22 Jul 2024


Record-breaking motor is ‘five times more powerful’

Researchers at Siemens have developed an electric motor that weighs just 50 kilograms, yet delivers a continuous output of about 260kW – about five times more than conventional drive systems of a similar weight.

The motor has been designed especially for use in aircraft. Its record-setting power-to-weight ratio will allow aircraft with takeoff weights of up to two tonnes to use electric drives for the first time.

To develop the new motors, Siemens’ experts scrutinised all of the components used in earlier motors and optimised them to their technical limits. New simulation techniques and sophisticated lightweight construction have resulted in a drive system with a power-to-weight ratio of 5kW/kg. Conventional industrial motors of a similar power rating deliver less than 1kW/kg, while drive systems used in electric vehicles achieve about 2kW/kg.

The new motor, which is scheduled for flight-testing before the end of 2015, is designed to operate at 2,500 rpm, allowing it to drive aircraft propellers directly, without needing gears.

As part of the development programme, experts from Siemens’ Large Drives and Corporate Technology divisions cut the weight of the motor’s end-shield from 10.5kg to 4.9kg. This aluminium component supports the motor bearing and the propeller, which is fixed to a continuous drive shaft. “It’s subject to very large forces whenever the nose of the aircraft moves up or down, so it’s an absolutely vital component for the safety of the aircraft,” explains Frank Anton, head of Siemens’ eAircraft operation. “That’s why, in the past, it was always pretty solid and therefore correspondingly heavy.”

The researchers have now have come up with a prototype end-shield made of carbon fibre-reinforced polymers that weighs just 2.3kg – less than a quarter of a conventional component.

The use of a cobalt-iron alloy in the motor’s stator results in high magnetisability, while the permanent magnets in the rotor are arranged in a so-called Halbach array. Four magnets are positioned next to each other so that the orientation of each field is in a different direction. One result of this is that magnetic flux can be directed optimally with a minimal use of material.

A new cooling concept has also helped to cut weight. “Because of the high current density, we needed a smart way of dealing with the waste heat,” Anton explains. “We use direct-cooled conductors and directly discharge the loss of copper to an electrically non-conductive cooling liquid – which in this case can be, for example, silicone oil or Galden.”

The new motor is powerful enough to propel a four-seater hybrid-electric aircraft and not far short of being sufficient for a regional airliner, which will need 500kW–2MW of power. Such aircraft will reduce not only CO2 emissions but also noise.

“We’re convinced that that the use of hybrid-electric drives in regional airliners with 50–100 passengers is a real medium-term possibility,” Anton says.


Airlines operating such aircraft will benefit from cost savings. “Kerosene accounts for over 50% of an aircraft’s lifecycle costs,” Anton explains. “The use of hybrid electric drives would reduce fuel consumption by around 25%, with the result that the total costs of an aircraft would fall by about 12%.”

This is because an intelligent hybrid drive combining an electric motor and a combustion engine can use turbines that not only are much smaller than today’s, but can also be operated continuously at peak efficiency during flight. Today’s turbines, by contrast, are designed to deliver a maximum level of power that is needed only during takeoff and ascent. At other times, they need only 60% of their maximum output.

“With a kerosene-electric hybrid drive system, the turbine would run continuously at optimum power and provide energy, via a generator, for the electric motor powering the propeller,” Anton explains. “During takeoff, extra energy would be provided by a battery.”

Anton reckons that Siemens is a least three years ahead of others developing lightweight motors for aviation. The company is now working with Airbus to turn this vision of electrically-powered flight into reality. Under a 2013 cooperation agreement, Siemens is focusing on the electric drive systems, while Airbus is working on new aviation concepts. If the engineers can develop motors that are even lighter and more powerful, the first 60–100-seater aircraft with a hybrid electric drive could be ready for takeoff by 2035.