= Kenneth E. Ward
{c}
\b[Kenneth E. Ward] was a <National Advisory Committee for Aeronautics> researcher whose <wind tunnel> investigations examined interactions between <aircraft> components. He also coauthored the systematic related-<airfoil> investigation with <Eastman N. Jacobs> and <Robert M. Pinkerton>.<Interference Effects and Drag of Struts on a Monoplane Wing by Kenneth E. Ward>[Byline, Introduction and Apparatus and Tests]{ref}<The Characteristics of 78 Related Airfoil Sections from Tests in the Variable-Density Wind Tunnel by Eastman N. Jacobs and others>[Report byline]{ref}
In his 1931 strut experiment, a 5-by-30-inch Göttingen 387 <airfoil> was tested first alone and then with inclined struts attached in different upper- and lower-surface positions. The <variable-density wind tunnel> operated at 20 atmospheres and approximately $Re=3.4\times10^6$. A repeated wing-alone test before and after the strut trials checked the comparison's repeatability. Separate strut measurements helped isolate <aerodynamic interference>.<Interference Effects and Drag of Struts on a Monoplane Wing by Kenneth E. Ward>[Printed pp.2–5, Apparatus and Tests and Discussion of Results]{ref}
The central question is whether component <drag> adds. Define an interaction residual at matched operating conditions by
$$
\Delta D_{\rm int}=D_{\rm combined}-D_{\rm wing}-D_{\rm struts}.
$$
For invented measurements of $30$, $20$ and$5\,\mathrm N$, respectively, \b[$\Delta D_{\rm int}=5\,\mathrm N$]. The assembly's drag increase is twice what the isolated struts contribute. Ward reported that interaction drag could be as large as the struts' own drag; the numerical forces here simply illustrate the subtraction.<Interference Effects and Drag of Struts on a Monoplane Wing by Kenneth E. Ward>[Summary and Discussion of Results, interference compared with isolated strut drag]{ref}
This <aircraft component drag interaction> is why a streamlined part cannot be assessed solely in isolation. Changing its location also changes neighboring <pressure> and <fluid flow>. Comparable <Reynolds numbers>, mounting corrections and repeat measurements are needed to distinguish that interaction from a changed test condition.
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