The company that developed the Sherpa cargo parachute system (that used GPS and mechanical controls to guide the direction of the descending parachute for pinpoint landings), has taken that technology one step farther. Using a parafoil (a parachute that can be controlled in such a way that the user can gain altitude and travel over long distances), and a cargo that contains a small propeller and engine, a unique type of UAV has been created. The U.S. Special Forces liked it so much that they bought 18 of them (at $560,000 each) for use in Afghanistan. The Snow Goose can stay in the air for up to 20 hours, get as high as 18,000 feet, and carry up to 600 pounds of cargo. The Snow Goose is guided by onboard GPS and mechanical flight controls controlled by a special microcomputer. The Special Forces are using them for things like delivering supplies, or dropping psychological warfare leaflets. 

While the Sherpa has been a big hit with the air force, allowing transport aircraft to accurately drop cargo by parachute, Snow Goose has some serious limitations. The parafoil is more vulnerable to bad weather than rigid wings are. Then again, all UAVs have shown themselves to be very unstable when the weather gets rough. 

There is a similar system, Onyx, from another manufacturer. Onyx is also being tried out. This is similar to Sherpa, but with a longer range.