Quote:
Originally Posted by dcb
So what is the verdict on open back or closed back?
Also, what is your time frame? I'm wondering if I'll have time to finish the auto CDA computing on the guino first. No biggie, but that is exactly the intended usage for it.
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dcb,your's is a very good question and while I won't have the definitive answer,here's how I understand it.Both open and closed boat-tails, when properly configured,allow for a reduction in cross-sectional area of the car's body without flow separation.As the air is decelerating down the slope of the boatail(top and sides),it is regaining pressure.Following the "ideal" teardrop path,every 10% of additional tail length is good for about a 10% reduction in area,10% increase in pressure,and 10% decrease in drag,either open or closed.( It's not a linear relationship because of the curved wall of the ideal teardrop,versus a straight-walled cone).According to Ford,if there is a "back" to the tail,air separating at the truncation(chop-off), will round the corner of the back,and slam into the vertical surface,providing a minute degree of thrust.Chrysler calls it "bursting".I have no quanta to tell you the difference in performance between the two,however,if you want to split hairs,it looks like the closed boat-tail crawls away with the victory cup.