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Lift and drag measurements are not easy values to obtain. Since the Navier-Stokes equations can not be solved, the only way to obtain these values is through experimentation. We could use a full size car in a very large wind tunnel to measure the lift and drag forces. However, using a smaller model (1:12 scale in this case) in a much smaller wind tunnel is more cost effective, and more practical. Lift and drag forces measured in this experiment must be scaled to use them for the full sized model. However, dimensionless values such as the drag and lift coefficients are the same for a model of any size. These are the values we are interested in.
Using a pressure transducer and a dynamometer, we found the lift and drag forces on the car at air velocities from 9 to 22 m/s. The Pitot tube (connected to the pressure transducer) was used to read the stagnation pressure of the ambient air in the tunnel. As the velocity of the air increased the stagnation pressure on the tube increased as well. This pressure was sent to the pressure transducer which read these digital values as voltage measurements, and then sent them to the computer.
The dynamometer is used to take many measurements of a force on a model. Since our car model is mounted off the wind tunnel surface, and only to the dynamometer, the measurements of force taken in the horizontal direction will be the drag forces acting on the model, and the force measurements taken in the vertical direction will be the lift forces acting on the model. The computer records these values as lift and drag which we can then use to find our lift and drag coefficients for the model.
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