Feedback attenuation and adaptive cancellation of blade vortex interactionon a helicopter blade element

Blade vortex interaction (BVI) noise has been recognized as the primary det erminant of the helicopter's far field acoustic signature. Given the limita tions of design in eliminating this dynamic phenomenon, there exists a need for control, We believe that this paper is the first model-based effort to attempt the same. We present herein the application, first of feedback con trol strategies, and then of adaptive cancellation on Leishman and Harihara n's linear aerodynamic model of a trailing edge flap. Lift fluctuations cau sed by vortices are taken as output disturbance, The contribution of the vo rtices to lift is obtained from Leishman's indicial model for gusts. The us e of an active structure for actuation is assumed, and the actuator is appr oximated as a lag element. To design an adaptive cancellation scheme that i s applicable not only to BVI but also to general problems with periodic dis turbances, we start with the classical sensitivity method, and arrive at an adaptive scheme whose stability me discuss via averaging, Sacks et al. arr ived at the same result by introducing a phase advance into a pseudogradien t scheme.