Tipover,

Can't offer any insight to your knife edge waggle, but can comment on the triangular stock on the trailing edge. I currently fly a G-202 in IAC full scale competition and use the equivalent of triangular stock on my ailerons. Actually, I use P-strip (it looks a little better and is easier to apply and remove), which is an extruded adhesive-backed rubber strip available at any hardware store and intended as a door sealer. A 12" long piece attached to the top and bottom of the trailing edge of the aileron and the trailing edge of the wing just before the hinge line, provides a "centering feel". You can actually feel a "notch" at the center position of the stick. I have mine located at the outer end of the aileron, but I've seen them at the mid-span as well as the inner end of the aileron and all seem to provide the same effect.

Some aerobatic aircraft have very thick trailing edges on their control surfaces; the Sukhoi for example, has ailerons with a trailing edge nearly 2cm thick. The purpose, I'm told, is to eliminate a vagueness around the center position. I would guess the triangular stock you saw on the rudder has the same purpose.