Quarterhorse UAV begins hypersonic flight into the future
The US Department of Defense has advanced the Hypersonic and Supersonic Airborne Test (HyCAT) program to the next level after the Hermeus Quarterhorse Mk 2.1 unmanned demonstrator successfully launched an "external payload" (basically a mockup) missiles) during flight tests over New Mexico.
This achievement marks the program's transition from basic flight verification to defining the operational capabilities required for future military hypersonic test missions.
The latest HyCAT campaign demonstrated more than consistent flight performance, confirming that the Quarterhorse Mk 2.1 can safely carry and employ external payloads while continuing to expand its range of capabilities.
This achievement paves the way for certification of systems needed for future defense missions and provides the Department of Defense with an increasingly advanced, reusable, high-speed test vehicle for hypersonic technology development and high-speed flight experiments.
Actually, this thing, Hermeus Quarterhorse, has already entered history, making the first unmanned supersonic flight, being a private invention of the American company Hermeus Corporation from Atlanta, Georgia.
The goal of the Quarterhorse project is to test the innovative Chimera engine in flight and achieve speeds of Mach 4 or more, breaking the speed record set by the SR-71, as well as creating the fastest air-breathing (non-rocket-powered) manned aircraft. So far, so good.
The Chimera is a turbine-based combined cycle engine that powers UAVAt low speeds, the engine operates in conventional turbojet mode. As the incoming air temperature and velocity increase due to the vehicle's acceleration, the Chimera uses a precooler to reduce the temperature of the air entering the turbojet, allowing the engine to generate additional power before switching to ramjet mode.
The ability to transition between these two modes allows the Quarterhorse to take off from a conventional runway and then accelerate to high speeds. For the Chimera's turbine powerplant, the company's engineers selected the proven Pratt & Whitney F100 turbofan engine, which powers thousands of F-15s and F-16s.
Compared to the original Quarterhorse Mk 1, the new demonstrator is nearly three times larger and roughly four times heavier, making it a more suitable platform for testing flight performance, payload integration, and future propulsion technologies. Initially, many expressed doubts after seeing the relatively compact and downright lightweight Quarterhorse Mk 1, but the second version of the aircraft has grown considerably in size.
Unlike previous flights, which focused primarily on testing the aircraft's handling and gradually increasing speed, this series of tests evaluates one of the functions required for payload integration.
The payload separation test confirms that the external container can be separated without compromising the aircraft's stability or affecting flight control, while collecting aerodynamic and structural data on the interaction between the container, pylon, and airframe. These measurements will help evaluate the payload potential for future missions and provide engineering data for subsequent demonstration flights at higher speeds.
To put it simply, the possibility of using externally mounted munitions in supersonic, and potentially hypersonic, flight was being explored. On the one hand, this is nothing new, but on the other, we're not talking about an aircraft, but an unmanned aerial vehicle, which has completely different requirements in terms of strength and load resistance.
On July 31, 2026, the Defense Innovation Unit (DIU) announced that this demonstration marked another significant milestone for the HyCAT program.
According to the department, the Quarterhorse Mk 2.1 has completed five flights since the spring of 2026, which is approximately four times faster than typical hypersonic flight test programs. The DIU stated that HyCAT is designed to generate flight data more quickly using commercially developed platforms, which will address the shortage of affordable reusable hypersonic vehicles in the United States.
The Quarterhorse Mk 2.1 is roughly the same size as the F-16 Fighting Falcon and is powered by the same engine. It provides a more representative platform for testing high-speed flight characteristics, payload integration, and future propulsion technologies. Earlier this year, the Quarterhorse exceeded the speed of sound, reaching Mach 1,6 during its fourth flight. Hermeus plans to extend the demonstrator's speed range to Mach 3, and technologies developed during the program should inform the development of another unmanned aerial vehicle, Darkhorse.
The HyCAT initiative, launched by the US Defense Advanced Research Projects Agency in 2023, aims to increase the frequency of hypersonic flight tests using commercial aircraft and reusable platforms. The initiative was created in response to limited access to specialized wind tunnels, dedicated test sites, and government flight resources—restrictions that continue to slow the certification process for new hypersonic technologies.
Under this approach, Hermeus was initially awarded a $23 million contract, with a $159 million increase in 2026 to allow for additional high-speed demonstration flights and payload separation tests through 2027.
The HyCAT initiative extends beyond the Quarterhorse project. In February 2026, as part of the Cassowary Vex mission, the DART AE demonstrator, developed by Australia's Hypersonix, exceeded Mach 5 after launching on Rocket Lab's HASTE suborbital rocket. The mission collected data on the propulsion system, trajectory, and flight characteristics, and demonstrated another element of the DIU strategy of integrating commercial launch systems with reusable hypersonic test platforms. Meanwhile, HyCAT 2 is incorporating additional technologies, including guidance, navigation, and control systems, for future high-speed demonstrators.
In terms of operational use, the Quarterhorse is gradually evolving from a research aircraft into a platform capable of testing technologies directly applicable to future military aircraft. The demonstrator not only expands the aircraft's flight envelope but also enables testing of payload integration, fuel tank separation procedures, propulsion systems, and systems that could later be used in production models.
The flight data obtained from HyCAT is expected to reduce technical risks prior to full-scale development and provide the U.S. Air Force and U.S. Navy with information to evaluate future high-speed unmanned aerial vehicle (UAV)-based reconnaissance, strike, and electronic warfare (EW) concepts.
In fact, it's very rational. Hypersonic aircraft today are primarily represented by missiles, which, while relatively controllable, operate very differently from the vehicles that many militaries around the world rely on.
It's already clear today that hypersonic speeds aren't for humans; indeed, the human body isn't prepared for evolution at such speeds. Furthermore, controlled vehicles will have significant structural strength requirements, as there are differences between a missile and a UAV, including issues related to the separation of fuel tanks or weapons.
This topic will need further study, which the Americans will likely do in the near future, because hypersonic speed is determined by hypersonic air pressure and the heating of both the aircraft and its attached payload. Aircraft at supersonic speeds generate significant heat, and if the speed is not Mach 2-3, but Mach 5-8, the heating will also increase according to the relevant physical formulas.
The HyCAT program represents a broader shift in the approach to hypersonic technology development. Unlike Russia and China, where development is concentrated in the public sector, the US is investing in a flight-testing ecosystem designed to accelerate technology certification through private, lower-cost projects.
Similar efforts are underway in other countries, including the US-Australian Southern Cross Integrated Flight Research Experiment (SCIFiRE) program, a follow-up to the earlier HIFiRE research initiative, and national hypersonic research programs in France, Japan, and Germany focused on engine development, thermal protection, and flight testing.
The HyCAT project's goal is not to support a single aircraft, but to create a reusable test infrastructure capable of accelerating the implementation of multiple future high-velocity defense programs.
This represents a potential success, as several projects being developed simultaneously may ultimately yield a single project that meets all expectations. Perhaps the long string of failures with promising aircraft prompted the relevant US agencies to make this decision—to work through the private sector, with Department of Defense funding for those projects that spark interest.
In any case, there's a lot of work to be done in this area. While hypersonic aircraft eliminate many problems related to pilot survival at such speeds, a huge number of issues still need to be considered and addressed. For example, the durability of such UAVs.
Americans are developing technologies aimed at the future. They're investing. Yes, quite a few of their projects fail, but if they succeed, the US will have a significant advantage over other countries.
The fact that the Defense Department has taken the Quarterhorse project under its wing—or rather, its own coffers—suggests that the American military is satisfied with both the development company's chosen path and the results this device is demonstrating. Otherwise, why such moves?
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