Greetings, Mike.
Sorry to say, but I believe the drawings you're using may not be entirely accurate. Based on the information I have, the early Caudron G.III featured elevator and rudder control through warping (French: gauchissement) ? that is, by changing the shape of the control surfaces via cable tension.
This means that when the elevator was deflected, it would bend into an arc, with the trailing edge curving upwards. To allow for this movement without overstressing or damaging the structure, the lower edge of the rudder was rounded, so that both surfaces could move freely and form the correct geometry when deflected together.
Later, when production was shifted to other factories, a simpler solution was introduced ? hinged control surfaces. At that point, the rudder was straightened and began to move like a conventional control surface. However, its previously rounded lower edge would have interfered with the now-hinged elevator. Therefore, the rudder?s lower edge was also straightened to avoid collision with the elevator during deflection.
This change is clearly visible in period photographs of early and late Caudron G.III aircraft.
In my opinion, it's an important visual and technical distinction between the early and late production versions, and it strongly influences how an accurate model should be represented.
