|
The problem here has been one of interpretation. The "template" is fine in that it is a low drag shape, an example of the maxim that long, tapered shapes generally give lowest drag. However, even a cursory read through any modern aerodynamics text will show that:
1) There isn't one ideal shape
2) when you take an ideal shape in free air and move it close to the ground, the effect of the ground introduces complexities to the flow
3) because of this, an ideal shape in ground proximity is not its free-air ideal shape cut in half (although this is used as a thought exercise in several aerodynamics textbooks--to understand mechanisms of both drag and lift)
4) the flow over a car is three-dimensional (highly three-dimensional, most textbooks put it), and can't be considered only in two-dimensional slices or profiles
5) the flow over an ideal shape depends on the entire body i.e. you can't take part of it (the tail) and apply it to a completely different body and expect that it will still be the lowest-drag solution. What happens at the front affects flow at the rear, and because of pressure transmission through air at the speed of sound, what happens at the rear affects flow at the front
6) unfortunately, through intent or not, the template has come to be seen here as all of these: the single ideal shape, cut in half with no concern for underside shaping aside from a simple diffuser, used as a "dimensional analysis" tool by considering a 2D profile only, applied to cars of various body geometries willy-nilly with little to no testing or verification and none (that I have seen) comparison testing of tapers of varying side angles, diffuser angles, top angles, and length on the same car
7) we now have tools for simple testing of drag changes. I'm getting a new vehicle this spring (well, old vehicle--my late grandfather's truck that I used to drive and has been sitting unused at my parents' house for the past several years) with a mechanical throttle connection specifically so I can test drag changes, which I can't do easily in my Prius. We can measure changes in ride height at speed, or panel pressures and see what body changes do to lift and airflow. There's no need to sit behind a keyboard and guess! I'm as guilty of that in years past as anyone here, but I've at least learned that much (between all the doom-scrolling of the last year or so).
|