Some vehicle aero flow visualizations with some nerdy scoop stuff

[Tommy]

Speaking of cubic inches knifing through the air - my favorite airplane used an aero concept from the 1950s that resulted in the Coke bottle shaped fuselage. Seen from above, the fuselage narrows as the wings widen. The idea was for the cross sectional area of the airplane to stay close to the same as the air moved from the front to the rear. You don't want the cross section pushing through the air to be any bigger than necessary (think Ford GT40), and you also don't want it abruptly changing size along its length.



Here's one more thought about air flow that many people don't realize. What we think of as air is mostly empty space with free floating molecules of nitrogen, oxygen, carbon dioxide, water and other things drifting through it. These molecules are packed closely enough that they bounce off each other sort of like balls on a pool table. That is why a disturbance 1,000 feet away will be relayed to our ears as sound in about a second by the bouncing molecules. Thus, the speed of sound is roughly 650 MPH on a typical day on the ground. This matters in car design because it means that as long as we are moving at less than the speed of sound, the air hitting the front of the car is being influenced by the air hitting the rear, and vice versa. You can see that in a wind tunnel where a change at the back of the car will cause the air flow well forward of that change to move. So, you can't think of the aero design of a car as a group of unconnected features (e.g., air dam, hood scoop, windshield rake, tail wing). They all work together, making the job of getting it right much more challenging.