62 September/October 2023 | E-Mobility Engineering by the computational algorithm and FEA, showing that the demonstrator’s rated torque will meet the design specification. Another 1 MW motor has been developed by Wright Electric. This was shown at this year’s Paris Air Show and will be tested at altitude in the NASA Electric Aircraft Testbed (NEAT). The system can be used as a motor or generator, enabling it to be configured as a turbo-generator or auxiliary power unit for high-altitude power. “Achieving 1 MW, specifically of shaft power, is an important step in achieving zero-emissions single-aisle flights of under 800 miles,” says Jeff Engler, founder and CEO of Wright Electric. “Commercial-class airplanes need megawatt-sized propulsion systems for a full passenger load at take-off. At the NEAT facility the motor will be tested at up to 40,000 ft.” The plan is to use the motor for the Wright Spirit. This is based on the BAe 146 four-engine aircraft to carry up to 100 passengers on flights of up to an hour. The company has been proving system components including a high efficiency, high power density inverter and a 2 MW motor. The Joint Technical Assessment Phase on the propulsion system includes Honeywell for the turbogenerator and fuel cells as well as the use of test facilities and aircraft, along with infrastructure and batteries from Eaglepitcher Technologies. The motor is currently being tested at 1.5 MW with a power of 2.25 MW for emergency take-offs to meet certification requirements. The plan is for flight testing with one all-electric engine this year, progressing to a full four-engine, zeroemissions flight of the 100-passenger, aircraft by 2026. Motor acoustics Greenjets is developing high-power motors for eVTOL and larger aircraft. It is using a mixture of additive manufacturing and traditional techniques for a motor design that can be scaled up. The company is part of the InCEPTion project in the UK to develop an ultraquiet motor by focusing on the design of the impeller blades of a turbine, to avoid audible frequencies from eVTOL designs that people find annoying. There are many metrics for quantifying noise that will have an impact on community acceptance, not just amplitude but also pitch and tonality. The level of sound, measured in ‘A-weighted decibels’ (dBA), adjusts the decibel values to take account of the frequencies the human ear is most sensitive to. Conventional helicopters are the benchmark for comparison with eVTOL noise, owing to their similarity in operation, and as such, predicted noise levels are often described as fractions of helicopter noise. A greater number of distributed motors reduces propeller diameter, decreasing tip speeds and improving the noise characteristics. While some aircraft developers report a noise value, few describe the conditions under which this noise would be recorded, such as the distance to the microphone and flight mode. A small sample of eVTOL aircraft shows noise levels from 60 dBA on takeoff and landing to 75 dBA in flight. In comparison, a four-seater Robinson R44 helicopter produces an overflight noise of about 80 dBA. The strongest evidence of eVTOL noise performance comes from a collaboration between Joby and NASA, which used a field array of more than 50 microphones to record noise at numerous flight speeds and altitudes. In cruise at 500 m overhead, the research confirmed a noise level of 45 dBA, with take-off and landing noise calculated as 65 dBA from 100 m. Another motor designer, Helix, has a unit called the SPX177, which provides 650 kW of continuous power but is aimed at automotive designs. “We needed an architecture that minimises losses and the heat generated, especially at high speed, which meant quite a change in the way the motor was wound, since minimising resistance losses results in a very low inductance machine,” says Helix chief engineer and project leader Derek Jordanou-Bailey. “The switching in the inverter can generate lots of noise and harmonics, which is more challenging with a lowinductance motor.” “The SPX177 weighs 41 kg, including the 13 kg inverter,” he says. “It is a dual three-phase motor, so its current is shared across two inverters – a necessary approach to meet the phase current demands at ‘normal’ DC voltages at this extremely high power level. “Six high-voltage cables connect the inverter to the motor, while an LV connector carries the various control signals.” The motor produced more than NASA is working with GE Aviation and MagniX to support its Electric Powertrain Flight Demonstration (Courtesy of NASA)
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