Experimental measurements of dynamic control surface effectiveness

This article reports on a low Reynolds number experimental study of the unsteady lift characteristics of an NACA 0009 airfoil pitched about its midchord, equipped with a 27% trailing-edge flap that could be independently deflected. The airfoil normal force, obtained from integrated surface pressure measurements, was captured during rapid, trailing-edge flap-only deflections; rapid, arbitrary, pitch-only excursions; and combined rapid pitch and flap-deflection motions. The measured aerodynamic response of the flapped airfoil to the various flap, airfoil, and airfoil flap combination motions was compared to theoretical and panel-code-computed aerodynamic-response predictions. These comparisons, and the results of flow visualization experiments, led to the observation that both the flap's effectiveness and the airfoil's lift-curve slope were higher during their motion than their steady-state values, and essentially matched their inviscid theoretical values.

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