Paul,

I need you to clear something up for me please.  The F1 diffusers
diverge both vertically and laterally aft of the rear axle centerline,
which would slow the airflow.  The undercar airflow speed would also
decrease (since it flows into the diffuser), raising pressure--the
opposite of what is needed.  What am I missing here?

Ron

Well the divergence in the duct cross sectional area causes a low pressure
area back there. Air wants to flow from a high pressure area (just behind
the front wheels under the tub) where the diffuser starts to the back of the diffuser. The area divergences causes a drop in pressure which causes a speed up of the air flowing under the diffuser. That causes a low pressure area on the under surface of the diffuser. This must be done carefully as a diffuser can "stall". Perhaps. I think. It must be tested full scale on the car or
in a wind tunnel with a moving ground plane as the air adjacent to the ground
is stationary while the air immediately adjacent to the front under surface
of the diffuser is moving at vehicle speed.

BTW The first time I tried a crude one on the Chaparral 2F in the late 1960's it had so much down force it ripped it self off. I had to beef it up. That gave me a clue to the potential. Of course we did not exploit that because we had high aspect ratio movable wings. I suspected a full width high mounted  wing would have a better down force to drag ratio but I could be wrong. I asked a Ferrari engineer at the 2008 Oxford  WMSS if he thought the down force to drag ratio of the diffuser was better than the current dumb and silly narrow span wing and he choose the diffuser. There is a reason gliders have long wings.


Paul Lamar