[aerohead]

The following artillery projectiles illustrate the relationship between low-speed subsonic, incompressible flow drag, and supersonic drag:
* The KRUPP ( Pringles potato chip can ) artillery projectile had a subsonic Cd 0.859, which peaks at Cd 1.598 @ MACH 2.5.
* The Charters-Thomas spherical cannon ball is Cd 0.4915, subsonic, rising to a peak Cd 1.014 @ MACH 1.7.
* The Gavre projectile has Cd 0.200, subsonic, peaking @ Cd 0.647, @ MACH 1.35.
* The Aberdeen projectile has Cd 0.158, subsonic, peaking at Cd 0.398 @ MACH 1.0.
* The Streamline Body of Revolution, of L/D= 2.5, from which the 'templates' are based, in free 'flight' is Cd 0.04, subsonic. They are not employed for transonic, nor supersonic velocities.
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* As a streamline 'Half-Body', held in mirror image ground reflection, with the ground clearance cut away, the body is Cd 0.08, subsonic.
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* Adding the wheels of the 1981 Volkswagen 'Flow-Body' long-tail would produce Cd 0.128.
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* Adding Goro Tamai's 70% wheel-drag reducing, 'fully-swept' wheel fairings would bring the drag back down to Cd 0.0944.
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This is where Wolf-Heinrich Hucho's comment about having off-the-shelf technology to build ( a conservative ) Cd 0.09 automobile came from in December of 1986 [ he actually allowed for as low as Cd 0.07 ].
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1) 'Half-bodies' are all he recommended.
2) He showed us the lowest L/D= 2.5:1 drag streamline body, at Reynolds number 10,000,000, Cd 0.04, in Figure 4.119, page- 200, 2nd-Edition.
3) He showed us the lowest drag half-body from which it was made, without ground clearance, in ground proximity, Cd 0.09, in Table 2.1, page- 61, 2nd-Ed.
4) From the ground rules of mirror image we know the half-body, with ground clearance is Cd 0.08.
5) We know what the addition of wheels does to drag.
6) We know what the addition of fully-swept wheel fairings means to wheel-drag reduction.
7) Between Hucho and Tamai, we're given a complete recipe for very-low-drag vehicles, as of December, 1986. Thirty-seven years ago!
8) It's all 'pre-tested', and complete pressure profiles were provided 101-years ago be Georg Fuhrmann: Theoretische und experimentelle Untersuchungen an Ballonmodellen. Jahrbuch der Motorluftschiff Studienges, 1911/12.