The U.S. Air Force Research Laboratory’s (AFRL) Boeing X-51A Waverider demonstrator successfully achieved sustained, scramjet-powered, air-breathing hypersonic flight above Mach 5 in its final test flight on May 1.
Although the Air Force is not yet commenting on details of the flight, the X-51A is thought to have experienced positive acceleration to speeds in excess of Mach 5 and run for the full duration of the planned powered phase of the test. Based on targets established for the previous test attempt, this could have been as long as 300 sec., followed by an unpowered gliding descent of around 500 sec. prior to impacting the sea in the Pacific Test range west of California. If these times and speeds are confirmed, they will represent new records for sustained, air-breathing hypersonic flight.
The X-51A is intended to prove the viability of a free-flying, scramjet-powered vehicle and is considered an essential building block toward the long-anticipated development of hypersonic weapons and other high-speed platforms. However, despite the partial success of the first flight, which reached Mach 4.88 under scramjet power in May 2010, that mission ended prematurely after a malfunction, as did the second flight in March 2011 and third in August 2012.
Coming in the wake of these disappointing prior tests, the success of the May 1 flight could therefore be pivotal in helping drive further research and development to meet the Air Force’s long-term goal of hypersonic capability. The test involved the last of the four vehicles to be built by Boeing and configured with a Pratt & Whitney Rocketdyne SJX61 dual-mode ramjet/scramjet engine, and incorporated improvements and lessons learned from the three former flights.
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The mission: Attack anywhere in the world in less than an hour.
Description and Purpose:
The X-51A Waverider program is a collaborative effort of the U.S. Air Force Research Laboratory, the Defense Advanced Research Projects Agency (DARPA), Pratt & Whitney Rocketdyne and Boeing to demonstrate hypersonic flight capability. The X-51A will demonstrate a scalable, robust endothermic hydrocarbon-fueled scramjet propulsion system in flight, high temperature materials, airframe/engine integration and other key technologies within the hypersonic Mach 4.5 to 6.5 range.
Pratt & Whitney Rocketdyne is the propulsion system provider. Vehicle integration is performed by Boeing Advanced Network & Space Systems, headquartered in Huntington Beach, Calif.
The X-51A Waverider is an unmanned, autonomous supersonic combustion, ramjet-powered hypersonic flight test demonstrator for the U.S. Air Force.
Length: Full stack 25 feet; Cruiser 14 feet; Interstage 5 feet; Solid rocket booster 6 feet
Power Plant: JP-7 fueled/cooled SJY61 supersonic combustion ramjet
Weight: Approx. 4,000 pounds
Fuel Capacity: Approx. 270 pounds JP-7 ( kilograms)
Speed: 3,600+ miles per hour (@ Mach 6)
Range: 400+ nautical miles
Ceiling: 70,000 + feet
During its first flight test in May 2010, after being released from a B-52, the solid rocket U.S. Army Tactical Missile booster ignited and took the X-51A Waverider to approximately Mach 4.5, at which point the scramjet engine took over and accelerated the vehicle to a flight speed of approximately Mach 5.0 for approximately 140 seconds. It then observed a decrease in thrust and acceleration for another 30 seconds before the test was terminated . The test was the longest of its kind, beating the previous record of 10 seconds set by the X-41.
The second flight test vehicle flew in June 2011, but soon after being dropped from a Boeing B-52 Stratofortress off the coast of California, the vehicle encountered a problem while nearing speeds of approximately Mach 5, forcing the planned flight test to end prematurely. The hypersonic vehicle attempted to restart several times and continued to orient itself to optimize engine start conditions before flying into the ocean as originally planned. However, the team was able to collect a significant amount of data from the test.
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