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May 12, 2023

Hermeus Disrupts Aviation at Hypersonic Speed with Ansys Simulation

Imagine boarding a flight in New York City and landing in Paris 90 minutes later or flying from Los Angeles to Honolulu in an hour. Such accelerated air travel may seem impossible, but a team of engineers has been working diligently since 2018 to make it a reality.

American startup Hermeus is developing air-breathing engines and hypersonic aircraft. Unlike rocket engines that carry both fuel and a supply of oxygen on board, air-breathing engines use oxygen from the atmosphere in the combustion of fuel and are much more efficient for atmospheric high-speed flight. One such engine the company is developing is Chimera — a proprietary, turbine-based combined cycle (TBCC) engine that serves as the life force of Hermeus aircraft.

The Chimera engine is capable of accelerating aircraft to reach Mach 5 speed — approximately 3,836 mph (6,173 kph) — and versions of this engine will power two uncrewed aerial systems (UAS) before being used in the Halcyon, a first-of-its-kind hypersonic passenger aircraft that could transport passengers five times faster than today’s commercial aircraft.

Flying at such speeds comes with a distinct set of challenges, including extreme temperatures and a host of engineering dynamics that require careful investigation before takeoff. For this reason, Hermeus has outlined an incremental product roadmap to analyze and de-risk the milestone engine technology using Ansys multiphysics simulation to ensure speed and safety for thermal, structural, fluid, and electromagnetic (EM) characteristics.

Chimera still

Hermeus’ proprietary turbine-based combined cycle (TBCC) engine, Chimera, is a hybrid turbojet-ramjet engine capable of powering hypersonic aircraft at Mach 5 speeds.

By integrating Ansys solutions, Hermeus validates engineering using a multiphysics approach, minimizes and complements physical testing with virtual validation, and maintains short- and long-term project goals. At this speed, the startup is aiming to debut Halcyon in 2029, which will not only improve personal travel, but has the potential to increase global economic growth significantly by accelerating the speed of commerce and enhancing cultural exchange.

Simulating for Speed

The Hermeus team has a saying: “It’s engineering, not science.” This philosophy drives their ambition to radically accelerate air travel. Essentially, Hermeus engineers believe that once you validate core technologies, you just have to piece those technologies together. They proved this when developing Chimera, which consists of an off-the-shelf turbojet, a ramjet, and a proprietary pre-cooler that reduces the temperature of air entering the turbojet.

The pre-cooler enables the turbojet to reach supersonic speeds around Mach 2 and then the ramjet can kick in and continue to accelerate up to Mach 5. As a result, the hybrid turbojet–ramjet engine demonstrates it is possible to transition from turbojet to ramjet mode — a transition that is necessary to take off from a regular runway at subsonic speed and accelerate to hypersonic speed successfully.

By implementing Ansys simulation, Hermeus gained the critical engineering insights needed to create a fully integrated system without having to build many physical prototypes. Engine analyses explored thermal and structural environments through Ansys Mechanical and computational fluid dynamics (CFD) in Ansys Fluent. With a comprehensive simulation tool set, Hermeus engineers virtually test dynamic environments, unprecedented speeds, and extreme temperatures more quickly, efficiently, and safely than physical testing allows.

“What we like about Ansys simulation is the user friendliness and integration of different physics and engineering disciplines,” says Federico Montanari, Principal Thermal Engineer at Hermeus. “For Chimera, we can look at details of its assembly from a thermal, mechanical, and fluids point of view, then put it all together.”

Through research and development opportunities, Hermeus will build autonomous uncrewed aircraft that de-risk the technology. These aircraft will provide Hermeus with the data and confidence necessary to operate and maintain safe commercial aircraft. Chimera will prove its power later this year with Hermeus’ first aircraft, Quarterhorse — a small UAS that will test the engine in flight, hit high-Mach speeds, and prove reusability.


Hermeus’ first aircraft, the Quarterhorse, is an autonomous uncrewed aerial system (UAS) that will test the Chimera engine’s capabilities for speed and reusability later this year.

“Hermeus is on a multiyear mission to test, de-risk, and prove our engine technology with autonomous aircraft before attempting passenger travel. For us, Ansys simulation is an accelerant,” says Skyler Shuford, founder and chief operating officer of Hermeus. “Developing hypersonic aircraft is complex and testing can be very expensive, so we don’t want to build something that inherently isn’t going to work. With Ansys simulation, we gain more confidence in the hardware we are building in a rapid way.”

Hermeus Quarterhorse

Hermeus simulates the flowfield around Quarterhorse in Ansys Fluent.

Hermeus’ second aircraft, Darkhorse, is a fully reusable, hypersonic, mid-size UAS. It will be powered by the Chimera II, a larger TBCC that will integrate the Pratt & Whitney F100 turbofan, which is used in F-15 and F-16 aircraft. By securing an off-the-shelf turbine engine, Hermeus will save significantly on the time and cost associated with research and development, while remaining on schedule to test the Chimera II in 2024 and debut the Darkhorse by 2025.

Halcyon is Hermeus’ largest development project. The passenger aircraft is capable of traveling more than 125 transoceanic routes at hypersonic speed, which is more than twice the speed of the now-retired supersonic Concorde. It has not yet been determined which engine will power the groundbreaking aircraft.


Halcyon is a hypersonic passenger aircraft that will transport passengers five times faster than today’s commercial aircraft. Hermeus is on a multiyear mission to debut this aircraft by 2029.

Validating the Hardware

In addition to the team’s use of Ansys simulation software, Hermeus integrates real-world data and physical testing to complement virtual testing. Hermeus will continue to use simulation as an active design tool to gain engineering insight and maintain its product roadmap goals. This aligns with a broader trend to “shift simulation left” by incorporating simulation earlier in the design process to inform development — rather than as a late-stage verification or post-analysis tool.

“Having simulations to couple the problem early gets us to a place where we can start building these systems, testing them, and then anchoring and validating these models,” says Shuford. “Then once we’re interpolating within the space of data that we have, we can move very, very fast.”

Hermeus engineers use a combination of both low- and high-fidelity tools to explore design space areas depending on the level of analysis needed. In the near future, the team anticipates a stronger focus on Python-based application programming interfaces (APIs) to support greater integration across tool sets. Ansys' portfolio supports such a shift with an open ecosystem that provides a rare opportunity to amalgamate different simulation workflows. Currently, Ansys’ multiphysics simulation tools help the team confirm sensitive engineering details through virtual testing and prototyping before building physical prototypes. Another advantage of virtual testing and prototyping is that by reducing physical testing the team cuts down on wasted material, cost, and energy consumption during manufacturing.

“We test ways in which we’re going to build things and to assess environments, for example, a thermal environment, which is one of the biggest challenges that we’re going to face as we fly faster,” says Montanari. “That is a very good place for a sophisticated, accurate, and fully capable simulation tools like Ansys Mechanical and Mechanical APDL to help us to predict heat transfer modes.”

Ansys Parametric Design Language (APDL) is a structured scripting language used to interact with the Mechanical solver. Mechanical APDL (MAPDL) helps automate tasks within Mechanical, including creating geometries and establishing solver settings for complex analyses.

With additional support from Ansys Elite Channel Partner Rand Simulation, Hermeus discovers new ways to incorporate the technology, such as how to apply MAPDL and Ansys’ EM tools to perform radiative transfer calculations more efficiently. As its name suggests, radiative transfer, also called radiation transport, is the transfer of energy in the form of EM radiation.

Soaring into the Future

The aviation industry is embracing digital transformation more than ever before to meet consumers’ needs, support sustainability, and achieve cost-efficient productivity.

Like fellow aircraft manufacturers, Hermeus is adopting Ansys’ multiphysics simulation tools to reach these goals. Unlike many other aircraft manufacturers, the company is transforming the future of flight with predictive insights. Hermeus is breaking down barriers to next-generation air travel by applying simulation to accomplish unprecedented engineering feats to make hypersonic passenger travel a viable mode of transportation.

Ansys will join hundreds of innovators from around the world to explore the latest advances in the aviation industry at the 2023 Paris Air Show from June 19-25 in France. Visit Ansys’ chalet #216 to see a model of Hermeus’ technology on display and learn more about how Ansys’ simulation is impacting aviation.

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