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Sport-Prototype - A Childhood Dream (Part 1)

by

Antonio Eiras

Conceiving a Sport-Prototype race car represents, by its peculiar characteristics, the childhood dream of any aerodynamics’ engineer.

 

In fact, this vehicles involving bodywork allows not only the exploitation of a big area for the generation of downforce, but, also, the maintenance of a linear undisturbed air flow, that surrounds it, in opposition to what happens in the open wheelers racing cars, by influence of the turbulent vortexes originated by the rotating wheels.

 

In these cars the level of aerodynamic efficiency reached, the relationship between the downforce, generated by the bodywork, and the drag produced by the vehicle, at the same speed, is nearly the double of the efficacy of an open wheeler racing car with a similar engine power.

 

Sport-Prototype cars are widely used all over the world, in distinct Championships, running in circuits that differ considerably on mechanical and aerodynamic solicitations.

 

When these cars run in a “Mickey mouse” type of circuit, with low to medium velocity curves, joint by short straight lines, the needs in downforce have to be obtained by the use of all the kind of wings, disposed on the bodywork, and working in high angles of attack.

 

In the case of Le Mans, like in any other velocity track, the rear wing, the only real wing that is usually used, works mainly on fine tuning of the front and rear axles aerodynamic loads, and for stability purposes.  

 

In this high velocity circuit, and, as we know, the level of aerodynamic loads created is directly proportional to the square of the velocity, the downforce generated by the bodywork itself, without the rear wing, is enough for the good handling of the car.

 

In La Sarthe, with it’s so long Hunaudiéres straight line, the high velocities reached with these cars forced the organizing entity, the ACO (Automobile Club de l’Ouest), to conceive and apply a specific Technical Regulation for their 24 Hours race.

 

And so, these regulations impose the use of a “skid block”, that is, like in open wheeler racing cars, longitudinally applied under the Reference Plan, between the front and rear axles.

 

Forward to the front axle, in a minimum span of 1 meter, the under floor of the car cannot be under a minimum of 50 mm over the same Reference Plan that extends backwards, under the cockpit.

 

All the under floor car surface, including the rear diffuser, and the round edges that joint this surface to the lateral faces of the side pods, are well limited by these specific Technical Regulations.

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