US-based hypersonic developer Hermeus has completed ground testing on the first iteration of its Quarterhorse remotely piloted aircraft.

The Atlanta-based company on 4 January said it had wrapped up ground-based evaluations for its Quarterhorse Mk 0 type – a non-flying test article that represents the first of four vehicles planned under the Quarterhorse programme.

Technical objectives for the Mk 0 included taxiing under remote command and control, evaluating radio frequency latency and ground handling qualities of the integrated systems and demonstrating human factor evaluations and pilot-in-the-loop steering and controls, according to Hermeus.

Quarterhorse Mk0

Source: Hermeus

The non-flying Quarterhorse Mk 0 is the first of four aircraft in the Quarterhorse programme, through which Hermeus aims to produce a hypersonic vehicle capable of surpassing the all-time airspeed record held by Lockheed Martin’s SR-71 Blackbird

Notably, the Quarterhorse vehicle was designed and constructed in under six months, the company says. All test objectives were completed in 37 days of deployed evaluations.

“Leveraging rapid and iterative design is how Hermeus will accelerate aircraft development on time lines that are relevant to our customers,” says chief executive and co-founder, AJ Piplica. “Test campaigns measured in days, instead of months or years, represent the pace required to mature hypersonic technology and field transformative aircraft.”

Quarterhorse testing took place at the US Air Force’s Arnold Engineering Development Complex in Tullahoma, Tennessee, where the Pentagon says it operates more than 68 aerodynamic and propulsion windtunnels, rocket and turbine engine test cells, environmental chambers, arc heaters, ballistic ranges, sled tracks, centrifuges and other specialised test units.

“Hermeus made the deliberate decision to perform these ground test operations on an air force base, allowing the team to interface directly with air force range and regulatory authorities,” the company says.

In November 2023, the Pentagon’s Defense Innovation Unit provided Hermeus with research and development funding to support the maturation of hypersonic technologies and development of a flight vehicle.

With Quarterhorse, Hermeus is seeking to deliver an uncrewed aircraft capable of reaching speeds of Mach 4 and beyond. The company says its target is to break the current airspeed record established by Lockheed Martin’s SR-71 Blackbird nearly 50 years ago.

Quarterhorse_Runway rendering

Source: Hermeus

Hermeus is targeting speeds of Mach 4 and beyond for its Quarterhorse Mk 3 uncrewed, remotely piloted hypersonic vehicle

In 1976, one of the twin-engined Blackbirds reached a velocity of 1,905kt (3,529km/h) – or M3.3, according to the USA’s Smithsonian National Air and Space Museum.

An SR-71 flight in 1990 covered the 1,998nm (6,550km) between Los Angeles and Washington, DC in just 1h 4min – with an average speed of 1,864kt.

To surpass that feat, Hermeus is developing its own powerplant called Chimera, which the company says will be capable of producing thrust sufficient to power M5 flight. The proprietary design is a turbine-based combined cycle engine, incorporating a pre-cooler, an off-the-shelf turbojet and a ramjet for high Mach speeds.

In order to break the M5 threshold for hypersonic flight, a vehicle needs two engine systems. A turbojet or rocket engine is used to reach an airspeed between M3 and M3.5, after which a ramjet or scramjet kicks in to accelerate flight to M5 and beyond.

The mid-flight transition between conventional propulsion and high-speed ramjet remains a significant technical hurdle that firms including Hermeus and engine-maker GE Aerospace are independently seeking to solve.

Hermeus plans to work its way through the engineering and development challenges using four progressively more capable Quarterhorse interactions.

Quarterhorse Mk 1 will be the first flight-capable aircraft, which the company hopes to launch in 2024 for remotely controlled subsonic flight. That vehicle is currently under construction, according to Hermeus.

The Mk 2 variant will seek to break the sound barrier and demonstrate autonomous supersonic flight below M3.

Hermeus aims for the final Quarterhorse Mk 3 type to become the “world’s fastest aircraft”, by successfully demonstrating ramjet transition and breaking the SR-71 flight speed record.

The company says it hopes to eventually adapt its hypersonic technology to power both military uncrewed aerial vehicles and commercial passenger aircraft.