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Charles D. Harris is the first named author, with James A. Blackwell, Jr., of the 1972 NASA report testing rear-upper-surface changes on a supercritical airfoil. The experiment examined a local off-design velocity peak while also checking the consequences at the design condition. The published summary reports that the particular attempted change adversely affected design-condition drag.^[ref]

The tests covered Mach numbers from $0.60$ to $0.81$ in a transonic wind tunnel. The models differed in rear-upper-surface shape while retaining their trailing-edge thickness; pressure measurements and a wake rake connected the geometric change to aerodynamic observations.^[ref]

An original comparison shows why an improvement needs its operating condition. Stipulate that a proposed modification changes drag coefficient by $-0.001$ at one condition and $+0.002$ at another. With the same reference dynamic pressure $q=10000\mathrm{Pa}$ and area $S=0.25{\mathrm{m}}^2$ for this arithmetic example,gives $-2.5\mathrm{N}$ and $+5.0\mathrm{N}$, respectively. The sign of the benefit reverses. These invented coefficients are not values reported by Harris; they isolate why suppressing one local feature cannot establish lower total drag throughout an operating range.

A useful experimental comparison therefore records the Mach number, Reynolds number, angle of attack, loading and surface condition with the measured pressure coefficient distribution and drag. Changes of boundary-layer transition or mounting effects can alter the result. The documented negative outcome is scientifically informative because it tests a specific geometric proposal rather than assuming that a locally smoother-looking flow must improve complete performance.

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.