Quote:
Originally Posted by aerohead
Yes, Morelli admonished:
* body shape must vary slowly
* body area must vary slowly
* body contour must vary slowly
* body must be as rounded as possible
* body pressure gradients must be as low as possible
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Unfortunately, some of these rules are deceptive or incorrect. Looking at any low drag current car quickly shows that.
For example, the 'body must be as rounded as possible' applies only in parts - at the rear of the car, we want clean separation and so rounded trailing edges will substantially increase drag. That's why low-drag cars have rear separation edges.
The same for 'body shape must vary slowly' - again, only in certain parts. As shown earlier, to reduce the strength of trailing vortex formation off rear slanted pillars, body shape often changes fast enough to have distinct edges.
It's not a good idea to apply rules of thumb to car modification. There are always exceptions, and as this list has shown, sometimes those exceptions are quite major.