There’s a new NASA X-plane in town, and like its predecessors, it’s a little bit goofy-looking. Unlike most of the space agency’s experimental aircraft, however, the new X-plane isn’t built to break speed barriers, carry astronauts, or test the possibilities of unmanned air combat. This one is designed to fight climate change.
NASA and Boeing announced on Tuesday that the Air Force had designated a new transonic, truss-winged aircraft as the X-66A. The design is a product of the Sustainable Flight Demonstrator project, a NASA-Boeing partnership to produce a single-aisle plane that promises to slash fuel consumption for commercial aircraft. The new aircraft looks like a giant glider with long, skinny wings propped up by diagonal struts to reduce drag. If widely adopted, the truss-winged design could transform sustainable air travel as we know it. The new X-66A is also the first X-plane designed specifically to achieve the goal of net-zero greenhouse gas emissions for airplanes.
“We’re incredibly proud of this designation, because it means that the X-66A will be the next in a long line of experimental aircraft used to validate breakthrough designs that have transformed aviation,” said Todd Citron, Boeing chief technology officer. “With the learnings gained from design, construction, and flight-testing, we’ll have an opportunity to shape the future of flight and contribute to the decarbonization of aerospace.”
Air travel is a massive contributor to climate change, and it’s getting more popular. Flying accounts for up to 4 percent of greenhouse gas emissions in the United States, and as more and more people fly, the United Nations expects carbon dioxide emissions from planes to triple by 2050. A transatlantic flight produces about a ton of CO2 per passenger, which amounts to about half the carbon footprint a person would produce by eating food for a year.
Unlike cars, you can’t simply bolt a battery onto a plane and make it electric. (Making an electric vehicle is more complicated than that, but you get the point.) Improvements to airplanes happen in small increments over the course of decades. Typically, a single-digit reduction in an aircraft’s fuel consumption would be meaningful. Boeing says the innovations in the new truss-braced wing concept will amount to a 30 percent reduction. That’s exactly the kind of leap NASA wanted to get out of the Sustainable Flight Demonstrator project, which Boeing won. The space agency will now help Boeing build, test, and fly a demonstrator aircraft — and its X-plane status, which the Air Force grants to revolutionary experimental aircraft configuration projects, could lead to additional support.
“If you think that, or have the perception that, aviation hasn’t been working on sustainability or environmentally friendliness, that’s a bad perception because every generation of aircraft that’s come out has been 15, 20, 25 percent better than the one it replaces,” Rich Wahls, NASA’s sustainable flight national partnership mission integration manager, told Vox in January. “What we’re trying to do now is skip a generation.”
The big idea behind the transonic truss-braced wing concept is an update to the aircraft configuration, or the plane’s architecture. Unlike the low-wing design that dominates the commercial aircraft configuration today, the new Boeing design has wings that stretch over the top of the plane’s tubular body. This reduces drag, but it also allows for a wider variety of propulsion systems, from bigger jet engines to exposed propellers. It’s also fast. The “transonic” part of the concept’s name refers to its ability to fly just shy of the speed of sound, or around 600 miles per hour.
NASA likes this idea so much it’s investing $425 million into the project under a Funded Space Act Agreement. Boeing and other partners will chip in an additional $725 million. Once Boeing builds a full-scale demonstrator aircraft, NASA says it will complete testing in the late 2020s, and if all goes well, the public could see the new technologies in commercial aircraft sometime in the 2030s.
If you squint your eyes, though, the new transonic truss-braced wing concept looks an awful lot like the commercial aircraft you see on runways today. That’s not a bad thing. For one, it’s not a radical redesign — unlike, say, the very odd-looking blended wing X-48 — that might scare off passengers. The similar design also has some benefits for the manufacturing process. But at the end of the day, new aircraft configuration alone won’t make these next-generation planes greener, according to Brent Cobleigh, project manager for NASA’s Sustainable Flight Demonstrator project.
“Lighter-weight materials, better aerodynamics, better propulsion systems, more direct operations,” Cobleigh said, “you need all of those together to squeeze as much efficiency out as we can, to make the biggest impact.”
Because, again, it’s really hard to make airplanes more efficient. And aircraft configuration is just one piece of the puzzle. More efficient propulsion systems and cleaner jet fuel are the other two moving parts that need to fit together. Further down the line, we’ll see designs for hybrid propulsion systems that use both jet fuel and batteries to power a plane. Fully electric planes are already taking to the skies, although it will be decades before we see big battery-powered passenger aircraft. In the near term, hydrogen increasingly seems like a viable replacement for the fossil fuels we currently put in planes. Rolls-Royce and easyJet successfully tested a hydrogen-powered jet engine, the world’s first, last year.
What we’ll see before those big breakthroughs are more incremental improvements. In early 2023, for example, Rolls-Royce showed off a new UltraFan propulsion system for plans, which it says offers a 25 percent jump in efficiency and can run on 100 percent sustainable aviation fuel, or SAF, which is a biofuel derived from waste material. Although it’s not a conventional fossil fuel, SAF still spews carbon into the atmosphere, and it’s also in short supply. Some commercial flights already use SAF mixed with conventional jet fuel, and United did a demo in 2021 with a flight from Chicago to Washington, DC, powered by 100 percent SAF. An innovation like SAF certainly is a move in the right direction — what you might call an evolutionary change — but it’s not what’s needed to make air travel as green as it can be.
“The revolutionary change would be to change the energy source, like, if you change to hydrogen or if you did hydrogen fuel cells,” explained Marty Bradley, a sustainable education educator and consultant who worked at Boeing when the company was exploring early truss-braced wing concepts. “That would be that big jump.”
Update, June 13, 4 pm ET: This story, originally published on February 2, has been updated with new information about the NASA-Boeing aircraft’s US Air Force X-plane designation.