James A. Blackwell, Jr.

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.^[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.^[ref]

An original pressure-load example illustrates that distinction. On normalized airfoil chord $0\le \xi \le 1$, stipulate two lower-minus-upper pressure coefficient distributions,Both integrate to one, giving the same chord-normal pressure force. Their first moments differ:At dynamic pressure $q=500\mathrm{Pa}$ and airfoil chord $c=0.20\mathrm{m}$, both loads are $qc=100N/m$. In this chord-normal-load model, nose-up-positive pressure moments about the quarter-chord are instead $-5$ and $-7\mathrm{N}\mathrm{m}$ 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.