Hot Wings

The race to reclaim supersonic flight.

December 2021

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Illustration of supersonic jet

Illustration: Brian Stauffer

The first time Norris Tie heard a plane break the sound barrier, he was working as an engineer at a spacecraft manufacturer in the Mojave Desert. “It sounded like a bomb went off,” he says. “I kind of jumped out of my seat.”

Older hands at the office were unfazed. It was probably just an F-18 from nearby Edwards Air Force Base, for generations the center of American supersonic test flights. But for Tie, MBA ’19, the sudden crack was like an exclamation point.

Ever since he was a kid enduring 12-hour flights to see family in China, Tie had been fascinated by commercial aviation’s stall in speed. In a world where technological advancements come fast and furious, why were airliners stuck in the same subsonic slow lane they’d been in since the ’60s? Even before studying aerospace engineering at UCLA, Tie became fixated on finding ways to fly faster.

Noise was always an obvious obstacle. Since the ’70s, civil supersonic flight over land generally has been outlawed precisely because of the roar that startled him at his desk. (The famous Concorde jet made only transatlantic journeys.) But by that moment in 2016, NASA was pushing forward on plans for an experimental jet capable of breaking the sound barrier with more whimper than bang. The boom in the desert was just visceral confirmation to Tie that this quest for quiet speed was where his future lay.

Five years later, Tie is focused on bringing the promise of a muted sonic boom to marketplace. With Tim MacDonald, MA ’15, PhD ’20, Tie is co-founder of Exosonic, a fledgling start-up developing a 70-seat commercial airliner designed to fly at 1.8 times the speed of sound with a fraction of the noise of a normal supersonic jet. The real hook? New York to Los Angeles in three hours, at business-class prices.

‘I just admire his audacity. Even among ambitious people, building a new supersonic airliner is ambitious squared.’

It’s a tall order, with a thicket of technical, financial, regulatory and environmental challenges that have already defeated more established rivals. In May, Aerion Supersonic, a Nevada-based company with similar dreams, abruptly shut down, citing the challenges of securing capital. Even in best-case scenarios, Exosonic won’t have an airliner ready until well into the next decade. This spring, the company began wind tunnel tests using a 3 percent scale model. But Tie, the company’s CEO, has faith in a “crawl-walk-run” strategy that calls for executing smaller supersonic projects while pursuing the larger prize. Over the past two years, Exosonic has received more than $2 million in contracts from the U.S. Air Force to start design on several supersonic vehicles including an executive transport jet and drones capable of mock air battles with human pilots. That’s peanuts compared with its multibillion-dollar aspirations but indicative, Tie says, of how they’re earning revenue as they move forward.

“I just admire his audacity,” says George Parker, MBA ’62, PhD ’67, professor emeritus of finance at the Graduate School of Business and a former board member of Continental Airlines. “Even among ambitious people, building a new supersonic airliner is ambitious squared.” The two met soon after Tie arrived as a student at the GSB, by which time Tie had already recruited MacDonald, then a doctoral student in aeronautics and astronautics and the creator of a software suite for designing unconventional aircraft. “I thought, ‘OK, this is an exciting project,’ ” recalls MacDonald, now Exosonic’s chief technology officer. “This is a way that we might really be able to push things forward in aviation.”

A casual observer would be forgiven for thinking the race to supersonic travel had been won decades ago. Indeed, from 1976 to 2003, the rich and reimbursed could rip across the Atlantic in less than 3 1/2 hours on the Concorde, a needle-nosed Franco-British collaboration capable of flying 1,350 mph. But the Concorde was a star-crossed bird—a fuel-thirsty extravagance birthed just as the oil shortages of the ’70s were making airlines leery of waste. And long before its maiden flight, headwinds had built against supersonic noise pollution.

Contrary to common perception, a supersonic jet doesn’t create a single boom; it drapes its din over a span of earth tens of miles wide the entire time it’s flying. And it’s grating. In 1964, the Federal Aviation Administration used Air Force fighters and bombers to subject Oklahoma City to eight booms a day for six months—Easter excepted—to gauge the effects on people and property. In the end, the Air Force and the FAA received more than 15,000 complaints. The response contributed to the United States’ decision to drop its own plans for a supersonic airliner. 

In the end, only 14 Concordes reached operation, an elite fleet consigned to crisscrossing the empty vastness of the Atlantic. By 2003, even they were grounded, done in by several factors, not least the high costs of maintaining more than a dozen highly specialized vehicles. Nothing has taken their place in the nearly two decades since. 

Portraits of Tie and MacDonaldFLIGHT FANCY: Tie (left) and MacDonald started scheming a supersonic redesign soon after Tie came to the GSB. (Photos: Courtesy Exosonic)


“It’s one of those few times that humankind, we actually regressed,” says Juan Alonso, a Stanford professor of aeronautics and astronautics whose research interests include supersonics. “We have fewer capabilities than we had before. We’re not used to that as a species.”

Exosonic is one of several outfits pushing to become Concorde’s supersonic successors. Earlier this year, Boom Supersonic, a Denver start-up, announced a deal to provide 15 supersonic jets to United Airlines for commercial use by 2029. The company was founded in 2014 by Blake Scholl, a Silicon Valley veteran and an aviation buff who likewise couldn’t understand the supersonic void. Early in his endeavor, he consulted with Alonso, who encouraged him that his vision was technically feasible.

Early next year, in the Mojave, Boom expects to launch XB-1, an experimental precursor to its eventual airliner. Bill Shoemaker, ’89, PhD ’94, a former Navy pilot with a doctorate in aeronautics and astronautics, will likely be at the controls. During his three years as Boom’s chief test pilot, his job has largely been as in-house skeptic, he says, pushing back on engineering assumptions. By first flight, he’ll have a different mindset. “What’s left is a sense of purpose and sense of responsibility to the team to make sure you do it right.”

Vast improvements in materials, propulsion systems, computer modeling and other factors should make Boom’s planes far more efficient than the Concorde and quieter at low speeds, especially at take-off, he says. But like its predecessor, Boom’s boom means it will be limited to going supersonic overseas.

Exosonic, though, is after something more radical, a boom so quiet that its planes can fly anywhere. The result, Tie says, would open a vast number of markets, driving ticket prices down from Concorde’s stratospheric levels. Exosonic wants to take flight routes presently lasting four to 11 hours and cut them in half. 

Since Concorde’s inception, scientists have known that a quiet sonic boom was possible in theory. Yet the computational power to realize the idea took decades to develop. As a jet surpasses the speed of sound—roughly 660 mph at normal cruising altitude—the plane begins to fly into its own noise. It’s traveling too slow to get out of the way. The resulting buildup of pressure on the plane’s leading edges—its nose, wings, tail, inlets and so forth—unleashes as shockwaves, which coalesce in the air to form the explosive bang-bang of a sonic boom. (Technically, a supersonic plane produces two booms: one associated with its nose, the other with its tail.) Shockwaves are unavoidable at supersonic speeds, but tweaking a plane’s geometry can manipulate them to keep them from combining forces. Done properly, the result is a gentle thump.

‘It’s one of those few times that humankind, we actually regressed. We’re not used to that as a species.’

Or that’s the expectation. NASA will soon bring the idea into the real world. Next year, it will begin flying the X-59, an experimental single-person jet with an elongated nose, like the proboscis of a mutant mosquito. (It’s the project Tie joined as an aeronautical engineer after hearing the boom in the desert and before attending the GSB.) The ultimate point of the project is to gather data to guide possible changes to the nation’s nearly 50-year supersonic ban. If the computations hold, the streaking plane’s boom will sound more like a car door slamming 20 feet down the street. With the Concorde, it was like the door was being slammed with you inside the vehicle.

Alonso, who worked on quiet supersonics at NASA headquarters from 2006 to 2008, has every confidence that the jet will nail its lines. It’s less certain, he says, how the public will react once the plane begins flying over population centers in 2024, the 60th anniversary of the Oklahoma experiment.  

Not everyone is delighted by the prospect of supersonic’s return. Some skeptics doubt that the business model of low-capacity, high-cost planes can survive any better now than it did in Concorde’s era. Developments like in-flight Wi-Fi may even have reduced the importance of cutting flight times for business passengers. And environmentalists see the threat of an already highly polluting industry expanding its carbon footprint through high-altitude soot emissions, condensation trails and a voracious appetite for jet fuel.

Supersonic flight is five to seven times more fuel intensive than subsonic alternatives, says Dan Rutherford, MS ’00, PhD ’06, program director with the International Council on Clean Transportation. And while both Boom and Exosonic have announced intentions to make their planes fly on low-carbon sustainable aviation fuel, Rutherford says such fuels are so costly that market forces could easily compel the airlines that buy their planes toward cheaper, more polluting alternatives. 

“I just honestly don’t think the economics will ever work on that,” he says. “If it’s too expensive, I think they’ll default back to the current jet fuel.”

Tie acknowledges the challenge of solving the environmental obstacles. It’s something he and his team will keep working on. But the subsonic era can’t last forever, he says, and he likes Exosonic’s chances of helping end it. At 29, he’s already been focused on flying faster for more than half his life.

“He’s got tenacity,” Parker says. “He will probably fail, but he may not. And if he doesn’t, he’ll be historic.”

Sam Scott is the senior writer at Stanford. Email him at

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