Martin
I can appreciate your question. I'm a 100% scale twin pilot and an rc twin pilot as well. In both places counter rotation is a real blessing. But as it turns out it does not appear to be such an issue in control line. I was have been around Frank Carlisle and his LA Heat twin project for a couple of years now. Frank powers it with a pair of brodak .40's. I have seen just about every combination of engines running that you can imagine from both to none to either one running while the other is not. The only difference discernable (except that when done are running its very quiet) is that the lap times change by about 0.8 seconds slower when only one is running. The plane still has good line tension, it still flies with authority, and I am sure Frank could still do many maneuvers with it on one. When a motor quits it does not mater which one goes first. The plane continues to fly securely until the other stops.
I am sure this has been a real relief to Frank as I was one of the folks harping to him that it could be a problem. Counter rotation can look cool but I do not think its an issue for a glow powered control line twin. If I were to do one in glow (I fly only electrics now where of course its very doable) I would do both running normally.
hope this helps
bob branch
ps, sorry bout the screaming bold type. I'm on a new computer and have no idea why it just suddenly did that when I went to scroll down to send.