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NASA demonstrated its intent to show leadership in advancing electric aviation with the unveiling in late March 2020 of its X-57 Maxwell experimental test aircraft. The aircraft is a product of&nbsp;the agency’s first crewed X-plane program in two decades, and three different models are due to take to the skies by early 2022.
The X-57 is based on the Italian Tecnam P2006T twin piston light aircraft but is fitted with&nbsp;14 electric motors. To enable this change, the NASA team, led by principal investigator Sean Clarke, has redesigned the aircraft’s wing. The agency says that by using an existing aircraft design, it will have baseline specifications that will be useful for assessing the performance of the electric powerplant.
“Normally, they design a wing and then the powerplant guys put a cell underneath, which screws up wing performance a bit,” Clarke explained to FutureFlight. “We designed a propulsion system from the beginning along with the wing. That’s a fundamental part of our aerodynamic approach.”
The goal of the project—which&nbsp;earned the X-plane designation reserved for NASA’s more radical technology advancement programs—was to design an aircraft for optimal cruise efficiency without worrying about stall speed or low-speed performance. Some of the knowledge that might most help to electrify aviation at large was an unintentional byproduct of NASA’s early work on the concept. 
Initially, NASA intended to use off-the-shelf propulsion technology, and the team wasn’t committed to an electric power source. It simply settled on battery power as the best way to achieve&nbsp;its main goal of improving power efficiency, based on the point energy density was getting to;&nbsp;and then the agency realized it needed to do some development work to get where it wanted to go.
Clarke explained that NASA soon realized that more work would need to be done to integrate electric propulsion with aircraft. The program will focus on developing standards for operations and maintenance. 
In the U.S., NASA, the FAA, and the Department of Defense have separate paths to certification for aircraft technology. However, since new electric vehicles are largely being targeted at potential urban air mobility applications, what NASA is learning about airworthiness standards for these could serve as a blueprint for FAA type certification requirements, while also providing valuable guidance for private-sector aircraft developers. 
To that end, the X-57 team has been publishing design criteria and documentation from early in the process and engaging more with industry than most NASA projects typically do, Clarke said. The agency also has been working with standards organizations ASTM International and RTCA to help inform and align the development of standards for new commercial aircraft with architectures similar to that of the X-57 Maxwell. 
The ability to self-certify its technology lets NASA move faster than commercial entities, which are, in some ways, working blindly toward still-unknown standards. So does the fact that NASA isn’t answering to stakeholders demanding a return on investment.
“Nobody should buy the X-57 and start commuting in it,” Clarke said. “But it’s useful for maturing technology and getting it to the point that they could be useful for other products. We’re interested in enabling this and making this new marketplace more accessible, more affordable, more efficient. Maybe it turns out this airplane isn’t very efficient. That’s still a successful project for us, because we learn its shortcomings.”
So far, NASA has tested the first of four modifications of the X-57 design—an experimental electric wing called the Hybrid Electric Integrated Systems Testbed was mounted atop a big rig, which drove at high speeds to simulate the effects of a wind tunnel. By the end of 2020, the agency plans to fly the first electrified P2006T, called Modification II, which is the same aircraft aerodynamically but powered by all-electric engines. NASA aims to decrease high-speed energy usage by nearly 70 percent through that change.
Modification III, which is being worked on in parallel with Modification II, will use the same powerplant but feature a structural redesign. A new, smaller-area, high-efficiency wing will be put on and the P2006T’s original motors will be replaced by electric motors developed by eVTOL aircraft pioneer Joby Aviation. 
The electric motors will be fitted closer to the wingtips and the new wing’s high aspect ratio and the electric motors’ lighter weight are expected to result in significant efficiency gains. The objective for this phase of the program is to demonstrate an additional energy reduction at cruise of one-third over Modification II. NASA hopes to be flight testing Modification III in 2021.
Modification IV, which the Maxwell team recently reworked to use the same wing as Modification III, should fly in late 2021 or early 2022. Representing the final configuration of the X-57, Modification IV is an opportunity for the team to look at the data from Modification III and make any necessary adjustments before taking to the air again.
The final X-57 model will be powered by two 60-kilowatt cruise motors and propellers and 12 10.5-kilowatt high-lift motors and propellers. This combination will be supported by 860 pounds of lithium-ion batteries that can provide 69.1 kilowatt-hours of power (of which 47 are usable). 
That’s expected to let the 3,000-pound Maxwell aircraft cruise at 172 mph and reach an altitude of 14,000 feet. The overall goal is a 500 percent increase in high-speed efficiency, compared with the standard Tecnam aircraft, without the carbon emissions. 
Whether NASA’s latest X-plane meets that goal—and whether doing so is practical—remains to be seen. But, if the agency can provide inspiration and guidance for electric aircraft developers, and also for regulators trying to define certification best practices in a new industry, that alone might make the project worthwhile. 
Correction:&nbsp;An earlier version of this article incorrectly stated that NASA had flown the Modification I version of the X-57. Modification I was not a flying aircraft prototype, but rather a phase of ground testing that involved an electrified wing mounted on top of a big rig.&nbsp;

Martha Jercinovich

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