Structural Optimization And Mach Scale Test Validation of A Low Vibration Rotor

A ten-foot diameter Mach-scaled wind tunnel test was performed to validate a four-bladed low vibration rotor design. Two different rotors were tested having identical planform, twist and airfoils. The reference rotor, similar to a scaled Model 360, was designed by using the traditional approach of keeping adequate separation between the rotor natural frequencies and the harmonic aerodynamic forcing. The low vibration rotor was defined by an analytical optimization procedure. During the wind tunnel test, hub loads were measured using a dynamically calibrated rotor balance and verified using a strain pattern analysis. The wind tunnel test results showed substantial reductions in the 4/rev vertical hub load and in the 4/rev hub moments for the low vibration rotor. As a byproduct, reductions were also measured in the vibratory bending moments.