Rolls-Royce has agreed to acquired Siemens' electric and hybrid-electric aerospace propulsion activities, furthering a stated ambition to play a "major role in the third era of aviation".

The transaction is set to be completed in late 2019, says the UK engine marker, without disclosing financial details.

Siemens' eAircraft business employs around 180 electrical designers and engineers across locations in Germany and Hungary.

R-R, Siemens and Airbus have been partners on the hybrid-electric E-Fan X demonstrator programme.

Under that effort, one of a BAe 146 regional jet's four turbofans will be replaced with an electric fan – powered by a combined gas turbine and electric generator in the aircraft's cabin – for flight tests scheduled to begin in 2021.

However, R-R and Siemens have been rivals in another, separate effort to propel high-performance single-engine aerobatic aircraft with battery-powered electric motors.

The acquisition will provide the UK manufacturer with "increased scale and additional expertise", states R-R Electrical director Rob Watson.

He argues that existing aircraft electrification efforts represent "the dawn of the third era of aviation" – after the advent of powered flight and introduction of the jet engine – and adds: "This [acquisition] will accelerate our ambitions in aerospace by adding vital skills and technology to our portfolio."

R-R chief technology officer Paul Stein identifies electrification as one of the manufacturer's focus areas as it seeks to reduce aviation's environmental impact – alongside programmes to improve the efficiency of gas turbine engines, and employment of biofuels.

“We believe that pure electric, or all-electric, propulsion will power smaller aircraft in the foreseeable future, while larger aircraft will rely upon hybrid-electric solutions that combine electrification with evolutions of the gas turbine," Stein states.

But he adds that building up electrical engineering skills will be "a vital part of the future of R-R".

The Derby-based manufacturer says that it will "look for opportunities" to work with Siemens in future on efforts to improve sustainability.