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INDUSTRY FOCUS MILITARY, AEROSPACE & DEFENCE Once the stuff of


QUEST FOR URBAN AIR MOBILITY


STEPS UP A GEAR U


rban air mobility (UAM), the concept of leveraging the airspace above cities to enable the safe and emission-free


transport of people and products, is an innovative and exciting field. According toMcKinsey’s Centre for FutureMobility, 72%and 64%of the 25 largest mainstream aerospace manufacturers and suppliers, respectively, are engaged in airmobility technologies. In fact there are currently a few hundred electric vertical take-off and landing (eVTOL) models being designed and dozens of real prototypes flying around. Unsurprisingly, interest in eVTOL aircraft has


been gaining traction due to their applications and potential benefits, which include not only passenger transport via air taxi – a Sita report predicts that flying taxis will be abundant at international airports by 2032 – but also the transportation and delivery of goods,medical and humanitarian assistance, and even firefighting. However, while the concept is exciting, UAM


is not without its challenges. eVTOL aircraft must operate in complex airspace and over congested urban areas, which means the need for reliability and redundancy is vital. Additionally, composites technology is critical to the development and growth of this market, as very strong yet lightweight materials are required to enable them to fly maximum distances with minimal electric power.


POTENTIAL PITFALLS Key to the success of these aircraft is the use of multiple electricmotors which are both highly reliable and power dense. The route to achieving power density in electric machines has historically been to operate permanentmagnet motors (PM) at higher speeds, often in excess of 10,000rpm. However, to become useful for air mobility aircraft and to reduce noise – a critical factor for UAM – these speeds need to be geared down by as much as seven times. Conventionally this introduces the requirement for a mechanical gearbox, raising the issues of


4


reliability, wear, maintenance and noise. NASA has been driving UAM development


for years. In 2018 the agency embarked on a programme which identified magnetic gears as being a potential technology for electric aircraft. While the original focus was on pure magnetic gears, a 2020 NASA paper titledOuter StatorMagneticallyGearedMotorsforUrban AirMobilityVehiclesstated that the concentric combination of a magnetic gear and a permanent magnet motor would be ideal for UAM aircraft, concluding that magnetically geared motors are a highly effective solution to preventing the pitfalls of a mechanically geared high-speed electric motor. Additionally, magnetically geared motors are key to ensuring efficiency.


MAGNETIC GEARS IN PRACTICE Magnomatics’ revolutionary magnetic gears have been implemented in a range of innovative industry solutions, including offshore wind, marine propulsion, and light rail. Having achieved success at large scale the company has turned its attention tomuch smallermachines, including drives for eVTOL aircraft. The company’s patented Pseudo Direct


Drive (PDD) consists of amagnetic gearmounted inside a stator and is designed to overcome the torque limitations of conventional direct drive electricalmachines. The outermagnetics of the magnetic gear are attached to the inner bore of the stator, and copper windings in the stator are used to drive the inner rotor of themagnetic gear. This is a relatively high-speed electric motor


with a relatively low load, which results in low currents and, hence, low temperatures. This in turn ensures great efficiency, long life, and prevents demagnetisation of the outer magnet


4 DESIGN SOLUTIONS SEPTEMBER 2023


science fiction, flying cars are becoming a reality thanks to the solutions being developed by large aerospace manufacturers and innovative startups.


David Latimer, deputy chair of Magnomatics, looks at the


role innovative


magnetically geared motors play in the pursuit of electric flight


array. The torque in the inner rotor is then geared up in the novel polepiece rotor, typically by between 5 and 10:1. The result is a very compact and highly efficient electric motor, which is perfect for the UAM market. The benefits of innovativemagnetically geared


motors such as PDD against conventional generator technology, particularly for electric aircraft, are drastic reductions in motor size, no minimum cooling requirements, and reduced maintenance requirements. Efficiency is also improved as there are no gearbox losses and, of course, gear wear is eliminated altogether. The capabilities of UAM solutions are increasingly and


successfully being tested. Themany thousands of


hours of test flights having been conducted to date


continue to highlight the potential of electric aircraft to improve air


mobility by moving people and cargo more


quickly, quietly, and cost effectively. The lower mass and compactness of the


PDD generator, when combined with partial load superior efficiency, low speed, high torque technology and improved reliability, makes it ideal for the innovative UAM market, helping it move rapidly from the realm of science fiction to reality.


Magnomatics www.magnomatics.com


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