Measurements of Unsteady Aeroelastic Model Deformation by Stereo Photogrammetry
Edward T. Schairer, Lawrence A. Hand · Journal of Aircraft · 1999
Stereo photogrammetry measurements of the deformation of simple, flat-plate, clipped delta wings that were undergoing aeroelastic oscillations in transonic flow are described. The measurements were made in High Reynolds number Channel 2 at NASA Ames Research Center. Two types of aeroelastic responses were measured: 1) highly damped responses in which the tip of the model was deflected and then released at subcritical dynamic pressures; and 2) responses excited by perturbations in the flow as the dynamic pressure was slowly increased until the model became unstable. The model was imaged by three synchronized black-and-white video cameras, and the data were recorded on videotape. Correlated images from two of these cameras were used to estimate the space coordinates of reference marks on the model at each instant, and the motion of each mark was estimated by fitting the deflection data with a damped sinusoid. The resulting estimates of the frequency and damping of the first-bending-mode oscillations compared favorably with strain-gauge measurements. A large increase in the phase difference between motions of the leading and the trailing edges was observed just before the models became unstable.