Engine Program Aims to Meet Military's Need for Speed
By Donna Miles
American Forces Press Service
WASHINGTON, Aug. 26, 2009 The F-22 Raptor and F-18 Hornet fighter jets are fast, screaming through the air at twice the speed of sound, but the SR-71 Blackbird was faster, flying Mach 3 until mechanical problems and exorbitant operating costs forced it out of service in the late 1990s.
Now, the Defense Advanced Research Projects Agency is striving to build an engine that will propel a hypersonic jet at Mach 4 and faster, while also bringing new efficiencies to ships and ground vehicles.
DARPA's Vulcan program kicked off this spring and aims to create the supersonic capability needed to engage targets or perform reconnaissance missions when time is of the essence, Thomas Bussing, program manager, told American Forces Press Service.
"Most of our aircraft are subsonic airplanes, so it takes them a long time to get where they need to be," Bussing said. "If you could travel beyond Mach 4, you could get there in potentially one-fourth the time it would take to get there with a conventional aircraft."
Increased airspeed will translate into more timely battlefield awareness for ground troops and an improved strike capability that takes out enemy forces before they can attack, Bussing said.
Until now, the science required to provide this level of capability eluded engineers and scientists alike.
The Vulcan is being developed as the first propulsion system to combine a full-scale, off-the-shelf turbine like those used in F-22 and F-18 fighter jets with a revolutionary new constant volume combustion engine. The dual-mode engine will basically consist of a constricted tube that compresses air as it combusts fuel.
"The CVC is really a paradigm shift in the way you burn fuel and air," Bussing explained. "Instead of burning fuel like you do in an automobile engine in a slow-burning process, the idea is to use a shock wave so you essentially get instantaneous combustion. If you can do that, it is a more efficient cycle, and you can extract more useful work."
These enhancements are expected to be able to accelerate the aircraft from zero to Mach 4-plus in a matter of minutes, Bussing said. The turbine will generate the initial low-speed propulsion, with the CVC engine kicking in at supersonic speeds.
But the technology being developed promises other benefits, too, he said. It will make ships' propulsion and power engines, as well as ground-based power generators, more efficient. Other applications include using shockwave technology to cut through the ash that builds up on coal power plant heat exchangers, boosting efficiency by 2 to 5 percent.
Those same shockwaves have other military applications, such as nonlethal weapons and psychological operations tools. Channeled through a series of tubes, for example, the waves will emit ear-shattering blasts. Fired at exactly the right sequence, they can create an amplitude and pulse that makes an intended target's stomach turn nauseous. "It's a noise generator that is very powerful," Bussing said. "If used correctly, you can generate a very effective nonlethal response."
The Vulcan will have application in production processes, too, he said. The waves it generates can accelerate particles to the extremely high speeds needed to create carbide, oxide or nitrite coatings.
"There is a whole series of products and techniques this concept enables," Bussing said. "This technology has a broad range of potential applications."
But for initial development, DARPA is focusing on applying the new technology in a multiple-Mach jet engine capable of supporting intelligence, surveillance and reconnaissance and strike missions.
Getting to this point took 15 years of rigorous testing, and Bussing estimated it will take another four to five years to complete the four-phased development program.
The first phase wraps up late next month with a review of the four competing contractors' conceptual designs. The next phase will test each component, then demonstrate how they operate together through experimental tests, some conducted in wind tunnels. Phase 3 will be a full-scale demonstration, which Bussing called the most important step in the program that proves out the technology.
The fourth phase will culminate with a test combining a full-scale version of the new CVC engine and turbine, to demonstrate how they operate from zero to Mach 2, then on to Mach 4. Bussing said the hope is to reach that point within five years.
DARPA, the Defense Department's super-high-tech, super-advanced research agency, is the only defense organization that could have taken on such an ambitious project involving such new, unproven technologies, Bussing said.
"This is a very high-risk technology, but one that promises very high payoff," he said. "So this is the right place for an organization like DARPA to be working in."
But achieving the Vulcan's promise will represent a major milestone, even by DARPA standards, Bussing said.
"There are many DARPA hard problems to make this work: for example, the way in which air is processed in these engines, the way the detonation event is created, the way the various components pieces are all coupled together," he said. "So it is technically very challenging. There is a lot of fundamental physics and technology that has to be worked out," he said. "But we have a high degree of confidence we can make this technology work."