Rolls-Royce is concluding work on a ground-based testbed to evaluate requirements for electric and hybrid-electric aircraft propulsion systems. According to Olaf Otto, customer director at the aircraft engine maker’s Electrical division, the group is “firmly focused” on future opportunities in this sector following its acquisition of Siemens's eAircraft business.
The ground test rig was developed in partnership with Cranfield University’s Aerospace Integration Centre. Rolls said it has never intended to use it for flight testing.
In late 2019, UK-based Rolls-Royce acquired the eAircraft electric motors unit of Germany’s Siemens group for an undisclosed sum, adding 180 electric propulsion specialists into the group. At the time, this move appeared to be linked to its plans to advance electric propulsion for larger aircraft through programs such as the E-Fan X cooperation with Airbus, but this project was abandoned in April 2020 before reaching the planned flight test stage. The program had received a significant share of £255 million in UK government funding announced in July 2018 by the Department for Business, Energy & Industrial Strategy and channeled through the Aerospace Technology Institute and UK Research and Innovation.
The E-Fan X project involved the development of a hybrid-electric technology demonstrator based on the four-engined BAE 146 regional jet. “On the E-Fan X program, we have created a hybrid-electric generation system at a scale never previously seen in our industry, comprised of an embedded AE2100 gas turbine driving a 2.5-MW generator and a 3,000-volt power electronics and electric propulsion unit,” Otto told FutureFlight. Having decided against proceeding to flight test the E-Fan X system, he said that the company is now “going through a short period of re-planning due to this decision to make sure we properly capture all the lessons, knowledge, and associated intellectual property.”
According to Otto, the acquisition of the Siemens eAircraft business has positioned Rolls-Royce to “firmly focus our efforts on developing all-electric and hybrid-electric propulsion system technology across a range of aircraft including eVTOLs.” He said that the group is looking to forge strategic partnerships with aircraft developers and other systems suppliers and has established an urban air mobility unit to address this sector.
Through the acquisition of the Siemens unit, Rolls-Royce is now a partner in Eviation Aircraft's Alice all-electric fixed-wing aircraft. However, it was recently replaced by rival Safran as electric motor provider for Bye Aerospace's eFlyer family of electric light aircraft.
In May 2020, Rolls-Royce chief engineer Tim Williams was recruited to the same position with UK-based eVTOL start-up Vertical Aerospace. It is working on an all-electric design designated the VA-1X.
Rolls-Royce has also been part of Airbus’s all-electric CityAirbus eVTOL technology demonstrator program, which has continued test flights in 2020. It provides the electrical propulsion unit and power distribution system for the four-seat design.
The group is also expanding its team of energy storage specialists and stepping up work on battery technology. Otto said that it is aiming to be able to certify batteries in the “sub-MW” class by around the mid-2020s.
However, it would appear that the primary focus of Rolls-Royce’s efforts in this space will be on hybrid-electric propulsion for smaller aircraft in applications such as regional commuter services (certifiable under EASA’s existing CS-23 rules), with the company having concluded that to develop technology for larger aircraft will take much longer.
“With that goal in mind, we are working together with selected airframers to adapt our technology to best fit their needs,” Otto explained. “For us, full system offerings include not only electrical machines but also the power electronics, cooling, cabling and power distribution and protection, and power generation and control systems, as well as energy storage.”
At the same time, the Rolls-Royce group has ambitions to deliver carbon-reducing power solutions beyond aerospace. It is also looking to deliver carbon-reducing power systems for marine, rail, defense, and industrial applications. For instance, the generator developed for E-Fan X program could be applied to domestic electricity supplies. The 2.5 MW unit, which the company said is about the size of a beer keg, could power around 2,500 homes.
The ground testing project at Cranfield is part of this wider effort to optimize configurations for new power systems and address safety issues. Work is continuing at a site in the northern Norwegian city of Trondheim to integrate the generator with Rolls-Royce’s control systems and thermal management systems. This equipment has been developed, respectively, at the company’s facilities at Derby in the UK and Indianapolis in the U.S. The overall Rolls-Royce Electrical team now spans six countries: the UK, the U.S., Singapore, Norway, Germany, and Hungary.
Meanwhile, Rolls-Royce continues to be a leading contributor to UK government-backed efforts to advance environmentally sustainable aviation. It is a partner in the new Project Napkin, backed by the Future Flight fund, which is tasked with developing a blueprint for accelerating and optimizing service entry for sustainable commercial flight. Along with other partners, the company is modeling the interaction and relationships between aircraft, airports, airspace, airlines, passengers, and communities.
Rolls-Royce is active in the UK’s Flight Zero initiative and as part of this is engaged in work to define prospects for hydrogen propulsion for aviation, addressing issues such as weight and storage size constraints. “Timing-wise, small hydrogen-powered aircraft could potentially become available early in the next decade,” said Otto. “Continued research on the effects of high-altitude water vapor emissions is also important to ensure a net positive impact on the environment.”
As a long-established supplier of aircraft propulsion systems, Rolls-Royce is committed to improving existing technology, by pursuing improved environmental performance from its existing Trent family turbofans and advocating for the use of sustainable aviation fuels. In this regard, work on hydrogen, hybrid-electric all-electric propulsion is being conducted as part of a longer-term innovation strategy.
The company is a founding member of the new Jet Zero Council established by the UK government in June 2020. It is represented on this body by its chief technology officer Paul Stein.
Separately, Rolls-Royce is also working on a project called Accel, which involves using a new battery pack to power a light aircraft that it hopes to fly at more than 300 mph to set a new speed record for an all-electric aircraft. The company has tested a full-scale replica of the aircraft’s core, called "ionBird," which includes a 500-hp electric power train and a battery with enough energy to supply 250 homes. The world record attempt is due to be made in early 2021.
