26 n MOTORS May 2024 www.drivesncontrols.com extremely power-dense motors run at high speeds – 10,000s of rpm. The Phasa-35 propulsion motors are not like that; they run at quite modest speeds. It is important to understand what inuences eciency – where the losses occur and why. For example, losses in the electromagnetically active components are aected by the operating temperature. For electrical steels, the losses decrease as the temperature rises. For electrical conductors, it’s the other way around – low temperatures reduce losses. Fortunately, the losses in the conductors dominate, so low temperatures work for us. Shedding heat through good design (electromagnetic and mechanical) reduces the temperature of the motor which, in turn, reduces losses, increasing potential mission capabilities. Commutation Mass and eciency reared their heads again here. We wanted super-lightweight sensors. They don’t come much lighter than digital Hall devices, but these don’t provide the most accurate switching points, leading to losses. Resolvers are often used in harsh aerospace applications, but they are relatively heavy. For this application, we chose an RLS encoder that provides accurate switching, but is also lightweight and has low power consumption. Usually, silicone-based systems won’t operate below -40°C, but with some clever thermal management, the Prismatic team overcame this problem. In February 2020, the Phasa-35 completed its maiden ight in Australia. The data gathered during the ight provided invaluable data, which was used to correlate actual performance with mathematical modelling and ground testing. On 25 June 2023, the Phasa-35 climbed to more than 66,000ft above New Mexico in the US, and held this altitude for about four hours, until sunset, before descending overnight to land rst thing in the morning. This ight has provided more insightful data, which is being used to construct a digital twin, as well as to inform ground-based testing. The rst motors that propelled the aircraft performed as expected. This has resulted in data being fed back into the base model for the motor electromagnetics, which will improve the design of future generations of motors. Since last year’s stratospheric ight, PMW and Prismatic have been working on upgrading the motors. The aim has been to improve the climb rate and eciency at altitude, to stretch mission capabilities even further. It’s been an interesting journey with a potentially patentable development. Hopefully, that will be the subject of another article in a year or two. PMW Dynamics and Prismatic continue to work closely together, modelling, testing, developing and building for the next generation of Phasa-35 propulsion systems – but the specications are highly condential. n One of the Phasa-35 motors being tested on a dynamometer during development. The image on the right shows the motor’s construction. The Phasa-35 aircraft being prepared for take-o
RkJQdWJsaXNoZXIy MjQ0NzM=