Quote:
manu said:

but i still think that the 911's drop off is better for aerodynamics, well as you say decreases drag but not lift,



I think we still have some confusion. The abrupt drop off of the whale tail has less lift and less drag than the slope of the 911's rear. The slope of the 911's rear is great enough that it increases drag and lift. The graph I included shows a decrease in drag and lift as the rear decklid is raised. I was told that the raindrop analogy if often applied incorrectly. I haven't taken any classes in fluid dynamics and so can only refer to people who know more than I do, but what I have stated so far is fact (not including any guesses as to why it's true, just the conclusions). My current guess is that as the speeds increase you need a longer and longer tail to the raindrop and it turns out that in order keep the car at a reasonable length it's better to cut off the end of the tail (so you have a flight slope to the roof leading to a drop) than to make the slope of the tail greater so that it comes to a point sooner (having a greater slope like the 911).