ORIGINAL: Woketman
Its a good rule for a good reason. After a typical jet (and just about any ROG R/C aircraft with trike landing gear) gets going pretty good on a takeoff roll, the weight on the nose gear is less and less in anticipation of rotation. This means that steering authority is rapidly going to zero. At the same time, control authority in yaw is increasing rapidly for the rudder(s). So if a gust of wind or a big runway rut turns the airframe towards the crowd, the only hope you have is rudder.
The main problem that I have with this rule is that it totally ignores whether the aircraft in question even has a vertical stab.
Thanks to this rule, you can not have a turbine powered scale B2 model. You can, however, have a ducted fan version of that same aircraft, which can just as easily exprience the same steering problem that you describe above, and can just as easily go into the crowd. For some reason though, lack of rudder control is not considered an issue for ducted fans or for prop planes - only for turbines. So, we once again have a rule which singles out turbines just for the sake of it. The truly interesting thing here, is that the turbines are the aircraft that are most likely to have wheel brakes that can help stop a wayward aircraft... e.g. your prop jobs generally don't have brakes, so that with them you have even less options for stopping that meat cleaver before you run into the crowd.
I'm all for having operational rudders if the aircraft in question permits it - but a blanket rule enforcing rudders even if the aicraft being modelled has no vertical stab ... that's just plain dumb.
Gordon