Quote:
Originally Posted by winkosmosis
I don't understand the use of that picture. It seems pretty arbitrary to overlay it on a vehicle. The entire flow is affected by the front of the vehicle, which never matches the shape of an aerofoil. The overlay isn't an aerofoil to begin with-- the point of an aerofoil is to have a curved front that allows the wing to function at a range of attack angles.
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the overlay is generated from a circular body of revolution with a thickness ratio of 2.5:1.This is the lowest drag form that exists."cars" with the lowest drag all have "half" of this shape.This is because of the "ground-reflection" or "mirroring" phenomena which exists for road vehicles in ground-effect,first reported on by Prandtl in the 1920s.------------------ What you see of your car,the "air" see's two of.One above the ground,and one below,just as if you'd parked your car on top of a mirror.Due to this phenomena,the "fineness ratio" of your car ( it's length divided by it's height ) is only half what you think it is.------------- To get to the ideal 2.5:1 fineness ratio,your car's length must be 5-X it's height.------------- Getting back to the overlay,most modern automobiles have attached flow up to their point of maximum cross-section,their "Frontal-Area".Where cars get dirty,is in the region behind the point of maximum cross-section,defined on the overlay as the high point of the car's roofline,wherever that occurs.------------------------------ If you scale your vehicle to fit under the overlay as we recommend and then construct any aft-body modification which respects the outline of the overlay,both top AND sides,your new "body" should experience no flow separation whatsoever,until it gets back to the "end" of your new body.This is exactly what Kamm was doing with his K-Cars.This is exactly what Jaray did to achieve Cd 0.13.This is exactly what Lay did to achieve Cd 0.13.This is what GM did with Sunraycer and what Honda did with Dream-2.If you extend the tail all the way to the point,you will have virtually eliminated all your profile drag ( 55 % of your aero drag ) and you've got a shot at Cd 0.10 as with Honda's car.