Abstract
A Mach-scale, rigid, counter-rotating coaxial rotor system, 80 inches in diameter and operating at a tip speed of 190 m/s was tested in hover in two configurations: two-bladed single rotor and two bladed counter-rotating coaxial rotor. Individual upper and lower rotor steady and vibratory hub loads were collected at four operating conditions for each rotor configuration. An in-place, uncoupled dynamic calibration was performed on both upper and lower rotor load cells using an electrodynamic shaker to correct unsteady thrust load measurements. The lower coaxial rotor exhibits significant four-per revolution vibrational loads with an average amplitude 11% of the mean thrust Full span three-dimensional blade deformations were measured for a single lower rotor blade at 11 azimuth locations between 66◦ and 126◦ with 6◦ resolution via the digital image correlation (DIC) optical method. From these measurements high resolution elastic axis flap-bending displacements, as well as blade sectional pitch angles were extracted and examined. The lower coaxial rotor was found to operate at higher pitch angles while also exhibiting increased variation in tip bending displacement when compared to the isolated rotor at similar blade loadings.
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