RE: Vintage K&B 61 power RPM
I have a old Kadet Senior that I built up many years ago and it would fly fine with a .35 engine on it. I had a old OS .60 open rocket four stroke engine on it and it had way too much power for flying the plane. Thus it wound up at 1/4 to 1/2 throttle most of the time for flying the plane around.
But the ARF Kadet Senior planes seem to need a .60 engine on them, as they seem to build up more more heavy in weight in comparison to the kit built versions.