Performance of a Mach-Scale Coaxial Counter-Rotating Rotor in Hover

A Mach-scale rotor system, 2.03 m in diameter, was built and hover tested in three configurations: two-bladed single rotor, four-bladed single rotor, and two-bladed coaxial counter-rotating rotor. The blades were untwisted with a VR-12 airfoil profile and a constant chord of 76.2 mm with a 3.8 mm trailing-edge tab. The hubs were rigid and had a vertical spacing of 13.8% rotor radius. Individual rotor steady and vibratory hub loads as well as lower-rotor push-rod loads were measured for several blade loadings up to 0.095. Mean loads were used to analyze rotor performance with an analytical momentum theory model as well as to validate an in-house, free-vortex wake model. Statistical analysis of the measured data revealed clear trends with a known confidence level. Because of mutual interference, the upper and lower rotors of the coaxial configuration consumed 18 and 49% more induced power than that of an isolated two-bladed rotor. The coaxial counter-rotating configuration was found to consume 6% less induc...

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