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NACA-TR-669 (1939), NTRS abstract: support interference inflated published drag coefficients and their apparent increase with section thickness; corrected data and correction methods are supplied.

NACA Report 460, originally published November 1933; primary PDF: ntrs.nasa.gov/api/citations/19930091108/downloads/19930091108.pdf . Apparatus and Methods describes duralumin models, dimensions, Reynolds number, tank pressure and measured forces/moments. The introduction and profile derivation explain systematic variation of thickness and mean-line form.