F1 wings double flap

Aerodynamic features of a 1983 wing

The need for wings profiles for sports cars has always been to produce greater downforce within geometrical constraints dictated by sports regulations with resulting in increase aerodynamic resistance.

At the time of this kind of wing (photo n.1) - Ferrari 126C3 wing (1983) - it was forbidden the setting wing on the run or at least the adoption of mechanisms to do so, already in 1969, the year after the first appearance of an wing in F1 (Ferrari, GP Spa - 1968) was established by the CSI (International Sport Commission) the wings' regular size: width less than 1.50m and height up to 0.80m from the ground undergoing a remarkable resizing from the first appearance of 1968 precisely.

Returning to the technical aspect, the increase of downforce is obtained by creating greater depression on the dorsal and consequent overpressure on the ventral (Fig.1) this is achieved by varying the average curvature of the wing.

The adimensional coefficient of –P is –Cp = -P / (1/2 x q x S x V2) where :

-P : downforce; S : frontal area; 1/2 x q x V2 : kinetic energy (Bernoulli’s theorem);

R : resistance

But, as we said, for regulatory issues it is not possible to have a variable wing geometry so that it can be exploited depending on the circuit, so the most profitable solution to this limitation was to curb the back of the profile by inserting of the so-called flap of a certain chord c (Fig.2) that allows to change the angle Id called the flap depression angle (wing segment of the trailing edge – B.U.).

This flap can rotate by varying wing characteristics by continuing contour although being a separate body; the flap of chord c is reported as a percentage to the size of the whole section, giving it a size: flap = 100 x c / C.

Therefore, as mentioned above, to obtain increasing downforce from the same profile, it is necessary to first create greater overpressure on the ventral and higher dorsal velocities through a small braking (drag) surface in the zone of the split flap which is variable in incidence, in practice a sort of airbrake in fact this solution is used in the aeronautical field as it is not expressly efficient in the automotive field where the flap is a second wing that is added to the basic profile with various inclinations (Fig.3)

The equivalent of the split flap is the nolder (Photo n.2-3-4) although if it is small in size, formed by an angular profile placed along the whole length of the wing edge, nolder corrections or adjustments occur replacing the entire angled profile by varying its height with respect to the trailing edge, paying attention to the height to avoid violating regulatory constraints (height from the ground).

The nolder can also be turned on the reverse side to the back so that it becomes a brake for the dorsal over velocity by reducing downforce and resistance to the detriment of aerodynamic efficiency at the same as -Cp and Cr (adimensional coeff.).

Cr = R / 1/2 x q x S x V2 (Fig.1)

However, the flap has complexities in determining the aerodynamic characteristics through calculation due to the slots created between the wing and the other; in fact, the air of the ventral zone that will invest in this gap will increase its kinetic energy by passing through the dorsal zone by increasing its velocity (Photo n.5-6-7) and retarding the fluid vein release point.

Shortly we can say that the depression that forms on the leading edge of the flap extends across the affected area to benefit the dorsal air flow of the entire wing by increasing its downforce.

We leave, in this occasion, the problems caused by the small vortices and the detachment of the boundary layer from the dorsal area with consequent decrease in -Cp values.

The configuration of our "double slot" wing allows to obtain high -Cp values and a kinetic energy supply of the slots, the first of the two flaps also acts as a deflector by turning the airflow towards the leading edge of the second flap; always in the configuration of this wing the two flaps are fixed while the entire wing can be adjusted through the fixing holes to the support (Photo n.8-9).

To define slot geometry, it does coincide the angle of the axes x and y with the end dorsal face of the base profile (lip) according to its distance from the leading edge you have the feature size of profile configuration. (Fig.4).

The variation along the x axis indicates how much the lip overhangs the leading edge of the flap while the variations along the y axis determine the height of the slot, all affecting on the downforce.

In conclusion, it was desirable to describe shortly the function of a double slot wing in use in the early 80s and in particular on the Ferrari 126 C3, listing some important terms in the aerodynamic field, also briefly mentioning their use in aeronautical field.

References :

E. Benzing - Wings Automobilia 1991; K. Hodl - drawings based on Wings; C.Galli - photos; Ferrari 126 C3 wing - property of C.Galli (a gift of the friend Dr. Valerio Stradi - Ferrari S.p.A. - 1983)