Full-Scale Demonstration of Higher Harmonic Control for Noise and Vibration Reduction on the XV-15 Rotor

Abstract

Abstract : A higher harmonic control (HHC) investigation was conducted on a full-scale, isolated XV-15 Rotor in helicopter mode in the NASA Ames 80- by 120-Foot Wind Tunnel to independently control noise, vibration, and trim. The higher harmonic blade root pitch was generated using swashplate oscillations. The radiated blade-vortex interaction (BVI) noise footprint was measured on a plane beneath the rotor with eight microphones mounted on an acoustic traverse. Test results showed that HHC is highly effective in reducing BVI noise, achieving a 12 dB reduction in peak noise level within the noise footprint. Blade pressure feedback was demonstrated to be a viable method for closed-loop noise control. Perturbations in trim parameters and test conditions had small to moderate effects on noise reduction with HHC. Some noise reduction was achieved with no increase in vibratory hub loads. Increases in control loads due to HHC generally limited further noise reduction. The vibration controller achieved about 50 percent reduction in vibratory hub loads with control loads limiting the HHC amplitude. An automatic trim controller was demonstrated to be robust, reaching all target thrust and flapping schedules under all conditions tested.