The Aerion Corp. decision in May 2021 to cease operations immediately raised questions on whether it was a “category killer,” the end of supersonic aspirations. After nearly two decades of design efforts, Aerion was believed to have the inside track to returning a civil supersonic aircraft to market. However, a lack of support from the investment community brought those efforts to a screeching halt, raising questions about the viability of supersonic.

The issues for Aerion were financial rather than a technological barrier as the company had accrued some four-dozen patents. Further, it was just one of several efforts underway, and at least one, involving a partnership between Skunk Works giant Lockheed Martin and NASA, may play a key role in the future of supersonic flight.

The Quesst for Supersonic

Lockheed Martin—which is no stranger to supersonic flight—and NASA are in the midst of a multi-year Quesst research project designed to gather data on supersonic noise signatures that could be used in a potential reevaluation of a ban on supersonic flight over land. This research will involve a series of supersonic flights of a specially designed “X” plane (the X-59) over various communities to assess noise impact.

The 100-foot-long X-59, however, isn’t the traditional supersonic aircraft of the past. It has special design features and technologies that will reduce the sonic boom to a “gentle thump” by the time the noise reaches the ground.

To accomplish this, the aircraft is incorporating an “out mold line” shape design to disperse supersonic shockwaves, buffering the traditional sonic boom. Its thin, long nose obscures visibility, so the team replaced the forward-facing window with an eXternal Vision System that uses sensors, computers, and HD displays to give a view that the window otherwise would have. Other features include swept-back wings spanning nearly 30 feet designed to reduce air drag.

The program recently surpassed some important milestones, including low-speed wind tunnel tests of a scaled model that occurred in mid-2022 at the Skunk Works facility in Palmdale, California, confirming flight control data.

That was followed by the announcement in November that the 13-foot-long, 22,000-pounds-thrust GE Aviation F414-GE-100 engine was installed on the X-59, which will fly at speeds up to Mach 1.4 and altitudes at 55,000 feet.

“The engine installation is the culmination of years of design and planning by the NASA, Lockheed Martin, and General Electric Aviation teams,” said Ray Castner, NASA’s propulsion performance lead for the X-59, who called the installation process smooth after months of developing the key procedures for the step.

This will be followed by a series of ground tests culminating in the first flight of the X-59 this year. The original aggressive schedule had slipped a few years and plans now call for the data-gathering flights to begin in the middle of the decade, following acoustic validation trials. However, the goal is still to have data in time for delivery to the International Civil Aviation Organization as it is anticipated to deliberate supersonic standards later in the decade.

‘Semi-stealth’

As this work progresses other supersonic developers are watching closely. One such company, Spike Aerospace, has unveiled plans for the 18-passenger, low-boom, Mach 1.6 S-512 business jet. It has assembled a team of engineers with experience from companies such as Gulfstream, Boeing, Eclipse, Icon, Embraer, and Honeywell, and is working with companies such as Greenpoint Technologies, Siemens, Maya Simulation, and Quartus Engineering for expertise in aircraft design, engineering, manufacturing, and testing. Last year, the company announced a memorandum of understanding for Tech Mahindra to assist with engineering, optimization, and composites.

Spike president and CEO Vik "Max" Kachoria, acknowledged that the company has been quiet as of late, but told AIN that “The S-512 program is moving along nicely and we are very excited about the progress made in the last few years.”

He further noted that such a development will take years of engineering, testing, and certification, so the company has decided to operate in a “semi-stealth mode where what we are doing is well known but the specifics are reserved for our key stakeholders…we have taken on the slogan ‘it’s good to be quiet.’’

Pointing to the demise of other “prominent programs,” Kachoria added, he was incorporating lessons learned for a future reveal.

Meanwhile, he further noted Spike has been carefully following the X-59 progress and is looking for the data that the program will generate on community tolerance of sonic booms and opportunities for aerodynamic shaping to minimize booms.

The Big Boom

At the same time, another supersonic developer, Boom Supersonic has remained in the headlines as it seeks to bring its four-engine, Mach 1.7 65-to-80 passenger Overture airliner to market. Boom has racked up commitments for 130 of the supersonic model from the likes of American Airlines, United Airlines, and Japan Airlines, and has assembled a team of suppliers including Northrop Grumman, Collins Aerospace, Eaton, and Safran Landing Systems, among others.

Notably, Boom’s customer base includes the U.S. Air Force, which will provide critical resources to help fund development.

Boom is targeting a 2025 rollout of the 201-foot-long aircraft that will have a 106-foot wing span and be capable of flying at 60,000 feet and have a 4,250-nm range. The company believes sustainability is a must for the future of the program, and as such is looking at the ability to run on 100 percent sustainable fuels.

A remaining question for the program is the powerplant. An exploratory partnership with Rolls-Royce ended last year, with the engine maker saying, “After careful consideration, Rolls-Royce has determined that the commercial aviation supersonic market is not currently a priority for us and, therefore, will not pursue further work on the program at this time.”

However, after that announcement, Boom brought Ric Parker, former Rolls-Royce chief technology officer and chair of the Singapore Aerospace Program, onto its board of advisors to lend technical, sustainability, and engine expertise. During the late September press announcement of the addition, Boom founder and CEO Blake Scholl hinted at forthcoming announcements, saying the company was preparing to unveil an engine partner and a “transformational new economic model for Overture.” At press time, those announcements had not yet been made.

Also imminent were anticipated groundbreaking for a factory in Greensboro, North Carolina, as well as the first flight of the precursor to Overture, XB-1.

A Hypersonic Leap

As others pursue supersonic, four alumni from SpaceX and Blue Origin who worked together at Generation Orbit on the development of the hypersonic rocket aircraft X-60A turned their eyes to hypersonics.

This was the foundation of Hermeus, which has ambitious to develop, two prototype aircraft—Quarterhorse and Darkhorse—and ultimately Halcyon, a 20-passenger Mach 5 aircraft that is planned for commercial markets.

With their expertise, the aerospace executives surmised that hypersonics may be a smoother path to market than supersonics because of military support applications.

Additionally, a Jefferies report noted “Hermeus believes hypersonic aircraft may actually be easier than supersonic because the hypersonic engine uses an off-the-shelf gas turbine engine and pre-cooler up to Mach 3 and then a ramjet to Mach 5, compared to building out the supply chain for a clean sheet supersonic engine.”

The team recently tested that out, successfully demonstrating turbojet to ramjet transition within its engine, Chimera. The Atlanta-based company called the demonstration “one of the most important technological feats to making operational hypersonic flight a reality.”

Chimera is a turbine-based combined-cycle engine that essentially is a hybrid between a turbojet and a ramjet. The ability to transition between the two will enable Hermeus’s first demonstrator aircraft, Quarterhorse, to take off from a regular runway and then accelerate to high-Mach speeds, the company explained.

Testing took place at the Notre Dame Turbomachinery Laboratory, which has the ability to provide heated air to simulate high-Mach temperatures and pressures, Hermeus said.

“The Notre Dame facility allowed us to create conditions similar to what we’ll see in flight,” said Hermeus chief technology officer Glenn Case. “Completing this testing on the ground significantly de-risks our Quarterhorse flight-test campaign, which will begin late next year.”

Hermeus added that the cost and speed in which it was able to reach the milestone is notable—the company designed, built, and tested the engine within 21 months for $18 million.

“This achievement is a major technical milestone for Hermeus,” said CEO AJ Piplica. “But more than that, it’s a proof point that demonstrates how our small team can rapidly design, build, and test hardware with budgets significantly smaller than industry peers.”

Chimera is designed with a pre-cooler to reduce the temperature of the air coming into the turbojet. Once the aircraft reaches Mach 3, the engine will bypass incoming air around the turbojet, enabling the ramjet to take over. The company noted its design is unique because most hypersonic platforms are powered by rocket engines not suitable for passenger flight.

With the demonstration complete, Hermeus is turning its focus on the completion of Quarterhorse for its first flight in late 2023.

Quarterhorse will provide research toward the next aircraft, the uncrewed hypersonic Darkhorse, which in turn will provide data to support the commercial aircraft Halycon. Hermeus has estimated a market for 500 hypersonic aircraft by 2030 with a price in excess of $200 million.

As for its theory on more accessible capital, Hermeus was able to secure a $100 million Series B funding round last year. Led by entrepreneur Sam Altman, the funding brought in investors Founder's Fund and In-Q-Tel (a strategic investor to U.S. Intelligence agencies and its allies), along with support from existing investors Khosla Ventures, Canaan Partners, Bling Capital, and Revolution’s Rise of the Rest. That was followed by a strategic investment that a Raytheon Technologies corporate venture capital group, RTX Ventures, made in the Atlanta hypersonics startup.

The U.S. Air Force and NASA had previously partnered with Hermeus on research surrounding the development of hypersonic aircraft. The U.S. Air Force had a $60 million contract, but in July, Hermeus announced that the service had selected the company to support the Advanced Battle Management System contract, which has a $950 million ceiling.

With government applications clearly established, questions have been raised about whether the market could support speedy aircraft at supersonic or hypersonic levels. Rolland Vincent, president of Rolland Vincent Associations and creator and director of JetNet iQ, says yes. He pointed to a recent JetNet iQ survey that found 4.1 percent selected “a supersonic business jet” in response to the question “If you have an opportunity to invest $500 million in the business aviation industry, where would you invest for the best return?” That number fell to 2 percent in Europe and 3.9 percent in North America but jumped to 5.7 percent in Latin America and the Caribbean and 6.1 percent in the rest of the world.

“Supersonic and hypersonic aircraft are still very much in the future for our industry,” Vincent said. “The unfortunate demise of Aerion was unexpected, at least in my opinion. They had invested an enormous amount of time, effort, and capital to refine their designs and build up industrial partnerships, and they created for themselves the best opportunity to be first to market.”

The top of the business jet market has strong pricing power and that will be “all the more so” with initial supersonic and eventual hypersonic aircraft, he added.

He further surmised that, somewhat ironically, the massive capital flowing into advanced air mobility will benefit the entire business aviation ecosystem. “Customers' desire for door-to-door speed is not confined to short-haul missions where these new ‘green’ air mobility aircraft will be operated. The imperative for supersonic and hypersonic designs will be to innovate to demonstrate environmental sensitivity.”

General Aviation Manufacturers Association president and CEO Pete Bunce agreed: “There is a keen eye on the continued development of new supersonic and hypersonic technologies. It is important that these and other new innovative technologies are focused on safety and strengthening our commitments to environmental sustainability.”