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Sometime later this year—perhaps this summer, perhaps this fall—an electric aircraft from NASA, the X-57, is set to take flight in California. It’s what NASA describes as its “first all-electric experiment aircraft,” and when it does lift off the ground, it won’t look the way that NASA has been depicting the plane on its website.
Instead of a whopping 14 electric motors and propellers, the aircraft will have just two. But those two motors, powered by more than 5,000 cylindrical battery cells in the aircraft’s fuselage, should be enough to get it up in the air before 2023 is over, which is when the X-57 program is set to power down, too.
Here’s what to know about how the plane will work, the challenges the program has faced, and how lessons from spaceflight helped inform the details of its battery system.
Modification 2
If the plane does indeed take flight this year as planned, it will do so in a form called Modification 2, which involves one electric motor and propeller on each wing giving the aircraft the thrust it needs to take to the skies.
While the aeronautics and space agency had hoped to fly the plane—which is based on a Tecnam P2006T—in additional configurations, known as Modifications 3 and 4, that won’t happen. Why? Because making a plane that flies safely on just electricity is hard, and the program is only funded through 2023. (IEEE Spectrum has more on the program’s original plans.)
“We’ve been learning a lot over the years, and we thought we’d be learning through flight tests—it turns out we had a lot of lessons to learn during the design and integration and airworthiness qualification steps, and so we ended up spending more time and resources on that,” says Sean Clark, the principle investigator for the X-57 program at NASA.
“And that’s been hugely valuable,” he adds. “But it means that we’re not going to end up having resources for those Mod 4 [or 3] flights.”
It will still fly as an all-electric plane, but in Mod 2, with two motors.
Exploding transistors
One glitch that the team had to iron out before the aircraft can safely take flight involves components that electricity from the batteries have to travel through before they reach the motors. The problem was with transistor modules inside the inverters, which change electricity from DC to AC.
“We were using these modules that are several transistors in a package—they were specced to be able to tolerate the types of environments we were expecting to put it in,” says Clark. “But every time we would test them, they would fail. We would have transistors just blowing up in our environmental test chamber.”
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A component failure—such as a piece of equipment blowing up—is the type of issue that aircraft makers prefer to resolve on the ground. Clark says they figured it out. “We did a lot of dissection of them—after they explode, it’s hard to know what went wrong,” he notes, lightheartedly, in a manner suggesting an engineer faced with a messy problem. The solution was newer hardware and “redesigning the inverter system basically from the ground up,” he notes.
They are now “working really well,” he adds. “We’ve put a full set through qualification, and they’ve all passed.”
Lessons from space
Traditional aircraft burn fossil fuels, an obviously flammable and explosive substance, to power their engines. Those working on electric aircraft, powered by batteries, need to ensure that the battery cells don’t spark fires, either. Last year in Kansas, for example, an FAA-sponsored test featured a pack of aviation batteries being dropped by 50 feet to ensure they could handle the impact. They did.
In the X-57, the batteries are a model known as 18650 cells, made by Samsung. The aircraft uses 5,120 of them, divided into 16 modules of 320 cells each. An individual module, which includes both battery cells and packaging, weighs around 51 pounds, Clark says. The trick is to make sure all of these components are packaged in the right way to avoid a fire, even if one battery experiences a failure. In other words, failure was an option, but they plan to manage any failure so that it does not start a blaze. “We found that there was not an industry standard for how to package these cells into a high-voltage, high-power pack, that would also protect them against cell failures,” Clark says.
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Help came from higher up. “We ended up redesigning the battery pack based on a lot of input from some of the design team that works on the space station here at NASA,” he adds. He notes that lithium batteries on the International Space Station, as well as in the EVA suits astronauts use and a device called the pistol grip tool, were relevant examples in the process. The key takeaways involved the spacing between the battery cells, as well how to handle the heat if a cell did malfunction, like by experiencing a thermal runaway. “What the Johnson [Space Center] team found was one of the most effective strategies is to actually let that heat from that cell go into the aluminum structure, but also have the other cells around it absorb a little bit of heat each,” he explains.
NASA isn’t alone in exploring the frontier of electric aviation, which represents one way that the aviation industry could be greener for short flights. Others working in the space include Beta Technologies, Joby Aviation, Archer Aviation, Wisk Aero, and Eviation with a plane called Alice. One prominent company, Kitty Hawk, shuttered last year.
Sometime this year, the X-57 should fly for the first time, likely making multiple sorties. “I’m still really excited about this technology,” says Clark. “I’m looking forward to my kids being able to take short flights in electric airplanes in 10, 15 years—it’s going to be a really great step for aviation.”
Watch a brief video about the aircraft, below:
