NASA is pulling the plug on its X-57 Maxwell electric airplane experiment without a single flight test on the books, the agency announced June 23, citing a newly discovered problem with the electric propulsion system that poses an “unacceptable” safety risk. According to NASA, the X-57 team will cease all operational activities by the end of September. It will take several months to completely wrap up the project, during which the team plans to publish technical papers detailing its successes and failures.
The X-57 is a modified Tecnam P2006T that NASA has been working to retrofit with an electric propulsion system. NASA launched the program in 2016. Originally, the plan was to replace the aircraft’s two Rotax engines with 14 electric propellers powered by rechargeable lithium-ion batteries and a distributed electric propulsion system.
However, the agency faced several setbacks in the X-57's development. The project got off to a rough start with the lithium-ion battery packs short-circuiting and overheating, causing thermal runaway events. After redesigning the battery packs and conducting a series of ground tests, NASA engineers determined that some components of the electrical system could not withstand the extreme temperatures and vibrations they might experience in flight.
In 2021, after the Covid-19 pandemic caused further delays, NASA scaled back the project’s objectives and decided it would only fund the program through the end of 2023. Rather than developing the so-called Mod IV version of the airplane with 14 electric propellers, the agency decided to focus on the Mod II, a prototype with only two electric propellers. That version of the aircraft was expected to fly before the end of this year—until NASA discovered another big problem that would ground the aircraft indefinitely.
“Unfortunately, we recently discovered a potential failure mode in the propulsion system that we've determined to pose an unacceptable risk to the pilot's safety and safety of personnel on the ground during ground tests,” Brad Flick, director of NASA's Armstrong Flight Research Center, said during a conference call with reporters. “Mitigation of that failure would take the project well beyond its planned end at the end of this fiscal year, so NASA has decided to end the project on time without taking the vehicle to flight.
“While we're not achieving those original project objectives or realizing the full value of taking the system to flight, the knowledge gained from the development of the X-57 has elevated the state of the industry and informed standards for current and future electrified aircraft,” Flick added.
Sean Clarke, NASA’s principal investigator for the X-57 project, said his team is still analyzing the cause of the latest glitch that thwarted its plans to fly this year. “As we got into the detailed analysis and airworthiness assessment of the motors themselves, we found that there were some potential failure modes with the motors mechanically under flight loads that we hadn't seen on the ground,” he said, adding that it would take too long to implement the necessary design changes. “In the months left of the project, that's just a little bit too much of a delay to fit in.”
The X-57 project has also eaten up a lot more of NASA’s federal budget than was originally intended. It was initially expected to cost $40 million to get the Mod IV in flight by May 2018. By the end of 2022, NASA said the program had incurred costs of more than $87 million, and the agency had budgeted for a total cost of $99 million through the end of FY 2023. According to NASA, the X-57 program would require at least another $64 million to complete the Mod IV by 2027, and the agency determined that “the small percentage of the industry that would benefit did not justify the additional cost and delay,” according to a report issued May 17 by the NASA Office of Inspector General.
Although the X-57 program failed to achieve a flight test, NASA said the project succeeded at its primary goal, which was to share what it learned with regulators and the aviation industry to help develop certification standards for electric aircraft. In fact, the X-57 team has published dozens of technical papers over the years detailing every aspect of its design and testing processes.
“NASA’s goal is to drive innovation through groundbreaking research and technology development. The X-57 project team has done just that by providing foundational information to industry through lessons learned, and we’re seeing the benefits borne out by American commercial aviation companies that are aiming to change the way we fly,” Flick said in an agency statement. “I’m incredibly proud of their tenacity and ingenuity as they led the way in advancing electrified propulsion. The future of electrified propulsion is possible because of their contributions.
“They did things that had never been done before, and that’s never easy,” Flick added. “While we prepare to finish this project later this year, I see a long list of achievements to celebrate and an industry that’s better today because of their work.”