High Quality Content by WIKIPEDIA articles! The Boeing X-51 (also known as X-51 WaveRider) is an unmanned scramjet demonstration aircraft for hypersonic (Mach 6, approximately 4,000 miles per hour (6,400 km/h) at altitude) flight testing. It successfully completed its first powered flight on 26 May 2010 and also achieved the longest duration flight at speeds over Mach 5.