|
The drawings of the Scion and VW are still wrong. The area right over the A-pillar is the lowest pressure, thus should be pointing up. Assuming a flat roof (station wagon, van, Scion) behind that the pressure increases until at some point, the pressure is zero, after which the pressure starts to go up (yes, we can get some down-force on the back end of our station wagons!). The streamlining template exploits this fact, and starts at the location where pressure is zero (relatively) and starts to taper, doing it's best to maintain zero pressure. If there is to be a positive pressure maintained, we would wind up with a longer than needed tail (think of this pressure as friction [skin drag], not a force pushing you forward). If a negative pressure is maintained, we wind up with a shorter tail, but higher Cd and lift on the tail. If length is not a constraint, we would want to go for the Aerodynamic Streamlining Template every time (or something close anyhow). When we start clipping the tail end off, a lower drag option may be to take that shorter length, but maintain the full boat tail. This may not be true if we cut off 10% of the tail, but is true (in my experience) for short tails, like on a Prius, Insight, or the SedanKamm I built for my car.
__________________
|