The Quarterhorse aircraft utilizes a mixed-cycle engine based on a turbine (TBCC), achieving speeds five times faster than the speed of sound.
The U.S. Air Force has allocated $60 million for the startup aviation company Hermeus to conduct tests on the prototype of the Quarterhorse supersonic aircraft, which is designed for both commercial and military operations. Capable of flying at Mach 5 (6,174 km/h) with a range of 7,400 km, this new aircraft employs a mixed-cycle engine that integrates a commercial GE jet turbine engine.
Founded by former employees of SpaceX, Blue Origin, and Generation Orbit, Hermeus aims to conduct test flights of the fastest reusable aircraft in the world within this decade. Named Quarterhorse, the vehicle will be made from titanium to withstand ultra-high speeds and features an elongated triangular wing design. It will also be the first aircraft equipped with a TBCC propulsion system.
Design of the Quarterhorse aircraft. (Photo: Hermeus).
The TBCC engine operates similarly to the engine used in the famous SR-71 Blackbird reconnaissance aircraft. This system uses a conventional jet turbine engine to propel the vehicle to sufficient speeds, enabling the operation of a scramjet engine.
Hermeus is testing a new engine that can achieve speeds of Mach 5 (6,174 km/h). This engine is designed for the small unmanned supersonic aircraft that Hermeus is developing for the U.S. Air Force but can be scaled up for passenger aircraft. The company hopes to conduct its first test flight by 2029.
The prototype will be significantly smaller than current passenger aircraft and the legendary supersonic Concorde, which seated 100 passengers. “To determine the size, we are developing a business class model for airlines. We focus on business and first class, and then consider parameters like speed and operating costs. The result is an aircraft with a 20-passenger cabin,” shared AJ Piplica, CEO of Hermeus.
The aircraft is expected to have a range of approximately 7,408 km, sufficient for transoceanic flights such as between New York and Paris.
The fastest flying aircraft to date is NASA’s X-43A. This unmanned aircraft, measuring about 3.7 meters long, achieved a speed of Mach 9.6 (11,854 km/h) in 2004. However, that flight lasted only a few seconds; the record for the longest flight at speeds above 6,174 km/h belongs to the Boeing X-51, another unmanned experimental aircraft. The Boeing X-51 flew for over 3 minutes in 2013 at a speed of 6,297 km/h. Both of these aircraft were launched mid-air from a B-52 bomber and then accelerated using rockets.
For passenger aircraft, the current speed record is 8,273 km/h, set in 1967 by the X-15 aircraft. Essentially, this was a rocket with a seat, designed to set records and also required mid-air launch from a B-52. For jet aircraft that take off and land on their own, the speed record is limited to 4,075 km/h, held by the military SR-71 Blackbird. The maximum speed of the Concorde was 2,519 km/h. Therefore, Hermeus’s passenger aircraft is expected to break the current record for the fastest jet.
Initially, Hermeus focused on developing the engine. Testing began in February 2020 with a new engine design based on the current engine model used in fighter jets produced by General Electric. This will be a hybrid version combining two traditional technologies: the jet turbine engine commonly found in passenger aircraft and the scramjet engine that operates only at supersonic speeds. This engine will be equipped on the Quarterhorse, the supersonic drone that Hermeus is developing in the $60 million contract with the U.S. Air Force.
Hermeus will use the hybrid engine in jet turbine mode during takeoff and landing, as well as at subsonic speeds. It will then gradually transition to scramjet mode from speeds of 3,704 km/h to 6,174 km/h.
Hermeus will face several challenges, such as selecting sustainable fuel due to the significantly higher consumption of supersonic aircraft compared to conventional jets. The company must also consider the temperature limits that the aircraft fuselage can withstand. The speed of the Concorde was heavily limited by temperature, as windows and the aircraft’s internal surfaces heated up by the end of the flight. Meanwhile, the SR-71 Blackbird needed to be constructed from rare titanium to endure extreme temperatures, and its cockpit glass was made from quartz due to the outer surface of the aircraft reaching 315 degrees Celsius during missions.
