The X-57 Maxwell program is to wrap up without achieving electric flight.
After struggling for years with a variety of technical problems and setbacks, NASA has decided to conclude its X-57 Maxwell electric aircraft demonstrator program at the end of September without attempting a flight.
The program announced its decision on June 23 on a conference call with reporters, disclosing that it had discovered “failure modes” that would take too long to fix.
“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,” says Sean Clarke, principal investigator with the X-57 program. “The motor design had a couple of particular failure modes that show up through our detailed analysis that show that it could seize up in flight and … could be a safety hazard to our pilots.”
The Maxwell program is still analyzing the problem and declined to share additional details about the issue, he says.
“We’ve got a great design in progress to fix it. It’s just it would take too long for us to go through and implement,” Clarke says. “We’d need to complete our design cycle, go through prototyping, and then go through component testing and system integration, and in the months that are left in the project, that’s just a little bit too much of a delay to fit in.”
The X-57 is based on the four-seat Tecnam P2006T turboprop. The twin-electric motor version that NASA initially wanted to fly was the “Modification II” configuration of the Maxwell, which incorporates Joby Aviation-developed JM-X57 electric cruise motors in place of the original Rotax 912 S3 piston engines, and used batteries in place of avgas.
NASA originally aimed to make a first flight using electrical power as soon as 2018. But development challenges with the battery system, electric control system and electromagnetic interference, among other issues–and compounded by complications from the COVID-19 pandemic–have put the program significantly behind schedule.
At the AIAA Aviation Forum on June 15, the X-57 program shared that it had discovered problems with its use of industrial-grade ball bearings that was forcing a redesign of the aircraft’s electric motors. It is not clear if the ball bearings issue is connected to the potential motor seizure.
The choice of steel ball bearings in the aircraft’s two electric motors that were “lower grades than aviation” standards caused unforeseen issues, said NASA Glenn Research Center systems engineer Dave Avanesian at the time. Among other issues, the ball bearings were not properly seated, resulting in “pretty high levels of vibration,” he said.
In a later stage of the program, NASA had planned to test the X-57 in a Modification III configuration that would have the Tecnam P2006T’s wing replaced with a high-aspect-ratio wing that has 12 nacelles distributed along its middle and two electric motors on its wingtips.
After that, a Modification IIII of the Maxwell would include installation of 12 electric motors on the nacelles. The X-57’s high-aspect-ratio wing and its wingtip motors would be optimized for efficiency during cruise. The 12 high-lift, electric-driven propellers would help the aircraft take off and then fold back during cruise. NASA believes the aircraft would be more efficient than the Tecnam P2006T, even with the extra weight and drag of the 12 electric-driven propellers.
Because of delays, NASA already had jettisoned its Modification III and Modification IIII goals in favor of using its remaining time on an attempt to make the Modification II version fly. Now that the the Modification II version will not fly, NASA will instead use its remaining time to wrap up the program, publish in scientific papers and share what it has learned with the public.
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