 Kenneth E. Ward

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.^[ref][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 $Re=3.4\times 10^6$. A repeated wing-alone test before and after the strut trials checked the comparison's repeatability. Separate strut measurements helped isolate aerodynamic interference.^[ref]

The central question is whether component drag adds. Define an interaction residual at matched operating conditions byFor invented measurements of $30$, $20$ and$5\mathrm{N}$, respectively, $\Delta D_{\mathrm{int}}=5\mathrm{N}$. 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.^[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.