A modified version of the Boeing X-48B blended wing body demonstrator, given its own X-plane designation by the U.S. Air Force as the X-48C, completed a 300-hour wind-tunnel test program at the NASA Langley Research Center in Virginia in September 2009. With a 21-foot wingspan, the 500-pound X-48 airplanes are 8.5 percent scale models of a heavy-lift, subsonic airplane with a 240-foot wingspan that the Boeing Phantom Works organization believes could be developed in the next 15 to 20 years for military cargo applications. In large part because of the way the engines are integrated into the vehicle - on top of instead of underneath of the wings - the BWB (Blended Wing Body) concept offers the potential to be quieter.