1MW Motor Innovation: MIT Engineers Develop Solution for Electric Aviation Challenges
Moving an aircraft through the air takes a lot of power—engineers at MIT are developing an electric motor that might be able to do the job.
To overcome aerodynamic drag and tire rolling resistance, a car traveling along a level roadway at 60 mph requires around 20 horsepower (hp) or around 15 kilowatts (kW). The thrust created by the interaction of the tires and the roadway propels the car forward—for an average car, that might be around 165 pounds of thrust at 60 mph. Traditional internal combustion engines convert fossil fuels into that thrust at an efficiency of less than 25 percent.
The electrical motor MIT engineers designed could help electrify aviation. Image used courtesy of Airbus via MIT
Electric vehicles (EVs) store energy from other sources (wind, solar, nuclear, or fossil fuel) and return it to an electric motor with an efficiency of around 90 percent. Battery technology has taken some time to reach energy density levels at a low enough cost to allow affordable EVs to travel reasonable distances, but its day has arrived.
One of the next major challenges is the electrification of aviation. The challenges are significant—not the least of which is the requirement for thrust to be produced by moving air with a propellor or using a ducted fan or turbofan. Creating the same 165 pounds of thrust at 60 mph for our average car using a six-foot diameter propellor would require a motor capable of producing approximately 2,332 horsepower. Aircraft have much lower aerodynamic drag coefficients than land-based vehicles; however, it is clear that if aviation is to be electrified, it will require some very powerful electric motors.
Massachusetts Institute of Technology (MIT) engineers are creating a 1-megawatt (MW) electric motor at a size and weight that could allow it to be used on commercial airliners. Electric aviation so far has been limited to small commuter-scale aircraft and electric vertical take-off and landing (eVTOL) designs powered by electric motors capable of producing several hundred kilowatts.
Major aircraft manufacturers like Boeing and Airbus hope to build larger-scale commercial aircraft by 2035, requiring innovative electric propulsion systems on the megawatt scale.
A one-megawatt electric motor produces 1,341 horsepower.
Megawatt-sized electric motors are not the largest in the world. Maritime motors powered by electricity have been constructed to produce more than 35 MW; however, these huge electrical devices are extremely heavy and impractical for use in aviation.
Major aircraft manufacturers hope to build larger-scale commercial electric aircraft. Image used courtesy of Pexels
According to MIT, the key is to co-optimize individual components and make them compatible while maximizing overall performance. An electric motor generates a magnetic field through its copper coils, and a magnet near the coil reacts to that magnetic field spinning in a direction that can be used to propel an EV or spin a propellor. In general, the way to make an electric motor more powerful is to make it larger, requiring more copper and making the motor heavier. Larger motors also produce more heat requiring additional cooling elements, which further increase the weight and the space needed to contain the propulsion system—a disadvantage on an aircraft. Building a better, more powerful motor for an electric aircraft requires innovation in materials, manufacturing, thermal management, structures and rotor dynamics, and power electronics.
MIT’s Aviation Solution
The MIT electric aviation solution consists of a high-speed rotor lined with magnets oriented with varying polarity. The MIT engineers have designed a compact low-loss stator that fits inside the rotor and contains an intricate array of copper windings. An advanced heat exchanger and a distributed power electronics system, made from 30 custom-built circuit boards, control the current running through the copper windings to control the motor speed and power output. According to MIT, the electric motor is about the size of a standard checked suitcase, as is the power electronics system. Altogether the system weighs less than an adult passenger.
MIT engineers worked carefully to integrate the various parts so that, for example, the distributed circuit boards are closely placed next to the electric motor to minimize electrical transmission loss and provide air cooling through the integrated heat exchanger.
Are Hybrids the Answer?
Although hydrogen fuel cell batteries could power the MIT megawatt electric motor, a hybrid gas-turbine aero engine could be a practical solution. A synthetically fueled gas turbine could provide the necessary power for takeoffs, while a megawatt-scale electric motor co-located on the turbine shaft could provide power during cruising. It could also offer regenerative energy to help recharge onboard storage batteries during descent and landing.
The MIT team has been working on each element of the megawatt motor individually, with plans to assemble the first working version and begin testing it in the fall of this year.