As technological milestones go, two inaugural flights set to take place in 2022 may well determine just how far away supersonic commercial air travel may be to become a reality again.
Late this summer, NASA’s X-59 Low-Boom Supersonic Demonstrator will enter the first of three phases of test flights to evaluate the public acceptability of low-[sonic] boom supersonic flight over land. Data from the flights will be used to inform an International Civil Aviation Organization (ICAO) Committee on Aviation Environmental Protection meeting scheduled for 2025 to establish a standard for an allowable loudness level created by a sonic boom when an aircraft breaks the sound barrier.
Separately, in 2022 Boom Supersonic expects to fly its XB-1, a demonstrator for its planned transoceanic airliner designed to carry 65 to 88 passengers and cruise at 1.7 times the speed of sound at 60,000 ft. compared to around Mach 0.8 for the fastest commercial aircraft today. United Airlines has ordered 15 “Overture” jets as long as the model, once developed, meets safety, operating and environmental sustainability requirements.
“In aerospace, we have a history of glory projects driven by national-prestige politics,” said Boom founder and CEO Blake Scholl. Noting that the Anglo-French Concorde was too noisy to be used at most airports, he added: “Learning from Concorde and building upon its foundation, we defined three core principles to guide every strategic decision and facet of [what we do]—speed, safety and sustainability. For us, these principles will enable supersonic flight that is affordable for passengers, profitable for airlines and capable of reaching economies of scale with tens of millions of air travelers.”
Boom expects to complete development in time for Overture to begin carrying passengers by 2029. if past is prologue, however, that target date may be overly ambitious—virtually all new clean-sheet commercial aircraft models have taken longer to enter revenue service than developers projected at the outset.
Regardless, supersonic commercial air travel is all but inevitable, according to many industry observers. The only question is whether it will be in this decade or the next. United’s commitment to purchase Overture jets would strongly suggest there’s a strong desire among some major airlines to add supersonic air travel service to their network of long-haul routes.
But first the aerospace industry will need to validate the technology for quieter sonic booms. Noise was the root cause of the Concorde’s demise.
Lockheed Martin is poised to start structural tests of the X-59 as part of final preparations for flight tests in Palmdale, CA. Assembly of the aircraft was completed in 2021 in Lockheed Martin’s Skunk Works and was transported to Texas for structural tests in December. With its extended nose section attached, the X-59 is almost 100 ft. long. Following the evaluation, the aircraft’s General Electric F414 engine will be installed.
The X-59 will start full envelope expansion tests—referring to the capabilities of an air vehicle’s design—when the aircraft is transferred to NASA Armstrong Flight Research Center at Edwards Air Force Base. “It will go pretty quickly to supersonic speed, and we will take the opportunity if it presents itself to make some initial [sound] measurements,” said Peter Coen, NASA’s Low-Boom Flight Demonstration mission integration manager.
Envelope expansion marks the first of three main flight test phases planned for the X-59, which is designed to re-shape the supersonic shock wave pattern to substantially reduce the sonic boom to more of a sonic “thump” when it reaches the ground. The second phase, starting next year, will consist of acoustic validation flights with measurements of the pressure taken in-flight at mid-field distances and on the ground.
In the third phase of the program, NASA will route X-59 flights directly over select U.S. cities between 2024 and 2026 and then gather data on the public’s reaction to the sound the aircraft produces. The target is to lower the classic “double thump” of a sonic boom to just 75 perceived decibels or less in supersonic cruise at Mach 1.4, according to Coen.