Quarterhorse edges closer to becoming a modern SR-71 successor

Hermeus's Quarterhorse aircraft is still pushing the supersonic flight envelope, but the US Department of Defense is already so keen on the concept that it's awarded the company US$159 million to explore the military applications of the technology.

The Quarterhorse project aims at creating a supersonic aircraft that is, in effect, the successor to the legendary Cold War SR-71 Blackbird, which is the holder of multiple speed records, including the official world airspeed record for a crewed, air-breathing jet aircraft after reaching Mach 3.32 in 1976.

Hermeus is pursuing this goal through a series of prototypes, each designed to test a different portion of the flight envelope, from taxiing and takeoff through to high-speed supersonic flight. Currently, the Quarterhorse Mk 2.1 has reached Mach 1.21, and there's still a lone way to go before it can challenge the Blackbird's laurels.

However, the US Army and Navy are very interested in how to adapt the Quarterhorse to their needs – so much so that they've added $159 million to an existing development contract, for a total of $219 million. It is to not only help in developing an aircraft that can reach high Mach numbers, but also to explore how such a platform could launch high-speed missiles and other payloads.

The latter is no small feat because supersonic speed dramatically changes the aerodynamics of an aircraft, making missile launches or bomb drops extremely difficult, to put it mildly. At subsonic speeds, the airflow over an airframe consists of relatively smooth, though complex, streams. Beyond the sound barrier, severe aerodynamic, mechanical, and thermodynamic complexities are introduced.

Airflow streams become violent, compressible flows characterized by complex, interacting shock waves. This means that a missile suspended on an external pylon or inside an internal weapons bay is subjected to extreme gradients in pressure and velocity. As a missile or other payload separates from the launcher, it has to go through these shock waves, which can shove it any direction and tilt any which way, including smack into the aircraft.

Because modern warplanes put a premium on stealth, internal weapon bays are preferred to reduce radar signatures, but opening the bays for launching creates a high-speed aerodynamic cavity. The result is high-decibel acoustic loads that can cause structural damage as well as buffeting that can prevent the missile from even leaving the bay.

As a result, the aircraft has to be designed to minimize these effects as well as the thermal stresses caused by supersonic flight. This is combined with the need for powered systems that use springs, pneumatics, or hydraulics to shove the missile clear and a mechanism to ignite the missile's motor only after it gets clear of the supersonic external flow to prevent it stalling or spinning out of control.

The new contract focuses on reducing the risk factors for Quarthorse, especially in propulsion, thermal management, and power generation, as well as being able to release payloads at speeds up to Mach 3. It will also examine how Quarterhorse can be adapted for mass production, so it can be used as either a Loyal Wingman along with crewed fighter aircraft or as a standalone strike/electronic attack platform. Additional studies will investigate replacin aluminum structures with steel for better durability, and the addition of spike inlets and other aerodynamic refinements necessary to maintain stable flight and payload release at speeds approaching and exceeding Mach 3.

“This program is about moving high-Mach capability out of the lab and into an operationally relevant environment,” said AJ Piplica, CEO and Co-founder of Hermeus. “By delivering flight-ready aircraft and demonstrating payload release at speed, we will prove this technology can create a decisive military advantage on a timeline that matters. Our focus is on providing the Air Force and Navy with the validated data they need to transition these platforms into the future force.”

Source: Hermes