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Future supersonic flights will be quiet and environmentally friendly

The new super(sonic) jets

The past “coronavirus years” were turbulent ones for aviation: Passenger planes were turned into “preighters,” while those who missed traveling could book “flights to nowhere.” But a few ambitious companies, apparently undeterred by travel restrictions and unpredictable passenger and freight volumes, continued to eagerly refine new innovations. One area that received particular attention last year is that of supersonic flight. This technology, which made its debut in the mid-20th century, was recently revived and refined again: The goal is to make it even faster, more environmentally friendly, and more attractive to a selected target group of international travelers.

Tupolew and Concorde: First operations in civilian flight

Like so many other innovations – from GPS tracking to robot vacuums – supersonic flight originated in the military. On October 14, 1947, the American rocket-powered aircraft Bell X-1 was the first to break the sound barrier with a manned flight, reaching a speed of 1,125 km/h (Mach 1.06) at an altitude of about 13,100 meters. Almost twenty years later, the Soviet design firm Tupolew launched the Tu-144, the first commercial supersonic plane on the market. The Tu-144 completed its maiden flight on December 31, 1968, closely followed by the British-French Concorde, which took off successfully for the first time on March 2, 1969. Although the Soviet variant took to the air two months earlier and, with its cruising speed of 2,430 km/h (Mach 2.20), was faster than the Concorde with its top speed of “merely” 2,179 km/h (Mach 2.02), the latter was in service much longer and more actively. While the Tu-144 was only in regular operation for six months and withdrawn from the race after two crashes, the legendary Concorde completed about 50,000 flights at supersonic speeds by 2003, transporting more than 2.5 million passengers. It was seen as the epitome of fast and sophisticated travel. There were no accidents aside from the tragic crash on July 25, 2000 in Paris, but due to the lack of passengers and the inefficiency caused by the high fuel consumption, operations were finally discontinued in 2003. The subject of commercial supersonic flights lost steam over the next few years, which was probably also caused by the high kerosene consumption and the noise pollution of the sonic boom.

“Baby Boom” in the midst of the coronavirus chaos

Civilian supersonic flight entered the public spotlight again in October 2020 when Boom Supersonic, a startup in Denver, Colorado, attracted media attention with the presentation of its “XB-1” prototype. This model, which is also affectionately known as “Baby Boom” and has space for exactly one pilot, is a small version (1:3 scale) of the planned Overture series model. The Overture was at first expected to reach a speed of Mach 2.2 and transport up to 75 passengers over a distance of 8,300 kilometers. This would have made her slightly faster than the legendary Concorde and turned her into the fastest commercial aircraft in the world. At this time Japan Airlines had already ordered 20 units and Virgin Group ten. Although the Overture will initially be used only as a passenger plane, company founder Blake Scholl also reports interest in further development for freight and military transports. In the transport sector, this would also make the plane by far the fastest way to get cargo shipments in the air.

A well-orchestrated introduction: “The Overture”

The first test flights of the XB-1 were scheduled for 2021 in the Mojave Desert, California, to show whether the design and technology would deliver what they had promised. The engine is a decisive factor in whether the Overture can actually reach high travel speeds. That’s why Boom Supersonic teamed up with Rolls Royce to collaborate on the development of an innovative propulsion system.

In the meantime Boom has adjusted some technical details and most recently has slightly changed the plane’s design. With a proposed speed of Mach 1.7 it will turn out “slower” than initially planned. The plane is set to be introduced in 2029 and will be able to transport 65 to 88 passengers over a distance of 7,870 kilometers. First test flights of this model are scheduled to begin in 2026 while a 400,000-square-foot manufacturing facility will be built at Piedmont Triad International Airport in Greensboro, North Carolina. By the way, North Carolina also happens to be home to the first flight in the history of aviation.

Boom’s recent success in developing the “Overture” has paid off: In June 2022 United Airlines announced that it had signed a deal to purchase 15 aircraft, with an option to buy 35 more. In August 2022 American Airlines followed, and agreed to purchase 20 planes with an option for a further 40 aircraft.

The "Overture" project looks like a Concorde 2.0.

Aerion: Powered by bio-fuel and gentle on the ears

Another U.S.-based company with ambitious plans for civilian supersonic flight is Aerion Corporation. Headquartered in Reno, Nevada, the aircraft manufacturer not only wants to exceed the speed of sound with its AS2 but also aims for CO2-neutral operation. The planned model is expected to be ready for flight by 2024 and will be used for business travel. Equipped with an engine from General Electric, it is designed to reach a speed of Mach 1.4 and a range of up to 9,260 km. To achieve CO2-neutral flights, Aerion Corporation wants to use the synthetic paraffinic kerosene fuel (SPK) from its partner Carbon Engineering. And Aerion’s ambitions go even further: The airplane manufacturer also aims to solve the problem of the sonic boom, namely with the “Mach cut-off” principle. But what actually causes a sonic boom?

Short digression into physics: How is a sonic boom created?

The principle behind a sonic boom is simple: Starting at around 1,100 km/h, an aircraft reaches the speed at which soundwaves travel in the air. At that point, since the sounds generated by the plane itself can no longer flow past the equally fast plane in all directions, they accumulate in front of the machine and create a “wall of sound” that is actually a high-pressure area. This shock wave is initially disk-shaped, creating a spectacular optical “cloud disk effect”. But if the aircraft exceeds Mach 1, it overtakes the shock wave, which now forms a “Mach cone.” At the tip of this cone, the sound compresses into an extremely loud bang: the sonic boom.

Currently prohibited: Supersonic flights over mainland

Back to Aerion and the “Mach cut-off,” the physical qualities of which have also been researched by NASA for years. The underlying principle: If the machine is moving just barely faster than the speed of sound and at a sufficient height above the Earth, there will still be a boom, but it won’t be heard all the way on the ground. If this principle could be implemented successfully, this would also enable supersonic flights over the mainland, which are currently prohibited due to the sonic boom. However, this would require precise knowledge of parameters such as temperature, wind conditions and the respective ambient pressure, which requires a complex sensor system in the machine.

The AS2: "quiet and environmentally friendly"

NASA is also researching quiet alternatives

In December 2020, NASA also announced new progress on the plans for the X-59 QueSST (for “Quiet Supersonic Transport”), which they commissioned from Lockheed Martin. This is an experimental aircraft that is designed to reach only 75 decibels even at a supersonic speed of 1,510 km/h or Mach 1.42, roughly corresponding to the traffic noise on a well-traveled road. Following the model’s approval for final assembly in December 2019, the initial flight of this quiet supersonic aircraft is expected in 2022. The aerospace agency is planning to let the X-59 fly over selected communities in 2024 and will then conduct surveys to evaluate public perceptions of the noise pollution. The data from these tests will be shared with regulators in the USA and worldwide in order to potentially pave the way for future supersonic flights over land.

Time is money: Attractive options for business travelers

The main target group for both Boom and Aerion in the near future is that of business travelers who won’t shy away from higher costs as long as they can save travel time. The Boom founder Blake Scholl can currently imagine 500 possible routes for this target group. The Overture could reduce the flight duration from London to New York from seven hours to three hours and 15 minutes, for example; it could travel from San Francisco to Tokyo in five-and-a-half hours instead of eleven and a flight from Los Angeles to Sydney might only take seven instead of 15 hours. Even if current research projects are focusing on passenger transport, an application for highly urgent freight shipments might also be not be too far off. While the fuel and cost efficiency will certainly still need to be refined for the next few years, we continue to watch the rapid development of these design and engineering marvels with wonder and excitement.