Prediction and Measurement of the Deformations of an Extremely Flexible Rotor Using Digital Image Correlation

This paper describes the aeroelastic modeling and measurement of the deformation of an extremely flexible rotor blade in hover. The objective of the study is to demonstrate the accuracy and reliability of the analysis as well as the measurement technique in order to support the future design of a morphing rotor micro aerial vehicle. The analytical model is based on an assumed-modes approach with flapwise bending and torsion degrees of freedom. The model is derived for rotor blades with very low torsional stiffness, non-symmetric cross section and incorporating a mass at the tip. Higher order terms are retained in the torsion degree-of- freedom, with particular attention on bifilar effects. The blade deformation is measured using stereoscopic digital image correlation (DIC), which provides measurements of flapwise bending deformation at a spatial resolution of 0.06% of the rotor blade span. Blade root pitch angle measured by the DIC is validated by laser sensor and load cell measurements. The aeroelastic model matches the slope of the flapwise bending deformation near the root of the blade, but over predicts the tip displacement. Predictions of spanwise blade twist show good agreement with measurements. Future plans to refine the aeroelastic model and to validate the measurement by DIC of spanwise bending deformations are described.