Hypersonic X-51 Unsuccessful -- Engine Not to Blame

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No confirmation yet, but sources are telling Aviation Week that yesterday's attempted Mach 6 flight of the U.S. Air Force Research Laboratory's Boeing X-51A Waverider hypersonic demonstrator was not a success - but that the vehicle's Pratt & Whitney Rocketdyne SJX61 dual-mode ramjet/scramjet engine was not to blame.

UPDATE - Wired's Danger Room tweeted earlier that a fin problem resulted in loss of control before the engine could start.

The Air Force Flight Test Center at Edwards AFB confirmed to Reuters earlier today that the X-51A and its booster were launched successfully from the B-52 mothership over the Pacific between 10:00 and 11:00am local time on Aug. 17, But there has been no news since. Details of the flight are expected to be announced today.

The latest X-51A included a series of hardware and software changes to overcome issues thought to have brought the second flight on June 13, 2011, to a premature end after only 9.5 sec. of powered flight at around Mach 5.

Another flight ended when the vehicle stack failed to separate from the B-52. The next attempt launched successfully, the vehicle separated from its booster, but its flight ended when the engine failed to transition from the ethylene fuel used to start the scramjet to the JP-7 fuel used for sustained flight. The inlet started, but then unstarted.

The first flight on May 25, 2010, reached Mach 4.88. Although it did not achieve the planned Mach 5, the test was considered a technical success as some 143 sec. of the vehicle’s 210 sec. of  powered flight time was under scramjet power -- 11 times longer than any previous air-breathing flight with a scramjet.

A fourth X-51A is close to completion at Boeing's Palmdale, Calif. plant, but is currently not funded for flight testing.

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