New correlation of experimental flap-lag-torsion damping

Abstract

Since 1982, when carefully done experiments measured the flap-lag-torsion damping of hingeless rotor at various RPM's and for a several combinations of flexure geometry and studies, various unsuccessful efforts have been made to improve predictions. In this investigation, we present new correlation based on a finite-state inflow methodology including standard eigenanalysis from an upgraded code version. Improved correlation has been performed with errors up to 20% of 5 rad/s (the largest measured damping) in contrast to errors of the order of 100% as predicted by the best elastic-blade stability code at the experiments time. Results confirm that most of the former discrepancies can be attributed to 3-D unsteady aerodynamic effects. They also show evidence that original values of airfoil lift slope and profile drag coefficient in the literature yield very good correlation, in contrast to the inclusion of recirculation and quasi-steady drag effects, which got correlation to worsen.