[aerohead]

In Fachsenfeld's 1951 book, he shares a research he and Kamm conducted at the FKFS, very similar to what Hoerner published in his Figure 3.26, regarding the 2-D flow, Gottingen 460, 20.5% thickness, airfoil section.
The FKFS model is a 2-D flow, 8-piece, composite, K-form, symmetrical airfoil, which represents measured Cds, ranging from, zero-aft-body, to 100% aft-body, representing 8-different 'wake areas', along -equal-length segments.
The Cd varies from, 0.58, to 0.065.
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What's germane to Jeff Howell et al.'s research is, the first 75% of the aft-body, which demonstrates a perfectly linear drag relation along its slope, as a function of wake area reduction, along the 'wing's' curved contour.
The last 25% becomes non-linear, with diminishing returns, as it goes asymptotic near 100% length and zero-wake.
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I've misplaced Kosin & Lehmann's streamlined body of revolution research. I'll try and hunt that down, as I'd like an example of a purely 'compound-curve' - surfaced tail.