2022 — the 75th anniversary of Chuck Yeager’s breaking the “sound barrier” — promises to keep NASA and Lockheed Martin researchers busy as they lay the groundwork for the return of supersonic air travel.
Carefully watching their progress is the handful of outfits proposing to field new fast civil transports, like Exosonic, Hermeus, Boom Aerospace, Japan’s new Supersonic Research Council and others.
A Very Busy Year
In January, NASA’s new X-59 supersonic demonstrator started a month of structural tests at Lockheed Martin’s plant in Fort Worth, Texas. Fuel system calibration tests will follow. Then the Mach 1.4 jet will be trucked back to that contractor’s famed Skunk Works for avionics, engine and subsystems installation; ground vibration, structural coupling, and electromagnetic interference tests; systems checkouts; engine runs; ejection-seat pyrotechnics loading; and ground taxi tests. A May flight readiness review should lead to the first flight this year. Its NASA colors also must be painted on.
“It will be a very busy year,” said Lockheed Martin Program Director David Richardson. Working at a 10-hour-day, six-day-week tempo in Texas and at the Palmdale, Calif., Skunk Works, he said, X-59 workers may not realize the airplane’s potential impact. “It’s a program that’s going to make a big difference.”
To cut costs and speed the $247.5 million X-59’s development, NASA and Lockheed Martin built it from parts of other aircraft — a U.S. Air Force F-16 landing gear, an F-117 control column, and a NASA T-38 rear cockpit and ejection seat.
New is the X-59’s delta wing, a single, continuous structure, “the backbone of the whole airplane,” Richardson said. Spanning 29 feet, 6 inches, it holds the fuel for the 25,000-pound-gross-weight, 99-foot-7-inch-long jet in wingtip-to-wingtip tanks. The fuselage, empennage and 38-foot-long nose attach to it. Fluid and electrical lines run along its top. The nacelle for the single, afterburner-equipped, 22,000-pound-thrust F414-GE-100 engine sits atop the wing’s centerline to reduce its risk of generating shock waves.
Also new is the X-59’s external vision system (XVS). There’s no forward window; the pilot can’t see over the fixed nose. Instead, the pilot will rely on a 4,000-pixel horizontal-resolution (4K) monitor fed by a 4K, forward-facing, nose-mounted camera and a retractable belly camera. The nose camera has a 20-degree-vertical by 30-degree-horizontal view. (Side windows let the pilot look left and right 180 degrees.) Computers with custom image-processing software will create an augmented-reality view of the forward line of sight, with graphical flight data overlays.
A Tolerable Thump
The X-59’s big difference? Helping to end a nearly 50-year FAA ban on civil supersonic flights over the U.S. NASA hopes the X-59 will show aviation regulators that a supersonic transport (SST) can be built and flown that will soften the explosive sonic boom to a tolerable thump.
Sound’s speed varies with temperature — about 660 kt (340 meters/second) at sea level and about 573 kt (295 meters/second) above 40,000 feet.
As a jet approaches the speed of sound (flying transonic), air against it compresses. Drag increases. This led to the 1940s belief in that sound barrier.When that compressed air meets sharp angles, shock waves result. That causes the double-clap boom. “What we’re doing with the X-59 design is trying to spread those waves out and make them weaker,” said Craig Nickol, NASA’s program manager for the low-boom flight demonstrator project.
The boom trails a jet for its entire supersonic cruise and can spread 50 miles wide. “We’re trying to solve a pretty big problem here, to avoid all of that” exposure, said Lori Ozoroski, project manager of NASA’s Commercial Supersonic Technology Project.
The Concorde’s boom measured about 105 perceived decibel level, according to NASA, which compares to nearby thunder or a car door slamming while you’re in the car. NASA wants to get the X-59’s boom below 75. It is designed to change the boom’s shape from an N, with a sharp peak and trough, to something more akin to an exaggerated tilde (~). NASA says that should sound like a car door slamming 20 feet away. The Japan Aerospace Exploration Agency (JAXA) is working with NASA and Boeing to validate the X-59’s low-boom design using a 1.62-scale X-59 model for wind tunnel tests at NASA and JAXA facilities. JAXA and NASA have collaborated on supersonic research for nearly 20 years.
Community response will determine its success. Starting in 2024, the demonstrator will fly over U.S. cities at 55,000 feet, with ground recorders capturing overflight sounds. Residents will be surveyed about aircraft noise, both after overflights and when no overflights occurred. That survey, concluding in 2026, is intended to determine whether X-59 flights produce tolerable background noise. (In addition to pursuing low-boom configurations, today’s SST developers want their aircraft to minimize adverse environmental conditions. They plan for 100% use of sustainable aviation fuels, for instance, and zero carbon footprints for their aircraft.)
“If we can prove the low-boom approach works over real communities, that’s the first step to enable this industry,” Nickol said.
The FAA’s 1973 ban hobbled SSTs, blocking operators’ profits from inland or overland routes (Europe to L.A. or Singapore). Serving Paris-Chicago or London-Dallas meant flying overland at fuel-guzzling subsonic speeds. In the mid-1970s, only two SSTs entered commercial service: Russia’s Tupolev Tu-144 (1975) and the Aérospatiale/British Aircraft Corp. Concorde (1976). Flying at Mach 2, each saw heavily subsidized but limited use. Commercial Tu-144 service ended in 1983, Concorde service in 2003.
Supersonic business jet projects in the 1990s and 2000s (Dassault, Russia’s Sukhoi paired with Gulfstream, Supersonic Aerospace International and Lockheed, and Spike Aerospace) failed to produce a jet, though Spike is still pursuing development of its 18-passenger, Mach 1.6 S-512.
Yeager piloted his rocket-powered Bell Aircraft X-1 to a speed of Mach 1.06 at 43,000 feet over Muroc Field, Calif., on Oct. 14, 1947. Today, civil air travelers are stuck with a Mach 0.99 speed limit.
A revived industry could sell $85 billion in business SSTs and $75 billion in commercial ones globally by 2040, says investment bank UBS. “We see supersonic bizjets viable in the late ‘20s and supersonic commercial jets in the mid-to-late ‘30s, with hypersonic (Mach 5) travel a decade later,” a UBS representative said.
Still, the SST industry’s foundation is shaky. Consider front-runner Aerion Supersonic.
Founded in 2003 by billionaire Robert Bass, it spent 18 years developing the 8-to-12-passenger, Mach 1.4 AS2 business jet, with a designed 4,500-5,500-nm range and $120 million price. Aerion worked with GE on the Affinity engine for it. Boeing, in 2019, made a significant investment, pledging engineering and manufacturing assistance. Aerion reported $11 billion-plus in orders.
But the Reno, Nev.-based company shut down on May 21, 2021, saying “it has proven hugely challenging” to secure new capital to start AS2 production by 2023. Squeezed by the 737 Max scandal and Covid-related global travel woes, Boeing cut funding for aircraft development. New subsonic business jets with Mach 0.9+ speeds and ranges 36% to 66% greater than the AS2’s hurt its prospects. Efforts to get private funding failed. Aerion liquidated its assets.
Exosonic is Optimistic
Despite that, SST proponents are optimistic. They include Norris Tie, co-founder of Berkeley, California-based Exosonic, set up in 2019 to build a low-boom, Mach 1.8, 70-passenger, 5,000-nm-range supersonic airliner. Exosonic has identified 340 overwater routes that can be flown supersonically, and 1,200 more that could be served by an SST cleared to fly overland.
Tie started Exosonic with Chief Technical Officer Tim MacDonald after they met at Stanford University. Tie’s drive to build an SST traces to the 12-hour flights he took as a child to visit family in China and was reinforced in conversations with business travelers.
“If people had the choice of working on an airplane or working on the ground, generally people would like to work on the ground,” Tie said.
“No one wants to work in an airplane.”
Unlike some competitors, Exosonic wants to fly supersonic overland. “We want to change the speed limit to a noise limit, where you can go faster than the speed of sound overland so long as you are quiet enough.”
Exosonic’s focus is on shaping its aircraft’s boom “as our kind of secret sauce,” said Tie, who worked for several years on the X-59 as a Lockheed Martin propulsion engineer. “We certainly think that’s achievable.”
NASA already has shown that. A 2003 experiment with the Defense Advanced Research Projects Agency, which modified the body of an F-5E jet, “was really the first time that anybody proved that you could shape and maintain a shape of a sonic boom,” NASA’s Ozoroski said. In 2004-2007, NASA and Gulfstream proved that a 24-foot extendable lance (dubbed Quiet Spike) on an F-15B’s nose could generate shock waves ahead of the fighter that prevented the jet’s shock waves from merging into an “N-wave” boom.
Exosonic’s original goal was delivering a certificated SST by 2030. The priority now is to develop supersonic uncrewed aerial vehicles (UAVs) for commercial and government customers this decade. (Last October, Exosonic received a USAF contract for a low-boom supersonic UAV demonstrator, which might be used as an adversary challenging USAF pilots in flight training.) It’s now shooting for SST delivery in the mid-2030s.
That pivot has several advantages, Tie said. With a short-term path to revenue, Exosonic can demonstrate technologies directly relevant to its SST and gain experience designing, manufacturing and maintaining supersonic aircraft. “To airlines, a big concern is can you actually maintain this aircraft,” he said. If you can’t sustain a new-technology airplane, “it’s just sitting on the ground as you wait to repair it.” With UAVs flying earlier, “we’ll really understand how to maintain, repair and overhaul our airplanes and engines and bring that experience to the supersonic airliner and ultimately to our airline customers.”
Exosonic has a separate USAF contract to develop an executive SST concept, such as a new Air Force One. “Having the Air Force’s feedback and support has been great in talking to other customers, some suppliers and key partners that we’ve been able to establish contact with” based on the contract awards, Tie said. “It’s also been very helpful in providing funding to hire employees and do some system design work and the administrative tasks required to support the efforts.”
Hermeus and Boom Each Partner Up, Too
Like Exosonic, Hermeus and Boom have USAF concept-development contracts.
Atlanta-based Hermeus, founded in 2018 by four commercial space industry veterans, aims to build a reusable, Mach 5 aircraft with current mature technology. “There really aren’t any science miracles that need to happen,” CEO AJ Piplica told the podcast Acquisition Talk. “It’s really focused on the engineering of how you get everything to work together at the system level efficiently enough to actually go fly a mission.”
Hermeus’ long-term vision is “accelerating the global human transportation network,” Piplica said. A hypersonic jet could cross the Atlantic in 90 minutes, a great capability for an Air Force One.
A $60 million USAF partnership helps fund flight testing of Hermeus’ first aircraft, the autonomous Quarterhorse, and validate its engine. That engine pairs a GE J85 turbojet (to propel Quarterhorse to Mach 2) with a ramjet to kick in at Mach 3 and take the jet to Mach 5. To bridge the gap, Hermeus developed a pre-cooler mounted before the J85. It will take 800-degree F high-speed air down to 125 degrees before it reaches the turbojet, allowing the J85 to boost Quarterhorse to Mach 3.
Hermeus unveiled the Quarterhorse prototype Nov. 9 at its Atlanta test site at DeKalb-Peachtree Airport, running its engine at full military afterburner power.
Hermeus also is partnering with NASA to develop aircraft concepts of operation, including analysis of high-Mach thrust performance, thermal management, integrated power generation, and cabin systems.
Centennial, Colo.-based Boom Aerospace, formed in 2014, entered a $60-million USAF strategic partnership in January to accelerate R&D on its Mach 1.7, 65-to-88-passenger Overture airliner for the presidential/executive transport mission. (In 2018, the company referred to it as a Mach 2.2 bird.) It plans on the 4,250-nm-range, Rolls-Royce-powered jet being flown over water. It aims to be flying passengers by 2030. Japan Airlines (a strategic partner), Virgin Group and United Airlines have ordered Overtures.
Boom is preparing to fly its single-seat, 73-foot-long XB-1 demonstrator, which was powered up late last year. It also is getting set to build its Overture production facility at Greensboro, N.C.’s Piedmont Triad International Airport (see sidebar page 53).
Across the Pacific, JAXA and industry partners last June established the Japan Supersonic Research Council to cooperate in supersonic research and development, including airframe designs to reduce sonic booms, and pursue joint development of supersonic aircraft in about 2030 by Japanese industry. Partners are the Japan Aircraft Development Corp., the Society of Japanese Aerospace Companies, Mitsubishi Heavy Industries, Kawasaki Heavy Industries, Subaru and IHI Corp. (formerly Ishikawajima-Harima Heavy Industries).
Back at Lockheed Martin, the team is particularly excited about the X-59. “It’s like the Spirit of St. Louis,” Richardson, the program director, said. “There’s only one. There’s an incredible amount of pride that we have here in being able to do this unique X-plane.”
With the Skunk Works noted for top-secret aircraft programs, “the other thing unique about it is that it is something that we can talk about with our families and our friends,” he added. “We don’t get to do that a lot in our careers.”