Hi,
The main source of drag in an open wheel car are the wheels. Some formula cars do limit the amount of drag generated by the front wheels by adding vertical barge boards to increase the pressure behind the wheels.
Barge boards where somehow used on this car for the rear wheels:
The GCR specifies that not aerodynamics should be used (I don't have the GCR with me, so I can't quote exactly what it says). My understanding of this is that "no aerodynamics" means no device used to generate downforce - but this is just an interpretation.
Are barge boards illegal in FV and is this why they are not used?
My understanding would be that barge boards, or other devices used to modify the air flow without generating lift are allowed. I saw something that may be a barge board on Mike's AM-5. It was made of transparent acrylic I believe, and attached to the front nose, between the bodywork and the front axle (close to the shock towers). I can't seem to find the picture for now.
It was a straight piece of acrylic though, and I don't think it was redirecting the airflow behind the wheels.