Quote:
Originally Posted by Viturro
yes, in the example i just want to know about the roof (the top) of the car. want to know about the difference about the kammback and the aileron.
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*The drag you're trying to reduce is pressure drag.
*The pressure drag is dependent upon where the flow separates from the body,as the entire wake will have THIS pressure.
*If the Kamm-Back is properly contoured,the air will stay attached to it until it ends,slowly decelerating (Bernoulli's Theorem) and gaining static pressure as it passes down the 'back.'
When the air does separate,it's at a higher overall pressure,and this higher pressure in communicated throughout the wake,increasing the base pressure behind the car,hence lowering the pressure drag.All good!
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*The 'aileron' is aspirated all around and can only act in the capacity of a deflector.
*The aileron has it's own frontal area and drag coefficient minimum (not to mention it's support structure) at zero-angle-of-attack,but when it is angled,as in your diagram it will produce lift,which is induced drag which the engine must overcome.
*The aileron may direct cambered airflow towards the wake,which is in itself a good thing,but it does nothing to slow the air and build static pressure,and again it's acting at the expense of power robbed from the engine for an overall net increase in drag.
*I suspect that the aileron would put a motorist in jeopardy,especially during wet road driving,where the car would be prone to hydroplaning.
*I've never seen a wing added to a car which did not increase its drag.