Later this year — maybe this summer, maybe this fall — a NASA electric plane, the X-57, is scheduled to take off in California. It’s what NASA describes as its “first all-electric experimental aircraft,” and when it takes off from the ground it won’t look like what NASA depicted the aircraft on its website.
Instead of a whopping 14 electric motors and propellers, the plane will only have two. But those two engines, powered by more than 5,000 cylindrical battery cells in the plane’s fuselage, should be enough to get it airborne before 2023 is over, when the X-57 program is also shut down.
Here, you’ll learn how the plane will operate, the challenges the program faced, and how space travel lessons helped inform the details of its battery system.
When the plane actually takes off as planned this year, it will do so in a form called Modification 2, where an electric motor and propeller on each wing will give the plane the thrust it needs to take to the skies.
While the aerospace agency had hoped to fly the aircraft – which is based on a Tecnam P2006T – in additional configurations known as Modifications 3 and 4, that will not happen. Why? Because it’s difficult to build an airplane that flies safely on electricity alone, and the program will only be funded until 2023. (IEEE Spectrum has more on the program’s original plans.)
“We’ve learned a lot over the years and thought we were learning through flight testing – it turned out we had a lot of lessons to learn during the design, integration and airworthiness qualification steps, so we ended up devoting more time and resources to it says Sean Clark, lead investigator for the X-57 program at NASA.
“And that was tremendously valuable,” he adds. “But it means we will end up having no resources for this mod 4 [or 3] flights.”
It will still fly as an all-electric aircraft, but in Mod 2 with two engines.
One flaw the team had to iron out before the plane could safely take off involves components through which the current from the batteries must flow before it reaches the motors. The problem was transistor modules in the inverters that convert the current from direct current to alternating current.
“We used these modules, which are multiple transistors in one package – they were specified to be able to tolerate the types of environments we expected them to be in,” says Clark. “But every time we tested them, they failed. In our environmental test chamber, transistors would simply explode.”
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The failure of a component – e.g. B. the explosion of a piece of equipment – is the kind of problem that aircraft manufacturers prefer to solve on the ground. Clark says they figured it out. “We dissected them extensively — after they explode, it’s hard to know what went wrong,” he notes lightheartedly, in a way reminiscent of an engineer faced with a messy problem. The solution was newer hardware and “a complete redesign of the inverter system from the ground up,” he notes.
They “are working really well now,” he adds. “We put a full set through qualifiers and they all passed.”
Lessons from Outer Space
Conventional airplanes burn fossil fuel, an obviously flammable and explosive substance, to power their engines. Anyone working on electric aircraft powered by batteries must ensure that the battery cells do not ignite fires either. Last year in Kansas, for example, a pack of flight batteries was dropped from 50 feet in an FAA-sponsored test to ensure they could handle the impact. They did.
In the X-57, the batteries are a model known as 18650 cells and are manufactured by Samsung. The aircraft uses 5,120 of these, divided into 16 modules of 320 cells each. A single module that includes both battery cells and packaging weighs about 51 pounds, Clark says. The trick is to make sure all of these components are properly packaged to avoid a fire even if a battery fails. In other words, failure was an option, but they plan to handle any failure in a way that doesn’t start a fire. “We found that there was no industry standard for how these cells could be packaged in a high-voltage, high-power package that would also protect them from cell failure,” says Clark.
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Help came from above. “Ultimately, we redesigned the battery pack based on a lot of input from some of the design teams working 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 that astronauts use, and a device called the pistol grip tool were relevant examples in this process. Key findings related to the spacing between battery cells and how to deal with heat when a cell is not working properly, such as thermal runaway. “What the hell [Space Center] The team found that one of the most effective strategies is to actually let the heat from this cell into the aluminum structure, but also let the other cells around it each absorb some heat,” he explains.
NASA isn’t the only one exploring the frontiers of electric aviation, which is one way the short-haul aviation industry could become greener. Others working in space include Beta Technologies, Joby Aviation, Archer Aviation, Wisk Aero and Eviation with an aircraft named Alice. One prominent company, Kitty Hawk, closed last year.
Sometime this year, the X-57 should fly for the first time and likely make multiple sorties. “I’m still very excited about this technology,” says Clark. “I’m looking forward to my kids being able to do short flights in electric planes in 10, 15 years – it’s going to be a really big step for aviation.”
Watch a short video about the plane below: