With the introduction of electric cars, we’ve come across something called “range anxiety” – will the car have enough power to reach its destination. This is even more alarming up in the air.

Although this could be a no-go for personal flying vehicles, it is achievable for urban air taxi services, which will fly set routes, for which range is calculated, with added margin for safety.

Volocopter is a German electric vertical take-off/landing (eVTOL) aircraft maker, which claims it has completed over 1500 flight tests for its VoloCity urban air taxi; see Figure 1. VoloCity has 18 rotors and nine lithium-ion (Li-ion) battery packs, each powering two rotors, which adds redundancy for failsafe assurance. Any unexpectedly rapid discharge of a single battery pack, or failure of an individual motor or inverter, will leave enough power for the multicopter to make urgent yet safe landing.

Figure 1: VoloCity by Volocopter

 The battery packs are exchangeable, cutting down on turnaround time in getting the vehicle back in the air with a full charge.

According to the manufacturer’s data, the empty vehicle weighs 700kg and has a maximum take-off weight of 900kg. This is enough to carry two passengers with baggage, says Volocopter, with a maximum flying range of 35km.

In a 2021 feasibility study, the UK Civil Aviation Authority analysed a theoretical air taxi service between Heathrow Airport and London City Airport. The direct aerial distance between the two destinations is about 24km, so the VoloCity could theoretically make the trip without stopping and still have nearly 50% range left. This suggests that technological capabilities are already good enough to support useful commercial services, although planners must consider the effects of airspace restrictions, emergency detours, adverse weather conditions and other factors. Making a stop on the way to exchange the battery may be an option if needed, although future generations of vehicles can be expected to fly farther.

Technological improvements

The automotive industry continues to increase the performance and driving range of electric vehicles by improving multiple aspects of their architecture, including battery technology, battery management and monitoring, and power electronics. Makers of urban air mobility (UAM) vehicles can find improvements in the same areas.

Battery technology

Batteries with high energy density are crucial to maximise range and endurance without compromising on payload capacity. Currently, Li-ion is the battery of choice, although the technology is approaching maturity, therefore its limitations.

Among the alternatives, supercapacitors could have a role, as might solid-state and lithium-sulphur batteries, which promise greater energy density and safety and lower lifecycle costs.

Battery management and monitoring

Better battery management can extend flying range through more accurate state-of-charge and state-of-health monitoring, with cell balancing to maintain capacity and efficiency. At the same time, ensuring battery safety is paramount and requires proper protection and effective and lightweight thermal management.

Power electronics

In the power electronics domain, wide-bandgap semiconductors can offer the same advantages in UAM vehicles as in roadgoing EVs. These include greater switching efficiency that allows increased operating frequency, smaller size in relation to voltage rating, tolerance for higher operating temperatures and better reliability. Raising the operating frequency allows the use of smaller passive components in the power supply circuitry, which can reduce module size and weight. Tolerance for increased operating temperature can permit simplified thermal management, leading to further weight savings.

Additionally, integration and overall system optimisation are essential for electric UAM vehicles, to balance the interplay between battery technology, motor technology, battery management and power electronics for better performance and safety.

Equally important to consider is the time to battery end-of-life, to avoid excessive degradation whilst in service. Disposal of retired batteries must be handled properly; perhaps a second life beckons in grid-connected storage, as already suggested for EV batteries.

Market development

Meanwhile, regulators are getting ready. The European Union Aviation Safety Agency claimed a world first in 2022 by proposing its regulatory framework for eVTOL services like air taxis. The framework covers aspects including airworthiness, air operation, flight crew licensing, and the rules of the air.

Forecasters see a vibrant future for UAM. Some operators want to start commercial air taxi services in major European cities by 2024. Market analyst house McKinsey sees the biggest operators handling some 20,000 flights per day by 2030, with the typical average flight lasting about 18 minutes.

By Mark Patrick, Director of Technical Content, Mouser Electronics