This all brings back the problems we faced in the late 1950's with control line. No problem with one flyer in the circle, but those crazy combat people were always crossing lines and crashing. Not sure that this adds to the discussion, but out here in Wyoming we seldom get more then 5 or 6 planes in the air at a time. Only worries are the industrial 2.4 controllers running illegal high power limits, skeet shooters and eagles claiming the airspace. jot