The Atlanta-based Hermeus Corp. said on Dec. 20 that it chose Raytheon Technologies [RTX] Pratt & Whitney F100 turbofan, which powers F-15 and F-16 fighters, as the turbine component of Hermeus’ planned Chimera II turbine-based combined cycle engine (TBCC)–a cross between a turbojet and ramjet engine–that is to generate hypersonic flight for Hermeus’ reusable Darkhorse drone.

Ramjets, which function best between Mach 3 and Mach 5, mix compressed air with ignited fuel to create thrust.

Hermeus is designing the Darkhorse for the military and intelligence market and believes that the TBCC, in contrast to rocket-based hypersonic engines, will allow Darkhorse to take-off from existing runways.

The selection of the F100 “keeps the Darkhorse program on track for engine testing in 2024,” Hermeus said on Dec. 20.

Hermeus has said that it plans to build its first hypersonic drone, Quarterhorse, and begin flight testing it late next year.

Chimera II is a more powerful version of Chimera, which is to equip Quarterhorse. The latter is to be smaller than Darkhorse.

Last month, Hermeus said that it had demonstrated turbojet to ramjet transition for Chimera at the Notre Dame Turbomachinery Laboratory, which supplies heated air to mimic high-Mach temperatures and pressures.(Defense Daily, Nov. 21).

Hermeus has said that it achieved accelerated testing of Chimera at the lab for less money–a design, build and test timeline of 21 months and $18 million.

In addition to Quarterhorse and Darkhorse, Hermeus is developing Halcyon, which is to be a Mach 5 commercial passenger aircraft.

In August last year, the U.S. Air Force announced that it had awarded a $60 million contract to Hermeus to speed the commercial development of hypersonic aircraft and propulsion systems (Defense Daily, Aug. 5, 2021).

The Air Force Life Cycle Management Center’s (AFLCMC) Presidential and Executive Airlift Directorate, the Air Force Research Laboratory, and venture capital funded the contract, part of a larger effort–the “Vector Initiative”–to spur high speed passenger travel and the possible advancement of Air Force technologies for senior leader transport; air mobility; intelligence, surveillance, and reconnaissance; and other missions.

“The contract establishes a number of objectives for Hermeus to meet within three years,” AFLCMC said last year, including increasing the understanding of enabling technology and mission capabilities for reusable hypersonic aircraft; scaling and flight testing a reusable hypersonic propulsion system; developing, building and testing three of Hermeus’ Quarterhorse concept aircraft; providing a payload integration guide for future hypersonic flight testing with Quarterhorse; and providing wargaming data for use in Air Force strategic analysis tools.

After the three-year contract with Hermeus, the Air Force plans to evaluate the company’s progress, the maturity of hypersonics, and the alignment of the Hermeus effort with service priorities.

In May, RTX Ventures, a capital investment group led by Raytheon, said that it made a strategic investment in Hermeus to develop commercial and military hypersonic aircraft (Defense Daily, May 12).

Hermeus has compared its Quarterhorse, which is to have a top speed of Mach 5 and a cruise altitude of 95,000 feet, to Lockheed Martin‘s [LMT] legendary SR-71 Blackbird, which first flew in 1964 and which had a top speed of more than Mach 3 and a cruise altittude of 85,000 feet.