XPost: rec.autos.sport.f1

Good discussion on F1 rake angle

What is the Rake Angle? As over 45% of the downforce of a car comes from undertray and around 35% from the rear, this is a crucial area to get
right. But it’s not just a case of raising the ride height; work has to
be done on bodywork, floor and exhausts to get the maximum. Basically
the Rake Angle is the deviation of the floor plane from the horizontal. Positive rake angle is higher end, and negative rake angle is higher
front of the car. Negative rake is not in use in racing.

"Wait," you say, "they have flat bottoms, they can't possibly be using
ground effects to keep them on the ground." Wrong. On any Formula 1 car,
and on any prototype LMP car by the way, the nose part of the flat
bottom is closer to the ground than the tail portion. Resultant angle is referred to as the rake angle, which is typically 2-3 degrees. That
small rake angle creates a shallow ground effects tunnel which produces
the vast majority of the total downforce generated by the car. As anyone
who has seen these cars can attest, the angle that the flat bottom makes
with the road is barely perceptible, yet that same small angle makes a
huge difference in the downforce generated by the car. Typically if a
team is experimenting with a large change in rake angle set-up for a
particular track they might crank in a 2-3 millimeters change in the
height of one end of the car or the other. That should indicate how
critical the rake angle is.

There are two significant effects of this in that a steeper rake angle
will accelerate the airflow beneath the car due to a greater release of pressure as it flows past the lowest point of the floor. A rake angle
generates a venturi-like effect under the floor, where the majority of
the ground effects (or downforce) is generated. This angle is extremely sensitive, even a few milimeters one way or the other, either on the
front or rear end of the car can have a significant effect on downforce.
A sportscar with almost 10m² (or cca 6m² in case of Formula 1 car) of
bottom area has huge potential for producing ground effects downforce.
But this will only work if you are producing something really precise
and stiff facing the ground.

According to engineers of rival teams, the higher rear end of the Red
Bull artificially adds volume to the diffuser, hence makes it "think"
it's bigger than it really is. The whole concept seems to be more
efficient at creating overall pressure change and downforce from the
floor and the diffuser. Beacuse from 2011 diffuser regulation changes,
difusser have smaller angle of the walls, and by raking the car
(lovering front and rising rear end of the car), it effectively makes
the diffuser steeper, as they are so tightly rescricted on exit height.
Newey actualy make the diffuser steeper without working against the
rules. Deffuser actualy „think“ that he have steeper angles and actualy increases diffuser angle relative to the ground. It's also very
difficult to keep the diffuser working well at high rear ride-heights -
with the increased height from the flor, a lot of air can leak into the diffuser from the sides, reducing its overall performance. So, to do
that efficiently, you have to seal sides of the diffuser to prevent air
leak into the diffuser. But around year 2011, Red Bull can use the
exhaust gases and their sidepod design more effectively than any other
team to 'seal' the diffuser and keep the airflow working through this under-floor area. After blown diffuser was banned, they have to look on
other possibilities to seal diffuser.

Credits to F1 writers blog

Nice. Could you share the blog name? TIA

http://www.formula1-dictionary.net/rake_angle.html

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