If at first your unmanned aerial vehicles don't succeed try, try again? After a series of unsuccessful tests with the Boeing X-50 Dragonfly and Groen Heliplane, the US government is once again trying to develop a high-speed, vertical takeoff-and-landing (VTOL) aircraft. DARPA just announced the VTOL X-Plane program, a 52-month, $130 million project with one mission: to build an aircraft that can exceed 300 knots, achieve a hover efficiency of 75 percent or better, and hit a cruise lift-to-drag ratio of 10 or more. In layman's terms, su
