Fourteen years after the retirement of the Aerospatiale/BAC Concorde, the dream of resuming civilian supersonic flight has seemed never more active than in 2017, with four major development efforts scheduled to pass key milestones before the year ends. Activity stretches across laboratories, boardrooms and assembly hangars dotted across the USA.
In Cleveland, Ohio, NASA’s Glenn Research Center is evaluating the aerodynamic characteristics of a preliminary design by Lockheed Martin’s Skunk Works for a jet called QueSST, shaped to muffle the double-crack thunder created by a supersonic shockwave, otherwise known as the sonic boom.
In Boston, start-up Spike Aerospace, funded mainly by Wall Street investors, is developing a subsonic demonstrator version of the supersonic S512 business jet scheduled for first delivery in 2023. Nearly 2,000 miles away in Denver, Colorado, rival start-up Boom – with financing from Silicon Valley, New York and London-based investors – is assembling the XB-1 supersonic demonstrator, with subsonic flight tests scheduled to begin by late 2017 to support an entry-into-service date in 2023.
Amidst these headline-grabbing projects, it’s perhaps forgivable to forget the company in Reno, Nevada, that has been working to conquer the challenge of civilian supersonic flight since a year before Concorde was retired. With the personal backing of oil billionaire Robert Bass and a partnership with Airbus Defence and Space, Aerion plans to soon select the engines that will power the AS2, the supersonic trijet unveiled in 2014.
Despite the flurry of activity this year, several fundamental questions about the feasibility of commercial supersonic travel are yet to be answered – not least is the question of financing. Spike has not disclosed how much funding it has received, but Boom has announced taking in a total of $41 million so far. As impressive as that is for any start-up, it’s the proverbial drop in the bucket towards creating a passenger-carrying aircraft with a level of performance unmatched anywhere in the industry today.
How big is that development and certification bucket? Aerion senior vice-president and chief financial officer Ernest Edwards offers a general estimate: “It’s probably a $4 billion operation.”
Aerion
Supersonic propulsion has existed for nearly 70 years, but the challenges of applying it to a commercial business model remain extraordinarily high. In the event that a company identifies the optimal airframe and engine combination and development goes smoothly, the manufacturer must still create a global support infrastructure that meets the requirements of a very demanding customer base.
“Progress may seem slow to the outside world,” Edwards says. “It’s not as easy as you think, and this all takes time.”
The new crop of private supersonic start-ups demonstrates that interest in the capability of supersonic travel has never wavered, but the challenges have not become easier to solve. In many ways, the task is harder now than in Concorde’s early days.
“Probably more significant today are landing and take-off restrictions,” Edwards says. “Those restrictions were faced by Concorde. It was blackballed in many countries throughout the world. Those requirements are far, far more stringent [now] than they were in those days. These are the challenges that exist.”
If American and European bans on sonic booms over populated areas are not repealed, can the market support a business jet that flies faster than the speed of sound only over water? Assuming such a market exists, is it possible for a large supersonic jet to meet community noise regulations during take-off and climb-out? Finally, will any of the industry’s three engine manufacturers step forward to develop a supersonic engine?
Aerion expects to soon learn the answer to the last question. The company launched in 2002, with Bass’s support for an aircraft that could benefit from decades of research by Richard Tracy, who conceived a design for the first natural laminar flow wing at supersonic speed. The global financial crisis that paralysed parts of the business aviation industry from 2008 to 2011 delayed the development of the original Aerion jet. By the time the company was ready to resume development, community noise regulations had become more severe, ruling out Aerion’s preferred propulsion system – Pratt & Whitney’s JT8D. Meanwhile, a new market survey recommended a shift from trans-Atlantic range to trans-Pacific.
Aerion re-opened negotiations with engine suppliers in 2014 as the AS2 concept was unveiled at EBACE. The company originally targeted engine selection in 2016, but the talks continue with no public timetable set for reaching a conclusion.
“We do have dates on the calendar by which time we’re hoping that we had engine selection. There’s a lot of timing that goes on after that announcement. I think we’d all agree that the sooner the better,” says Ernest Edwards, Aerion’s senior vice-president and chief commercial officer. “I don’t want to make a rushed decision. It’s a big decision. It’s a decision the whole airplane rests on and it has to be the right engine.”
For more than a year, Aerion has insisted that a “couple” of commercial turbofan engines had been proposed that could be modified for a supersonic application. The company has not named the suppliers, but GE Aviation and Rolls-Royce have expressed interest in the commercial supersonic market. Both companies have deep experience with supersonic engines – although both are also struggling to cope with existing commitments in the subsonic commercial market.
“The manufacturers have to come back to us and say, ‘This is what we can give you, and this is how much it costs and this is when we can deliver it to you’,” Edwards says.
The task of persuading the engine manufacturers to commit to the supersonic market could be tricky. Pratt & Whitney supported the original design with a modified version of the JT8D, but backed away from expressing interest as Aerion redesigned the AS2 and switched to quieter engines. Still, Aerion believes other manufacturers are ready to propose modified versions of off-the-shelf powerplants.
Boom promises subsonic demonstrator flights this year and entry-into-service in 2023
Boom
“There are engines in use today that can be modified and adapted for what we need to do. Given that’s the fact, it’s incremental business [for the manufacturers],” Edwards says. “I think that’s how they look at it. I don’t think they’d be talking to us if this wasn’t something they were interested in getting into.”
Despite the absence of a public timetable, Aerion is under pressure to finalise an agreement with an engine partner. New and even stricter community noise regulations take effect in 2017 for aircraft that weigh more than 54,400kg (120,000lb). The new standards make it even harder to select an engine with an inlet fan narrow enough to supply enough thrust to cruise at supersonic speed, yet wide enough to provide the fuel efficiency required to enable trans-Pacific range.
The AS2 is designed to weigh less than 54,400kg, but Aerion’s engineering team is aware that aircraft weights tend to grow through the development and certification process. In the past, Aerion’s plan was to file an application for airworthiness certification to the US Federal Aviation Administration in 2016, allowing the aircraft to be grandfathered under the previous take-off noise standard even if the design weight crosses the 54,400kg threshold. That plan is no longer possible because of the delays in the engine selection process.
“If you’d have asked the question a year or 18 months ago we’d say that was still the plan,” Edwards says. “But you’ve got to prepare for Plan B.”
For Aerion, Plan B means designing the AS2 to stay under the 54,400kg limit, while preparing to meet the stricter standard for take-off noise. That can be a tall order for an aircraft with a G450-sized passenger cabin and the capability of cruising at Mach 1.4 from San Francisco to Tokyo.
Aerion designed the AS2 to fly up to 4,700nm at Mach 1.4 or 5,300nm at Mach 0.95. The latter speed may be subsonic but it’s still 0.03 Mach faster than the Gulfstream G650. However, If the AS2 is required to meet the take-off community noise standards that become effective this year for aircraft over 54,400kg, the company might have to start thinking about trade-offs.
“Do we want A or B? To get the same range, do we sacrifice a little bit of speed? Based on the analysis that we continue to do, 4,750nm is our goal,” Edwards says. “It’s not a deal-killer if we don’t reach 4,750nm for whatever reason. As we study the flights – long range and ultra-long-range in the widebody [business jet] category, we’re surprised by the data we’re seeing, and how infrequently the maximum ranges are ever used. We do want to go faster.”
Such are the challenges for even a well-financed, committed engineering team that has dedicated more than 15 years to solving the problem of commercial supersonic flight. Although start-ups Boom and Spike promise to deliver a certificated aircraft within six years, the road can be long and filled with unexpected twists – not unlike the subsonic business aviation industry.
It’s an industry Aerion’s executive team knows well. Forty years ago, Tracy was the chief engineer for the LearAvia Lear Fan, a composite, turboprop-powered business aircraft that failed in development. He then performed advanced design work on the LearFan 600 business jet, which, after multiple twists and turns, entered service in 1980 as the Canadair CL-600 Challenger, which remains in production today with Bombardier.
By the 1990s, Tracy had launched a new concept for a supersonic natural laminar flow wing. Only a handful of aircraft in history have been designed to cruise at supersonic speed without afterburners, including the Convair B-58, Lockheed SR-71 and Concorde. But each of those designs suffered from heavy fuel consumption that limited range. One of the problems driving the fuel consumption was a wing design in which a smooth flow of air too easily transitions into drag-inducing turbulent streams.
Tracy set out to solve this problem when he formed the Asset Research Group in 1991. Three years later, he patented a design for a supersonic natural laminar flow that departs from the standard delta wing planform found on most commercial and military aircraft designed for supersonic cruise. Instead, Tracy proposed an extremely thin wing swept at an angle shallower than the angle of the supersonic shockwave, preventing the formation of spanwise subsonic flows that easily trip a smooth airflow into turbulent. Such a design, Tracy theorised, could reduce the drag caused by the wing by 50% in supersonic cruise.
Eight years later, Tracy found a financial backer in Bass, who relaunched Asset Research Group as Aerion Corporation. Since 2002, Tracy and his team have been steadily working out the details of the supersonic natural laminar flow wing. With NASA’s support, Aerion initially performed a demonstration of supersonic natural laminar flow in a wind tunnel. A second series of wind tunnel tests examined the effect on laminar flow of manufacturing tolerances for flush rivets and joints. A NASA-owned Boeing F-15 flew supersonic test flights with a subscale wing panel to verify the wind tunnel data. Along the way, Aerion has developed a database of software with design codes for supersonic aircraft, a repository that mostly does not exist outside of the most experienced military aircraft designers.
After 15 years, Aerion finds itself in the unusual position of being a veteran start-up business, still chasing the dream of fielding the original product. As far as the company has come since 2002, the path to certification and delivery remains long and uncertain.
“You can’t get that money back,” Ernest says. “So there’s only one way forward.”
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Source: FlightGlobal.com
