Scramjet technology may be a propellant for hypersonic flight

Hypersonic flight has long intrigued Lab aeronautical engineer Preston Carter. His HyperSoar concept for an aircraft that would fly at 6,700 miles per hour — fast enough to get you anywhere on the globe in less than two hours — won wide-spread attention in the industry and news media when it was unveiled in 1998.

Currently in the midst of a two-year assignment to the Defense Advanced Research Projects Agency (DARPA) as Scramjet Program Manager, Carter recently oversaw the first successful free flight of an experimental hypersonic vehicle powered by scramjet engines, a propulsion system that could someday power hypersonic craft.

The miniature (four-inch-diameter) test vehicle and engine were launched last summer from a light-gas gun and flown along a 240-foot tunnel, producing enough thrust to reach a top speed of Mach 7.1 (5,325 mph).

"In a way, this flight was reminiscent of the Wright Brothers’ first flight: short, but important," said Carter, a member of the Lab’s Engineering Directorate.

The scramjet (supersonic combustion ramjet) was launched from a gun because such engines must travel at hypersonic speed in order to capture and compress air to supersonic speed for combustion. The test engine was integrated within a cylindrical vehicle with an on-board hydrocarbon (ethylene) fuel system.

"In the technical community, it’s well known that the key to making a scramjet-powered vehicle work is integration — designing the airframe, engine and support systems to work synergistically," Carter said. "Scramjet technology itself is really very advanced due to many years of wind tunnel tests. However, demonstration of an airframe and an engine working together must be done in flight, and this flight was a first step along that path."

The test was conducted at the U.S. Air Force’s Arnold Engineering Development Center in Tennessee by DARPA and GASL, a division of Allied Aerospace Industries Incorporated.

Additional flight tests are planned, with higher performance scramjet engines and longer flight durations.

Carter is in his first year at DARPA.

"Working as a DARPA program manager, here in DC, has been an incredible learning experience," Carter said. "There’s a great deal of excitement in the hypersonic community right now, and we’ve made a lot progress. But there’s still much I wish to accomplish before I’m finished here."
Carter is looking forward to returning to the Lab after his stint at DARPA.

"I miss the people, and the broad-based science, and I’m eager to share what I’ve learned."