The X-48 is currently developed under a joint-venture by Boeing Phantom Works and the NASA Langley Research Center. At first a remote-controlled model of the aircraft was built at the Stanford University, with a length of 5.2 m. The next step was the 10.7 m long X-48A, which was built by the NASA Langley Research Center. The first flight of this variant was scheduled to take place in 2004, however the X-48A program was cancelled.In November of the year 2005, Boeing announced that they are currently working on the third model, the X-48B and now the US Air Force joined the project. And on 20th July 2006, at the Dryden Flight Research Center, the unmanned prototype (wingspan of 6.4 m and a weight of 250 kg) of the X-48B was first flown successfully. The aircraft reached a speed of 222 km/h at an altitude of 2,286 m. In the end of March 2007, the X-48B program was finished after 80 made test flights, making it the most extensively UAV project, ever undertaken by the NASA. The present record holder was the X-45 with 40 flights. The X-48B met all the requirements. In future, the X-48B is going to be equipped with a new fly-by-wire system for the “Phase 1.5” flight test series for the “Environmentally Responsible Aviation Project” of the NASA to collect data for more environmental aviation, with the aim of reducing noise, lowering fuel consumption and greenhouse gas production.
In 2012, a modified X-48C with two, instead of three engines, was tested.