NACA-TN-3356

Abstract

Two models were tested for which the rate of change of sidewash with angle of sideslip could be varied. For the first model, this effect was obtained by mounting auxiliary vertical fins on the fuselage at the assumed center of gravity; for the second model, the change in the gradient of the sidewash was accomplished by varying the vertical position of the wing. In effect, these models permitted a systematic variation of the sidewash gradient at the vertical tail. <br>Both models were tested in steady-yawing flow and by the freely damped oscillation-in-yaw technique to establish the effect of the lag of the sidewash on the unsteady lateral damping of these models. <br>An analysis indicated that the oscillatory damping in yaw is proportional to a factor which depends on the lag of the sidewash whereas the steady-state damping is independent of the lag of the sidewash. Secondly, the directional stability is influenced by the static sidewash under both steady- and oscillatory-flow conditions but is not affected by the lag of the sidewash. The experimental results of this investigation verified qualitatively these analytically predicted trends. No consistent effect of frequency on the oscillatory damping in yaw was evident in the frequency range covered by this investigation.