At last years F3A Eurochamps Christophe had an additional piece of thin ply glued to his rudder to create a "T" shape when you look down on it. His original rudder trailing edge was thin (about 1/16 - 3/32" ) and the bit of ply took it out to around 3/8" I would say. He wasn't around to ask but I presume this would give your rudder the aerodynamic characteristics of a rudder with a trailing edge thickness of 3/8?

In Romilly this year BPLR had something similar on his rudder but it was out to about 1/2" and it was faired in. Why not just build a rudder with 1/2" trailing edge thickness?

Apart from a bit extra drag and a softer feel around neutral what does a thicker trailing edge give you?

Thanks,

Angus

Nothing.

If you look at downforce wings on some cars you'll see a similar but one sided lip they call a "Gurney Flap" after Dan Gurney, the racer that introduced these lips to car racing. The Gurney Flap is supposed to provide more lift but it's not as good as just using more camber. Selig tested such flaps in his early windtunnel work and from what I saw that was the outcome. More lift but far more drag that could be obtained with more camber. It's possible that this lip on the rear of the rudder is there to get more response out of the rudder if it's already at max throw and limited by structural factors. Or it may be there to soften the response as suggested. Either way it would certainly add drag

More likely as a quick fix for tail wag. (Airflow separation between fin and rudder)

I use a Gurney flap to counteract about a .2 degree washin on a wing.
Uses 1/8" sq. balsa, 6 inches long, on the upper trailing edge out at the tip.
It works well, letting me center the rudder for level flight on a REM plane.
I have a 2M glider I'm going to do that to also, to get the rudder centered.

drag -and that is what is wanted
This has been a problem on some of the "designs" in that the rudders are just too sensitive - It is caused on some models by th addition of a huge aerodynamic counterbalance - which simply self servos . On others some drag helps eliminate a minor vagel likely due to lateral area setup.