MIT aeroengineers are creating a 1-megawatt electrical motor that is a stepping stone toward electrifying commercial airliners. Pictured are some industrial concepts for hybrid-electric aircraft. (Image: @Airbus SAS 2023)

Aerospace engineers designed a 1-megawatt electrical motor that is a stepping stone toward electrifying the largest aircraft.

Aviation’s huge carbon footprint could shrink significantly with electrification. To date, however, only small all-electric planes have gotten off the ground. Their electric motors generate hundreds of kilowatts of power. To electrify larger, heavier jets, such as commercial airliners, megawatt-scale motors are required. These would be propelled by hybrid or turbo-electric propulsion systems, where an electrical machine is coupled with a gas turbine aero-engine.

To meet this need, a team of MIT engineers is now creating a one-megawatt motor that could be a key stepping stone toward electrifying larger aircraft. The team has designed and tested the major components of the motor and shown, through detailed computations, that the coupled components can work as a whole to generate one megawatt of power, at a weight and size competitive with current small aero-engines.

For all-electric applications, the team envisions the motor could be paired with a source of electricity such as a battery or a fuel cell. The motor could then turn the electrical energy into mechanical work to power a plane’s propellers. The electrical machine could also be paired with a traditional turbofan jet engine to run as a hybrid propulsion system, providing electric propulsion during certain phases of a flight.

No matter what we use as an energy carrier — batteries, hydrogen, ammonia, or sustainable aviation fuel — independent of all that, megawatt-class motors will be a key enabler for greening aviation,” said Zoltan Spakovszky, the T. Wilson Professor in Aeronautics, and the Director of the Gas Turbine Laboratory (GTL) at MIT, who leads the project.

To prevent the worst impacts from human-induced climate change, scientists have determined that global emissions of carbon dioxide must reach net zero by 2050. Meeting this target for aviation, Spakovszky says, will require “step-change achievements” in the design of unconventional aircraft, smart and flexible fuel systems, advanced materials, and safe and efficient electrified propulsion. Multiple aerospace companies are focused on electrified propulsion and the design of megawatt-scale electric machines that are powerful and light enough to propel passenger aircraft.

“There is no silver bullet to make this happen — the devil is in the details,” Spakovszky said. “This is hard engineering, in terms of co-optimizing individual components and making them compatible with each other while maximizing overall performance. To do this means we have to push the boundaries in materials, manufacturing, thermal management, structures and rotordynamics, and power electronics.”

Electric machines have been around for over 150 years, with the understanding that the bigger the appliance or vehicle, the larger the copper coils and the magnetic rotor, making the machine heavier. The more power the electrical machine generates, the more heat it produces, which requires additional elements to keep the components cool — all of which can take up space and add significant weight to the system, making it challenging for airplane applications.

“Heavy stuff doesn’t go on airplanes,” Spakovszky says. “So, we had to come up with a compact, lightweight, and powerful architecture.”

As designed, the MIT electric motor and power electronics are each about the size of a checked suitcase weighing less than an adult passenger.

The motor’s main components are: a high-speed rotor, lined with an array of magnets with varying orientations of polarity; a compact low-loss stator that fits inside the rotor and contains an intricate array of copper windings; an advanced heat exchanger that keeps the components cool while transmitting the torque of the machine; and a distributed power electronics system, made from 30 custom-built circuit boards, that precisely change the currents running through each of the stator’s copper windings, at high frequency.

“I believe this is the first truly co-optimized integrated design,” Spakovszky said. “Which means we did a very extensive design-space exploration where all considerations from thermal management to rotor dynamics, to power electronics, and electrical machine architecture were assessed in an integrated way to find out what is the best possible combination to get the required specific power at one megawatt.”

As a whole system, the motor is designed such that the distributed circuit boards are close coupled with the electrical machine to minimize transmission loss and to allow effective air cooling through the integrated heat exchanger.

“This is a high-speed machine, and to keep it rotating while creating torque, the magnetic fields have to be traveling very quickly, which we can do through our circuit boards switching at high frequency,” Spakovszky said.

To mitigate risk, the team has built and tested each of the major components individually, and shown that they can operate as designed and at conditions exceeding normal operational demands. The researchers plan to assemble the first fully working electric motor and start testing it in the fall.

Once the MIT team can demonstrate the electric motor as a whole, they say the design could power regional aircraft and could also be a companion to conventional jet engines, to enable hybrid-electric propulsion systems. The team also envisions that multiple one-megawatt motors could power multiple fans distributed along the wing on future aircraft configurations. Looking ahead, the foundations of the one-megawatt electrical machine design could potentially be scaled up to multi-megawatt motors, to power larger passenger planes.