Electric motors for aircraft | Deep insight E-Mobility Engineering | September/October 2023 59 for the laminations of the stators, to reduce weight and reduce eddy current losses with thinner layers to achieve the same effect as thicker steel. Motors “One of the great impediments to motors in aerospace is the power density and continuous power output, rather than the duty cycle,” says David Sercombe, project lead for the 350 and 650 kW motor programmes at MagniX. “The motor is then a primary structure, or it should be if you are to save weight. “So the development involves materials and effective motor cooling, and that’s where a lot of our IP has been developed. Then come the structure, bearings and mounts that make a motor suitable for a long life in an aircraft.” The company is working with Eviation on Alice, a ground-up design for a nineseater electric aircraft with a range of 250 nautical miles and using two 700 kW motors. “The first step is to get the technical balance right. The next is taking that through flight trials and certification,” Sercombe says. “We have flown on five platforms, which gives direct experience of how the motor performs in the air when it interacts with all the systems and going back through the inverter and the controllers. We couple that with R33 [an FAA method of compliance to support certification of advanced flight controls] for a path to certification. Then it is a case of looking at the endurance, the interaction with a series of propellers, and what novel faults might occur.” Novel faults “One thing is to have dual or quadstyle systems with multiple segments so that faults can be isolated,” Sercombe says. “This is important, as in most applications you can glide or autorotate, but the ability to still produce power is desirable. “At the same time, we learn from the failure modes in other industries, so we can continue with as much Motor technology She adds, “The core of the motor and the electronics were developed 5 years ago, and since then it has been all about proving the development, working with the regulator and proving the compliance. The next stage will be writing the test plans and getting them approved. “At the moment, nothing is certified for a passenger commercial aircraft, so that is the vast majority of what we do. “We are not chasing the next kilo of weight, we have the motor and electronics at the point where we are happy with it, so it’s about getting the system into service. The certification hurdle is huge, and you can’t be changing the design every 3 months. Aerospace is a very different environment to any other industry, and that really makes it more conservative.” Other suppliers share that view. Arnold for example is working on r&d and design of the various motor technologies, from rotors and stators to sleevings. Its aerospace experience means it knows what is likely to be approved, making sure it is possible to manufacture the designs, and that the required strength of magnet exists. Arnold has at least one project moving to the next phase, with orders, and in the direction of approval. However, for rotor manufacturing it has not yet been able to put the carbon fibre sleeving through the FAA certification process, and these are integral to the rotor assembly. Customers then develop their own stators and present the entire motor for approval. While Inconel or stainless steel have been used for years for rotors and stators, carbon fibre is lighter and has lower inductive losses, so electric aircraft have every incentive to adopt the technology. Once the technology is approved for smaller electric aircraft then the larger companies are more likely to look at it, says Arnold. Some are also using Arnold’s nongrain oriented silicon thin steel material MagniX is working on motor designs targeting 350 and 650 kW of power – this is the 650 kW version (Courtesy of MagniX)
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