The Virgin Group's Richard Branson is no stranger to fanfare.
Whether Branson is starting a new cruise line, founding the space-tourism company Virgin Galactic or merely trying to fly around the world in a hot-air balloon, his involvement in a venture is sure to generate headlines.
So when Branson in November announced Virgin Galactic's intention to offer second-generation, commercial supersonic flights beginning in 2023, headlines proliferated.
"New supersonic jet faster than Concorde unveiled," read a fairly typical Nov. 16 headline, this one online in Britain's Independent.
That announcement, which Virgin Galactic made in conjunction with the Denver-based aerospace startup Boom Technology, wasn't exactly a kickoff. The past few years had already brought a renewed surge in interest among aerospace innovators to build the first supersonic passenger jets since British Airways and Air France took the Concorde out of service in 2003.
Boom formed two years ago with the sole goal of designing a commercial supersonic passenger jet. And two other companies, Aerion Corp. and Spike Aerospace, have been engineering supersonic business jets for longer than that -- Aerion with the assistance of Airbus. Meanwhile, NASA contracted with Lockheed Martin in early 2016 for the engineering of a test supersonic aircraft designed to reduce the level of sonic booms.
A rendering of the interior of a commercial supersonic passenger jet from Boom Technology, which is working in conjunction with Virgin Galactic. Every passenger would have a window seat.
Still, Boom's November unveiling of the XB-1, a subscale prototype of its planned supersonic passenger airliner, combined with Branson's announcement that Virgin Galactic has an option on Boom's first 10 airframes, brought the glamorous idea of supersonic travel back to a mass audience. The question now is whether technological advances, including improvements in aircraft materials, engines and, potentially, in sonic-boom reduction, can make supersonic travel economically viable in a way the Concorde never achieved.
Bullish on 'next generation'
For NASA, the answer to that question is yes.
"We think that this will be the next generation of commercial transport by air," said John Carter, manager of the agency's Quiet Supersonic Technology preliminary design team, who is based at the Armstrong Flight Research Center in California. "It is going to shorten the time between major cities. We think it is going to be a new industry, and we want to make sure U.S. companies are the first to market with supersonic commercial vehicles."
For now though, a major challenge in the commercial viability of supersonic flights is the sonic boom. The U.S. prohibits civil supersonic flights over land due to the disturbances that repeated booms would cause to neighborhoods in the flight paths. Other parts of the world follow the standard set by the U.N.'s civil-aviation arm, which seeks to ensure that "no unacceptable situation for the public" is caused by commercial supersonic aircraft.
That's where NASA comes in. In February, the agency entered into a $20 million contract with Lockheed Martin for design development of a one-man test craft that could deliver a quiet enough boom to be acceptable over land.
Carter said the goal of the project team is for that boom to sound like 75 decibels from an altitude of 50,000 feet, a bit quieter than a telephone dial tone. By comparison, the Concorde often exceeded 110 perceived noise decibels, according to a U.K. government study of the aircraft's initial flights in 1976. That's roughly equivalent to the noise at a nightclub.
The noise of a boom is especially onerous because it's not a one-time blast that occurs when an aircraft crosses the speed of sound threshold, as some misunderstand it to be. Rather, the boom trails with an aircraft as long as it is flying at supersonic speed.
To minimize booms, the NASA and Lockheed Martin teams have focused on the aircraft's shape. Pressure waves, said Carter, work their way off the front of a plane, and it's the sharp corners of the waves that create a sonic boom.
By adding curvature to the shape of the craft, NASA hopes to reduce the intensity of the pressure waves, and ultimately the energy impact from the waves, which human ears perceive as a sonic boom.
In an effort to soften what's known as the plane's pressure signature, NASA is carefully developing a number of design elements, including the shape of the aircraft's nose, how the wings fit into the fuselage and the manner in which the horizontal tails cut through the air.
So far, Carter said, computer modeling is suggesting that the design they have come up with will hold perceived boom noise to the 75-decibel level.
Lockheed Martin is scheduled to deliver the preliminary design of the prototype by the middle of the year. Then, pending funding approval, NASA will begin the second part of the project, the goal of which is to launch a one-man test craft by 2020.
Ultimately, Carter said, the purpose of the entire project is to enable the development of a federal noise standard for overland sonic booms. Only then would more aircraft manufacturers be likely to invest in the development of low-boom supersonic planes.
Carter predicted that low-boom commercial aircraft could be on the market in the late 2020s.
Hurdles to development
The absence of legal, overland sonic-air travel makes the economics of supersonic aircraft development, as well as the crafts' eventual operational fortunes, especially tricky.
For all its fame, just 20 Concordes were ever built, and six of those were prototypes, making the aircraft a commercial failure by almost any standard. Demand for Concorde flights -- it cruised at around Mach 2, going from London to New York in approximately 3.5 hours -- was diminished by its high fuel burn, which translated into roundtrip ticket prices on British Airways that were routinely $10,000 or more at the time the service was the discontinued in 2003.
Overland regulations, coupled with those high sticker prices, sharply limited viable Concorde routes.
In an email last month, Boeing spokesman Tom Kim cited overland regulations as the biggest challenge to the development of a Concorde successor.
"Boeing has no supersonic civil aircraft product under development, but we maintain a continuing interest in technologies that could one day lead to an environmentally acceptable and economically viable supersonic airliner," Kim wrote.
Boom Technologies, however, argues that in light of today's demand for overseas business travel, the time is ripe for the return of commercial supersonic flights.
"Because of advanced composite materials and advancement in engine technologies and advancements in aerodynamics, we can build a jet that is 30% more efficient than the Concorde," said Erin Fisher, Boom Technologies' head of flight control systems.
With the advance of carbon-fiber composite technologies, developers are able to build supersonic aircraft that will be lighter and more fuel efficient than the Concorde. Carbon fiber and other composites are also more durable than the aluminum alloys used in earlier generations of commercial aircraft. As a result, said Jeff Miller, vice president of marketing at Aerion, aircraft developers can experiment with shapes that would not have previously been viable.
A rendering of the AS2 supersonic business jet that Aerion is developing in cooperation with Airbus.
Aerion, Miller said, has been testing new shapes since 2002, and in 2014 the company partnered with Airbus in the development of its eight- to 11-seat business jet called AS2. Renderings show a craft with a thin, quadrilateral wing shape that Miller said will help it cut through the air with less turbulence and less drag than aircraft with the traditional triangular delta wing.
Engineers at Boom are also counting on improving aerodynamics to fuel their enterprise. The XB-1 prototype has a more rounded shape than the tubular Concorde did, especially through the midsection of the aircraft.
Fisher said the designers are refining the shape by running thousands of aerodynamic simulations.
Ultimately, she said, the 42- to 50-seat Boom supersonic aircraft will run at the same fuel burn per seat mile as the business class of a modern widebody aircraft. Branson has already set a target starting roundtrip London-to-New York ticket price of $5,000. The plane, Boom said, will fly at Mach 2.2, 10% faster than the Concorde.
"If you can pay $5,000 from London to New York, would you choose a subsonic or a supersonic jet?" Fisher asked.
Skeptics of its viability
Of course, modern widebody aircraft typically have 200 or more coach and premium-economy class seats to augment revenue from business class, a luxury that Boom aircraft operators wouldn't have. Thus, some analysts said the economics of supersonic flying simply don't work, even when accounting for efficiency upgrades.
"Pie in the sky is perhaps the most appropriate analogy," aviation analyst Bob Mann of R.W. Mann & Co. said of the proposed supersonic ventures.
He said the operating economics of supersonic flying are innately challenging. Beyond the cost of purchasing the aircraft, unit costs for fuel and maintenance are higher for supersonic planes than on traditional jetliners.
And those issues would have to be overcome despite the problem of flying over land, as well as the limited range that can be expected from fast-flying, high fuel-burn aircraft.
"You would have to assume very cheap fuel -- forever -- for starters," Mann said.
The Boom XB-1 prototype was unveiled in November, one-third the size of the planned supersonic jet. The XB-1 is to begin subsonic testing in late 2017.
Richard Aboulafia, an aircraft industry analyst with the Fairfax, Va.-based Teal Group, said that the case for supersonic flying has also eroded in recent years as WiFi connectivity has enabled people to conduct business from the sky.
"You were motivated to fly faster because you were cut off from the world. You were floating in space," Aboulafia said.
He added that a thin supersonic jet can't match the comfort level business fliers are able to experience on today's widebody aircraft.
Beyond the economic issues, both Aboulafia and Mann are skeptical about whether ventures such as Boom, Aerion and Spike can produce an engine that will meet modern supersonic needs.
Aboulafia said that neither GE Aviation, Pratt & Whitney nor Rolls-Royce, the world's three dominant commercial jet-engine designers, have given any indication that they are working on a new civil supersonic engine.
Such an engine is needed because modern commercial engines operate at high bypass ratios -- measured by comparing the amount of air that is propelled by their large diameter turbine-driven fans around the engine core to the amount of air that flows through that hot core. High bypass engines boost fuel efficiency but provide less boost. In addition, their larger fans create more drag than is desirable for supersonic flight. For those reasons, military supersonic jets have smaller turbine fans and lower bypass ratios than current commercial planes, as did previous generations of less fuel-efficient commercial aircraft.
In interviews, Boom, Aerion and Spike all said that they are not designing a new engine from the ground up. Rather, each plans to undertake the less costly option of modifying existing engines in concert with one of the major engine manufacturers.
Aerion's Miller, for example, said that a key step will be to reduce the size of the fan blades for the engine of its AS2 jet.
A rendering of the planned Spike S-512 supersonic business jet. It would hold 18 passengers and cost $100 million.
Meeting the challenge
Despite the challenges, Boom, Aerion and Spike expect to have supersonic planes in the air within the next five years. Boom has set the most aggressive timeline, saying it will begin supersonic test flights near California's Edwards Air Force Base in 2018. Spike is targeting a 2019 test flight for its 18-passenger S-512 business jet, company president Vik Kachoria said. Aerion anticipates a first test flight for the AS2 in 2022.
The companies have chosen sharply different business models in their attempt to bring about the second generation of civilian supersonic flight.
Fisher said Boom is confident in the viability of its commercial aircraft model but also finds that model more appealing than the business-jet route.
"When we create a commercial jet we can bring supersonic technology to everyone and actually make the world a smaller place," she said.
The company isn't counting on low-boom technology or flying over land.
Similarly, Aerion is building the AS2 with the expectation that it will fly at supersonic speeds only on transoceanic routes. The top speed is targeted for Mach 1.5, or 1,150 mph. Miller said the plane will also be able to fly efficiently over land at Mach .95, which is roughly 35% faster than the typical commercial aircraft flies now.
He said Aerion chose to go the business-jet route because it is more confident in the demand. Spike, too, is confident that today's global economy has made conditions ripe for a supersonic business jet.
"There are so many more wealthy individuals, companies and countries than there were 10 years ago," Kachoria said.
He also said that there are fewer technological hurdles in designing a smaller supersonic business jet than in designing a supersonic commercial aircraft. Kachoria cited fuel efficiency and aircraft stability as two challenges that aren't as steep.
But Spike, unlike Boom and Aerion, is building its jet as a low-boom aircraft with the intention of operating over land at a perceived decibel level of 75 or less from the get-go. Such flights wouldn't be enabled under current rules in the U.S., but Kachoria believes they'd meet the regulations in Europe, Asia and the Middle East.
"I think the only way to make a supersonic jet viable is to have a low-boom aircraft that is flying over land," he said.