Scholl, who founded Boom Supersonic in 2014, watches as his chief test pilot, former U.S. Navy fighter hotshot Bill “Doc” Shoemaker, and Boom propulsion engineer Ben Murphy coax the engine through its runup to full afterburner: Fuel squirts into the exhaust, boosting the jet’s thrust—and noise—by about 50 percent. All that energy barrels down an exhaust port and out of the building, which is nestled in the foothills of the Rocky Mountains in Colorado Springs, Colorado. In less than a minute, the test, one of dozens Scholl’s team will perform, confirms that the older-generation engine can handle the stress they’ll be subjecting it to. The J85 is GE’s workhorse military turbojet. Three of them will power Boom’s XB-1, a one-third-scale demonstration model of the $200 million, 55-seat carbon-fiber airliner the company hopes to see streaking across the sky at twice the speed of sound by 2025. It would be difficult to overstate the challenges Boom faces as it chases this goal and all the ways its plan could go wrong. Seventy-one years after Chuck Yeager punched through the sound barrier in the Bell X-1, the Concorde and the Soviet Union’s Tupolev Tu-144 remain the only airliners to achieve Mach speed. Neither worked out. The Tupolev mostly carried cargo, making just 102 flights with passengers. British Airways and Air France lost money on most Concorde trips despite exorbitant ticket prices and hefty government subsidies. They grounded the airplanes in 2003 after 27 years of glamorous—if fiscally strained—service. The business case doesn’t appear much better today. Even as Blue Origin and Virgin Galactic make steady progress toward the day tourists will glimpse space through the porthole of a rocket ship, no one’s figured out how to make supersonic transport economically feasible. The problem lies in maximizing fuel efficiency while reducing engine noise and mitigating the sonic boom that inevitably accompanies anything moving faster than the speed of sound. When you throw in the requirement that this tech turn a profit, the puzzle is so fiendishly difficult to solve that Boeing and Airbus all but quit trying, launching precisely zero efforts since the Concorde’s last flight. Why bother, when airlines show little interest in jets that carry fewer people, burn more fuel, and can fly only over oceans because of the awful racket they make? For Scholl, the path to that vision is clear. Boom’s success hinges on developing a jet engine capable of achieving supersonic speeds without that fuel-guzzling afterburner. And he believes the boom problem won’t be a problem for his company. His business plan relies on convincing airlines that with new, more-efficient technology, they’ll make plenty of money shuttling business-class passengers across the Atlantic in three hours or the Pacific in six. The Virgin Group and Japan Airlines are among five carriers so intrigued by the idea that they’ve lined up to buy Boom’s airplanes, should they make it to production. That’s one way of sparking a supersonic revival. The other is to technologically hush the boom and open up an avenue the U.S. and Europe closed to everyone but the military in the 1970s: overland flights, where Mach speeds let you cross the country in the time it takes to watch a movie. The market could be huge, but so are the costs, which is why two other aviation upstarts—Aerion and Spike—are focused on the lucrative business-jet sector. Those companies believe they can mitigate sonic booms with aerodynamic tweaks and clever flying. NASA has spent decades pursuing the same objective, and in 2018, the Trump administration allocated a healthy slice of its $633.9 million aeronautics research budget to the task. Fifteen years after the Concorde’s last landing, civilian aviation might be ready to go supersonic again. Scholl founded Boom because he was surprised no one was applying advances in aviation tech to supersonic jets. “We’re trying to do for commercial airplanes what SpaceX is doing for rockets,” he says. The company expects to spend $6 billion or $7 billion bringing its jet, dubbed “the Overture,” to market. So far it has raised about $141 million. That’s only a little more than it’ll cost to build the XB‑1. Starting so small is unusual—but essential given that Boom’s ultimate goal is a 170,000-odd-pound airliner capable of Mach 2.2. It’s highly likely they won’t get it right the first time, Scholl admits. Boom’s headquarters, a gleaming white hangar in a suburb of Denver, bustles with activity. In one corner, a team assembles a mock-up of the Overture’s interior, which features wide seats, wood trim, and a locker under each berth instead of an overhead bin. Not far away, engineers stress-test the carbon-fiber horizontal stabilizer—that’s the little winglet on a plane’s tail—of the XB-1 demonstrator. A growing collection of parts, including a pile of Goodyear aircraft tires, fills one room. Here and there you see models of the airliner, ambitiously sporting the liveries of carriers from around the world. At 170 feet long, the jet will be a bit shorter than a Boeing 777. With a pinpoint nose and triangular delta wing that spans just 60 feet, it will look like a dart. A full-size mock-up of the demonstrator, which will carry two people at 1,400 mph, sits in the middle of the hangar. Airplanes are typically designed around their engines, and the ones that will power the Overture are perhaps its greatest barrier to success—because they don’t exist. For its business to work, Boom needs a propulsion system far more fuel efficient than its demonstration plane’s J85s or even the Rolls-Royce/Snecma Olympus 593 turbojets the Concorde used. That means ditching the afterburner that injects fuel into the exhaust for a second kick of thrust. This extra boost used to be essential for supersonic flight, but aviation tech has come a long way; the newest Mach fighters can speed along without afterburners. “Modern engine technology will get you all the thrust you need without them,” Scholl says. Trouble is, no one makes an engine that’s both capable of supersonic speed without an afterburner and able to generate enough range for airline use. Rolls-Royce, Pratt & Whitney, and GE are developing proposals, but no one’s discussing specifics for the Boom effort yet. Assuming it does produce a powerplant with the needed specs, Boom will have to go through its own aerodynamic contortions to make it work. The company’s engineers are developing a variable-geometry air inlet for the XB‑1 that will maximize efficiency at both supersonic cruising velocities and the relatively slow pace required for takeoff and landing. The carbon-fiber inlet has a hinged flap that lets it change size. At Mach speed, that flap angles upward into the airflow to create a smaller opening, impeding the air coming in while cruising so it flows through the turbine at the right speed and pressure. When going subsonic, the panel retracts to allow the engine to gulp the air required for everything else. It’s not a part you find on many aircraft, and data from recent wind-tunnel tests suggests Boom’s inlet works. “It’s one of the most complex pieces of the airplane,” Scholl says. “Amazingly, we nailed it on the first try.” Boom still has a long way to go though. Developing a new airliner takes years in a process often rife with delays, overruns, and missteps even before regulators dig into things like manufacturing and flight-safety procedures. The French and British consortium that developed the Concorde spent 20 years and $37 billion (today’s dollars) on the project, drawing heavily from government coffers to pull it off. Airbus needed 17 years and some $25 billion to bring the A380 to market, while Boeing devoted eight years and at least $32 billion to the 787 Dreamliner. Still, no less an aviation luminary than Virgin Group founder Richard Branson is betting that Boom can pull it off. His company has offered Boom engineering, manufacturing, and flight-test assistance—and preordered 10 jets. Aerion and Spike have in some ways even loftier ambitions than Scholl’s outfit: They want to quell the sonic boom, something that has vexed generations of aeronautical engineers. Aircraft compress the air around them as they move through the sky, violently jamming together the molecules that comprise Earth’s atmosphere into pressure waves. These waves, which radiate around the airplane like rings from a pebble dropped in a pond, typically dissipate without much fuss. But when a craft exceeds the speed of sound, it races ahead of those ripples, which collapse into a single shock wave and create a percussive boom that sounds like a thunderclap. The airplane’s tail then creates a second shockwave, and a second boom. No one aboard hears the cacophony, but everyone along the flight path can, even when the jet is cruising at altitudes beyond 50,000 feet. The Concorde generated a boom loud enough to rattle windows, startle people, and frighten animals. This prompted the U.S. and many European nations to ban overland flights by supersonic airliners. Boom isn’t concerned about the boom because it is focusing on oceanic flights. Aerion and Spike don’t have the luxury of ignoring the problem, because bizjets must be capable of flying everywhere. While Aerion aims to quiet its airplane by flying it at a speed and altitude that can keep the boom from reaching the ground, Spike thinks aerodynamic sculpting can minimize the racket. Research by Lockheed Martin’s famed Skunk Works division suggests this would work if the craft flies at a prescribed altitude and with the right attitude, so to speak. Spike will almost certainly crib from Lockheed’s ongoing work with NASA on its X-59 QueSST, a “quiet” supersonic jet intended to prove the viability of boom-suppression tech. Mitigating the sound requires directing airflow over the wings and fuselage so the shock waves the airplane sheds don’t combine into a big bang, Lockheed program manager Peter Iosifidis says. “The most important aspect of the design is its shape—what’s touching the air,” he says. Small horizontal stabilizers called canards mounted in front of the wings help, as does a curved and tapered fuselage. Engineers are also integrating quieting measures, such as removing the windshield to decrease the pressure wave it creates (pilots fly by camera), adjusting the airplane’s angle of attack, and tuning its weight to help it maintain the 55,000-foot altitude “sweet spot” needed for these tactics to succeed. Theoretically, these tricks should work. Proving it is the point of the X-59, which Lockheed expects to fly by 2021. The goal is to generate a sonic boom with a perceived decibel level of 75 for anyone on the ground. That’s about as loud as slamming your car door. If successful, the results could convince the U.S. and Europe to reverse their bans on overland commercial supersonic flights. Spike is betting everything on that scenario. The company flew an unmanned, small-scale demonstrator in October 2017 to prove its design could fly. It expects to begin testing a full-size version by the end of 2019 and, if everything works as expected, will start building its S-512 jet that should see test flights in 2021. Spike hopes its airplane will hit the market three years later, in 2024. Its aircraft is notable for having just two engines and no weight-adding windows; its 18 or so passengers will instead view the outside world through enormous, high-resolution digital displays. Aerion’s timeline is only slightly less ambitious: It plans to fly a prototype of its 8-to-12-passenger AS2 in 2023, get it certified by 2025, and deliver airplanes to its customers the year after that. One impediment tobringing back supersonic air travel is solving the technological riddles. The bigger challenge is making it pay. Although the Concorde remains an engineering marvel, it was a commercial failure. British Airways and Air France couldn’t make it profitable. Read Next: Planes of the future will feature virtual reality, yoga studios, and lots of cauliflower Scholl is convinced he can. His pitch goes like this: Boom’s airliner will be smaller, lighter, and more fuel efficient than the Concorde, and therefore cheaper to operate. Flying from, say, London to New York in three hours would allow airlines to make twice as many flights each day and pack them with high-revenue business-class passengers. He sees even greater appeal in crossing the Pacific in six hours. His argument convinced Japan Airlines to invest $10 million in Boom and preorder 20 planes, bringing the order sheet to five airlines and 76 jets. Boom’s internal studies suggest a demand for as many as 1,800 commercial supersonic aircraft by 2035. But aviation analyst Richard Aboulafia, who follows the three supersonic startups closely, questions whether any of them will raise enough money to reach market. “That $6 billion for Boom to reach certification is an honest, good-faith number, but I think they will have a lot of trouble securing it,” he says. Even with investments and preorders, it’s impossible to predict whether that interest will persist or if the plane will meet its performance goals, he says. Then there are the environmental concerns. The new generation of supersonic aircraft could burn five to seven times as much fuel as conventional jets, exceeding their CO2 emission limits by 70 percent, according to a study the International Council on Clean Transportation released in July 2018. To be fair, the report used fuel-consumption estimates gleaned from publicly available data on Boom’s airliner, which hasn’t even flown yet. Scholl argues that the report underestimated the fuel burn of conventional jets while overestimating that of supersonic ones. He believes Boom’s airplane will be at least as efficient in cost per available seat-mile—a common fuel-economy metric in the airline industry—as conventional business-class service. Still, supersonic travel remains glamorous, and carriers might see that as a way of attracting affluent customers. “If airlines or business-jet providers want to differentiate themselves, supersonic sure will do it,” Aboulafia says. Boom is definitely going for glamorous. With its needle-like fuselage, pinpoint-sharp nose, and triangular delta wing, the Overture is one cool-looking craft. The planned interior is no less impressive. A virtual-reality demo offers a glimpse of what crossing the sky at 1,400 mph could be like. No one gets stuck in the middle because there’s just one passenger on either side of the aisle. There’s lots of leather, gleaming surfaces, and polished wood. Every one if its 55 seats faces a giant screen, and customers watch the scenery through large round windows. Scholl says the cabin will be so insulated that you won’t hear the engines. “Our goal is to exude tranquility,” he says. And maybe that’s the real sell: “Tranquility” is not a word anyone uses to describe air travel these days. Neither is “lucrative,” at least when it comes to supersonic transport. The engineers and entrepreneurs working on a new generation of high-speed civilian airplanes aim to change that, with models that could make traveling beyond the speed of sound quieter, cleaner, more glamorous, and, yes, more profitable than the iconic jet that started it all.
