Thursday, 17 March 2011

X-51A Next Hypersonic Flight

From Fighter Planes


Air Force engineers currently plan to fly the second X-51A Waverider hypersonic flight test demonstrator as early as March 22.

Four X-51As were built for the Air Force by teams at Boeing and Pratt & Whitney Rocketdyne. The X-51A made history on its inaugural hypersonic flight test on May 26, 2010, when it was launched from Edwards Air Force Base, Calif., tucked under the wing of a B-52 Stratofortress. After release, it ultimately accelerated to Mach 5 under scramjet power. The flight was about 10 times longer than any previous hypersonic scramjet flight and "80 to 90 percent" of flight test objectives were achieved, program officials said.

Underscoring the complexity and uncertainty of hypersonic flight testing, Charlie Brink, the Air Force Research Laboratory X-51A program manager, noted that not everything went perfectly on the first flight test. The vehicle failed to accelerate as quickly as anticipated and the flight test had to be terminated after 143 seconds under scramjet power. A perfect flight would have lasted another 100 seconds and accelerated the X-51A cruiser to Mach 6.

X-51A Waverider Hypersonic Aircraft

After the flight, members of the flight test team independently scoured over telemetry data for a month. Then they conducted a comprehensive "fault tree analysis" to identify every piece of anomalous data to determine the root cause.

Program officials already knew from wind tunnel engine tests about the intense heat the scramjet engine and hypersonic flight creates. During flight, the scramjet engine actually grows about three-fourths of an inch. The effect complicates design for such things as interface seals.

The Boeing "Phantom Works" and Pratt & Whitney Rocketdyne teams pulled the engines from the three remaining flight test vehicles and focused on the interface between the rear of the fuel-cooled engine and its vehicle mounted nozzle. Mr. Brink said the effort identified an "apparent thermal seal breach" at the interface which was not as tight as it needed to be. This caused some of the hot gases that should have provided thrust to leak into the rear of the cruiser.

In the end, the team made design changes to make it a "much more robust" interface. All of the remaining X-51As have been modified with the new beefed up design.

Mission and weather permitting, a B-52 test crew will take off March 16 from the Air Force Flight Test Center at Edwards AFB and the flight test team will run through a dress rehearsal for the entire flight profile for the next hypersonic mission, albeit without the X-51A attached.

The second X-51 is waiting in a hangar at Edwards AFB and is ready to fly, Mr. Brink said. He added the next flight is scheduled for March 22 over the Navy's Point Mugu Sea Range but a number of factors with the flight-test vehicle, weather, range availability, and supporting test assets could slip the flight date to the right.

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