Aerion Unveils Major Updates To AS2 Supersonic Business Jet Design
As its team of aerospace heavyweights continues to grow, aircraft developer Aerion Supersonic has unveiled a finalized design for the AS2 business jet, which it believes is not only sustainable but also lays a solid foundation for a follow-on family of high-speed commercial and military derivatives.
With a radically new swept delta wing, revised underslung engines and a sleeker empennage, the configuration differs fundamentally from previous AS2 iterations and is emblematic of a greater level of maturity both for the aircraft design and the company itself, says Aerion CEO Tom Vice. “It’s representative of the amount of innovation we’ve been putting into the airplane,” he says. “But we’ve been putting an equal amount of thought into our long-term strategic plan and the way we look at the marketplace.”
- Delta wing replaces laminar flow design for better all-around performance
- Empennage and wing changes enable shorter, lighter design
Notwithstanding the devastating impact of the COVID-19 pandemic on air travel in 2020, Aerion believes the appetite for reduced journey times and enhanced global mobility will inevitably return in a post-pandemic world. Regardless of whether this happens sooner or later, the company acknowledges that long-term market acceptance of the AS2 still hinges on achieving environmental sustainability, both in terms of noise and emissions.
Combining low noise and carbon-neutral performance while meeting the AS2’s original ambitious performance goals “is really, really hard,” says Vice. Designed to supercruise with nonafterburning engines over ranges around 5,000 nm at up to Mach 1.4, with a cabin large enough for 12 passengers, the AS2 design was already challenging without the sustainability factor. “[The prerequisites] pulled us in a lot of different directions,” he says. “Our task was to optimize around those competing requirements and come up with an aircraft that could meet them all simultaneously.”
The configuration is led by Aerion’s aerodynamic design team in the company’s Reno, Nevada, headquarters and a Palo Alto, California-based group that developed a proprietary multidisciplinary design optimization tool for the supersonic aircraft project. “Those two teams have been working together nonstop over many years, especially the last two, and that’s why this airplane looks the way it does,” says Vice.
First unveiled by founder Robert Bass in 2004, the year after the retirement of the Anglo-French Concorde, the initial Aerion configuration was designed to operate in a new market niche below that Mach 2.2 airliner. Targeted at supersonic speeds over water, it was also tailored for efficient high subsonic, or transonic, flight around Mach 0.96 over land where, in most countries, no sonic boom is allowed.
To fill this hitherto untapped market, the configuration employed a novel wing design shaped for passive supersonic natural laminar flow (SNLF)—a condition in which the boundary layer flow remains stable for longer before becoming turbulent and causing friction drag. The technology was championed by aerodynamicist Richard Tracy—-Aerion’s co-founder and chief technology officer—who believed the low-drag, low-aspect-ratio shape would permit the aircraft to fly with limited transonic drag penalty at high subsonic speed over land and, where permitted, supersonically up to Mach 1.6.
Initial development focused on thin wing profiles in which shaping, rather than active control systems such as suction, could stabilize the boundary layer through pressure distribution. Encouraged by flight-test results of a scaled wing section with NASA in 2010, Aerion estimated the SNLF wing would have 20% less drag than a conventional delta wing and contended that increasing laminar flow fraction could lead to significant weight savings.
Although the overall design morphed from a twinjet to a trijet in 2014 as takeoff and landing noise considerations became a bigger factor, the configuration—by then called the AS2—retained its unusual trapezoidal wing as Aerion went through partnerships with Airbus and, in 2017, Lockheed Martin. The same basic wing shape, though now supporting engines slung under the wing and mounted on the upper fuselage, also continued as a feature until recently, well after the company’s pivotal new partnership with Boeing.
The teaming with Boeing, unveiled in February 2019 just a few months after Aerion signed up GE (GE Aviation) as engine supplier with the Affinity, helped dramatically accelerate the AS2 project. In addition to Boeing, which will support engineering, manufacturing and flight testing, a raft of other partners and suppliers have joined the program. These notably include Honeywell, which is providing the avionics, and Safran for landing gear and nacelles. UK-based GKN Aerospace and Fokker Technologies, which that company acquired in 2015, are providing electrical wiring and the empennage structure. Spirit AeroSystems will supply the forward fuselage.
Spain-based Aernnova will provide the midfuselage structure, while Potez Aeronautique of France is supplying doors. Systems and components will also be provided by Eaton and Parker, and Siemens Digital Industries Software has been selected to support design and development. “We intend to announce others fairly soon as we finalize a couple of last systems,” says Vice.
The latest design update also reflects Aerion’s decision to increase the AS2’s overland speed capability with a technique it calls boomless cruise. With competition stirring, including potential low-boom designs that in the future may build on technology being tested in NASA’s X-59 demonstrator program, the company is keen to make the AS2 equally attractive for transcontinental as well as transoceanic missions. Aerion therefore aims to offer a boomless cruise capability up to around Mach 1.2 by exploiting the Mach cutoff phenomenon in which thicker air at lower altitude refracts the boom away from the ground under particular atmospheric conditions.
Achieving this speed regime with a wing optimized for SNLF was a challenge. “You’re going to fly an airplane in the highest drag region, which is Mach cutoff. To do that, you’ve got to be a very efficient aircraft in virtually every segment of the flight,” says Vice. “So when we started to look at this, we had to think of every element of drag—not just wave drag, but pressure drag, skin friction, lift-induced and of course all the miscellaneous. You have to solve all of those problems.”
As a result, no one technology could dominate, says Vice. “So you see a lot less supersonic natural laminar flow on this airplane because we had to get an aircraft that could meet all of the different competing flight regimes,” he says. “This [new delta wing configuration] just turned out to be an extremely high-performing design for us.” The look of the AS2 is therefore transformed, with a more substantial cranked arrow delta wing planform and pronounced area-ruling around the midfuselage.
The 79-ft.-span wing has large actuated leading and trailing edges for improved low-speed flight and field performance—an important factor for meeting noise regulations with reduced engine power for takeoff. Although no details are being given about the movable surfaces, the trailing edge is believed to support a set of high-speed flaperons inboard, midspan flaps and low-speed ailerons outboard. The leading edge is made up of fixed sections inboard that appear to incorporate laminar flow treatment, while the movable devices extend from the engine nacelle to almost the wingtip.
Two wing-mounted GE Affinity turbofans project forward, enclosed in slim Safran-supplied nacelles. The third engine is mounted in the tail and exhausts through a nozzle directly below the horizontal stabilizer—now mounted immediately aft of the tailfin rather than on top, as in earlier iterations. “The tail sizing allowed us to get to a much shorter airplane,” says Vice, who notes the AS2 is now 144 ft. 11 in. long, compared to almost 180 ft. in earlier iterations.
The shortened length is an outcome of “a combination of the wing sizing, the trailing edge and the tail itself,” he adds. “We didn’t need a big moment arm to get the nose back down at low speed.” The new configuration, which will not require a foreplane, will also allow landing approaches at a shallower angle of attack compared to the Concorde, which relied on vortex--generated lift at low speed. The AS2 will have better visibility over the nose during approach, but, even though it will not require a droop nose like the retired airliner, it will be fitted with an enhanced vision system for improved crew situational awareness.
With a gross weight of 139,000 lb., the aircraft will carry up to 70,000 lb. of fuel and a payload of 8,000 lb. As in the Concorde, the AS2 fuel system will be used to redistribute weight and balance during flight to maintain trim and compensate for changes in the center of pressure, which occurs during the transition to supersonic flight. The aircraft will feature a fly-by-wire flight control system and a 3,000-psi hydraulic system.
Unlike the previous design, in which the engines were shown enclosed behind relatively thick-lipped subsonic--type inlets, the AS2 now features axisymmetric spiked, external compression inlets. “I won’t say a lot about what we do with that inlet, but it meets all of the really tough requirements for inlet distortion for engines that try to be all things to all speed regimes,” says Vice. The spike, which shocks the flow down to subsonic speeds for inlet recovery, forms part of what Vice describes as a “quite sophisticated inlet.”
Although Aerion declines to comment, the front of the inlet is thought to include an automatically controlled variable-geometry section. This may be actuated by translating the spike longitudinally to vary the cone ramp angle, thus controlling the flow area and the shock system. Without describing the specific movement of the inlet ring, Vice says only that “if you watch this aircraft go through about Mach 0.4, I think you’d find it quite an interesting ballet.”
He adds: “We really wanted to have an aircraft that was superefficient at Mach 0.95 and superefficient at Mach 1.4, while at the same time minimizing noise. These are not loud [aircraft]. In fact, they meet the most stringent noise rules.” Vice was speaking shortly after the FAA proposed noise certification regulations that, in the case of the AS2, would set a noise limit at the lateral certification measurement point of 96.5 EPNdB, a flyover limit of 94 EPNdB and an approach limit of 100.2 EPNdB.
To minimize noise on takeoff, the proposed rules would allow use of “variable noise reduction systems,” or dynamic systems such as variable geometry inlets. It would also allow for a programmed lapse rate, which the FAA says is “a fully automated feature incorporated into the engine controls as part of the engine thrust rating structure, as a means of reducing noise.”
Work on the Affinity, the world’s first purpose-designed nonafterburning commercial supersonic engine, is meanwhile underway at GE Aviation, where a product design review is scheduled for later in 2020. “We’re working closely on that timeline,” says Brad Mottier, vice president and general manager of business and general aviation and integrated systems for GE Aviation. “This is a real program; it’s not just a paper exercise. We have hundreds of engineers who are assigned to this full-time, and that number is going to probably triple by the end of the year.”
The company, which launched the Affinity in 2017, has completed the initial design review with Aerion and is assessing benchmarking noise data from a “first-of-its-kind acoustic test on an engine to give us the sound reference for a multistage fan design for aeroacoustics and environmental impacts,” says Mottier. “We ultimately have to build this, so we’re also started to engage with our supply chain.”
Citing competitive reasons, GE and Aerion remain deliberately vague over the heritage and architectural details of the core, which Vice describes simply as off-the-shelf. “The reason why I don’t talk about the core is because it is an incredibly high-performance engine that gives us enormous competitive advantage,” he says. “It is also the basis of the first of a family of Affinity engines, and Aerion is going to be the first of a family of supersonic aircraft. And the last thing either Brad [Mottier] or I want is for our competitors to understand what we are really doing.”
Now thought to be based on a modified version of the high-pressure core of the F110, itself derived from the same F101 core at the heart of the CFM56, the medium-bypass 20,000-lb.-thrust-class Affinity incorporates a new low-pressure system with features not previously seen on any commercial engine. In early renditions, these included a distinctive two-stage fan made up of wide-chord titanium blisks in place of the usual single-stage fan and low-pressure compressor, or booster, found in conventional subsonic engines. Novel features, possibly including a fore-and-aft translating variable geometry system, are also thought to be integrated into the exhaust system to optimize performance and reduce noise.
“Since the end of last year and early this year, we’ve been doing testing on our exhaust system,” says Joel Kirk, advanced systems design and technology leader at GE Aviation. “The work includes acoustic testing and performance testing, as we are trying to optimize those two. There’s obviously a trade there between them, so we are in the process of gathering the data and we’ll continue through midyear. Then we’ll be in a good position to downselect on our exhaust configuration,” he adds.
As part of its push for sustainability Aerion is also designing the AS2 to use 100% alternative jet fuel, rather than a blend. Much of the initial focus for this is at GE. “We’ll be doing combustion testing this summer,” says Kirk. “We’ve already completed a round in February, and we’ll be doing more to show a best-in-class combustion technology.”
Aerion meanwhile aimed to hold an aircraft-level preliminary design review (PDR) in October as part of plans to make first flight in 2024 and debut the AS2 in service in 2026. However, Vice says the COVID-19 pandemic may well change the timeline. “Like every company in the world today, we’re stepping back and taking a hard look at the economic impact of the coronavirus,” he says. “We have a solid liquidity position that takes us well into the middle of next year, even into the fall if necessary, and we are watching closely the volatility and uncertainty in the marketplace.”
The company is also watching the impact on the supply chain. “We’re likely to have to slow things down, and we’re going through that replanning now,” he adds. “But we are on a good solid footing for the overall plan, and we will see what the impact is to the PDR as we get through the next four or five months.”
Aerion has “taken very prudent actions to look at every element of cost,” says Vice. “We’ve cut costs, but the one thing that we will not do is lay people off or furlough. We have built one of the most incredibly talented creative teams, I think, anywhere in the world. And our liquidity position is such that we don’t have to do anything like that. So we’re in good shape. Although there are likely to be some impacts on the program, which will be pushed out, we are very confident that we’ll get through this virus and the economic impacts with it. We’ll come out the other side stronger and get through PDR and get the airplanes delivered.”
Aerion is offering a military AS2 derivative dubbed the High-Altitude Supercruise (HASC) platform to serve as a U.S. high-altitude surveillance and eavesdropping aircraft for the Army, Air Force and Navy. The concept includes new capabilities such as a high-altitude testbed platform for a powerful new class of high-energy lasers with power levels of 500 kW or more.
Aerion’s novel approach also cedes ownership of the design to the military. The baseline concept builds on the commercial-certified empennage, engines, wing and centerbody but adds a customized forward fuselage that would house a government-owned mission system and payload, says Stew Miller, Aerion’s executive vice president of strategic systems. Allowing military control of the design, production and sustainment of a fully modular forward fuselage section “changes the model and it empowers the customer,” Miller says. “This is not a [military] modification,” he adds.
Aerion hopes to propose the idea for the Army’s Aerial Intelligence, Surveillance and Reconnaissance aircraft program, which seeks to acquire up to 10 modified business jets for the role.