The future of urban air mobility

This guest feature from David Latimer, the CEO of Magnomatics. considers the financial implications of eVTOL (electric vertical take-off and landing) aircraft.

And while there are the more established companies who will be involved in clandestine programmes, the fact is that the VTOL industry is seeing some very interesting parallels with the burgeoning electric vehicle market back in 2008. Consider the then-new entrants like Tesla, Coda, and Fisker that were emerging at the time – and all the while the mainstream automotive industry was in crisis.

New companies emerging

On the 11^th of August 2021, Joby Aviation listed on the New York Stock Exchange with a valuation of $4.5 billion. The California-based company, which has been developing an all-electric aircraft for aerial ridesharing, believes it has enough money – $1.6 billion – to fund the technology through to the start of commercial operations.

What’s more, Joby has already completed over 1,000 test flights and agreed a path to G1 certification of the aircraft with the Federal Aviation Administration (FAA).

The company has also taken the first steps towards becoming the first eVTOL airline with application for Part 135 Air Carrier Certificate issued by the FAA. Joby expect to start operations of their quiet, all electric aircraft with a pilot and four passengers in 2024. This will make it possible for us to see the first eVTOL airline this decade.

Joby Aviation is not alone. Palo Alto-based Archer Aviation (valued at $1.5 billion) unveiled its Maker aircraft in June 2021. It also plans to be in service by 2024. Meanwhile, in Europe, Munich-based Lilium is working towards joint EASA and FAA certification of its seven-seater aircraft also by 2024. It, too, has announced its intention to list on NASDAQ. German rivals Volocopter are also targeting first commercial operations in two to three years.

Electric motors and magnetic gears

One common feature in the developing market is that all the solutions use multiple electric motors, which makes the performance density of the motors critical and a key for a breakthrough.

In industry technical expert Jonathon Bird’sReview of Electric Aircraft Drivetrain Motor Technology, Bird discusses the relative merits of various technologies, examining the continuous performance density of 25 different commercially available motors. Configurations include both axial and radial flux machines. Some are air-cooled some use liquids.

The route to power density in electric machines has historically been to operate permanent magnet motors (PM) at higher speeds, often in excess of 10,000 revolutions per minute. To become useful for UAM aircraft, the high speeds need to be geared down by as much as seven times. Conventionally, this introduces the requirement for a mechanical gear box, raising the issues of reliability, wear, maintenance and noise.

Bird introduces the idea of magnetic gears reference torque densities of 49Nm/kg (Newton metres per kilogram) at a scale of 100 newton metres, close to the torque density of mechanical gears. He also references the outer stator magnetically gear motors (OSMGM) proposed by Tallerico et al.

In an OSMGM, a magnetic gear is integrated with a conventional stator. Crucially, by integrating a magnetic gear with a motor, the inner high-speed magnetic rotor fulfills two functions. It is both the high-speed rotor of a PM motor and the high-speed rotor of the magnetic gear. This reduces the overall mass of the OSMGM. Tallerico et al went on to develop a high-fidelity design of an OSMGM with a torque density of over 30Nm/kg and above 95% efficiency. They also concluded that this was roughly double what could be achieved using a direct drive electric motor for UAM.

Made in the UK

Magnomatics was spun out of the University of Sheffield in 2006 to commercialise UAM technology based on magnetic gears. Among its patented products is the Pseudo Direct Drive, which is an OSMGM.

Whilst being aware of work at NASA, the company’s early application priorities have been to develop the technology for offshore wind, marine propulsion and light rail. And it has built a demonstration direct drive 500-kilowatt generator for offshore wind with a torque of 200,000Nm and efficiency in excess of 97%.

Magnomatics has been able to successfully license its proprietary PDD technology in the above sectors to blue chip organisations and is now turning its attention to the UAM market, where there is a natural fit for the novel and patented technology.

The company is also currently designing UAM propulsion motors based on PDD technology, which may even outperform all other machines currently available on the market – with initial demonstration machines due to be operational as early as 2022.