Image courtesy Hermeus / Vimeo
Hermeus is now one lightning-footed step closer to achieving hypersonic flight. The aircraft developer with backing from Raytheon and the U.S. military announced on Thursday that its engine, Chimera, successfully transitioned from turbojet to ramjet.
The testing took place at the Notre Dame Turbomachinery Laboratory which provides heated air to simulate high-Mach temperatures and pressures.
“The … 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.”
The engine is a turbine-based combined cycle engine (TBCC), a hybrid between a turbojet and a ramjet. The company says that, ultimately, the two modes will allow Hermeus’ first aircraft, the Quarterhorse, to take off from a regular runway and then accelerate up to high-Mach speeds.
“This is probably the most critical challenge in unlocking hypersonic flight,” Case said in a company video highlighting the successful test.
Hermeus says its team completed its test run in 21 months at a cost of $18 million.
The name Chimera comes from a mythical fire-breathing creature with parts taken from various animals.
“Like our engine, it’s a hybrid,” Hermeus states on its webpage for the engine.
It is built from a GE J85-21 turbojet core, which the company says did not need new development of turbomachinery and since it was built on legacy engine technology, it’s already been proven capable of reaching speeds of Mach 5.
The GE J85-21 was first used in the 1950s and powered Vietnam-era military jets, including the Cessna A-37 Dragonfly and Northrop F-5.
In a statement, Hermeus noted that the engine in turbojet mode operates like any jet aircraft, but the performance limit is reached around Mach 2. Chimera has a pre-cooler that reduces the temperature of the air taken in by the turbojet, allowing more performance before the ramjet transition around Mach 3, where the incoming air around the turbojet is bypassed.
“A ramjet is a simple propulsion system which rams the incoming high-pressure air to create compression,” Hermeus explained in a statement about the test. “Fuel is mixed with this compressed air and ignited for thrust. Ramjets are optimal between Mach 3 and Mach 5.”
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The Quarterhorse is being designed to be able to haul around 20 passengers, the company has said. However, hypersonic flights cannot take place over the continental U.S. and its projected range will not work for trans-Pacific flights without a pit stop. Thus, New York to Paris looks to be the longest hypothetical leg.
Last year, Hermeus announced a goal of beginning test flights before the end of the decade. It has now pushed its flight testing schedule to begin in late 2023.
“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.”
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