Quote:
Originally Posted by winkosmosis
Why do people use those aerofoil overlays? The shape of anything you add to your car should be based on the local airflow conditions.
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The overlay is based on ideal aero flow.The ( aprox 2.5:1 ) teardrop form depicted has the lowest drag recorded for a three-dimensional body of revolution in ground-effect.Mair was able to cheat it a bit,but nowhere else has empirical research demonstrated a form with lower profile drag.We choose this for the template because it's a no-brainer.If your vehicle has attached flow up to its location of frontal area,if scaled properly scaled and placed under the template,any modification based on this architecture,both over and around the vehicle,will be guaranteed to provide separation-free flow for any length,up to its full length.------------ Anything above or below the line will have higher drag.In free air this form has Cd0.04.On the ground this form has Cd0.08.When you add really skinny tires to this form you get Cd0.10,the theoretical minimum for a vehicle in ground-effect.Some wing-sections have lower profile drag but they suffer from higher skin friction at thickness ratios above 3.84:1 and wing section drag is considered 2-dimensional,not 3-dimensional.