The world's biggest radio controlled C-17 Globemaster III model flying from a grass airfield. With almost 20 ft wingspan and a takeoff weight of over 260lbs, this is without doubt a really big model aircraft.
The thing that amazes me is that these guys are allowed to fly these huge things between and very close to the high tension power lines. In Australia they would be kicked out in five minutes.
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http://www.metacafe.com/fplayer/1593449/c_17_globemaster_1_9_scale.swf"