ORIGINAL: Dr1Driver
Tall Paul,
Control surface shape contributes more than you realize. Turbulence begins at the TE and travels forward. Any shape that helps make a clean break when the air passes the surface helps prevent flutter. Flutter can be caused by the conditions you mention, AND by the airflow separating from the surface due to turbulence.
Dr.1
I round the trailing edges on those surfaces I don't taper.
I've played with square and round and found zero difference.
Here's the rudder and elevator on my Morris Top Cap...
Nicely rounded.
Same on my Fazer, Wacky Waco, Ultimate....
On my 3D foamies, the foam is cut square in the kit, and I leave it that way.
Any flutter is due to excessive speed with very large chord surfaces.
Stiffening the control system to move the point of flutter excitation beyond the speed capability of the airplane works for models just as it does for full-scale, when flutter is encountered.