Many moons ago when I completed my 1900 ground school by a very experienced guy he mentioned the VNE limit was due to control surface flutter.
So installed on the UB series was small blister on each aileron and the rudder to project a small area into the airflow, when the aircraft was travelling at high speed (ie descent), apparently this helps protect against the onset of flutter with airflow separtion at the trailing edge of the wing.
On the UC, UE series the blisters have been removed from the aileron but still remain on the rudder.
Please feel free to correct me
Coastrider - are we back at the SAS in KWT