Quarterhorse Mk 2.1

Quarterhorse Mk 2.1 is an uncrewed supersonic test aircraft developed by Hermeus of the United States, first flown on 2 March 2026. It is the second vehicle in the company's Quarterhorse programme, an incremental series of prototypes built to validate the technology for a future reusable, Mach 5-class aircraft.

Overview

Hermeus develops Quarterhorse under a partnership with the US Air Force, begun with an AFWERX Strategic Funding Increase award supporting the Air Force Research Laboratory, with the goal of building a reusable high-speed aircraft faster than any in current service. The programme follows a "build and fly" approach: each prototype is flown to gather data that informs the design of the next, faster vehicle, rather than relying solely on ground testing and simulation.

The first aircraft in the series, Quarterhorse Mk 1, made its subsonic first flight at Edwards Air Force Base in May 2025. Mk 2.1, reported to be roughly three times larger and four times heavier than Mk 1, followed with its own first flight at Spaceport America in New Mexico on 2 March 2026, flying over White Sands Missile Range airspace under an FAA Special Airworthiness Certificate.

On its third test flight, on 26 May 2026, Mk 2.1 exceeded the speed of sound, reaching Mach 1.21 (about 1,484 km/h). Hermeus describes this as the first supersonic flight by a privately developed, unmanned jet aircraft.

Design and capabilities

Mk 2.1 is a delta-wing jet aircraft powered by a Pratt & Whitney F100 turbofan — the same engine family used in the F-16 fighter — fitted with a precooler of Hermeus's own design at the air intake. The precooler lowers the temperature of incoming air before it reaches the engine, a technique intended to let a conventional turbofan keep operating efficiently at speeds and temperatures that would otherwise damage it. Hermeus has not published the aircraft's length, weight or maximum speed; the company has said it is targeting speeds beyond Mach 2.5 for the Mk 2 family as flight testing continues.

Hermeus plans a further prototype, Mk 3, intended to fly faster than Mach 3 using a new propulsion system, as a step toward its stated long-term goal of a Mach 5 aircraft.

Frequently asked questions

How fast has the Quarterhorse Mk 2.1 flown?

It reached Mach 1.21 on 26 May 2026, its third test flight, making it the first privately developed unmanned jet to fly supersonically.

When did the Quarterhorse Mk 2.1 first fly?

It first flew on 2 March 2026 at Spaceport America in New Mexico.

What engine does it use?

A Pratt & Whitney F100 turbofan fitted with a Hermeus-designed precooler at the air intake.

Who operates the Quarterhorse programme?

Hermeus flies the test aircraft itself, under a development partnership with the US Air Force.

Is the Quarterhorse Mk 2.1 crewed?

No. It is an uncrewed test aircraft.