LowNSlow,Disregard earlier post (if you've read it)
If your Cub is on a permit,and your doing an annual and you have removed control surfaces then I presume that you have a PFA inspector involved, ask Him/Her what's required. And yes It's an aerodynamic/vibrational thing not weight. Any structure with an air flow over it becomes prone to resonance, you must have seen the footage of "Galloping gertie" aka the Tacoma narrows bridge. Control surfaces are susceptable to these effects, which is why Mass balance weight is added to move their natural resonance frequency to a range outside of any vibrations caused by airflow in normal flight
Best of luck with the rebuild.
[This message has been edited by Windy Militant (edited 21 September 2000).]