Hermeus logs first supersonic flight with experimental Quarterhorse jet

The uncrewed Quarterhorse Mk 2.1 reached a top speed of Mach 1.21.

US aviation start-up Hermeus has logged its first-ever supersonic flight with one of the company’s experimental Quarterhorse aircraft.

Flying from Spaceport America in New Mexico, the Quarterhorse Mk 2.1 vehicle reached a top speed of Mach 2.1 over the US Army’s White Sands Missile Range, Hermeus announced on 26 May.

The sortie was only the third flight for the Quarterhorse Mk 2.1 and comes less than three months after the uncrewed jet’s first test flight in early March. Both of the first and second Mk 2.1 flights were subsonic.

“This flight demonstrates a pace of execution that is extremely rare in modern aviation,” says Hermeus co-founder and cheif executive AJ Piplica. “Our country’s ability to deliver new asymmetric military capability at scale depends on teams that can solve hard technical challenges quickly.”

In April, the Federal Aviation Administration approved Heremus to conduct up to seven supersonic flights before the end of 2026, signalling that more such events are likely to follow.

Piplica has repeatedly said that rapid iteration within the aircraft design and fabrication process is a key element of Hermeus’ business strategy. The company’s long-term goal is the development of a reusable aircraft capable of breaking the M5 (3,307kt) hypersonic barrier.

Hermeus says its current engineering and testing timeline puts the company on a path to deliver an operational hypersonic vehicle before 2030. That milestone is expected to be achieved with the forthcoming Quarterhorse Mk 3.

Within the Mk 2 series, Hermeus plans to build three variants that will each push further toward the M5 threshold. The Mk 2.1 has now broken the supersonic barrier, while the Mk 2.2 and Mk 2.3 successors will push into higher Mach speeds.

The Mk 2.2 is already being fabricated, according to Hermeus, with the Mk 2.3 “soon to follow”.

Notably, the Quarterhorse family of vehicles is designed to take off and land under their own power, unlike most of the other experimental hypersonic vehicles and munitions currently in development.

Advanced propulsion technologies are central to the company’s hypersonic goals. While the Quarterhorse Mk 2.1 is powered by a standard Pratt & Whitney F100 turbofan fighter jet engine, successive aircraft designs will use cutting-edge enhancements like pre-cooling.

Heremus is currently developing a turbine-based combined cycle (TBCC) propulsion system called Chimera that will combine the F100 with an integrated ramjet engine to allow for a single aircraft to transition through subsonic, supersonic and hypersonic flight.

This will be achieved in part via a proprietary pre-cooling system that will chill engine intake air before compression and combustion, allowing a standard turbofan engine to operate at higher speeds, with greater efficiency and reduced performance degradation.

In theory, that will allow Quarterhorse aircraft to reach airspeeds of around M3.5 – roughly the point at which current high-speed ramjet designs can achieve compression significant enough to produce ignition and generate thrust.