Quote:
Originally Posted by aerohead
1) Mair's model consisted of an elliptical nose, of 1,3-D in length, A cylindrical main body of 3-D in length, and the boat-tailed section of 1.9-D, which creates a total length of 6.2-diameters.
2) All values reflect zero viscosity effects, only pressure drag. Nothing to do with boundary layer thickness.
3) The take-away for aero modders is the 'lead- in' profile, leading to the final downslope angle. It's a known quantity.
4) Without the boat-tail we're looking at Cd 0.204 for Mair's model with skin friction.
5) With the boat-tail, Cd 0.066.
6) This 'lead-in' profile basically exists on all PGA Regulation golf balls.
7) 'Compound-curvature' roof modifications can entail 800-man-hours of construction time. Some form of Go NoGo might save many hundreds of hours of fabrication time. This would make something like Mair's profile quite
valuable. It may not be perfect, but short of a few hundreds of thousands of dollars for laboratory R & D, it might be handy for some with a more meager budget.
8) This was the original premise for sharing it. And perhaps why Hucho and others have presented it.
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Here's what Hucho actually presented when talking about Mair's research (emphasis in original text!):
Quote:
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Fig. 4.43 shows the extent to which the drag of a body of revolution can be reduced by tapering. The optimal tapering angle of 22 degrees given in this diagram should be taken only as indicative; the specific optimal angle depends on the upstream history of the flow.
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(Hucho, W.H. "Aerodynamic Drag of Passenger Vehicles." In
Aerodynamics of Road Vehicles, 4th edition, W.H. Hucho, ed. [Warrendale: SAE, 1998], 164).
Note the caveats; he doesn't give a blanket "go/no go" because
there is no blanket "go/no go"--it depends on the shape and features of the particular car in question, not some hypothetical ideal.