= Wind-tunnel model support correction
A \b[wind-tunnel model support correction] estimates the aerodynamic contribution of a model's mounting system to measured <forces> and <torques>. It can include the support's direct load and the altered <fluid flow> produced when support and model are together. An <empty-tunnel support tare> addresses the first effect but need not identify the second.
For a single load channel, write the defined measurement model as
$$
Y_{MS}=F_M+F_S+I_{MS},\qquad Y_S=F_S,\qquad Y_{MS}-Y_S=F_M+I_{MS}.
$$
Here $F_M$ is the desired isolated-model load, $F_S$ is the support-only load and $I_{MS}$ is the <wind-tunnel support interaction residual>. The equations assume the same channel zero, conditions and support configuration, with other loads already removed. For stipulated values $F_M=20\,\mathrm N$, $F_S=3\,\mathrm N$ and $I_{MS}=2\,\mathrm N$, simple tare subtraction reports $22\,\mathrm N$, retaining a 10% bias relative to the desired load.
This limitation affected real design data. In their 1939 report, <Eastman N. Jacobs> and <Ira H. Abbott> found that support interference had made published <airfoil> <drag coefficients> too large and had exaggerated their increase with section thickness. Their correction therefore changed more than a single constant offset: it affected the inferred trend used to compare <airfoil> shapes.<Airfoil Section Data Obtained in the NACA Variable-Density Tunnel as Affected by Support Interference and Other Corrections by Eastman N. Jacobs and Ira H. Abbott>[NTRS abstract, support interference and thickness trend]{ref}
A proposed diagnostic repeats measurements with altered supports or attachment positions while maintaining a common target condition. Dependence on the mounting arrangement demonstrates a setup sensitivity; extrapolating to an unmounted model requires a justified <mathematical model>, not merely averaging the mounts. Wind-off orientation tares, support-only wind-on loads and model–support interactions answer different questions. Record each separately and propagate its <measurement uncertainty> through the reported correction.
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