= Robert M. Pinkerton
{c}
\b[Robert M. Pinkerton] investigated <airfoil> aerodynamics at the <National Advisory Committee for Aeronautics>. He coauthored the related-section study with <Eastman N. Jacobs> and <Kenneth E. Ward> and later compared measured <surface pressure> distributions with <potential flow> calculations.<The Characteristics of 78 Related Airfoil Sections from Tests in the Variable-Density Wind Tunnel by Eastman N. Jacobs and others>[Report byline]{ref}<Calculated and Measured Pressure Distributions over the Midspan Section of the NACA 4412 Airfoil by Robert M. Pinkerton>[Byline and abstract]{ref}
His 1937 report describes a 5-by-30-inch <NACA 4412> model in a <variable-density wind tunnel>, with 54 pressure orifices at the middle of the span. Seventeen <angles of attack>, from −20 to 30 degrees, were tested at a <Reynolds number> of approximately$3\times10^6$. These readings test the distribution of <pressure>, not merely whether the total <lift> happens to agree with a calculation.<Calculated and Measured Pressure Distributions over the Midspan Section of the NACA 4412 Airfoil by Robert M. Pinkerton>[NTRS abstract, apparatus and conditions]{ref}
An original simplified example explains the extra information. If a thin <airfoil> has a constant difference $C_{p,\rm lower}-C_{p,\rm upper}=0.8$ over its chord, its <surface pressure integration for airfoil lift> gives the normal-force approximation
$$
c_n\simeq\int_0^1(C_{p,\rm lower}-C_{p,\rm upper})\,d(x/c)=0.8.
$$
With <dynamic pressure> $q=500\,\mathrm{Pa}$ and <airfoil chord> $c=0.20\,\mathrm m$, the normal force per unit span is $qc\,c_n=80\,\mathrm{N/m}$. A different distribution can give the same integral while producing a different <pitching moment> or <boundary layer> behavior. These are invented uniform data, not Pinkerton's measurements.
Finite pressure-tap spacing and <pressure-tap position error> can change the inferred integral. A measured distribution therefore offers both a stricter test of <potential flow> and a way to see where its assumptions cease to describe the actual <fluid flow>.
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