Brawn BGP001 - rear diffuser design
Brawn have a quite different central channel to their diffuser, with the shape of the deformable structure being used to create a sort of double-decker (black arrows) design. However, the most important and controversial aspect is that to work properly this section of the diffuser needs to be fed by air. Highlighted in yellow, you can easily see the hole in the reference plane (red arrow), which actually starts far further forward than is apparent from the drawing, thanks to the small dimensions of the gearbox. The hole increases the speed of airflow as it heads towards the higher rear venturi section, where it expands and creates more downforce. Other teams are arguing that the presence of the hole is against the regulations.
Brawn, Toyota, Williams - the diffuser controversy
The controversy surrounding the Brawn, Toyota and Williams diffusers (which will be considered by the FIA's International Court of Appeal on April 14) goes beyond their external shape and dimensions. More important is the fact that all three designs use a 'window' or hole (red arrow) to feed the diffuser. That hole is horizontal in the case of the Williams, vertical for the other two teams, and is located where the floor's step plane meets the reference plane (black arrow). Rivals' cars, such as Ferrari's on the right, feature no such hole at this point. This difference stems from the question of whether the diffuser's three channels can be considered as separate entities, or whether they must be considered as one (enclosed) whole. Given the wording of the regulations, one can argue a case either way, though the majority of teams apparently took the spirit of the rules to mean that all three channels must have the same height and length, with no holes to feed them.