Quote:
Originally Posted by Vman455
kachi22, I don't mean to single you out here, but at the same time this needs to be addressed: This is way too simplistic, but it's one of those "rules of thumb" that get thrown around here constantly. Drag is one of the three components of the aerodynamic force resultant that forms from pressures acting on the entire surface of a car.
As I posted about in another thread recently, a well-shaped car can have a lot of forward-facing surface area subject to negative pressure differential from atmospheric--the implications of which (that this reduces overall drag because of the contribution of thrust) appeared to go over the heads of nearly everyone who subsequently commented in the thread.
Incidentally, Julian Edgar later told me that Rob Palin, former Tesla aerodynamicist, said that lowering pressures on forward-facing surfaces by careful shaping was a key strategy for reducing drag in the development of the Model S. This runs counter to the prevailing wisdom here that beyond a certain amount of rounding--just enough to support attached flow--shaping of the front of a car has little to no effect on drag and everything important happens at the back because the prevailing wisdom is overly simplistic to the point that it is not true.
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* The Model S isn't necessarily the poster child for low drag. The are a dozen ICE automobiles on the road today with as low a Cd if 'electrified.' Some lower.
* As to the forebody, and it's effect on aft-body, you may recall Hucho discussing aerodynamic 'saturation,' a situation in which, at some degree of radius, any further 'softening' results in zero gain as to drag. This was 1976. SAE Paper No. 760185, Hucho et al..
* Drag reduction is the most important aspect of road vehicle aerodynamics, which makes the aft-body the most important area of the vehicle.
* And it may seem 'simplistic', because it is 'simple,' unless you introduce 'complex' body shapes, as Bearman discusses in his July 23, 1979 paper. Or Glenn D. Thompson, Standards Development and Support Branch, U.S. E.P.A., Figure 5, Page 11, ' Prediction of Dynamometer Power Absorption to Simulate Light Duty Vehicle Road Load,' shares in his 'template' advocacy.
* One can make aerodynamics as complicated as they like, however, since 1922, there's been no need. It's a 'Paris Dressmaker' issue.