Airbus E-Fan: Building a Better Electric Motor

Since the earliest days of powered flight, propulsion technology has mattered more than anything else in humankind's quest to break the bonds of earth and rise triumphantly into thin air.

For the Wright Flyer it was a 180-pound, 12-horsepower gasoline piston engine built by Orville and Wilbur's trusty mechanic, Charles ­Taylor. For the P-51D Mustang, the mighty Rolls-Royce Merlin V-12 did the honors. In the case of Concorde, four twin-spool afterburning Olympus 593 turbojets made supersonic commercial air travel a reality.

It stands to reason, then, that before the profound shift to electric-powered flight can become an everyday reality, we'll first need a breakthrough in electric propulsion technology, transforming electric airplanes from mere aeronautical curiosities to practical means of long-range transportation.

German engineering firm Siemens may have hit upon just such a technological innovation with a new high-output electric motor to power bigger airplanes, with maximum takeoff weights of 4,000 pounds.

Weighing in at a little over 100 pounds and with an impressive power-to-weight ratio of 5-to-1, the latest electric aero motor from Siemens delivers a continuous output of 260 kilowatts (the gasoline-piston engine equivalent of about 350 hp), compared with just 60 kW for the electric motor tested in flight by Siemens, Airbus and Diamond Aircraft in an HK36 motorglider last year.

To develop the new motor Siemens studied every component of previous motors and optimized each to their technological limits. New simulation techniques and lightweight construction, the company says, enabled the drive system to achieve its unparalleled performance of 5 kilowatts per kilogram. Comparable motors used in industrial applications deliver less than 1 kW per kilogram, while drive systems used in electric cars offer about 2 kW per kilogram.

Also, because the new motor delivers its performance at a rotational speed of just 2,500 rpm, it can drive propellers directly without requiring energy-sapping reduction gears.

"This innovation will make it possible to build series hybrid-electric aircraft with four or more seats" with speed and range similar to those of today's piston-powered light airplanes, says Frank Anton, head of eAircraft at Siemens Corporate Technology, the company's research unit. 

The Siemens motor is scheduled to begin flight-testing before the end of the year. In the next step, researchers say they will attempt to boost output even further.

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