have you tried creating a search and destroy waypoint over the area? make it's diameter about 200 metres, and put a cyle waypoint right next to it.
also bear in mind that a chopper needs a significant target upon which to fire. i daresay you've tried looking for target loons from a chopper in flight. it ain't easy. if all else fails, get yourself the invisible targets addon and spread a few around the area. unfortunately the ground troops will fire at it too, but at least the chopper will engage.
try the waypoints first, and work from there.