Hermeus took another step forward in its quest to bring hypersonic transportation to market, 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 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 ramet 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.