[donee]

Hi All,

Aerohead has it right. The issue is cross-wind stability. The Kamm-back is a drag compromise to achieve cross-wind stability. Now depending on the vehicles the stability issue will or will not be as much an issue. A pickup truck for example has the CG way forward, and the cap boatail is actually mostly in front of the rear wheels - not much of a problem. A hatchback civic is similar, but the boatail is now behind the rear wheels, but the rear wheels are way back on the car. As other cars have body parts much farther back behind the rear wheels, the boat tail is probably OK on this vehicle too.

Why no Kamm-backs in nature? Because animals can do variable shapes, and twist their tails to allign with the direction of flow. They can also do vectored thrust. Besides animals can do active fluid dynamic control. Ocean going fish also do not need to align with the roadway, and can just go into and then crosswise to currents. And currents in the ocean are very slow compared to tuna speeds. So cross-wind or cross-current has also been designed for over evolutionary time, or are just not as big a consideration.