2011-36-0275 Project and Construction of a Measuring System to Determine the Forces Applied to Automotive Airfoils Gertz, Luiz Carlos Lutheran University of Brazil Cervieri, André Lutheran University of Brazil Rodrigues, Antônio Flávio Aires Lutheran University of Brazil Da Silveira, Marilia Amaral Lutheran University of Brazil Ferreto, Claudio Júnior Lutheran University of Brazil Pelzer, Tiago da Costa Lutheran University of Brazil Copyright © 2011 SAE International ABSTRACT This paper presents a system developed for measurement of force, based on a load cell. The aim was to design a device capable of measuring the components of the force, drag and lift, which acted over automotive spoilers. In order to enable the system to measure the drag and the lift force, it was necessary to develop a system capable of measuring only the components of interest, uncoupling efforts, such as multiple solicitations and vibration. Measurements of force were carried out over an airfoil, employing the measuring system described in this paper. The results showed that the values of the forces that acted over the airfoil were in agreement to the expected. Airfoils are used mainly in automotive racing cars to increase adherence between the tires and ground. Car prepares have made use of theirs experience to determine the best type and angle of attack for the airfoils. With the help of system developed by the authors, preparers of racing cars can measure the efforts and know their effects over the cars. INTRODUCTION Airfoil is a profile designed in such a way that, when subjected to a given fluid flow, the fluid will have different speeds at the top and the bottom of the airfoil [1,2,3]. It is the shape of a wing or blade. When the fluid passes over an airfoil, it speeds up, decreasing the air pressure in that region according to Bernoulli’s principle. Therefore, there will be negative pressure in the top. In the bottom part, the pressure will be positive, generating a force. The component of this force, perpendicular to the direction of the flow, is called lift. The component parallel to the direction of motion is called drag. In aircraft, the position of wing is such that the lift force acts upward, making the flight possible [1,2,3]. The aerodynamic profile of the cars is under the action of the same forces that act over the airfoils. Thus, when air flows over the top surface of the car, they are formed regions of low pressure, an effect that becomes very significant at high speeds, causing a decrease of the adherence between the tires and ground [1,3]. In racing cars, this decrease in adherence affects the performance of the cars, especially on curves. Automotive airfoils are designed to generate negative lift, or to compensate the positive lift generated by the flow of air over the surface of the car [1,3]. Many car preparers make use of their experiences acquired during the tests to adjust the airfoils and their positions [3,4]. The racing drivers, during the tests, act as sensors of the airfoil, giving the information to the team that allow adjusting the position and angle of attack, according to the behavior of the car on the road [3,4].