Siemens and Emrax claim best power to weight ratio for electric motors in the 5 to 10 kilowatt per kg range

Siemens researchers have developed a new type of electric motor that, with a weight of just 50 kilograms, delivers a continuous output of about 260 kilowatts – five times more than comparable drive systems. The motor has been specially designed for use in aircraft. Thanks to its record-setting power-to-weight ratio, larger aircraft with takeoff weights of up to two tons will now be able to use electric drives for the first time. To implement the world-record motor, Siemens’ experts scrutinized all the components of previous motors and optimized them up to their technical limits. New simulation techniques and sophisticated lightweight construction enabled the drive system to achieve a unique weight-to-performance ratio of five kilowatts (kW) per kilogram (kg). The electric motors of comparable strength that are used in industrial applications deliver less than one kW per kg. The performance of the drive systems used in electric vehicles is about two kW per kg. Since the new motor delivers its record-setting performance at rotational speeds of just 2,500 revolutions per minute, it can drive propellers directly, without the use of a transmission.

The key to electric plane performance is still the energy density of the batteries or other power storage. The weight of the batteries tends to outweight the motor by about one hundred to one.

Industrial electric motors used in heavy machinery that produce less than 1 kW per kilogram, or even to more efficient electric motors for vehicles that generate around 2 kW per kilogram.

Emrax electric motors claim about 8 to 10 KW per kg. It would be interesting to know if all power and weight metrics are being consistently specified.

EMRAX motor is a completely new type of pancake axial flux brushless synchronous three phase AC (Alternating Current) electric motor. It can also work as a generator – technical data are the same – either EMRAX is used as a motor or as a generator.

March 2015: Prototype EMRAX 348 is cooming (1200 Nm /350 kW at 3000 RPM, weight 42 kg, diameter 348 mm, length 107 mm, IP65). First prototype will be ready for testing in next few months. Also we are preparing documentation for EMRAX 348T, which can deliver power 600 kW, torque 2400 Nm, weight 70 kg, dimensions: dia 348 mm length 170 mm.

Here is an Emrax electric motor manual

Here are some tables of power to weight ratio for non-electric and electric motors

Superconducting electric engines and motors might eventually be able to achieve 40-80 kilowatts per kilogram of power to weight.

There was a design of vertical takeoff and vertical passenger electric planes. Also, Elon Musk has talked about creating a supersonic certical takeoff and vertical landing electric passenger plane. This would enable airports without runways to be in cities. The design was based upon batteries that had 1000 wh/kg and superconducting engines that had 7-8 kw/kg.

Before 2020 it would seem we are on track for volume production of lithium sulfur, lithium seawater and other forms of high energy density batteries (600 wh/kg to 1500 wh/kg).

The superconducting engines seem to be farther away but appear to be feasible. Superconducting wire will be scaling up production and getting to lower cost over the next few years and continuing to improve in production volume and costs over the next decades. In 20 years, the superconducting engines with 7-8 kw/kg or better could be achieved.

The commercial status of superconductors for various applications was reviewed for a 2013 conference in Spain.

The solar Impulse 2 website is here

The Solar Impulse 2 had four electric motors powered from solar cells and 4 x 41 kWh lithium-ion batteries (633 kg), providing 13 kW, electric motors (17.4 HP) each. In March 2015, Piccard and Borschberg began a circumnavigation of the globe with Solar Impulse 2, departing from Abu Dhabi in the United Arab Emirates. The aircraft is scheduled to return to Abu Dhabi in August 2015

SOURCES – Siemens, Wikipedia, solarimpulse