HD, Yes I fly a clockwork aircraft and also more sophisticated general aviation aircraft. I can tell you that having a radio is not the be all and end all. Many times I have been flying under radio control from one of the flight information centre's and have had another aircraft go wizzing past that I was not advised of causing me to take avoiding action. Also when I used to fly at a certain airfield in southern england where none of us used a radio or transponder. We never had any mid air collisions until we had mandatory radio, then we had a collision which killed 4 people. The answer
is always - look out of the cockpit and look before you turn.