Quote:
Originally Posted by Piwoslaw
In this case, the sooner the airflow detaches the better.
EDIT: The following in red isn't exactly true, see post #10 for details.
I saw a chart somewhere (can't find it right now, grrrr). Pretty much it showed that as the rear angle gets steeper (starting from 0°=flat) lift decreases until 12°-14°, then it increases again until 26°-28° when airflow detaches and lift goes down again.
So, if you can find the spot where the tangent is 12° and make a small "step", then the airflow will detach there, reducing lift at the best point. Many new cars already have this small "step" around the top of the rear window. |
I have also seen somewhere, just cant find it, where if you take an ideal aerodynamic shape, and start chopping off the back end, bit by bit, you won't seriously affect the cd of it until you chop it near it's widest point.
This is why I say a short Kamm spoiler will do some serious good. I'm not just pulling this idea out of my butt. I have put a lot of serious thought into this. Look at current automotive designs for aero cues. They put a Kamm spoiler on them where the roof line starts to break and transition over the rear hatch. (RX 350) This is because this point is where the flow separation will occur, or, where the shape of the car seriously deviates from the "Ideal" aero shape which had been maintained to that point.
And hey, worst case, the materials and time used to make what I propose are tiny compared to trying to cover the whole back end of your car with coroplast. If it does not work, not much lost.