Over the last decade there have been numerous studies and research programs—government and industry-funded—as well as work in universities, aerospace academies, and other science-based organizations, looking into alternative powerplant solutions for next-generation civil air transport aircraft that could reduce today’s dependency on oil-based fuels and meet increasingly demanding environmental requirements. These visionary projects often included futuristic-looking proposals that would look the part in any science fiction movie.

In the meantime, the global airline sector has continued to add thousands of aircraft orders to the sales backlogs of the leading aerospace manufacturers, taking the production of existing, conventional designs right though toward the end of the next decade. As long as customers were happy to keep buying no-risk established products it seemed as if there would be little room for any seriously disruptive moves in the civil market any time soon.

But on November 28 in London a new industry-teaming agreement was announced that could lead to one of the most significant shifts in recent times toward the practical application of hybrid-electric technology for commercial aircraft, and a test-bed aircraft will take to the air in just over two years. This partnership between Airbus, Rolls-Royce, and Siemens will develop a near-term flight demonstrator that will combine some of the world’s most expert experience in electrical and propulsion technologies in a modified airframe that will be the largest yet hybrid flying R&D platform.

Introducing the E-Fan X

The new partnership program has been given the title E-Fan X and the propulsion system is to be installed in a modified BAE 146 four-engine jetliner, the design of which is suited for this application with a large cabin, high wing, and easily accessed pylon-mounted underwing engines. It is intended that following extensive ground testing, and provisionally fitted on the 146, it will undergo flight testing from 2020, with one of the standard turbofan engines replaced by a 2-MW electric motor.

Once the maturity of the system has been proven, provision has been made to replace a second gas turbine engine with another electric motor.

Airbus has invested much time and effort in previous electric-powered test aircraft, starting with the Cri-Cri, and including the e-Genius, E-Star, and the more recent E-Fan 1.2. This work and Airbus E-Aircraft Systems House collaboration with Siemens is seen as paving the way for a future hybrid single-aisle commercial aircraft that is safe, efficient, and cost effective.

“We see hybrid-electric propulsion as a compelling technology for the future of aviation,” said Paul Eremenko, Project Director from Airbus.

The E-Fan X demonstrator will look at and explore all the challenges of developing a high-power propulsion system, including thermal effects, electric thrust management, altitude and dynamic effects on electric systems, and other issues such as electromagnetic compatibility. The objective is to push forward and mature the technology, performance, safety, and reliability of hybrid-electric technology. Other major aspects of the program will be to establish new requirements for future certification of electrically powered aircraft and the training needs of a new generation of designers and engineers to bring such commercial aircraft closer to reality.

Partner expertise

The three partners will be exploiting to the full their extensive specialist experience. Airbus will be responsible for overall integration as well as the control architecture of the hybrid-electric propulsion system and batteries, and integration with the flight controls. Rolls-Royce will be responsible for the turbo-shaft engine, 2-MW generator, and power electronics. The engine company will also work on the fan adaption to the existing nacelle and the Siemens electric motor. Siemens will deliver the 2-MW electric motors and their power electronic unit, as well as the inverter, DC/DC converter, and power distribution system. This comes on top of the E-Aircraft Systems House collaboration begun in 2016, which aims at development and maturation of various propulsion system components and their terrestrial demonstration across various power classes.

“The E-Fan X enables us to build on our electrical expertise to revolutionize flight and welcome in the third generation of aviation. This is an exciting time for us as this technological advancement will result in Rolls-Royce creating the world’s most powerful flying generator,” Rolls-Royce’s CTO, Paul Stein, said at the launch.

Speaking for Siemens, its CTO, Roland Busch, said, “In April 2016 we opened a new chapter in electric mobility with the collaboration with Airbus. In building up electric propulsion for aircraft, we are creating new perspectives for the company and for society. With this partnership we now take the next step to demonstrating the technology in the air.”

What has been driving this move toward a radical new approach to aircraft propulsion has been the ever-stricter moves, globally, toward improved environmental performance. Conventional gas-turbine technology has been advanced greatly with new blade technology, and the use of new materials, to the point where low-noise and emissions levels and fuel consumption are reaching near optimum performance.

Even such big steps as geared turbofans, in conjunction with new materials and manufacturing methods, are probably getting close to the point where it is difficult to make further substantial game-changing improvements to the performance of jet engines, and undoubtedly electric propulsion, via the path of hybrid designs, now seems an inevitable future course for aerospace.

Piston engines reached their zenith in the 1950s and soon declined as pure jets and turbo-props took over, and we may be set to see the last generation of new jet engines over the next 20+ years, so beyond that there is an emerging market for another propulsion revolution, and electrics and hybrids will be part of that.

The European Commission has established a 2050 target goal in its Flightpath 2050 Vision for Aviation of reducing CO₂ by 60%, NOx by 90%, and noise by 75%. At present these ambitious targets are unreachable with today’s technologies, so change must come. This new European initiative could start to turn the corner in finally ending the status quo when it comes to designing and powering up new aircraft. For the first time it will be possible to fully appreciate and test solutions toward solving the technical challenges that lie ahead by flying a comparatively large platform test-bed in its natural element: the sky. If all goes well then scaling up the results into a genuine all-new narrow body Airbus product will truly be disruptive—and a challenge Boeing will not be able to ignore.