Nothing DIY about this, but it was too cool to resist. From Gizmag:
Two Global Hawk unmanned aircraft have flown in close formation at distances as close as 30 feet (9 m) for the first time. The series of flights took place between January 11 and May 30 this year and marked a major milestone on the way to demonstrating the first autonomous aerial refueling between two unmanned, high-altitude aircraft as part of DARPA’s Autonomous High-Altitude Refueling (AHR) program.
The flights were conducted by a team from Northrop Grumman, DARPA and NASA Dryden Flight Research Center and involved two modified NASA Global Hawk UAVs. The trailing aircraft was configured as a tanker aircraft, while the lead aircraft was configured as a receiver and extended and retracted its aerial refueling hose several times during the flights. Fuel systems were also fully integrated into the UAVs and ground tested.
During the ninth and final test flight lasting over 2.5 hours, the two aircraft rendezvoused at 44,800 feet and spent the majority of the time flying autonomously within one wingspan (100 ft/30 m) of each other. This was designed to demonstrate that High Altitude Long Endurance (HALE) aircraft can safely and autonomously operate under the conditions of in-flight refueling.