Servo -Flap Rotor Design Parameters Identification via Spectral Analysis of Flight Data

Servo -flap rotor design parameters were studied using multichannel spectral analysis. Vibratory data collected from nine different locations , including servo -flap mid -span vertical bending, four parameters from the ro tating system, and four parameters from the fixed system were examined . Th is study analyz ed vibratory data from a well -tuned four -blade helicopter during high -speed forward and hover flights . Through spectral analysis , we were able to identify vibratory en ergy distributions at multiple harmonics of the fundamental rotating frequency at all nine locations. The power spectrum for the vertical bending measured at the mid -span of the servo -flap during high speed flight indicates the existence of the vibration e nergy concentrated around the first two harmonics. Higher order harmonics larger than 3/rev drop to about 1.45% of the energy observed at 1/rev . We also used the cross -spectrum to determine the linear relationships at different harmonics of the rotating fr equency between servo -flap vertical bending and rotating system and fixed system parameters. During high -speed flight, the phase of servo -flap vertical bending was found to be 80 ° ahead of blade vertical bending and 55 ° ahead of blade torsion at the freque ncy of 1/rev. Nomenclature