Controlled Dive to Get to First Mach 5 Drones in 2026

By Brian Wang

Hypersonic plane startup, Hermeus, plans to make a plane faster than the SR-71 blackbird spy plane. the SR-71 could reach mach 3.3 and fly at 85000 to 100,000 feet in altitude.

Quarterhorse Mk 2 will fly with this precooler-F100 engine combination and be capable of hitting speeds greater than Mach 2.5. The entire Chimera engine, which includes a ramjet, will power Hermeus’ following aircraft, Quarterhorse Mk 3. This aircraft will reach speeds close to Mach 4 and pave the way for future Hermeus aircraft that will fly at hypersonic speeds.

The 2026 Quarterhorse Mk 3 prototype will fly to Mach 3.3 and beyond and get high altitude like the SR-71 then it will have a controlled dive to get towards mach 5 as it switches to the ramjet. The ramjet is not efficient in until speeds are near mach 5. Previous hypersonic designs have involved three engines. Hermeus will only use two engines. They will pre-cool the regular engine to get up to mach 3.3 or more then they use gravity to bridge the inefficient gap to get up to efficient ramjet speeds.

The planned, controlled dive is explained in this video by the technical lead of Hermeus.

Quarterhorse Development Timeline:

Mk 1: The first flyable version of Quarterhorse, Mk 1, is set for flight tests later in 2024. These tests will focus on high-speed takeoffs and landings

Mk 2: Scheduled for 2025, Mk 2 will be powered by a Pratt and Whitney F100 engine, enabling supersonic flight. This version will serve as a precursor to the full hypersonic capabilities planned for future iterations

Mk 3: Expected to be developed by 2026, Mk 3 will incorporate Hermeus' Chimera II propulsion system, which includes a modified F100 engine. This version aims to achieve speeds faster than Mach 3.3, supporting Defense Department testing.

Getting to Hypersonic Speed

Turbojet Mode: At lower speeds, the Chimera engine operates in turbojet mode, similar to conventional jet engines. This mode is effective up to approximately Mach 2+, where the performance of turbojets starts to decline due to increased air temperature and speed.

Pre-cooler Functionality: To extend the operational range of the turbojet, Chimera incorporates a pre-cooler that reduces the temperature of incoming air. This allows the turbojet to function efficiently to Mach 3 by providing additional performance headroom and could enable operation up to nearly mach 4.

Transition to Ramjet Mode: As the aircraft accelerates to Mach 4, the engine begins to bypass the turbojet, and the ramjet takes over. The ramjet operates by compressing incoming high-speed air without the need for a compressor, mixing it with fuel, and igniting the mixture to produce thrust. This mode is optimal for speeds between Mach 3.5 and Mach 5. This is where the Hermeus drones or jets will be put into a dive.

Testing and Validation: The mode transition has been tested and validated in lab conditions that simulate high-Mach temperatures and pressures, significantly reducing the risks associated with the Quarterhorse's flight test campaign.

Like Quarterhorse, Darkhorse will be powered by a Hermeus-developed turbine-based combined cycle engine. This version of Chimera is significantly more powerful as it integrates the Pratt & Whitney F100.

Hypersonic aircraft represent a major step change in defense technology, offering unprecedented speed, altitude, and maneuverability. These attributes allow Darkhorse to operate responsively in contested environments.

Halcyon will be a passenger aircraft capable of accelerating 125+ trans-oceanic routes at hypersonic speeds – five times faster than any commercial aircraft today.  This will require more powerful engines to be developed. Passengers would not accept crash diving from mach 3.5 to mach 5 to reach their destination.