Supersonic drone with speed up to 6,174km/h

The Quarterhorse aircraft uses a turbine-based combined cycle (TBCC) engine, capable of speeds five times the speed of sound.

The US Air Force has awarded $60 million to aviation startup Hermeus to test its Quarterhorse hypersonic aircraft, designed for commercial and military use. Capable of flying at Mach 5 (6,174 km/h) and with a range of 7,400 km , the new aircraft uses a turbine-based combined-cycle engine that combines GE commercial jet turbine engines.

Founded by former SpaceX, Blue Origin, and Generation Orbit employees, Hermeus aims to fly the world's fastest reusable aircraft within the decade. Named Quarterhorse, the vehicle will be built from titanium, capable of handling ultra-high speeds, and feature a streamlined delta wing design. It will also be the first aircraft to feature a TBCC propulsion system.

Design of the Quarterhorse aircraft. (Photo: Hermeus).

The TBBC engine works similarly to the engine on the famous SR-71 Blackbird spy plane. The system uses a conventional turbojet engine to propel the vehicle to a high enough speed to allow the ramjet engine to operate.

Hermeus is testing a new engine that can reach speeds of Mach 5 (6,174 km/h). The engine is designed for a small hypersonic drone that Hermeus is building for the US Air Force but could be scaled up to fit in a passenger plane. Hermeus hopes to conduct its first flight test in 2029.

The plane will be much smaller than today's passenger planes, including the legendary Concorde, which carried 100 passengers. "To figure out the size, we built a business jet for an airline. We focused on business class and first class, then looked at some parameters like speed and operating costs. The result is a plane with a cabin for 20 passengers ," said AJ Piplica, CEO of Hermeus.

The aircraft's range will be around 7,408 km, enough for a transoceanic journey like between New York and Paris.

The fastest powered aircraft is NASA's X-43A . The 12-foot-long unmanned aircraft reached Mach 9.6 (7,400 mph) in 2004. But that flight only lasted a few seconds; the record for the longest flight at speeds above 3,800 mph belongs to the Boeing X-51 , another unmanned experimental aircraft. The Boeing X-51 flew for more than three minutes in 2013 at 3,800 mph. Both aircraft were launched mid-air from B-52 bombers and then accelerated by rockets.

For passenger aircraft, the current speed record is 8,273 km/h, set in 1967 by the X-15. This was essentially a rocket with a seat, designed to achieve the record and also needed to be launched in mid-air by a B-52. For jet aircraft that take off and land on their own, the speed record is 4,075 km/h, held by the military aircraft SR-71 Blackbird. The Concorde's top speed is 2,519 km/h. So the Hermeus passenger plane would break the current record for the fastest jet.

Hermeus is initially focusing on engine development. Testing began in February 2020 on a new engine design based on the current engine used in General Electric fighter jets. It will be a hybrid of two traditional technologies: the turbojet engine commonly used in passenger aircraft and the ramjet engine that only operates at supersonic speeds. The engine will power the Quarterhorse, a supersonic drone that Hermeus is developing as part of a $60 million deal with the U.S. Air Force.

Hermeus will use the hybrid engine in turbojet mode during takeoff and landing, as well as at subsonic speeds. The engine will then gradually transition to ramjet mode from 2,300 mph to 3,800 mph.

Hermeus will have to address a number of issues, including choosing a sustainable fuel because supersonic aircraft burn much more than conventional jets. The company will also need to consider the temperatures the fuselage can withstand. The Concorde's speed was severely limited by the heat generated by the windows and interior surfaces of the plane at the end of a flight. The SR-71 Blackbird, meanwhile, needed to be built with the rare metal titanium to withstand extreme temperatures and quartz glass for its cockpit glass because the outside of the plane could reach 315 degrees Celsius during a mission.