Something Old, Something

Founded in 2018 with a stated mission of “radically accelerating air travel,” Atlanta-based Hermeus is about the business of developing a trio of hypersonic aircraft. For all its implicit hyperbole, hypersonic is a valid aerospace term describing velocities greater than five-times the speed of sound—Mach 5.0.

In pursuit of its ambitious goal, Hermeus has taken on powerful partners the likes of the United States Air Force and NASA. So allied, the company has developed a series of autonomous aircraft for purpose of vetting inchoate technologies and addressing urgent national security challenges.

On 20 December 2022, Hermeus announced it had selected Pratt & Whitney’s F100 turbofan engine to serve as the turbine portion of its combined-cycle hypersonic engine—to which the company has ascribed the apposite moniker Chimera II.

For more than half-a-century, the 29,000-pound-thrust F100 engine has powered Boeing’s F-15 and Lockheed-Martin’s F-16 fighters—racking up north of thirty-million flight hours over innumerable sorties, training hops, demonstration flights, and combat deployments. By basing its hypersonic powerplant on an off-the-shelf engine, Hermeus posits it will save “billions of dollars in research and development costs and years of schedule.”

Chimera II comprises a hybridization of turbine and a ramjet architectures to facilitate both low-speed and high-speed flight, thereby allowing aircraft powered by the contraption to operate from extant airports—a feat beyond the purview of rocket-propelled hypersonic vehicles. Chimera II will power Darkhorse, a 45-foot-long, hypersonic UAV being developed by Hermeus for defense and intelligence customers. Darkhorse is a delta-winged, twin-tailed derivative of Quarterhorse, a proof-of-concept flight vehicle which—in addition to substantiating Hermeus’s penchant for equine sobriquets—is powered by the GE-J85-based Chimera engine from which the Chimera II evolved. Quarterhorse is slated to fly in late 2023.

By dint of Chimera II’s combined-cycle design, Darkhorse will take-off, land, and low-speed-cruise under turbojet power. Once the aircraft reaches Mach-3, however, diverters will bypass incoming air around the turbojet and into the ramjet, which will accelerate Darkhorse to hypersonic speeds.

Flight tests of Darkhorse are expected to commence in the mid-2020s.

FMI: www.hermeus.com