The Boeing X-51WaveRider is an unmanned scramjet demonstration aircraft for hypersonic (Mach 6, approximately 6,400 km/h at altitude) flight testing. It successfully completed its first free-flight on 26 May 2010 and also achieved the longest duration flight at speeds over Mach 5.
X-51 Test Flight. Courtesy Video | Air Force News | Date: 05.25.2010. X-51, an unmanned scramjet aircraft which is capable of Mach 6, approximately 4,000 miles per hour. Scenes include the X-51 leaving the rail of a B-52 aircraft and flying away from the B-52.