The Shift to Electric Propulsion

With the advent of the Airbus A380, Airbus A350, and Boeing 787, large civil transports are evolving into increasingly more electric aircraft and platforms that use high levels of electric power for onboard systems. The electrical system produces, conditions, and distributes power to all of the other systems that need it—flight deck displays, flight controls, in-flight entertainment, and more. The power demand on a modern twin-aisle aircraft is now in the megawatt range. This ever-increasing demand requires onboard power generation solutions in addition to engine-mounted generators. The Boeing 787, for example, makes use of two lithium-ion batteries, one for its auxiliary power unit and a second to turn on its flight deck computers.

Despite the shift occurring in large commercial aircraft, electric propulsion is more strongly emerging in general aviation, i.e., personal-sized aircraft. The Pipistrel Taurus G4, the first all-electric four-seat aircraft, is a perfect example of this trend. In addition, electric propulsion development is underway for the commercial class of transports for the thin-haul sector, although this technology is still in its formative stages. In the July/August issue of Aerospace America, an article by Adam Hadhazy entitled “Fly the Electric Skies: Reinvigorating Short-Haul Flight with Hybrid-Electric Aircraft” outlines the state of the art of the technologies that are making electric propulsion a reality. For large civil transports, most planners and analysts forecast a lengthy time frame (decades) before hybrid electric propulsion (HEP) or electric propulsion (EP) solutions could become technically feasible. In any event, given the current interest in HEP and EP technologies, ranging from small aircraft to large aircraft, it is not surprising that many companies and organizations are executing robust research and advanced development programs in this area.

So why the interest in more electric aircraft and electric/hybrid electric propulsion systems? Highly variable energy costs, concern for environmental impacts, and more stringent environmental regulations have combined to cause the aircraft industry to look at possible alternative approaches to aircraft power and propulsion systems. The industry is exploring biofuels and other alternative fuels, liquefied natural gas, hybrid electric propulsion and electric propulsion solutions, and fuel-efficient alternative architectures such as blended wing body aircraft.

Technical barriers to electric propulsion development include the management of high-voltage systems, high energy density storage solutions, and thermal issues. Research is underway to find advanced materials needed for large motors. And there are few standards for large aircraft electrical subsystems akin to the old U.S. military standards and although standards are needed, their development must be led via industry consensus.

Because of the wide-ranging impact and the integrated nature of technologies associated with more electric aircraft and electric/hybrid electric propulsion systems, not surprisingly, various communities within AIAA have an interest in these topics. AIAA has identified electric aircraft, hybrid electric propulsion, and energy for aerospace applications broadly as priority growth areas. To coordinate the needs of these communities, an Aircraft Electric/Hybrid Electric Power and Propulsion (AEPP) Working Group has been stood up to engage all interested parties from within and from outside of AIAA to benefit the aeronautics industry by helping it to make advances in EA and HEP technologies.

The Aircraft Electric/Hybrid Electric Power and Propulsion Working Group is considering a myriad of activities and is working many of the technical and non-technical issues that will need to be addressed by our industry in this area. As a first step AIAA supported a two-and-a-half-day Transformational Electric Flight Workshop & Expo at the 2017 AVIATION Forum and a three-day Aircraft Electric Propulsion and Power track at the 2017 Propulsion and Energy Forum. The working group is also organizing a panel session on standards and certification at the 2018 SciTech Forum. In addition discussions are ongoing with IEEE to organize a joint workshop at the 2018 Propulsion and Energy Forum and an IEEE mini-conference in summer 2019. To disseminate the outcomes from the workshops and other activities, summary and outbrief sessions are being organized for three AIAA forums (SciTech, AVIATION, Propulsion and Energy) with the intent of communicating data, research, and information on the status of the technologies surrounding the electric/hybrid electric aircraft and propulsion topics as well as the activities of the working group. Expect to see more electric aircraft sessions at future AVIATION Forums!

From doing energy storage requirements projections, to coordinating with sister technical professional societies such as ASME or IEEE, to standards development, to report outs on systems studies, AIAA is the technical professional society at the forefront of this transformative technology. ★

The Shift to Electric Propulsion