Rolls-Royce (www.rolls-royce.com) has taken a significant step towards providing hybrid-electric propulsion systems for the next generation of aircraft, with successful ground tests in Indianapolis of a hybrid system using its M250 gas turbine — originally developed to power helicopters.

The tests are part of one of the world’s most comprehensive hybrid aerospace turbine engine development and integration programmes, paving the way for experimental flights on aircraft in 2021.

Rolls-Royce successfully tested the hybrid version of the M250 gas turbine recently in three operating modes: Series Hybrid, Parallel Hybrid and Turbo-Electric.

The M250 hybrid is planned to be used as a propulsion plant with power ranging from 500kW to 1MW; it has the potential to transform aviation power.

It will be used across a range of transport platforms to enable distributed electric propulsion, including EVTOLs (hybrid electric vertical take-off and landing vehicles), general aviation aircraft and hybrid helicopters.

Mike Mekhiche, deputy director of Rolls-Royce Electrical, said: “Rolls-Royce has always been a pioneer in aviation, and one of the key elements of our strategy is to champion electrification across all our businesses.

"The successful testing of the hybrid M250 system is an important step forward in providing a hybrid-electric propulsion system that will enable a new class of quieter and cleaner air transport.”

Rolls-Royce engineers based in the USA, the UK and Singapore have developed this engine into a hybrid-electric propulsion system.

The M250 gas turbine engine has powered more than 170 varieties of fixed-wing military, civilian aircraft and helicopters since its initial development.

Rolls-Royce selected this engine for its maturity, power density, ease of maintenance, and high reliability.

In the last 50 years, M250 variants have logged more than 250 million flight hours, and nearly 33,000 M250 engines have been delivered to customers.

Dr Mekhiche said: “Electrification is one of the most exciting developments in aviation since the birth of the jumbo jet.

“We are determined to use our pedigree in aerospace to be at the forefront of developing innovative propulsion systems to meet the needs of the next chapter in aviation.

"When this happens, it’s going to transform the way aero transport is designed and produced, reducing the time required to travel, revolutionising cargo delivery and changing the way we design our cities and infrastructure.”

The Rolls-Royce hybrid electric propulsion system demonstrator integrates an M250 gas turbine engine with a high-energy-density battery system, electric generators, power converters and an advanced power management and control system.

The power management system optimises the overall propulsion performance in order for the system to be suitable across a variety of platforms, including EVTOL, while delivering efficiency gains, reduced noise and lower emissions.