Airbus and Siemens investigate hybrid-electric propulsion systems for low emission aviation

Hybrid-electric aircraft that produce significantly lower emissions than existing aeroplanes could be in the sky by 2030, as a result of a collaboration between Airbus and Siemens.

Siemens 2

The two companies have launched a joint project to investigate various hybrid/electric propulsion systems by 2020, in a bid to determine which are the most technically feasible, and how soon they could be applied to aircraft, according to Martin Nuesseler, head of e-aircraft systems at Airbus.

“We are targeting a significant further fuel reduction on top of the improvements we will reach in the next years by incremental optimisation of existing systems,” he said. “In the years 2030 and beyond our project could gain an additional 30-40 per cent step in carbon fuel reduction.”

Airbus is already working on efforts to investigate electric aircraft, including its E-Thrust project with Rolls-Royce, which has developed a concept vehicle based on distributed propulsion.

E-Thrust: electrically distributed propulsion system concept
E-Thrust: electrically distributed propulsion system concept

The concept centres on a single large gas turbine, which would generate electricity to power six electric fans producing thrust. Such a system could significantly reduce emissions and improve fuel efficiency, and offers scope for greater flexibility in the design of aircraft.

“But what is missing are the technologies to support this idea,” said Nuesseler. “So this is a gap we would like to close with this project, to determine if the technologies are feasible, does the performance support such a concept, and in what timeframe?”

The 200-strong project team will develop prototypes for the different propulsion systems, which will be designed for aircraft of power classes ranging from a few hundred kilowatts up to 10 or more megawatts, said Dr Frank Anton, head of electric aircraft at Siemens Corporate Technology.

“We are looking at all those technologies that in the long run will be able to propel large aircraft, of 60-100 passengers, over distances of around 1000 kilometres,” he said.

The companies expect the aircraft to enter commercial operation by around 2030, he said.

One of the biggest challenges will be in achieving a sufficiently high power to weight ratio for the drive system, said Anton. “The power electronics, electric motors and generators will need to improve by a factor of 10 over and above what is possible today,” he said.

A second challenge will be to make the technology work in the harsh environment of an aircraft, where it will be subject to low temperatures, wind, rain and cloud, said Anton.

“In order to do that we have to look at all sorts of new technologies, including possibly superconductivity for some of the components,” he said.

A further challenge will be in transporting the electric current from the gas turbine in the body of the aircraft to the motors under the wings, without adding too much additional weight. So lightweight cables will be needed to transport the electricity, said Anton.

Siemens last year unveiled a 50 kilogram electric motor with a power output of 260 kilowatts, or enough to power a 2-tonne, four-seater electric aircraft when used in conjunction with a small jet engine. This motor has a power to weight ratio of 5kW/kg, or a factor of five higher than existing industrial motors.

Since then the company has begun installing the motor into a flying testbed, in order to investigate how it performs in flight. The technology is also being scaled up to larger motors of around 1MW, as part of the collaboration with Airbus.

Initially though, one of the project’s first priorities will be to find the right electrical and technological standards for electric aircraft, said Nuesseler. “Today there are lots of small projects going on, which have made their own assumptions on what kind of technologies and voltage levels work, and these cannot be brought together consistently,” he said. “So the first step will be to define the right standards to push the technologies forward.”