For the second time in just over nine months, an Atlanta-based company this week debuted a new supersonic test aircraft.
Hermeus on Monday said it completed the maiden flight of its Quarterhorse Mk 2.1, one of several test articles the company is developing as it iterates toward its flagship Darkhorse—a reusable, multi-mission, hypersonic uncrewed aircraft system (UAS) for defense and national security missions.
The sortie followed the debut test flight of the company’s Quarterhorse Mk 1 in May. That flight came about one year after Hermeus unveiled the clean sheet design. Like its aircraft, the company wants to move fast.
“We’re building and flying aircraft on timelines that match the urgency of the world we’re in,” said AJ Piplica, founder and CEO of Hermeus. “Today’s flight kicks off a critical flight test campaign that will ultimately get us to supersonic speeds, bringing the United States closer to having the high-speed capability it needs now, not decades from now.”
The Mk 2.1 is the largest and fastest vehicle Hermeus has developed. About the size of an F-16, it’s three times larger, four times heavier, and “significantly faster” than the Mk 1. Unlike the Mk 1’s conventional, low aspect ratio wing, it incorporates a delta wing design.
The aircraft is powered by a unique engine system, Chimera, that combines a Pratt & Whitney F100 turbojet with a ramjet. Most hypersonic concepts, such as Stratolaunch’s Talon-A2, need pure rocket engines to propel them to hypersonic speeds.
The idea behind Chimera is to enable runway takeoffs using existing infrastructure in turbojet mode, switching to the more efficient ramjet during high-speed cruise. An F100 precooler system lowers the temperature of incoming air to increase turbine speed, aiding the transition to ramjet mode, which is difficult at lower speeds.
The Mk 2.1’s maiden sortie took place over White Sands Missile Range, one of the military’s largest test ranges, at Spaceport America in New Mexico. Pilots commanded the aircraft remotely from a ground-based flight deck. Teams evaluated system performance, handling, and a few unspecified “operational procedures,” Hermeus said. It did not share performance data such as speed.
The company aims to break the sound barrier using the Mk 2.1, though it won’t be the final test vehicle. Hermeus said another Quarterhorse model, the Mk 2.2, will be the “world’s fastest unmanned aircraft.”
The company expects the final iteration of the design, Mk 3, to surpass the Lockheed SR-71 Blackbird’s airspeed record of about Mach 3.3, or nearly 2,200 mph. Hermeus hopes to take the Mk 3 all the way up to Mach 5—fast enough to fly between New York City and London in about 90 minutes. It is targeting a flight test cadence of one new aircraft per year.
Road to Supersonic
The Quarterhorse program is only an intermediate phase of Hermeus’ future plans. The company aims to emulate programs such as SpaceX’s Starship, gradually increasing speed and performance with new test articles.
“Instead of waiting years between tests, we build and fly them in rapid succession,” Hermeus wrote in a social media post. “Real data from one flight feeds directly into the next, letting us steadily push the limits of speed and performance.”
Hermeus first demonstrated a subscale Chimera engine prototype in 2020. Two years later, it achieved the transition from turbojet to ramjet mode with a full-scale engine.
During that time, Hermeus unveiled the Quarterhorse program and began building the Mk 0—the company’s first fully integrated vehicle, serving as an iron bird test rig. That testing wrapped up in late 2023 as it transitioned to the Mk 1, which was designed primarily to demonstrate high-speed takeoffs and landings.
Manufacturing of the Mk 2.1 had already begun when the Mk 1 took to the skies in May. Hermeus set a target to fly it by the end of 2025.
Though it ultimately missed the mark by a few months, the company remains one of the leaders in developing the technology, as evidenced by its engagements with the U.S. military.
The firm in 2021 announced a $60 million U.S. Air Force partnership for Quarterhorse flight testing. The following year, it earned a Phase II Small Business Innovation Research (SBIR) contract from the Pentagon to further study the design and share data and analysis with the military. A Defense Innovation Unit (DIU) contract in 2023 called for further demonstrations to help the military mature future hypersonic aircraft and systems.
Hermeus’ partnership with the Air Force for its advanced battle management systems program has a ceiling of up to $950 million. The company so far has received more than $76M in federal contracts, per HigherGov.