Direct derivative measurements in the presence of sting plunging

This paper presents a review and extension of methods for determining the effects of sting oscillation on the measurement of dynamic derivatives due to oscillatory pitching. It is shown that two of the methods based on linear models will reduce to the same result, applicable to low-lift configurations. The location of the effective axis of rotation is determined for a model executing planar oscillations in two degrees of freedom. The equations for the effect of plunging on the derivatives can be simplified by relating the sting deflection parameters to the coordinate of this axis. The implications for analysis of sting plunging oscillation in dynamic tests of aircraft models at high angles of attack are also discussed. The effective rotation center could be determined by a simple method, and the associated effects evaluated, in pitch-oscilla tion tests of the Standard Dynamics Model at angles up to 45 deg. The axis shift was found to produce the main effect on the measured data.