H3X’s 33-kW (44-hp) integrated electric motor drive is just more than 5 in. in diameter.

U.S. startup H3X is beginning deliveries of a high power-density electric motor to customers for testing in aerospace and defense applications, including electric aircraft.

The HPDM-30 integrated motor drive weighs 4.1 kg (9 lb.) and has been tested at up to 33 kW continuous power, suitable for use in uncrewed aircraft and smaller vehicles.

Denver-based H3X is developing advanced radial-flux permanent-magnet motors that use novel materials and manufacturing to maximize power density. The startup is targeting 10 kW/kg for the integrated motor and inverter/controller. This compares with power densities of up to 5 kW/kg for existing aircraft electric motors.

H3X is working under the first phase of a NASA small-business innovation research contract to design a motor to power a 25%-scale model of the Subsonic Single Aft Engine (SUSAN) concept. SUSAN is a design for a 180-seat aircraft with 750-mi. economic range and a hybrid-electric powertrain comprising a single aft turbofan producing thrust and generating electrical power for distributed wing-mounted engines.

The startup also is working with the U.S. Air Force’s AFWerx innovation arm to characterize the performance of its HPDM-250 integrated motor drive demonstrator. This produces 250 kW peak power with a power density of up to 15 kW/kg in direct-drive configuration. The goal is to flight-test the motor, replacing one of the powerplants on an existing twin-engine aircraft, says Max Liben, H3X co-founder and chief technology officer.

H3X’s first product, the HPDM-30, uses the same core motor technology as the HPDM-250 demonstrator but has a different inverter. The motor drive is designed to be scalable to 120 kW, the fast-switching silicon-carbide inverter covering the full power range, Liben says. “We initially planned not to go smaller than 250 kW, but there was so much demand from various sectors for a smaller motor drive.”

In H3X’s motor, the magnetic core is made from laminated steel sheets that are stamped, stacked and bonded together to produce the rotor and stator. “We achieve a high stacking factor of more than 98%, which means the finished core is 98% steel and 2% adhesive,” he says. 

The startup also achieves a high copper fill factor and high thermal conductivity in the motor windings, enabling high current densities that produce more force. “We fill the slots with as much copper as we physically can. Thermal conductivity within the copper is 5-10 times better that the state of the art,” Liben says. “Air is a bad conductor, so we remove as much as we can and replace it with a good conductor. It’s a challenging materials problem.” Motor and inverter have integrated liquid cooling.

Beyond the HPDM-30, H3X plans to develop a 200-kW motor drive for aerospace applications as well as a multisector design that will be available in configurations with 2-12 segments producing up to 2.8 megawatts of continuous power with a power density of more than 12 kW/kg. 

In the multi-sector design, the 200-kW motor is “unrolled” into an arc segment that then is replicated: four segments will produce 800 kW of continuous power. The design provides significant fault tolerance, Liben says. Each sector has an independent three-phase inverter and winding. After a single inverter or winding failure, a two-sector motor will still produce half power; a 12-sector motor will lose only 1/12th of its power, he says.

As the motor is scaled up, its output speed drops. The 200-kW motor will run at 20,000 rpm and require a gearbox. An 800-kW motor will operate at 5,000 rpm without a gearbox. “Megawatt-class systems to power aircraft will likely directly couple to the propulsor,” Liben says, adding the motor drives can then be stacked together on the same shaft to produce multimegawatt systems capable of powering single-aisle commercial aircraft.  

Graham leads Aviation Week's coverage of technology, focusing on engineering and technology across the aerospace industry, with a special focus on identifying technologies of strategic importance to aviation, aerospace and defense.

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