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Wings - How They Work (Part 1)
This work was the first in a series of five, conducted between 2005 and 2006, in which I’ve tried to explain, as simple and clear as possible, how the aerodynamics of a racing car works. During four years I’ve studied the fundamentals of aerodynamics, having completed my training with a priceless internship in the wind tunnel of Fondmetal in Bologna, Italy, at the invitation of Toyota Motorsport, during a test session of the Formula 1 Team, in late September 2003.
With the theoretical and practical knowledge accumulated, I decided to proceed with the completion of these works, giving special attention to the pinnacle of technology and where aerodynamics is applied in an extreme and unique way, that is the vehicle of Formula 1, but addressing also the very particular cases of the vehicles of Sport-Prototypes and of the DTM.
Let's start by trying to explain the mode of operation of the front wings of a Formula 1 car, which basic principles will help us later to realize how the aerodynamics of a competition vehicle work as a whole.
Wings were originally designed to meet the old desire of humanity to fly. They were born from the observation of birds and are designed to create lift and make airplanes fly.
Its use in inverted profile in automobile racing had an inconsequential experience in a Porsche of the 50s, a decade before it was installed, with great success, by Jim Hall in the Chaparral CanAm and Sport, before Colin Chapman used it, discreetly, in the 1968 Lotus 49B, and Mauro Forghieri applied it, prominent in the rear chassis of the Ferrari 312, in the GP Belgium of the same year.
Since these early experiments, the wings have undergone a remarkable evolution, and have been used in all types of racing cars, in a systematic way, to increase their effectiveness.
In the first illustration we have an example of the complexity and elegance of the front wing of the 2005 Renault R25 of Formula 1, in which we compare the original wing used in the beginning of the Championship, with the one introduced in the G.P. of S. Marino, even more complex, and, apparently, more efficient.
The wings applied in racing cars have some peculiarities that have been developed along the last four decades. As we can see in the image 2, besides inverted profile, they can have side fins (a), flux separators (b), and central supports (c). As it happens with airplane wings, they have a main plane (d), and one, or more, secondary profiles, or “flaps” (e), separated by slots. Each profile has a leading edge (f) and a trailing edge (g). In the trailing edge (g) of the last “flap”, it can be applied, a small, yet very efficient appendix, the so-called “Gurney flap” (h).
The relation between the wing’s span (i) and it’s cord (j), in other words, the distance between the leading edge of the principal profile and the trailing edge of the last “flap”, is directly related to the probable efficiency of the wing.
In (k) we can notice the device which allows the regulation of the angle of attack of the flap and front wing.
In a racing car, the use of an inverted wing intended primarily to create a negative lift (in opposition to the positive lift created by the wing of an airplane or a bird, which allows them to fly) that develops in direct proportion to the square of the speed at which the vehicle is travelling.
On the one hand, this downforce causes the increase of stability, of the adherence and of the vehicle’s traction, which allows a bigger speed of passage in curve, bigger efficiency in braking and acceleration, and a bigger resistance to side forces. There is a whole profit in global efficiency of the car, which also gets a better use of the tires.
On the other hand, it generates the creation of a longitudinal drag force that increases, sometimes in significant way, the resistance of the vehicle to advance, with consequent increase of the fuel consumption, and reduction of the attainable maximum speed.
In the case of a wing working in a superior ground distance to half of its cord, as it happens in the 3a illustration, the above-mentioned negative lift is created by the difference of pressures in the airflows that pass above and below the wing. The air that flows under the wing has to be able to run a superior distance to the one that flows over the same profile of wing. For this motive, and supposing that the two fluxes are separated, in the same instant, in the leading edge of the wing, the air that flows under the wing is going to be forced to flow more quickly, to leave the wing at the same time, in the trailing edge, that the air that flows over the wing.