The U.S. Defense Advanced Research Projects Agency (DARPA) has indicated the next generation U.S. fighter aircraft will forego stealth for hypersonic speed with an announcement of its plan to build a Mach 5 hypersonic engine.

In DARPA's own words, "Speed is the new stealth."

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In 2012, DARPA noted the United States is gradually losing the "strategic advantage" that its stealth warplanes have long provided since competitor countries' stealth and counter-stealth capabilities are improving.

To arrest this decline, DARPA strongly argues the U.S. will need "the new stealth" of hypersonic aircraft.

DARPA said its new endeavor, the Advanced Full Range Engine (AFRE) program, will develop an aircraft propulsion system that can reach hypersonic speeds plus the full breadth of speeds below this range. Hypersonic speed is traditionally meant to mean speeds in excess of Mach 5 or 5,300 km/h at high altitudes.

U.S. Air Force or U.S. Navy jet fighters powered by these powerful hypersonic engines can mount missions at far longer ranges while reaching their targets far faster than current fighters with speeds in excess of Mach 2. Hypersonic U.S. fighters will also counter advances made in hypersonics by strategic competitors such as China and Russia.

Currently, hypersonic engines such as scramjets need to use disposable rockets for one-time boosts to reach their operating speed of Mach 3.5. This disadvantage limits the usefulness of fighters powered by scramjets.

"Instead of designing an entirely new kind of engine, we're envisioning an inventive hybrid system that would combine and improve upon the best of off-the-shelf turbine and ramjet/scramjet technologies," said Christopher Clay, DARPA program manager.

AFRE aims to explore a turbine-based combined cycle (TBCC) engine concept. An engine such as this uses a turbine engine for low-speed operations and a dual-mode ramjet for high-speed operations. Unlike traditional ramjets, a dual-mode ramjet works efficiently whether air flowing through it is subsonic (as in a ramjet) or supersonic (as in a scramjet).

AFRE will be a reusable hypersonic engine having a regular turbine engine and a dual combined cycle engine capable of exceeding Mach 5.

It will develop critical hypersonic technologies and culminate in ground-based testing of a full-scale, integrated technology demonstration system. If tests succeed, further development of the AFRE technology will require flight testing in a follow-on demonstration program.

The AFRE program has two phases. Phase I will include AFRE system design and subscale and large scale component development and ground demonstration. Phase II will see large-scale, integrated test series of the integrated low speed and high speed flowpaths. 

TagsDefense Advanced Research Projects Agency, DARPA, hypersonic fighters, hypersonic engines, Advanced Full Range Engine