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It is surprisingly kind of anticlimactic, Tristan Geppetto Brandenburg says about the time he broke the sound barrier. You dont hear a sonic boom from the cockpit because you are leaving the shock waves behind you. You can only feel that she is happy flying at supersonic speed.Brandenburg is the chief test pilot of Boom Supersonic. And the she hes referring to is the XB-1, a long, thin dart designed to cut through the air in the most efficient way possible. Last month, the XB-1 broke the sound barrier over the Mojave Desert. The event positions Boom Supersonic to produce the first supersonic airliner since the Concorde was grounded in 2003.Getting there will take time. And there are plenty of challenges to overcome, including designing a new engine that can cut down on fuel costs. But Boom Supersonic is confident that it can solve these challenges. If it succeeds, were on the cusp of a new era of air travel that will bring Concorde speed for business class prices.The seeds of Boom SupersonicThe success of the XB-1 is the culmination of a not-so-noisy trip that started when Blake Scholl, the founder and CEO of Boom Supersonic, visited the Museum of Flight in Seattle in his 20s and got into the Concorde for the first time. It was 2007, just four years after the mighty anglo-french beast had been retired. He was surprised that the most amazing airliner ever built was in a museum, not in the skies. I never got to fly on Concorde, he says. He just didnt have the money to spare. It was twenty thousand a ticket and that is, you know, thats really for royalty and rock stars. Its not for ordinary people. But that day I set a lifetime goal of flying supersonic. [Photo: Boom Supersonic]A high school dropout and self-made entrepreneur, Scholl started his career at Amazon in the late 1990s. When everybody else thought it was just an online bookstore, he says. He left Amazon to cofound Kima Labs, a mobile technology startup that was acquired by Groupon in 2012. At that point, he had the money to fly on the Concorde, but it was too latethe legendary airplane retired in 2003 because it was deemed too expensive and too dangerous to fly. Still, Scholl was hopeful. He kept waiting for someone to announce a supersonic jet. He recalls setting a Google search alert because he wanted to be the first to know so he could buy a ticket right away. I kind of assumed somebody would do it. But, after 10 years, it was just crickets.In early 2014, Scholl took aircraft design classes. Back then there were some efforts at creating a supertime business jet, he says. But that would take the price of flying supersonic from $20,000 up to like $20 million. Not exactly a winning formula to democratize really fast flights. Thats when Scholl decided to do something about it. I said, okay, well, nobody is doing this. So theres probably a good reason why, but I want to understand it for myself. Why couldnt you make a supersonic airliner?The Concord was too expensive for the average traveler, but there was still a large market for ultrafast flight in the business world. Thats tens of millions of passengers every year, Scholl points out. If you look at the anatomy of international air travel, its about 20% of seats, but its half the revenue and about 80% of the profit. Business class is where all the money is for international travel. Knowing the price of a business class flatbed, Scholl made calculations to see if it was possible to fly a modern supersonic jet and make a profit. His idea was to create a jet that could allow current business class passengers to get to their destination in half the time at the same price of what they were paying now. He discovered that to make it work economically, it only required a single digit improvement from Concord in fuel efficiency. And I was like, wow, thats pretty small. Its been 50 years. Every generation of airplanes is significantly better efficiency-wise than the generation that came before it. Weve gone through several generations since Concord. We can do this, he thought.I bought every textbook I could find. I read them, I did the problem sets. I did calculus and physics, because I hadnt had any since high school. I took an airplane design class, and I built a spreadsheet model of the airplane and a spreadsheet model of the market. The conclusion was that you didnt have to invent anything to do this. He sought feedback from a Stanford professor, who reviewed his calculations and encouraged him to aim for more speed and more profit, saying the estimates in his spreadsheet were conservative. All the technology he needed was already flying in other airplanes. The 20-year-old technology in the Boeing 707 is all you need to do supersonic, he says. You take a 707, scale it down, make it long and skinny, and put twice as many engines so you can go twice as fast.Of course, it wasnt that simple. But Scholl did think it was doable, so he invested half of his share of the proceeds from the sale of Kima Labs into a new venture to make his dream come true. If he could achieve what everyone thought was impossible, he could change aviation forever. He founded Boom Supersonic and became the CEO in 2015.[Photo: Boom Supersonic]From spreadsheet to composite realityFast-forward to 2024. After multiple design changes, Boom Supersonic made the XB-1, a 62-foot-long jet with short delta-shaped wings that make it look like the tip of a spear. It really looks like prototype planes that the United States built after World War II to fly as fast as an airplane can fly.And like those X-planes flown by heroes like Chuck Yeager, the XB-1 fuselage compresses the air molecules in front of it, creating a force that, when the plane finally goes faster than the speed of sound, unleashes a deafening boom noise that everyone on the ground can hear, shattering windows, dogs, and people alike.NASA tried to mitigate this boom by making an even sharper, longer airplane, the X-59, which will fly later in the year. Thanks to its aerodynamic shape, the X-59 will generate a sound shock that, in theory, will feel like a thump. But while Brandenburg couldnt feel the shockwaves made by XB-1, his ride did cause a very loud boom every time it got supersonic. And yet, nobody on the ground got to hear it.[Image: Boom Supersonic]While Boom built the one-third-scale Mach 2.2-capable XB-1 to test the technologies for the Overture the commercial airliner that Boom Supersonic plans to launch in 2029the latter will be a Mach 1.7 vehicle Mach 1.7 (roughly 1,300 miles per hour). Its more balanced for the economics, says Nick Sheryka, chief flight test engineer at Boom Supersonic. Building a prototype for Mach 2.2 was an incredibly challenging thing to do. We didnt operate XB-1 all the way up to Mach 2.2, but all the design considerations and the difficulty level in designing and building it were based on that key assumption.[Image: Boom Supersonic]The XB-1 is a complex machine with tens of thousands of parts, but most of them are not custom-made. To design and build every single part of the plane, like all military supersonic jets in existence, would have been prohibitively expensive. The design team had to work with what they had and only design parts that you couldnt find anywhere else. We had to make that trade for almost each and every part on the airplane, Sheryka says. Obviously the shape of the aircraft, its structure, the carbon fiber and titanium fuselage of the aircraft, the wings, that was all our design, he adds. The company also created their own landing gear from scratch.The rest was all off-the-shelf parts, what in the industry calls Line Replaceable Unit (LRU), a chunk of a system that you strip off another airplane or something that you could buy from a supplier. Things like the flight control actuators, which is what moves the surfaces that control the plane, were taken from other airplanes. It was a prudent balance of work that needed to be custom versus things that would work off-the-shelf, Sheryka tells me.Sometimes these parts were modified. The data acquisition software necessary to measure things around the plane was a collection of commercial [computer] boxes. They present data to the pilot or the ground system, but they run customized software that Boom wrote explicitly for the project.[Image: Boom Supersonic]One of the biggest design challenges was the modification of the most crucial part for the airplane: its engine. While they are developing a new type of engine for the Overturecalled SymphonyBoom Supersonic couldnt invest the amount required to develop an engine for a one-off prototype. We used surplus military engines for XB-1, he says. But these needed to be modified. When it comes to supersonic propulsion systems, there are essentially two components, the jet engine and the intake. The jet engine, while subsonic in its internal workings, requires a separate component to handle supersonic air. This component is known as the intake or inlet, which serves as an adapter to transition supersonic air to subsonic conditions.[Image: Boom Supersonic]The intakes primary function is to slow down the supersonic air, compressing it in preparation for combustion. The design of intakes for supersonic aircraft can be quite complex. For instance, the SR-71 Blackbirdthe Cold Warera USAF spy plane that holds the record for the fastest air-breathing manned jet in historyfeatures a distinctive spike-like shape in front of its engine, while the Concorde employed rectangular intakes. These designs pose significant challenges in aerodynamic engineering, potentially surpassing the complexity of the engine itself. In the development of the XB-1, our team designed its own intake for the engine we bought, Scholl describes. For Overture we will get our own engines and our own intakes.The result is the first private supersonic airplane in the world, made for orders of magnitude less than most supersonic planes (this is correct and we cant really make a direct comparison with F-35, X-59 or Concorde). Any aircraft thats ever been supersonic is effectively a government program, Sheryka says. There are either military programs or government-sponsored programs, like the Concorde. There wasnt even a turnkey provider, like NASA has done outsourcing the X-59 to Lockheed Martin (with taxpayer dollars). Maybe its more prudent to hire a company to do the prototype for us, Sheryka says. But that didnt exist either.[Photo: Boom Supersonic]The Boom Supersonic is also unique because its been the first clean sheet (designed from the ground up) supersonic aircraft to fly in the United States since the F-35, a military jet fighter developed by Lockheed Martin, which began its layout in the early 90s. The total development timeline for the XB-1 was about eight years. Conceptual design began in earnest in 2016. That design matured in early 2017, when we started doing real detail level engineering, making the drawings, spec-ing components, and ordering them, Sheryka tells me. The hardware started rolling through the door in late 2017, early 2018, and assembly began in 2019 until 2020.There was obviously a huge impact there with COVID. It absolutely impacted the timeline because you cant assemble an airplane if people are remote, Sheryka says. The vehicle started to look complete in the 2020 time frame. Then they began a ground testing campaign in 2021, activating systems for the first time, from electrical power to fuel to hydraulics. They started to do engine runs at the end of 2021 throughout the end of 2022, which is what NASA is currently doing with the X-59. In 2023, XB-1 was shipped to California, first flying in 2024. Four supersonic flights later, on February 10, 2025, Boom Supersonic completed all its tests successfully.The funny thing? They never expected any of those flights to be silent. And yet they were, according to NASA itself, who photographed the sound shockwaves and measured the noise in the ground.[Image: Boom Supersonic]The key to supersonic flight without the boomBrandenburg made the silent boom happen, flying the XB-1 at the right speed and altitude. Its a function of physics, he tells me. Its a function of the atmosphere. The ground crew works to figure out what the actual atmosphere conditions are and then take advantage of those to make the magic happen. They tell you the optimal altitude that presents a good compromise between fuel consumption for range, speed, and to achieve Mach cutoff.Temperature and wind gradients affect the local speed of sound. This makes the sonic shockwave bend as it travels through the air. Eventually, if youve got enough of the temperature differential and a shallow enough shock wave, this physical phenomenon will actually reverse the shock wave and send it back up the atmosphere. Thats why nobody can hear it. There is a boom that comes off the airplane, but it makes a kind of U-turn in the sky, Scholl explains. And as long as the boom is coming off the airplane at the right angle and its high enough, you can think of it as the bottom of the U never touches the ground. And as long as the bottom of the U never touches the ground, theres no audible boom.Unlike the X-59s low-boom approach, where people will hear a distant thud, Boomless Cruiseas Boom Supersonic is branding its Mach cutoff flightaims to entirely eliminate the boom at ground level. The X-59 is designed to manage the shockwaves through its airframe design. The way the engine is placed way on its tail, the fact that theres no cockpit breaking the flow of air, and its extreme Pinocchio nose reduces the sonic boom. Scholl says the approach works, but theres still a boom. With Boomless Cruise, there literally is none.Tristan Geppetto Brandenburg [Photo: Boom Supersonic]Brandenburg tells me that flying XB-1 felt incredibly exciting, especially after the small team spent years building it. Its like the ultimate test flight. Youre getting into this airplane that youve been working on for years, and its finally time to take it for a spin, he says. Once in the air, however, the machine was one of the hardest he has ever flown. The machine didnt use the usual fly-by-wire technology that modern jets use, where a computer interprets your joystick motion and moves the airplane control surfaces to go into the direction the pilot wants. Instead, it was all direct control, which required a lot of effort and concentration, especially as he was approaching the sound barrier and everything started to rattle like it did for pilots back in the late 40s and 50s. The machine was built for speed, Geppetto says, not for maneuverability, so it was very hard to turn it around.Then, 11 minutes and 37 seconds into the first test flight, at an altitude of 33,100 feet over Mojave Desert, Brandenburg silently broke the sound barrier. The rattling anger of the flying beast he was flying disappeared: The XB-1 supersonic was the best she had ever flown. It was her happy place. I could pitch, roll, and everything felt much easier to control. Everything felt smoother. So it was really exciting to take the airplane to her happy place. It was one of only two airplanes that he had flown that seemed to be happier supersonic than they were subsonic. The other one was the F-104 Starfighter, a plane that looks as sci-fi as the XB-1. Ive flown supersonic in the T-38, F-5 and F-18, but those ones seem to be happier at the Mach 0.85 to 0.9 range. The XB1 was the happiest supersonic.[Image: Boom Supersonic]Design lessonsThe XB-1 is effectively a testing ground for Overture. One of the key innovations that will be carried over to their future supersonic airliner is the virtual cockpit. Like the X-59s external visibility system, a big screen that offers an augmented reality view of what lies in front of the pilot, the XB-1 also had a screen designed to provide Geppetto with enhanced situational awareness. His was a tiny TV screen, but it worked great. The virtual cockpit is a significant advancement, he says. It allows us to integrate all the necessary information into a single, intuitive display. This reduces pilot workload and enhances safety, particularly at supersonic speeds. Its also necessary to see the runway when taking off and landing, as Overture will not have a moving nose, like the Concorde did to allow pilots to physically see the landing strip.[Photo: Boom Supersonic]There were other invaluable lessons learned from the XB-1s development which will be crucial for Overtures success, like the way the inlet behaved, the creation process of the fuselage, or how silent boom actually works. Sheryka says that the design process was a lesson unto itself. Were willing to fail along the way. We want to try a few things, iterate, and learn. This enables us to go much faster and ultimately have a much better product. However, he underscores the importance of being willing to iterate, have prototypes, and conduct tests that dont pass, all in pursuit of a successful product. This philosophy is at the heart of Overtures approach.Now, the future of Overture hinges on the development of the Symphony engines, which will be specifically designed for enhanced transonic performance, enabling Boomless Cruise. This technology is pivotal in achieving supersonic flight without the sonic boom. If they can pull it off, Scholl says the Symphony engine will be the real game-changer. It will allow Overture to fly at Mach 1.7 over water and at controlled supersonic speeds over land, while still maintaining economic viability.Scholl says that Overture is designed to fit within existing airport infrastructure. The airplane will be able to operate from existing gates and runways, making it practical for commercial use. He claims that it will be impossible for something like the X-59 to scale to airliner size because it will be absurdly long and impossible to fit in current airports without redesigning or building new gates.But Scholl is aware that hes talking about step 5,000 in a long path to commercial supersonic travel. They are perhaps at step 500. XB-1 has proven that his idea works and that a silent boom can be achieved without extreme investments or weird designs. He still needs to build capable engines, a totally new airframe, a whole range of subsystems from electrical to landing gear, and pass all the imaginable tests and regulations. Its going to be very hard, but now he knows there is a runway. He just needs his old supersonic dream to taxi to it, talk to the tower, and take off.
