Can some clever sole please tell me what the section at the top of the rudder in front of the hinge line is called please, usually found on aerobatic aircraft

thanks

lozza

counter balance....

shows up on elevators too... and even on ailerons on a few foamies (Nikitas Animal for one)

Technically those are aerodynamic balances, intended to relieve pedal and stick forces for the pilot.
There's no real reason for them on a model, but they do look nice and "scaley".
For exremely large surfaces with extremely large deflections on 3D models, they take some of the load off the servo gears..
As in... Ron Shuler's 40% Extra..
4 servos on the elevator
A monster servo on the rudder

I have successfully used airodynamic balances on both rudder and elevator to allow the lower powered servos (futab148's) to move very large surfaces on 1/4 scale models. Worked well with adequate throw and no servo stalling. In the process of my experiments, I did find that it is best to keep that area forward of the hinge line to not exceed 10% of the surface or I got hunting or oscillations around neautral. You can make these surfaces do dual purpose as; properly weighted, they also provide static balance which can be very helpful on elevators and ailerons.

thanks to everyone for your replys

lozza