Hypersonic Engine with 3D Printed Parts Achieves Key Milestone in Hypersonic Flight

Hypersonic aircraft startup Hermeus has set a new milestone as Chimera, its flagship turbine-based cycle engine, demonstrated it can successfully transition from turbojet to ramjet. Such a transition allows reusable hypersonic planes to take off from regular runways before accelerating up to high-Mach speeds, one of the essential technological feats to making operational hypersonic flight a reality.

Render of Hermeus’ future commercial hypersonic aircraft, the Halcyon. Image courtesy of Hermeus.

This milestone reflects the brand’s promise of building the world’s fastest aircraft to connect people faster and bring much-needed innovation to commercial flight. According to Hermeus, once its planes reach Mach 5 – more than twice the speed of the supersonic Concorde – passengers will be able to cross the Atlantic in 90 minutes or go from Los Angeles to Honolulu in one hour.

To power the startup’s first plane, a remotely piloted hypersonic aircraft called Quarterhorse, Hermeus will use the Chimera engine, which uses 15% of additively manufactured parts. For the task, engineers acquired Velo3D’s original Sapphire and large-format Sapphire XC machines. The printers, both of which are calibrated for Inconel 718, are not just being used to build parts for Hermeus’ Chimera engine but also for the Quarterhorse aircraft.

Hermeus engineer depowders the first of many builds off the Velo3D Sapphire system. Image courtesy of Hermeus via LinkedIn.

Last September, Hermeus Chief Technology Officer (CTO) Glenn Case said metal 3D printing is a core component of the brand’s plan to vertically integrate production. Manufacturing in-house allows the startup to keep up a tight feedback loop between engineers and technicians which is key to the company’s ability to iterate quickly. Additionally, vertical integration eases reliance on outside vendors and allows for better control of the supply chain, which has become one of the key after-effects of the pandemic in the aviation industry, negatively impacting aircraft operations worldwide.

Given this whirlwind scenario, 3D printing has become a more feasible option to counter intermittent supply chain disruptions. Hermeus’ use of Velo3D’s AM technology is a great example of this, especially since Sapphire will help increase performance, consolidate components, reduce aircraft weight and minimize external dependencies.

Expressing his enthusiasm for the latest application of Velo3D’s machines, Founder and CEO Benny Buller said, “Hypersonics is an extremely challenging subset of the aviation industry and at the speeds that Hermeus will achieve, temperature, vibration, and aerodynamics play major factors in the flight of the aircraft.”

Building Chimera

In just 21 months and using $18 million, the Hermeus team designed, built, and tested Chimera. More than a technical milestone for Hermeus, this achievement is a “proof of point” that demonstrates how a small group of people can rapidly take hardware from prototype to testing with significantly smaller budgets than other industry peers, explains Hermeus Founder and CEO AJ Piplica.

While most hypersonic platforms use rockets, Hermeus’ approach will allow the company to use existing infrastructure at traditional airports. In addition, by making a full-range air-breathing hypersonic engine that does not require a rocket to accelerate, Hermeus sets the stage for operational hypersonic flight – meaning aircraft that can be rapidly re-used. This makes the flagship turbine-based combined cycle engine (TBCC)  Chimera engine unique in the field of hypersonics.

Hermeus’ Chimera, a full-scale Mach 5 engine with 3D printed parts. Image courtesy of Hermeus.

An additional benefit of this engine design is that it accommodates existing transportation infrastructure. This is important not just for hypersonic testing but critical given Hermeus’ goal of radically accelerating passenger travel through hypersonic flight.

Furthermore, the engine is built on legacy technology. On the path to hypersonic passenger aircraft, Hermeus teamed up with NASA to commercialize high-speed flight technology that the agency has been exploring for decades. Under the Space Act Agreement (SAA), the technical solutions developed by NASA and Hermeus via this partnership are the core of the TBCC for the first series of aircraft.

Powering hypersonic flight

Once operational, the company says Chimera will use low speeds in turbojet mode, just like any jet aircraft. But as the temperature and the speed of the incoming air increase, turbojets will hit their performance limit at around Mach 2. Then Chimera’s pre-cooler is expected to reduce the temperature of the air coming into the turbojet, allowing Hermeus to “squeeze out” a bit more performance from the turbojet before transitioning to ramjet. Finally, at around Mach 3, Chimera will begin to bypass the incoming air around the turbojet, and the ramjet will take over completely.

Chimera is a turbine-based combined cycle engine (TBCC), a hybrid between a turbojet and a ramjet. Image courtesy of Hermeus.

Following Chimera’s successful full-throttle ground testing in June 2022, the team moved to the Notre Dame Turbomachinery Laboratory’s hypersonic research facility for its latest testing campaign. Hermeus used the lab’s recently inaugurated high-Mach combustion testing cell, which releases heated air to simulate high-Mach temperatures and pressures.

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

With the transition from turbojet to ramjet demonstrated repeatedly, the Hermeus team is now racing to manufacture the first Quarterhorse aircraft that will begin flight testing in late 2023. Hermeus estimates that the first passenger aircraft could start flying in 2029.