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A lot of research effort continues on electric propulsion for aircraft, and challenges remain. As I blogged in 2016, many programs are aimed at developing viable battery-electric or solar propulsion for smaller aircraft. One US-based program is NASA’s Scalable Convergent Electric Propulsion Technology and Operations Research (SCEPTOR) subproject, which is developing the manned X-57 Maxwell experimental aircraft featuring a distributed electric propulsion system (more on that below).  SCEPTOR is part of NASA’s Convergent Aeronautics Solution (CAS) initiative, which falls under the agency’s Transformative Aeronautics Concepts Program. NASA’s goal of meeting and overcoming the challenges of today’s aviation starts with potentially revolutionary ideas, and CAS was instrumental in supporting the idea of zero-carbon-emitting distributed electric propulsion, says the agency.

As defined in a 2010 technical paper authored by Hyun Dae Kim of NASA Glenn Research Center (Cleveland, OH, US), a distributed electric propulsion system means integrating a propulsion system within an airframe such that the aircraft gets the full synergistic benefits of coupling of the airframe aerodynamics and the propulsion thrust stream by distributing thrust using many propulsors on the airframe. OK, in other words, the X-57 will have many small battery-powered electric motors, 14 in all, distributed along the length of the wing (12 high-lift motors along the leading edge of the wing and two larger wingtip cruise motors). NASA says the X-57 will undergo as many as three configurations, with the final configuration to feature 14 electric motors and propellers. The 12 smaller electric motors will be used to generate lift during takeoff and landing only, while the two wingtip motors will be used during cruise. The goal of the X-57 program is to demonstrate a 500% increase in high-speed cruise efficiency, zero in-flight carbon emissions, and flight that is much quieter for the community on the ground.

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NASA chose the Tecnam (Capua, Italy) P2006T twin-engine, high-wing aircraft for the X-57, in part because the all-aluminum P2006T is the lightest certified commercial twin in existence. Two P2006T fuselages have already been shipped to the US and are undergoing a series of planned modifications and tests, which will culminate in the integration of a carbon composite wing, with integrated motors, that has already undergone low-speed ground testing using a modified big rig truck at Edwards AFB. NASA says the experimental, high-aspect ratio wing will feature a large reduction in area, with wing loading increasing from 17 pounds per square foot to 45 pounds per square foot. These changes will produce more efficient cruise flight by decreasing friction drag. NASA plans to demonstrate, soon, that the high-aspect ratio wing with the integrated high-lift motor system will allow the X-57 to take off and land at the same speed as the baseline P2006T, which will make the aircraft less sensitive to gusts and turbulence, leading to a smoother flight.

The wing is being designed at NASA Langley in Virginia, and fabricated by Xperimental (San Luis Obispo, CA, US). The wing will be integrated onto the fuselage once the electric power validation flights are complete. The battery system was developed by Electric Power Systems (City of Industry, CA, US).

This trend toward electric aircraft is will be something I’ll continue to follow. It’ll be interesting to see how it gets applied to the next generations of single-aisle commercial aircraft. Here’s a video of the X-57 Maxwell concept: