With the third X-51A WaveRider failing to reach hypersonic speed due to a fin failure last August, it seemed the United States Air Force would possibly forgo the fourth (and final) run. On the morning of May 1st, however, that last X-51A got its chance to soar, successfully reaching Mach 5.1 during a record 370-second flight. According to the Wright Patterson Air Force base, the aircraft's rocket booster helped it hit Mach 4.8 about 26 seconds after being released from a B-2H at 50K feet, at which point its air-fed
