LOS ANGELES (AP) — An experimental, unmanned aircraft developed for the U.S. Air Force went hypersonic during a test off the Southern California coast, traveling at more than 3,000 mph, the Air Force said Friday. The X-51A WaveRider flew for more than three minutes under power from its exotic scramjet engine and hit a speed of Mach 5.1, or more than five times the speed of sound. The test on Wednesday marked the fourth and final flight of an X-51A by the Air Force, which has spent $300 million studying scramjet technology that it hopes can be used to deliver strikes around the globe within minutes.