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Final X-51A Scramjet Flight Exceeds 5.0 Mach

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An unmanned X-51A WaveRider aircraft reached 5.1 Mach, Monday, pushed to more than 3,000 miles per hour over the Pacific Ocean near Point Mugu, Calif., by a scramjet engine. The Air Force said Wednesday that the WaveRider was carried aloft from Edwards Air Force Base by a B-52. It was released over the ocean at about 50,000 feet and accelerated to 4.8 Mach in 26 seconds by way of solid rocket booster. The aircraft, which is designed to ride its own shockwave, then lit its air-breathing scramjet engine and accelerated to 5.1 Mach at 60,000 feet, covering 264 miles in just over six minutes. The effort follows an early program success followed by two less fruitful attempts.

A first success in 2010 took an X-51A test vehicle to 5.0 Mach. The effort was followed by two failures. A June 2011 test was shut down early due to a disruption in airflow to the engine. An August 2012 test failed when, 15 seconds after the vehicle separated from its boosters, vehicle control was lost. Wednesday's attempt ended when the X-51A broke up in the Pacific. The flight was the fourth of its kind seeking to establish the viability of high-speed scramjet propulsion with an air-breathing engine. It produced 370 seconds of data collection and is the culmination of an estimated $2 billion spent on hypersonic technologies over the past decade by the Pentagon. No further flights are planned for X-51A aircraft, but it is expected to serve as the foundation for future hypersonic research chasing the long-term goal of practical hypersonic flight.

A scramjet uses fuel to cool the engine, which in turn heats the fuel that ignites when injected into the engine's supersonic flow. Ramjets operate similarly, but the airflow through the engine is subsonic. Aside from its longevity, the X-51A scramjet's flight still operated in the Mach 3 to Mach 6 regime shared by ramjet engines. Watch Boeing's explanatory video here.

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