First Flight For Quarterhorse Prototype That Aims To Lead To A Reusable Hypersonic Jet

Yahoo

28-05-2025

Aviation startup Hermeus has completed the first flight of its uncrewed Quarterhorse Mk 1, as part of its hypersonic test aircraft project. Hermeus aims to eventually build an uncrewed flight vehicle capable of beating the SR-71's absolute speed record for an air-breathing crewed aircraft — 2,193.2 miles per hour, achieved in 1976 — and then to explore the hypersonic realm, which is defined as anything over Mach 5. These objectives are still a long way off, however, and it appears that Quarterhorse Mk 1 won't explore supersonic flight.
Announced today, the Quarterhorse Mk 1 first took to the air last week at Edwards Air Force Base, California, when it 'achieved stable flight and landed smoothly,' according to the company. A video released by Hermeus appears to show a takeoff and then a brief period in the air, followed by it setting down shortly after on the Edwards lakebed.
'Mk 1's flight validated our rapid, iterative approach to airplane development and advanced our mission to radically accelerate aviation,' Hermeus added. Among the byproducts of this approach is the relatively 'rough' external finish of the Mk 1 aircraft.
A first flight for the Mk 1 flying prototype had been planned for some time toward the end of 2024. It's unclear why this timeline slipped.
The Mk 1 was preceded by a 'dynamic iron bird' test rig, also known as Quarterhorse Mk 0, which you can read more about here. This non-flying prototype was used to validate major aircraft subsystems, including in taxi runs at the Air Force's Arnold Engineering Development Complex (AEDC) in Tullahoma, Tennessee.Throughout the project, Hermeus has stressed rapid, iterative development and prototyping. The non-flying Quarterhorse Mk 0 was built in just six months, and all its test objectives were completed in 37 days of testing.
Now, with the Mk 1, Hermeus says it went 'from clean sheet to flight-ready' in a little over a year.
As part of this effort, the company is building four Quarterhorse aircraft of successively greater complexity and scope.
The Mk 1 aircraft flown last week was built to verify takeoff and landing of an uncrewed aircraft in this configuration, and is not apparently planned to trial high-speed flight. It is powered by a General Electric J85 turbojet, as used in the Air Force's T-38 Talon jet trainer, for example.
Other aspects of the flight-test program for the Quarterhorse Mk 1 are examining aerodynamics, stability, and control. Testing of the Mk 1 is also intended to validate various subsystems, including propulsion, fuel systems, hydraulics, power, thermal management, avionics, flight software, telemetry, flight termination, and command and control.
The Mk 1 will be followed by the Quarterhorse Mk 2, intended to reach supersonic speeds below Mach 3. Currently, the Mk 2, which will be around the same size as an F-16, is in production at Hermeus' headquarters in Atlanta. The company says it should fly before the end of this year. This will be powered by a Pratt & Whitney F100 turbofan engine, also used in the F-16.
Finally, Quarterhorse Mk 3 will hit speeds beyond Mach 3 and, as Hermeus states, 'demonstrate turbojet-to-ramjet mode transition in flight and break the all-time airspeed record held by the SR-71.'
Notably, the Mk 1 that is now embarking on the flight-test program is not the same vehicle as the 'prototype' that Hermeus rolled out in November 2021, as The War Zone reported at the time. This vehicle lacked any obvious flight control surfaces or landing gear, but did feature a functioning engine with afterburner, as seen in the video embedded here.
At the heart of the Quarterhorse series will be a so-called turbine-based combined cycle (TBCC) engine. This combines a ramjet or scramjet — optimized for very high speeds — with a more traditional jet turbine, which can be used for takeoff, landing, and other lower-speed portions of flight.
You can read more about the specific advantages of a TBCC powerplant in this previous story.
As with any high-speed aircraft program, especially one that aims to eventually explore the hypersonic realm, the challenges are great and the potential for failure is high.
However, if all goes to plan, Hermeus' Quarterhorse series could feed into the Air Force's broader effort to explore potential future hypersonic and supersonic executive transport aircraft concepts.
Beyond that, some of the various technologies that Hermeus is working on could be used in other applications by the U.S. military.
In particular, Hermeus has pointed to the potential for its technologies to be used for missions including the transport of time-critical cargo and reconnaissance. For these applications, the company proposes what it describes as a 'mid-size autonomous aircraft.'
In the past, the U.S. military has repeatedly shown interest in finding ways to rapidly deliver military cargo around the globe, and there have been persistent references made to a potential future hypersonic and strike reconnaissance aircraft. More modest proposals could see Hermeus providing a testbed for hypersonic technologies or even building surrogate hypersonic targets.
Air Force interest in Hermeus' work has already been formalized. Hermeus received $60 million in funding from the Air Force and venture capital firms to support the Quarterhorse flight test program, the company announced in 2021.
Hermeus has claimed that its Quarterhorse program is primarily aimed at commercial markets, with the potential of fielding 'the fastest reusable aircraft in the world.' While the idea of resurrecting supersonic passenger travel has long been tempting, it's so far failed to yield any practical hardware and has seen other startups fold.
Whether the Quarterhorse series eventually leads to some kind of 'son of Concorde' is highly questionable, but there's no doubt that the military has expressed interest in at least exploring the potential of very high-speed uncrewed aerial vehicles.
As well as the promise of performance, Hermeus' approach also reflects Air Force interests in the rapid development of iterative designs, an idea that has been around for a while, but which is now widely seen as critical to ensuring capabilities, and combat mass, especially when it comes to crewed aircraft, drones, and munitions.
Hermeus uses the term 'hardware richness' to describe building multiple prototypes in quick succession, which should allow multiple aircraft to complete their full development cycles in a very short time period. If the company is able to master this, it could provide a way of churning out new (uncrewed) aircraft designs as a 'pace not seen in the U.S. since the 1950s.'
Clearly, there are very many challenges that lie ahead if Hermeus is to succeed in bringing a reusable hypersonic aircraft to the hardware stage, and doing it quickly. In the meantime, we can now look forward to the first flight of the faster and more capable Quarterhorse Mk 2, planned for later this year.
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