NACA-RM-A52G07

Abstract

INTRODUCTION <br>Increasing attention is being directed to the dynamic characteristics of aircraft. One reason for this is that present0day high flight speeds require correspondingly faster and more precise aircraft control which may be considerably affected by the dynamics of aircraft. In addition, the trend toward high flight altitudes and tailless aircraft configurations has resulted in decreased aerodynamic damping. The need for adequate information on aerodynamic damping is particularly acute in the transonic mach number range. <br>The damping of the short-period longitudinal oscillations of an aircraft is to a large degree dependent upon the damping of single-degree-of-freedom pitching oscillations about the aircraft center of gravity. Experimental results have been presented in reference 1 for several triangular wing configurations in which the damping was obtained from measurements of the logarithmic decrement of single-degree-of-freedom pitching oscillations in a wind tunnel. Following this investigation and its evidence of dynamic instability at transonic mach numbers, a device was single-degree-of-freedom forced-oscillation technique. This equipment could be used to measure damping under unstable aerodynamic conditions and also permitted the systematic investigation of the effects of frequency and amplitude. <br>The purpose of this report is to present data showing the effects on the damping in pitch caused by variations in mach number, Reynolds number, angle of attack, frequency, oscillation amplitude, and longitudinal position of the pitching axis as measured with the forced-oscillation apparatus. A comparison with damping-in-pitch coefficients determined by the free-oscillation technique (reference 1) is also presented.