing more comprehensive mission-driven battery testing standards based on flight mission profiles.For the industry, this is not merely an academic exercise but a critical technical hurdle for enabling eVTOL commercialization. Only when battery safety margins can be accurately quantified and managed in real time can eVTOLs truly take to urban skies and become a mainstream mode of transportation.
In summary: The future of eVTOL depends not only on how high and far it can fly, but also on its ability to land safely—and the key to achieving this lies in understanding and managing battery power capability and health.
