Why RB5 collect their diffuser between Rear wing end plates?

[Scania]

what fuction it has? It make the diffuser more narrow
.

[ISLAMATRON]

It extends the effective diffuser length... which toyota does with its use of the rear crash structure... but RBR does allow diffuser exit outside of the rear wing endplates.

[RacingManiac]

I am sure it also helps the interaction between the rear wing and the diffuser, using the low pressure area under the rear wing to help extract more flow out of the diffuser.

[Gecko]

I am sure it also helps the interaction between the rear wing and the diffuser, using the low pressure area under the rear wing to help extract more flow out of the diffuser.

This is the main reason, the flow is simply more twodimensional between the rear end plates and therefore the interaction between the diffuser and the wing is larger. At the same time the effectiveness of the diffuser is also increased (lesser drag and more lift), even if the effect is not as large as that of the effect of the endplates on the wing, as the diffuser is working in ground effect. The diffuser might be narrower which somewhat reduces the effectiveness, but it seems that overall the effect is positive as so clearly demonstrated last weekend .

[modbaraban]

what fuction it has? It make the diffuser more narrow
.

It was discussed here viewtopic.php?p=94860#p94860