= James A. Blackwell, Jr.
{c}
<James A. Blackwell, Jr.> coauthored NASA's 1972 study of rear-upper-surface modifications to a <supercritical airfoil> with <Charles D. Harris>. The report connects specified shape changes with measured aerodynamic loads.<Wind-tunnel Investigation of Effects of Rear Upper Surface Modification on an NASA Supercritical Airfoil by Charles D. Harris and James A. Blackwell, Jr.>[Title and first text page, published byline]{ref}
The apparatus combined surface pressure orifices with a downstream rake for the <fluid wake>, in the Langley 8-foot transonic <wind tunnel>. Surface readings characterized the <pressure coefficient> distribution, while wake measurements supplied separate information for <drag>. These observations constrain different parts of the aerodynamic response.<Wind-tunnel Investigation of Effects of Rear Upper Surface Modification on an NASA Supercritical Airfoil by Charles D. Harris and James A. Blackwell, Jr.>[Printed pp. 4–6, Apparatus and Techniques]{ref}
An original pressure-load example illustrates that distinction. On normalized <airfoil chord> $0\le\xi\le1$, stipulate two lower-minus-upper <pressure coefficient> distributions,
$$
f_0(\xi)=1,\qquad f_1(\xi)=1+0.6(2\xi-1).
$$
Both integrate to one, giving the same chord-normal pressure <force>. Their first moments differ:
$$
\int_0^1\xi f_0(\xi)\,d\xi=\frac12,\qquad
\int_0^1\xi f_1(\xi)\,d\xi=0.6.
$$
At <dynamic pressure> $q=500\,\mathrm{Pa}$ and <airfoil chord> $c=0.20\,\mathrm m$, both loads are $qc=100\,\mathrm{N/m}$. In this chord-normal-load model, nose-up-positive pressure moments about the quarter-chord are instead \b[$-5$ and $-7\,\mathrm{N\,m}$ per metre of span]. Equal integrated force therefore does not establish equal load location or <pitching moment>. These profiles are invented, not reconstructed report data; a measured pressure distribution also does not by itself include the full <viscous stress> contribution to <drag>.
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