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Flat Underfloor - A Big Hidden Wing (Part 3)

by

Antonio Eiras

In the early nineties, Ferrari tried, successfully, the application of this principle to the rear lateral diffusers, and, instead of a soft and continuous transition between the surface of the step plan and the lean plan of the rear diffusers (see drawing of the Venturi Tunnel on the "Wings" article), it started to present a “step” in straight angle, causing an air acceleration, similar to what happened with the "Gurney flap."

 

The “step” (drawing 5-a) went being tested successively, in wind tunnel, until it reached a quite complex form that, as it was told in confidence to me by an old Ferrari engineer,”...nobody realised the reason why that worked better than a straight angle, but there were not doubts that it was more efficient in the tests that we performed"!.

 

After being accelerated in it’s passage by the “step”, the air that flowed along the step plan will be aspirated and drained by the divergent duct of the rear lateral diffuser, witch develops to the limit, allowed by regulation, represented by the rear axis, where it will unite, smoothly, with the air that flowed, first over the flux separator created immediately ahead the rear wheels by the narrowing in the "bottle of Coke" side pods, and later, by the superior surface of the lateral diffusers.

 

One part of the air that flows under the step plan will be aspirated by the central rear diffuser, which efficacy is limited by the compulsory extension of the reference plan until the rear axis level.

 

a - Safety structure of rear impact energy absorption.

b - Small rear central diffuser, in the continuity of the "skid block."

c - Flux deviator of the rear lateral diffuser.

d - Lateral splitter of the rear lateral diffuser.

e - "Skid block."

f - Reference plan.

g - Step plan.

g - Splitter attached to the flux deviator placed backwards ahead of the side pods.

h - Superior splitter of the advanced placed flux deviator, ahead of the side pods.

i - Suspended flux deviator of the front wing’s inferior face.

j - Front wing’s main profile.

k - Splitter attached to the end plates of the front wing.

l - Inferior splitter of the advanced placed flux deviator, ahead of the side pods.

m -Flux deviators that operate together ahead the side pods.

n - Splitter that extends ahead the step plan and helps to channel more air under this plan.

o - Splitter that works as a "slat".

p - Rear lateral diffuser.

q - Small splitters in the inferior boards of the lateral walls of the rear central diffuser.

r - Superior rear wing’s main profile.

s - Inferior rear wing.

t - Rear wing’s end plate.

 

However, the lateral openings of the central diffuser, that allow it to work in continuity with the lateral diffusers, will drain not only part of the air that flows under the step plan, as well as aspirate some of the air flux that passes under the reference plan and the "skid block".

 

In McLaren’s MP4/20 and immediately behind the level of the rear axis, we can find a small diffuser, that continues backwards the inferior surface of the "skid block" and that will allow some small additional earnings of aerodynamic load. 

 

The central rear diffuser (drawing 6) was limited, by 2005’s technical regulations, to the 15 cm on each side of the central line of the car, and it could be extended until the level of the trailing edge of the rear wing. This rear limit was rarely used, because, since the interaction of the rear wing’s inferior profile with the air flux drained by the rear diffusers, had a frankly positive effect over the diffusers function, powering significantly it’s air aspiration capacity, it was verified that the central diffuser extension until the allowed rear limit, had, as a result, the loss of this interaction with the rear wing, with consequent loose of rear diffusers efficiency.

 

The rear diffusers drawing and it’s interaction with the inferior profile of the rear wing is extremely delicate, specific of each car, because in aerodynamics, as in all the other operation areas of these cars, a good solution for a vehicle may not be a good solution when applied in another vehicle.

 

And it is extremely important, for the good operation of these cars, that the diffusers allow a good drainage and aspiration of the air that flows under the under floor surface, because, as it told, in confidence to me, the same engineer: " ...it is important to channel the largest possible amount of air to go under the car, but never again more air that the one the rear diffusers can get to aspirate."

 

Like all the other areas in Formula 1, as in almost all race cars categories, the flat under floor surface is one of the technicians' constant concerns, and it is under a permanent study and evolution.

 

With the efficient improvement of the rear diffusers, the technicians will be able to guide a larger amount of air under the cars, with the creation of larger aerodynamic loads in their central part, among the axis, turning these race cars less dependent of the front and rear wings, consequently more stable in all points of the circuits, and under the different race conditions. Maybe its development can be a solution to allow a larger number of overtaking in all circuit motoring categories, helping to increase the emotion in motor racing.

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