China is also interested in becoming a player in electric aviation and state media reported in 2019 the first flight of a four-seat electric aircraft. The Chinese RX4E aircraft reportedly weighs 1,200 kilograms and can fly up to 300 kilometers on one charge. The plan is that the lightweight carbon fiber aircraft will have an even longer range as advances in battery technology arrive.
The E-Fan X started in 2017 as a joint project between Airbus, Rolls-Royce, and Siemens. E-Fan X was a Hybrid electric aircraft demonstrator being developed by a partnership of Airbus, Rolls-Royce plc, and Siemens.
A British Aerospace BAe 146 short-haul and regional airliner was used as a flying testbed, with one of its four turbofans replaced by a 2 MW (2,700 hp) electric motor. Airbus was in charge of the project and system integration and built the control architecture. Rolls-Royce adapted the Siemens motor and the fan to the existing jet engine nacelle, and Siemens was responsible for the electric motor and its power electronic control unit, the inverter, DC/DC converter, and power distribution. The goal was an electric fan engine as part of a hybrid system to help reduce fuel consumption and noise while cutting back on CO2 emissions.
“When we launched the E-Fan X project in 2017, we set out with the ambition to push the limits by testing disruptive technologies in a game-changing approach to future aircraft,” said Grazia Vittadini, Airbus Chief Technology Officer in a company news release. “And we did just that: E-Fan X has shattered preconceived notions of what is possible in future flight. This helped us to pave the way for an industry-wide decarbonization movement of which we’re proud to take the lead,” she added.
The first flight of the E-Fan X hybrid was scheduled for 2021 but was canceled in April 2020. Rolls-Royce CTO Paul Stein said in a company media release, “…it has become clear to both parties that the actual requirement to carry out a test flight with all the elements integrated is not critical at this time. As an aircraft, E-Fan X was always designed to be a demonstrator only and never for actual use as a product in service.” Stein added that Rolls-Royce plans to complete ground-testing of the power generation system and that, “…our power generation system can and will be integrated into any future aircraft that is developed requiring a hybrid-electric propulsion system, including a comprehensive flight-test program to ensure that all industry safety requirements are met.”
Vittadini, the Airbus CTO, noted that over the past three years successful E-Fan X milestones included:
- Serial hybrid-electric propulsion: Hybrid architectures, high-voltage systems, and batteries are indispensable technology bricks for several other demonstrator projects across our wider R&T portfolio to diversify power sources. We will continue to develop and mature them at our E-Aircraft System Test House.
- New pathways for disruptive CO2 reduction: Exploring the possibilities—and limitations of—serial hybrid-electric propulsion also opened up inquiry into new technology pathways. Hydrogen is one of them, which is equal parts a huge opportunity as it is a new challenge.
- Future certification and regulatory acceptance: From the start, we have been consistently delighted by our customers’—and indeed, the entire aviation ecosystem’s—overwhelming enthusiasm for E-Fan X. With our research partnerships on hybrid-electric and hydrogen airport infrastructure and operations, we will have laid a foundation for the future industry-wide adoption and regulatory acceptance of alternative-propulsion commercial aircraft.
Going Another Direction
The second point may provide a clue as to why the E-Fan X program was terminated. On September 21, 2020, Airbus announced its new ZEROe hydrogen-powered aircraft project. “As recently as five years ago, hydrogen propulsion wasn’t even on our radar as a viable emission-reduction technology pathway,” said Glenn Llewellyn, Airbus Vice President, Zero-Emission Aircraft in a media release. “But convincing data from other transport industries quickly changed all that. Today, we’re excited by the incredible potential hydrogen offers aviation in terms of disruptive emissions reduction.” According to Airbus calculations, hydrogen has the potential to reduce aviation’s CO2 emissions by up to 50%.
The airbus media released explains that in an aircraft, there are two potential types of hydrogen propulsion: hydrogen combustion and hydrogen fuel cells. Airbus has proposed three different zero-emission “concept” aircraft – known as ZEROe – to investigate hydrogen-hybrid aircraft. They are powered by modified gas turbine engines that burn liquid hydrogen as fuel. They also use hydrogen fuel cells to create electrical power that complements the gas turbine, resulting in a “highly efficient hybrid-electric propulsion system.”
What the abrupt change away from batteries and toward hydrogen seems to signal is that batteries won’t progress fast enough to produce the power and energy densities needed for commercial airliner flight. Even with breakthroughs in solid electrolytes and lithium foil electrodes, Airbus clearly feels like the numbers won’t add up. Lifting an airliner off the ground and sustaining its flight over hundreds or even thousands of miles takes massive amounts of energy—the kind exploited in today's fossil jet fuels, and potentially from hydrogen in the future.